E-Bike Wiki - User contributions [en]

Premade or DIY

2023-12-03T23:04:28Z

Kopaz:

Premade or DIY, the decision can be tough. Most people don't have any experience in assembling mechanical devices or electrical work.

Overall, DIY seems to be the way to go if you can. Often times, Premade E-bikes come with proprietary batteries & controllers. Some may allow batteries of other brands, some may not.

Therefore, worst case scenario, if you want to get new batteries (that aren't same brand) or customize your prebuilt bike further, you may need to do wiring/soldering work by replacing controller & program new ones if necessary.
There are many off the shelf parts for batteries & controllers that aren't proprietary on market. Therefore, for long term ownership, DIY Ebike is more stable, but requires more knowledge since you're not relying on manufacturer/dealership warranty.

Being said, Electrical & Mechanical knowledge is needed due to high current that Ebikes use. This danger goes up as current output increases. If you are not unsure about learning new knowledge or purely due to lack of confidence, Prebuilt Ebikes/mopeds of vetted brand can be a safer bet.

'''Know your bike!''' We highly recommend you not convert 'department store' bikes such as Walmart, Canadian tire, etc due to their low part and assembly quality and instead stick to bicycles sold by bike shops or 2nd hand bikes.

[[File:EbikeWorkflowDiagv1.2.drawio.png|1000px|frameless|Flow diagram for premade vs diy]]

File:EbikeWorkflowDiag.v1.2.drawio.png

2023-12-03T23:03:45Z

Kopaz:

File:EbikeWorkflowDiagv1.2.drawio.png

2023-12-03T23:01:41Z

Kopaz:

flowchart for diy vs prebuilt, v1.2

Premade or DIY

2023-12-03T22:26:00Z

Kopaz: diy vs prebuilt flow diagram added & rewritten main body

Premade or DIY, the decision can be tough. Most people don't have any experience in assembling mechanical devices or electrical work.

Overall, DIY seems to be the way to go if you can. Often times, Premade E-bikes come with proprietary batteries & controllers. Some may allow batteries of other brands, some may not.

Therefore, worst case scenario, if you want to get new batteries (that aren't same brand) or customize your prebuilt bike further, you may need to do wiring/soldering work by replacing controller & program new ones if necessary.
There are many off the shelf parts for batteries & controllers that aren't proprietary on market. Therefore, for long term ownership, DIY Ebike is more stable, but requires more knowledge since you're not relying on manufacturer/dealership warranty.

Being said, Electrical & Mechanical knowledge is needed due to high current that Ebikes use. This danger goes up as current output increases. If you are not unsure about learning new knowledge or purely due to lack of confidence, Prebuilt Ebikes/mopeds of vetted brand can be a safer bet.

'''Know your bike!''' We highly recommend you not convert 'department store' bikes such as Walmart, Canadian tire, etc due to their low part and assembly quality and instead stick to bicycles sold by bike shops or 2nd hand bikes.

[[File:EbikeWorkflowDiag.drawio.png|1000px|frameless|Flow diagram for premade vs diy]]

File:EbikeWorkflowDiag.drawio.png

2023-12-03T22:16:08Z

Kopaz:

Flow diagram for diy vs premade.

DIY-battery

2023-11-27T04:21:22Z

Kopaz: /* Prerequisite software/knowledge */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform If you can pass this quiz without using internet for help, you have bare minimum qualification to continue. (You must get everything right)]

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.
[[DIY-case]] has helpful resources/practices if you are making your own battery case.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)
Refer to [[Cell selection]] for detailed guide.

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.
For calculating current capacity for your busbars for parallel group, [https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm There's a website that calculates resistance for a given sheet metal.] I'm sure you can find others, but that's just 1 example.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-11-27T04:20:47Z

Kopaz: /* Safety */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.
[[DIY-case]] has helpful resources/practices if you are making your own battery case.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)
Refer to [[Cell selection]] for detailed guide.

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.
For calculating current capacity for your busbars for parallel group, [https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm There's a website that calculates resistance for a given sheet metal.] I'm sure you can find others, but that's just 1 example.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-11-27T04:20:14Z

Kopaz: /* Safety */ add quiz link

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform If you can pass this quiz without using internet for help, you have bare minimum qualification to scroll. (You must get everything right)]

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.
[[DIY-case]] has helpful resources/practices if you are making your own battery case.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)
Refer to [[Cell selection]] for detailed guide.

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.
For calculating current capacity for your busbars for parallel group, [https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm There's a website that calculates resistance for a given sheet metal.] I'm sure you can find others, but that's just 1 example.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-11-27T04:18:36Z

Kopaz:

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.
[[DIY-case]] has helpful resources/practices if you are making your own battery case.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)
Refer to [[Cell selection]] for detailed guide.

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.
For calculating current capacity for your busbars for parallel group, [https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm There's a website that calculates resistance for a given sheet metal.] I'm sure you can find others, but that's just 1 example.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

Cell selection

2023-11-27T04:16:34Z

Kopaz: Electrochemistry 102 cell selection guide created

Electrochemistry 102 (DIY Battery 102)

Generally, for most NMC Li-Ion Cylindrical cells, you have 3 types:
Example cells are all 21700, but same logic applies for 18650s and generally most rechargeable LIBs.

