Difference between pages "DIY-battery" and "Batteries"

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(Add explanation for cell formats used in ebikes.)
 
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'''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.
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.  
Prerequisite software/knowledge (before building a pack)


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.
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.


You know how to use the [https://ebikewiki.com/index.php/Simulator|Grin simulator] - You need to know how much current your battery will be drawing.
==Common cell formats==
The vast majority of E-bike batteries are based on 18650/21700 Li-ion cell type batteries. This is due to:


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


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.batteryspace.com/prod-specs/11514.pdf LG M50LT datasheet, from batteryspace], [https://www.batemo.de/products/batemo-cell-library/lg-energy-solution-inr21700-m50lt/ Simplified datasheet of M50LT, courtesy of Batemo.de]
*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.


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


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


*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.
[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.


*Do not leave individual cells outside packaging unkept. Store them in a container, if possible.
[https://lunacycle.com/18650-ebike-battery-pack/ Luna Cycle] - high quality batteries shipped from USA


*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.
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


*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)
==Reputable Cell Providers==


*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.
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.


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


'''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://www.imrbatteries.com/ IMRBatteries]
 
 
==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]

Revision as of 00:16, 17 September 2023

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 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.

Where to buy:

We currently recommend the following dealers.

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.

Luna Cycle - high quality batteries shipped from USA

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.

nkon.nl

IMRBatteries