1. High Capacity, Low discharge rating, Cheap cells. (5Ah, 1~2C C rating) High IR of the cells (hence low C rate)

Ex: M50 Variants, Samsung XX(Number)-E Variants

2. High/Low Capacity, Slightly higher discharge rating (than group 1), Slightly more expensive cells than grp 1. (4~5Ah, closer to 5Ah, 1.5C~3C Rating) Slightly lower IR than group 1 cells.

Ex: M50LT (latest M50 variant), Samsung G/S Variants.

3. Low capacity (on 4Ah Ballpark range), High discharge rating. Expensive. Low IR of the cells. about half of group 1s, but refer to your datasheet.

Ex: Molicell (P42A, P45B)

Use case:
Use Cells on Group 1 for high capacity packs that won't get lot of continuous load, around 1~1.5x of their Amp-hr rating.

Group 2 cells are for balanced uses, but should still be avoided for heavy C rating uses (above 2C)

Group 3 cells are basically "Throw money at your problem" solution to cell selection. most expensive, but will do the job. High C rating design packs require extra busbars to reduce IR of the battery.
[https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm Calculate resistance of metals]

Batteries

2023-11-15T02:29:50Z

Kopaz: /* Where NOT to buy */

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

'''DO NOT bypass BMS to "fix" a battery! BMS is usually the last-line of defense for safety and overriding will have serious consequences, like overcharging cells risking fire & injury.''' If batteries don't charge, it doesn't charge for a reason. forcing charge into it will have serious consequences.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

==Where NOT to buy==

1. All batteries available on large e-commerce websites (i.e. Amazon, Ebay, Aliexpress, Alibaba, etc).

These websites are filled with low-quality battery manufacturers & drop sellers that wants to maximize cost. a typical ebike battery starts around $400USD, give or take. They often take 10~20% on listing/maintenance fee (excluding taxes), so you can kinda see what kind of raw cost we're dealing with here.

2. Unit Pack Power

They used to be recommended, but after several fires & reports from community & outside community, they are no longer recommended.

3. BTRpower

These guys seem to use pouch cells, and unless you know what you're doing, you should not be using pouch cells on e-bikes.

Remember, a good ethical manufacturer will give you at minimum, what cells they are using & reasonable margin for continuous current/peak current of the cells.

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.

Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

==Battery Troubleshooting==
[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform This test will give you most basic knowledge & potential issues encountered when self-servicing battery.]

Disclaimer: The above quiz is not meant to be a certification and should only be used for educational purposes only. The test mostly covers about cylindrical cell formats, as they are most common type of cells used in E-bike batteries.

Questions/Concerns/Comments of that quiz should be forwarded to Kopaz at [https://discord.gg/wawDk8xzzQ E-bike discord server].

Batteries

2023-11-15T02:24:22Z

Kopaz: Where not to buy (aka, blacklist) added. Please discuss if I should remove btrpower.

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

'''DO NOT bypass BMS to "fix" a battery! BMS is usually the last-line of defense for safety and overriding will have serious consequences, like overcharging cells risking fire & injury.''' If batteries don't charge, it doesn't charge for a reason. forcing charge into it will have serious consequences.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

==Where NOT to buy==

1. All batteries available on large e-commerce websites (i.e. Amazon, Ebay, Aliexpress, Alibaba, etc).

These websites are filled with low-quality battery manufacturers & drop sellers that wants to maximize cost. a typical ebike battery starts around $400USD, give or take.

2. Unit Pack Power

They used to be recommended, but after several fires & reports from community & outside community, they are no longer recommended.

3. BTRpower

These guys seem to use pouch cells, and unless you know what you're doing, you should not be using pouch cells on e-bikes.

Remember, a good ethical manufacturer will give you at minimum, what cells they are using & reasonable margin for continuous current/peak current of the cells.

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.

Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

==Battery Troubleshooting==
[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform This test will give you most basic knowledge & potential issues encountered when self-servicing battery.]

Disclaimer: The above quiz is not meant to be a certification and should only be used for educational purposes only. The test mostly covers about cylindrical cell formats, as they are most common type of cells used in E-bike batteries.

Questions/Concerns/Comments of that quiz should be forwarded to Kopaz at [https://discord.gg/wawDk8xzzQ E-bike discord server].

Battery Thermal Management Methods

2023-11-03T14:54:58Z

Kopaz:

'''Intent:''' To educate readers on common PEV (Personal Electric Vehicle - EVs below size/carry capacity of a car) battery thermal management methods, and consequences of improper thermal management on rechargeable batteries.

==Introduction==
Battery thermal management will always have a form of heat exchange system.

'''What is a heat exchanger?''' This is a glorified term for anything that can move heat from one place to another. For example, the copper pipes on your laptop/desktop CPU/GPU where it connects to heat sink/fin to a fan is a type of heat exchanger i.e. radiative, using a fan. Since this system requires power to operate, It can be considered as an '''active''' type of heat exchange.

Therefore, the definition of '''Active management''' in this scope of article (and generally, outside the article) means that the system transfers enthalpy from one place to another while using power. For example, a fan would be transferring electrical energy to ohmic heat (from coils of the fan) + Kinetic energy (to drive the fan itself), pulling/pushing air (containing heat, aka, enthalpy) from one place to another.

'''Passive management''', in our scope, would be type of system that does '''not''' use energy to transfer enthalpy from one place to another: Heat sink/fins would be good example of this (and probably the only one, in the scope of this article). Since the system does not have a form of active device to block enthalpy transfer, this system, in theory, even out the temperature (enthalpy) of two system.

Practically speaking, most (if not all) e-bike batteries that are commercial uses passive management. Electric vehicles, however, often (if not always) employ some form of '''active management''' to manage enthalpy of batteries.

==Active vs Passive==
So why do Electric Vehicles use active method? Here are some following reasons.

===1. Active temperature management of batteries take up less space, on larger batteries.===
Imagine an EV that has battery mounted to the car. A typical EV, at minimum, starts around 40kWh worth of batteries: This is about 70 times more energy stored than a typical 48V12Ah Hailong battery that we put on e-bikes.

Often times, these batteries are mounted underneath the car, because that's pretty much the only practical place (and only) place to put batteries. (A primary reason of this is that it creates lower center of mass, improving stability of the car! this also applies to ebikes and motorcycles as well)

Now, we have to cool these batteries, so they don't cook off and become fireworks. Well, so, where do I put the heatsink? Underneath the battery?

Well, the heat fin wouldn't do well there, and it's most likely going to get damaged. Above? people sit on there. Sides? that's outside the car, and we won't be able to utilize much space.

What about watercooling like we do with computers? We can have copper pipes inside a plate that touches the battery; the cold (or hot) water can flow through this plate, and then cool/warm the battery. The waste heat can have a centralized radiator that is located on front of the car, and it can be passively cooled when the car is driving.

Needlessly, this type of system would cost more & a lot more complicated than simply putting fins on side of the battery.

===2. Active temperature management can '''control''' the flow of enthalpy on a battery.===

This is crucial. Let's say you can't put your ebike indoors, and you can't take the battery out of the bicycle. Also, it's winter, and you live in Canada. since most ebikes don't have a way to control enthalpy, the enthalpy outside the battery will slowly cool down the battery to ambient temperature.

Now, Typically, discharging batteries in cold is not ''terrible'', per se; but cold cells have higher internal resistance, leading to more waste heat (also causing a self-heating effect).

'''But, what if you tried to charge the battery while the battery is cold? Well, that can be reader's homework. (Hint: Nothing good happens to it)'''

==Battery thermal management in PEV Batteries==

Most of the methods that EVs use to control temperature of batteries don't work well on PEVs, and many times it's not necessary to do this; especially if the designer considered thermal management already when designing batteries.

Here's some reasons on why:

1. PEV batteries are much smaller in volume & size.

This enables PEV batteries to dissipate heat much faster, provided it has good contact with the outer casing.

2. PEV batteries are often placed in locations exposed to atmosphere.

This further helps to cool PEV batteries to ambient temperature.

3. PEV batteries (due to profit margin & competition) often leaves no room for active cooling features.

This is a deterrence factor, and consumer education can help defeat this issue.

However, with battery makers (who often do not know in-depth knowledge about consequences of improper BTMS, or simply neglect the importance) who sell batteries in e-commerce sites such as Amazon, Ebay do not equip their batteries to be suitable for long term use.

This goes back to the primary purpose of this article - to educate readers on potential consequences of improperly thermal managed batteries. Since e-bike batteries are passive cooled, e-bike batteries are especially susceptible to this.

==Consequences of passive cooling batteries==

Imagine I have 100 18650 batteries, and I want to make a battery pack with it. I can manipulate them quite a bit to get different shapes; [[DIY-battery]] takes about this to some degree.

Generally, you can make something thicker (more layers in between outer cells), or thinner. The internal resistance of each cell generates ohmic heat to heat the cells.

Now, imagine which battery would have more even temperature. A thicker battery or a thinner battery? <Insert cell designs here for visualization>

The best way to visualization would be using CFD simulations; But you can also intuitively guess as well (mainly because almost nobody reading this probably has access to a CFD, or even CAD software).

Imagine a heatsink copper pipe with multiple CPUs connected in a row in series to the pipe. What would happen if you were to give all of those CPUs same power (let's say, 10W) with only fan & fins on the end? You could deduce that the copper section furthest away from the fan would be hottest, because there are other CPUs generating enthalpy to the system next to one another.

What about a same setup but each CPUs are given their own heatsink independent from one another and has their own heat fins & fans?

Odds are, the CPUs would have more uniform temperatures.

Battery Thermal Management Methods

2023-11-03T14:16:05Z

Kopaz: /* Active vs Passive */

Battery Thermal Management Methods

2023-11-03T14:12:19Z

Kopaz: /* Active vs Passive */

Battery Thermal Management Methods

2023-11-02T19:21:09Z

Kopaz:

Battery Thermal Management Methods

2023-11-02T18:56:42Z

Kopaz: BTMM/BTMS article created (currently inaccessible to public, no ref links on existing article)

Batteries

2023-11-01T22:32:46Z

Kopaz: Warnings added on BMS bypass "methods" to fix batteries.

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

'''DO NOT bypass BMS to "fix" a battery! BMS is usually the last-line of defense for safety and overriding will have serious consequences, like overcharging cells risking fire & injury.''' If batteries don't charge, it doesn't charge for a reason. forcing charge into it will have serious consequences.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

Unit Pack Power used to be on our list, but due to several recently raised safety concerns and a couple of known fires, we no longer recommend this seller

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.

Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

==Battery Troubleshooting==
[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform This test will give you most basic knowledge & potential issues encountered when self-servicing battery.]

Disclaimer: The above quiz is not meant to be a certification and should only be used for educational purposes only. The test mostly covers about cylindrical cell formats, as they are most common type of cells used in E-bike batteries.

Questions/Concerns/Comments of that quiz should be forwarded to Kopaz at [https://discord.gg/wawDk8xzzQ E-bike discord server].

Batteries

2023-10-24T00:40:18Z

Kopaz: /* Battery Troubleshooting */

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

Unit Pack Power used to be on our list, but due to several recently raised safety concerns and a couple of known fires, we no longer recommend this seller

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.

Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

==Battery Troubleshooting==
[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform This test will give you most basic knowledge & potential issues encountered when self-servicing battery.]

Disclaimer: The above quiz is not meant to be a certification and should only be used for educational purposes only. The test mostly covers about cylindrical cell formats, as they are most common type of cells used in E-bike batteries.

Questions/Concerns/Comments of that quiz should be forwarded to Kopaz at [https://discord.gg/wawDk8xzzQ E-bike discord server].

Batteries

2023-10-24T00:39:20Z

Kopaz: Battery troubleshooting, link to quiz.

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

Unit Pack Power used to be on our list, but due to several recently raised safety concerns and a couple of known fires, we no longer recommend this seller

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.

Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

==Battery Troubleshooting==
[https://docs.google.com/forms/d/e/1FAIpQLSd-Jee1HL-Nlk5ZMCbuMsobD1qEIL67Lgq1BAB8IZPk3SZLIQ/viewform This test will give you most basic knowledge & potential issues encountered when self-servicing battery.]

Disclaimer: The above quiz is not meant to be a certification and should only be used for educational purposes only. The test mostly covers about cylindrical cell formats, as they are most common type of cells used in E-bike batteries.
Questions/Concerns/Comments of that quiz should be forwarded to Kopaz at [https://discord.gg/wawDk8xzzQ E-bike discord server].

Batteries

2023-10-16T01:47:57Z

Kopaz: /* Cell Lifespan */

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

Unit Pack Power used to be on our list, but due to several recently raised safety concerns and a couple of known fires, we no longer recommend this seller

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.

Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

Batteries

2023-10-16T01:46:44Z

Kopaz: Cell lifespan read added

It is very important to only buy high quality lithium ion batteries. Improperly build battery packs can lead to catastrophic fires resulting in loss of property and life.

Lithium-ion batteries can combust when improperly charged or discharged and can't be extinguished by water. as such there are only a few retailers we are willing to endorse. Its highly recommended to go with these resellers or at least do serious research on who you plan to buy packs from. Do not buy battery packs off random ebay/amazon/aliexpress pages, their quality often leaves much to be desired.

==Common battery pack formulas==
To find out nominal voltage of your pack, do: Number of series * 3.6V (3.2V for LiFePO4). e.g, 15S4P would have, 3.6V*15S = 54V Nominal voltage.

For capacity for the pack, First, find the datasheet for the cells used in the pack, then find nominal energy capacity of the cell (in Wh, watt hours). Then, do series*parallel of the pack (e.g, 15s4p=60 cells) * nominal energy of the cell (let's say, 18wh per cell). = 1080Wh.

To find maximum continuous discharge capacity of the battery pack, look at the datasheet again, and look for "standard discharge" or something along the lines of standard discharge.

They are almost always a number followed by a C.
After you find the C-rating (that is what it's called), use the above formula to find capacity of the pack, then multiply the number by the c-count. that is the absolute maximum your battery pack can handle for discharging.

Divide the number by nominal voltage for that number in amps.
E.G. 15S*4P*18wh=1080Wh. I found the cells to have 2C rating. 1080Wh*2 = 2160W.

I already know 15S = 54V Nominal, 2160W / 54V = 40A. So, in this case, the minimum (with no safety margin for BMS) BMS I should get would be 40A, capable of taking 15S Battery.

'''*Note: This number is absolute maximum continuous rating. Therefore, it is advised that you use this number (for programming BMS) as PEAK DISCHARGE, and for continuous usage, use 70~80% of what the actual datasheet, unless datasheet says otherwise (i.e. explicit mentions of peak discharge capability, usually described as ~amps/watts, 10s.'''

'''If you are unable to find proper documentation/datasheet for the cells you have for the battery pack, we suggest not using it.'''

==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:

*Better customizability due to shape of shells. This results in more variety of configurations without losing volumetric space; bicycles often have complex non-rectangular spaces that batteries are attached to.

*Pouch cell (prismatic) type batteries (small format, we are talking about size of phone batteries here) do not have structural integrity unlike cylindrical cells have. this results in worse reliability for these cells against impacts.

*Pouch cells often have inferior c-rating (continuous current output) rating than cylindrical cells.

*Larger prismatic cells are harder (if not outright impossible) to be used on ebikes, due to their size being a constraint. See point 1.

*Lastly, LFP/Lifepo4 cells have inferior power density compared to li-ion. This becomes a less of an issue for larger electric vehicles (i.e. motorcycles, cars, boats), whereas on a bicycle weight becomes an issue because most bicycles are not designed to have tens of kilograms of extra weight apart from rider's weight. This would mean that you would need to upgrade the frame/tires/motors to ones that can support more weight, and at that point you're essentially turning an electric bicycle to a motorcycle. Additionally, typical LFP/pouch cell battery packs (often prismatic/rectangular) are never meant to be mounted/tied to a bicycle.

==Where to buy:==
We currently recommend the following dealers.

[https://em3ev.com/ EM3ev] - High quality hand-made batteries shipped from China. Comes equipped with a bluetooth compatible BMS so you can monitor your batteries health and performance with a cellphone app. Highly recommended.

[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - High quality batteries shipped from USA

[https://www.affordableebikes.ca/ Affordable E-bikes.ca] - Sells/ships batteries from Canada.

Unit Pack Power used to be on our list, but due to several recently raised safety concerns and a couple of known fires, we no longer recommend this seller

==Reputable Cell Providers==

Here, we are listing battery cell suppliers known by members to sell legit cells. Cells are purchased only when someone wishes to make a DIY battery pack.

[https://www.nkon.nl/ nkon.nl]

[https://www.imrbatteries.com/ IMRBatteries]

==DIY battery packs==
If you cannot find battery packs that satisfy your needs, or you want to make/design on your own, [[DIY-battery]] can help you get started.

Finding a quality case that meets your needs can be challenging; [[DIY-case]] can help you with designing one.

==Cell Lifespan==
Use cells to their rated-C, do not overheat them. Some heat is inevitable/preferred even, because batteries' IR generally increase as cell temperature drops. There's a whole control method to proper temperature balance of cells.
Generally, you should strive for 20~80% SOC for charge-discharge cycle, but if you want to further lengthen cell lifespan, you can charge-discharge on a narrower SOC range, but this has diminishing returns (compared to 0%-100% to 20~80%).
[https://www.nrel.gov/transportation/battery-lifespan.html Further read/Reference]

Batteries

2023-10-11T18:47:55Z

Kopaz: /* DIY battery packs */

Batteries

2023-10-11T18:37:51Z

Kopaz:

Batteries

2023-10-06T22:20:36Z

Kopaz: /* Where to buy: */ Affordable ebikesdotca added to where to buy link.

Batteries

2023-10-01T16:07:51Z

Kopaz: More disclaimer regarding datasheet intepretation (i.e. cont. discharge)

Batteries

2023-10-01T15:59:04Z

Kopaz: /* Common battery pack formulas */

Batteries

2023-10-01T15:58:28Z

Kopaz: /* Common battery pack formulas */

Batteries

2023-10-01T15:53:54Z

Kopaz: /* Common battery pack formulas */

Batteries

2023-10-01T15:52:58Z

Kopaz: /* Common battery pack formulas */

Batteries

2023-10-01T15:52:40Z

Kopaz: Battery formula math added.

DIY-battery

2023-09-28T14:46:10Z

Kopaz: /* Start-to-Finish cycle */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.
[[DIY-case]] has helpful resources/practices if you are making your own battery case.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.
For calculating current capacity for your busbars for parallel group, [https://chemandy.com/calculators/rectangular-conductor-resistance-calculator.htm There's a website that calculates resistance for a given sheet metal.] I'm sure you can find others, but that's just 1 example.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-27T09:54:16Z

Kopaz: DIY-case link added

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.
[[DIY-case]] has helpful resources/practices if you are making your own battery case.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-case

2023-09-27T09:48:47Z

Kopaz: design practice added for fff cases.

'''Intent:''' To be a beginner (and intermediate guide) on making DIY cases. This guide is mainly designed for cases made with FFF/FDM printers. However, design technique/guideline can also apply to non-FFF printed cases where apply.

==General design guidelines==
[[DIY-battery]] Has most of the info, but TLDR: Best practice is to make 3D model of your battery pack, and then design case from there. Always leave space for BMS and other padding/dampening materials.

10%~20% of space should be more than enough, if you don't know what you're doing.
FFF Printer users: Do not make "tall" cases that are printed bottom to top as a whole. account for tolerances. if you are printing cases that has fasters on it with no metal threads, pretend those fastener holes to be expendable. FFF plastic threads don't last long.

===Limitation of FFF/FDM===
Due to how the printer works (bottom to top), anything that are printed bottom-top that relies on any side with 3d printed material is prone to fracture.

'''Layer adhesion:''' Most people who use FDM printers as a hobbyist don't know the secrets of making strongest parts with FDM printers. and that is by not making parts that relies on layer adhesion strength.

Analogy: Think of a house with bricks, but no mortars/support/adhesive. you kick one brick; the whole wall loses support. The further down this case fractures, more likely the whole part will just rip apart.
If you have to make a case that is "tall", pretend that you're banned from using infill, and print as slowly as possible with maximum heat possible for best adhesion.

===Best printing/design practice (for FFF/FDM)===
Generally, if you are printing a case, you're printing some sort of box. now, divide this box into sides (you'll get 6).

Now, model in a such way that these cases all have threads and will rely on fasteners to hold their weight. more fasteners, more weight that are evenly distributed.

Something like handles would most likely be printed in 1 or 2 parts: in this case, print the handle bottom to top sideways (so, tangent/perpendicular to the force being applied). Bottom to top would result in you holding the battery with handle that relies on layer adhesion.

Fractured handle while carrying = battery drops = potential fire hazard.

===Case sides with multiple part===
For example, 1 side of the case that is 2 parts (most likely split in 2 along the center).

This is bad practice because you've created a gap where water/moisture can seep through without having good way of sealing this gap. also, due to this gap, your case is structurally vulnerable, since there isn't anything holding on the side of case that is split.

So, if you are making a battery that is larger than your 3d printer's build area/volume, please reconsider.

==Other methods of making case==

1. Cut sheet metal, with FFF printed plastic or other forms of structural part for its exoskeleton/frame.

2. Plywood, but probably a bad idea if you're leaving case out in the weather. In this case, consider coating plywood so it doesn't rot.

3. SLS. Most likely inaccessible for majority of people reading this, but your college makerspace might have this. In case of SLS, the argument of layer adhesion strength would not apply, as this only applies to FDM. You can also make a custom order to companies that do printing service, but they often charge you a ton so this might not be acceptable for some.

DIY-case

2023-09-27T09:08:48Z

Kopaz: DIY-case created, content to be added.

DIY-battery

2023-09-27T09:06:41Z

Kopaz: /* Design */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info. '''Do not use cells that does not have reliable datasheet. This also applies for batterypacks as well.'''

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-18T05:56:18Z

Kopaz: /* Safety */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not mix battery packs of different cells (model, chemistry) in parallel, unless if you know what you are doing. Eg: I wire a 36V battery and 48V battery in parallel. Result: House fire.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-17T23:39:45Z

Kopaz: /* Start-to-Finish cycle */ grammar fix.

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-17T23:37:06Z

Kopaz:

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the[[Simulator]]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

Batteries

2023-09-17T00:27:26Z

Kopaz: /* Common cell formats */ Add power density

Batteries

2023-09-17T00:16:57Z

Kopaz: Add explanation for cell formats used in ebikes.

DIY-battery

2023-09-17T00:06:40Z

Kopaz: Add disclaimer (guide only intended for 18650/21700 liion)

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

'''Note:''' This guide is intended to be a guide mainly for 18650/21700 cells, as these two formats are the most commonly found format on ebike battery.

Why is this article not addressing prismatic cells, e.g. LFP/Lifepo4? Refer to [[Batteries|Batteries.]]

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-16T08:32:03Z

Kopaz: /* Design */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline. Most cells can handle power load above their continuous output for short period of time. Cell datasheets '''should''' have this info.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-16T08:30:38Z

Kopaz: /* Example case 2 */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''Example:''' if I put 6 cells sharing same junction, 67A / 6 cells = 11.17 Amps per cell.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-16T08:27:37Z

Kopaz: /* Example case 2 */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction. Each cell, in theory, is sharing 67 amps of load, divided by number of the cell per parallel group.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-16T08:25:46Z

Kopaz: /* Design */ Add example showing constraints of batterypack design

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

You might have noticed that even twice the 1000W (typically, the legal high-end limit of an ebike, depending on your flavor of jurisdiction) would require output current nearing 40A. '''In reality, there are very little (if any) model of cells that can do this kind of continuous output current without suffering from voltage sag.''' So, unless we want these cells to get really hot (Remember I^2R from whatever source you used to learn Ohm's law), we need to put more cells in parallel. Practically speaking, you merely put more cells sharing same junction.

'''For those who are considering using a manufactured battery case,''' this is most likely your constraint for building packs. If you want high current output/battery capacity on your bicycle, you will most likely have to put multiple battery packs in parallel.
Having said this, find out how much cells you can put in the battery case. This includes space reserved for BMS, balance wiring and padding for your cells.

'''Example:''' After doing modeling/sketch, at most, I can put 70 18650 cells on case I bought. I want this pack to have at least 40 Amps continuous output at 52V. 70 cells / 14 Series = 5 cells per parallel group. This means that each cell would need to have continuous output current of: 40 Amps divided by 5 cells = 8 Amps per cell.

'''Example 2:''' On the same case I bought from example 1, instead of doing 52V nominal voltage, I gotta go fast; I want to make my pack output same 40 Amps at 72V, instead of 52V. 70 cells / 20 Series = 3.5 Cells per group. I can't have 1/2 of a cell, so I'll have to round it down.

(Note: .5 cell * 20 series = 10 cells, so you're basically wasting space that 10 more cells can sit on.)

At 3 Cells per group doing 40A continuous output current, 40 Amps / 3 Cells = 13.3 Amps of continuous output per cell.

DIY-battery

2023-09-16T08:01:07Z

Kopaz: /* Design */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V nominal voltage, you would need 14 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A; at 60V nominal voltage, you would need 16 cell groups in series.

DIY-battery

2023-09-16T08:00:14Z

Kopaz: /* Example case 2 */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V Nominal voltage. You would need 16 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. Each series group would need to have continuous output of 67A. You would need 16 cell groups in series.

DIY-battery

2023-09-16T07:59:41Z

Kopaz: /* Example case 1 */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. Each series group would need to have continuous output of 39A; at 52V Nominal voltage. You would need 16 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. The battery would need to have continuous output current of 67A. You would need 16 cell groups in series.

DIY-battery

2023-09-16T07:56:41Z

Kopaz: /* Prerequisite software/knowledge */

'''Intent:''' This page is created as a guideline whether if assembling/designing your own battery pack is a viable option compared to buying a pre-made battery.

==Prerequisite software/knowledge==

Ability to draw 2D schematics/diagrams. - you need to do this if you are trying to make a pack with a certain dimension constraint. use of CAD is encouraged.

You know how to use the [[Simulator]] - You need to know how much current your battery will be drawing.

Ohm's law. Since we are not going into AC power, complex number/angle is not needed.

Ability to read battery cell datasheet. - As the wiki page becomes older, more cell info will be added to the page; but for cells that are not on this wiki/internet in a simplified format, reading datasheet will be necessary. [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]

You will most likely see terminologies that you've never encountered before, this will be explained along the article.

==Safety==
[https://www.youtube.com/watch?v=l_jeTcT6qBQ Batteries become explosives if they are uncontrollably discharged.] Therefore, at all times, you must respect the cell and equipment that you are using and know how to operate them. This would mean:

*Do not solder directly onto cells, unless you know what you're doing. you are thermally stressing the cell. In practical term, this would be putting soldering iron onto cell junction for extended period of times. The industry uses spot welders or screw-on terminals to reduce thermal stress on cells.

*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.

*Do not use used cells, if possible. Used cells are not recommended because they will have different internal resistance (IR) and it will be harder for BMS to balance packs with different IR and increase chance of cell failure.

*Do not make a battery pack without a BMS. Always use BMS from reputable sellers with appropriate discharge rating. For example, 30A battery should have at most, 30A BMS, preferably slightly lower for safety margin)

*Do not place/use conductive objects when making battery, if possible. This is generally unavoidable when using spot welders. In this case, cover the areas that you are not working on to reduce likelihood of shorts.

*Do not charge batteries unattended. Especially a battery pack you built for first time.

*In case of actual fire, do not try to put out the fire, Li-ion fires are uncontrollable and specialized fire extinguishers are needed. [https://www.youtube.com/watch?v=HQFff-KQ7EY Even this is not enough for large li-ion fire]

'''If this is your first electronics project, stop what you're doing. You're most likely to screw something up and burn your house down. If you don't know how to use a soldering iron and doesn't know how to use a multimeter, consider doing some other electronics project (learn from makerspace) then try again later.'''

(Reminder: add self-served knowledge assessment. - kopaz)

==Equipment requirement==

===Soldering iron===
depending on design, you may not even have to solder anything, but you most likely will for balance wires. Balance wires are used by the Battery Management System (Hereinafter BMS) to read a pack's voltage for charge/discharge/storage.
Pinecil will work for balance wires, but a higher power soldering iron will be necessary if you are soldering bus wire/plates.

===Battery case===
The shape/volume of the case determines how much cell you can fit in the case. You can 3D Print a battery case, and this will be explained further. In general, injection-molded/hardcase plastic battery case (if designed/manufactured well) will be almost always superior to a 3D printed/handmade case. Therefore, the latter cases are for more experimental purpose that market does not provide i.e. very large in dimension, custom mounting/hole for heatsinking, etc.

===Spot welder===
Spot welder of your choice, and something that won't fail after using it for an hour. They are either battery-powered, or supercap-powered. [https://www.nasa.gov/sites/default/files/atoms/files/prc-0009_current.pdf NASA's guideline on spot welding.]
Most li-po based spot welders on ecommerce site doesn't seem to last long. Expect anything under $100 be a "lottery", more or less.

===Multimeter===
used for troubleshooting. Red probe goes on V+, Negative probe goes on V-. '''Do not mix these up.'''
Cheap, reliable multimeter will do. we're not measuring high voltage here. Something like fluke 101 works.

===2D/3D CAD software===
To your preference - there are hobbyist/entry level software that usually has limited/featureset comapred to hobbyist-level and professional (career)-level software, but for this purpose, as long as you can do 2D sketch and do 3D model using sketch, it will work. Example: [https://www.tinkercad.com/ Tinkercad] [https://www.autodesk.com/products/fusion-360/free-trial Fusion 360] [https://www.freecad.org/index.php FreeCAD]

==Start-to-Finish cycle==

*Decide equipment of your choice first. depending on how complicated you want your design to be, CAD software may be recommended, but a simple sketch drawing might also do.

*Calculate power & speed requirement of your ebike. Refer to the [https://ebikewiki.com/index.php/Simulator|Grin simulator]. Hint: Faster ebike usually need a battery of higher voltage, or a motor with high KV rating (how much the motor will spin per volt), with enough power output to sustain this power (usually a peak at startup due to torque requirement, then gradually slopes down).

*Plan out what cell sizes you will be using (the most common sizes are 18650 (18mm*65.0mm) and 21700 (21mm*70.0mm). I hope you already have a battery case designed/purchased. If not, purchase/design a battery case first to your shape/dimension, make a mockup of your cells, including busbar/nickel strip so you don't mess up and burn your house down. Feel free to ask for help on our [https://discord.gg/ATZ8eet6fy Discord server].

*Select cells. You will most likely end up spending some time doing this, if you've never done something like component selection before. In general - Cells are characterized by (to price, cheaper to expensive):
Low power density, low max/continuous power output (usually the cheapest - prismatic cells fall into this sort of category, and entry level cells that are commonly found in powerbank packs)

Medium~high power density, low~medium continuous power output (something like LG M50 series linked above falls into this category). Slightly higher than the entry level cells, but still not the best. Example:

Medium power density, medium~high power continuous power output. Example: [https://litechpower.com/htmledit/uploadfiles//20210628200957892.PDF Molicel INR-21700-P42A]

The "easiest" way of choosing cells without risking thermal runaway would be simply choosing cells like P42A, bundle them in parallel to have desired Amp-hour, then wire them in series to have desired nominal voltage of your pack. Naturally, by doing this, you will run into cost issue.

*'''The best way of buying cells at cheapest rate is by buying them in hundreds or thousands. The price difference will vary from sellers, but they all follow this trend, one way or another (unless there is a sale/clearance). This is the break-even point you need to consider before making your pack, if cost is priority.
'''
Typically, nominal voltage for e-bike packs are usually multiples of 12 - 36, 48, 60, 72V (with exception of 52V). Above 72V is the area where you're pretending that you are an e-bike, but really isn't an e-bike (more like a dirtbike/motorcycle. again, depending on max power/speed due to different motor winding, this varies).
*Along with cells, buy other consumables for your battery, like cell holders '''(Unless you know what you are doing, always use a cell holder)''' and nickel strips (don't forget BMS and some padding). You can get screw-on style for making batteries parallel without having to spot welder, namely, by screwing terminal caps. Example [https://vruzend.com/ here] and [https://18650.lt/ here]. This is actually fairly common design choice outside PEVs, but they take up more volumetric space and more expensive (and proprietary) than simply spotwelding strips directly onto cells.

*For safety precautions, measure cell voltage one by one before connecting them in parallel. Every cell should be at same voltage level to 2~3 decimal points. They should all be on storage SOC (60%) per ICAO transportation reasons (I am not linking here, but feel free to read the legalese on your own). This means about 3.8V per series. You have a questionable/sus supplier, if you have cells that are fully charged/drained. Contact supplier and decide if you want to share the supplier to us on our [https://discord.gg/ATZ8eet6fy Discord server].

*Connect cells in parallel. Depending on dimension/shape, you may not be able to simply line them up (i.e., 1s*x amount of p-group, on a line). If you've been following this rundown, you should already have layout of your battery pack. Simply follow that, wire balance leads (V- goes to the V- of first series group, S1 goes to V+ of first series group, and so on, to the last series group). The last series group and V+ should be on a separate junction (series group balance lead should be soldered onto your busbar/nickel plate, other should be on output i.e., V+). Appropriately pad the battery pack to the case and, organize your balance wires so they aren't spaghetti. This might sound funny, but having balance lead that aren't spaghetti will be easier for you to troubleshoot & reduce likelihood of accidental shorts.

*Place thermistors onto cells wherever appropriate. this will be explained further.

*Program the BMS as necessary. The things you should be looking out for the most is:

1. Battery capacity (in amp-hour)

2. Nominal voltage (in Volts)

3. Maximum continuous discharge (in amps. this is NOT amp-hour)

4. Peak discharge (usually to 10s, also in amps. Refer to your cell datasheet and independent tests)

5. Charge-voltage cutoff, and Discharge-voltage cutoff (and alarm)
*Do not configure your pack to discharge from 100% SOC to 0% SOC, and vice versa. This will reduce your battery lifespan significantly. [https://www.nrel.gov/transportation/battery-lifespan.html Further read]

6. Charge/discharge temperature protection (High temperature and low temperature). Refer to your cell's datasheet. Do not leave your battery unattended.

==Design==
You use the simulator to find power requirement of your setup, then you use the peak power consumption as your baseline.

Depending on your design decision/riding habit, this can be flexible to some degree. 10s should be the absolute maximum for "peak" power output of your battery (this will also depend on the cells you are using). Dimension is also fairly simple - Either you find a case that fits on wherever you are placing battery on, or you design a custom case and use that as a baseline.
Custom design cases will be explained in detail in a separate article.
'''Note: Continuous output will vary, such as terrain grade, speed, air resistance and weight of rider/bicycle. Only use example cases below, as examples only.'''

===Example case 1===
Let's say we have an e-bike setup that will do 2000W continuous with a battery pack that has nominal voltage of 52V. The battery would need to have continuous output of 39A at 52V Nominal voltage. You would need 16 cell groups in series.

===Example case 2===
We want to make an e-bike setup that will do 4000W continuous with a battery pack that has nominal voltage of 60V. The battery would need to have continuous output current of 67A. You would need 16 cell groups in series.