Difference between pages "Volts and Amps" and "DIY-battery"

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(Created page with "Volts, Amp, Amp hours, watts and watt hours, what do they mean for an e-bike? These are the units of measurements for batteries, controllers and motors. Lets dive into what each means in detail: ==Volts== Volts is directly related to max RPM for a given motor. For a given battery voltage will slowly decrease as it discharges (See https://cdn.discordapp.com/attachments/593205534862082075/620503053178503181/1545991790982-png.png for chart). ==Current== Current (measure...")
 
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Volts, Amp, Amp hours, watts and watt hours, what do they mean for an e-bike?
'''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 (before building a pack)


These are the units of measurements for batteries, controllers and motors. Lets dive into what each means in detail:
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.


==Volts==
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.
Volts is directly related to max RPM for a given motor. For a given battery voltage will slowly decrease as it discharges (See https://cdn.discordapp.com/attachments/593205534862082075/620503053178503181/1545991790982-png.png for chart).


==Current==
Ohm's law. Since we are not going into AC power, complex number/angle is not needed.  
Current (measured in amps) is directly related to the torque of your motor. You will often see a controller specify its 'battery amps' and 'phase amps'. Phase amps are your peak torque at lower RPM, where the controller can exchange voltage for amps to give you extra torque at low speed. Battery amps are what will be drawn from the battery. You absolutely must have a battery rated for the same or more amps then your controller is rated to use or you will damage your battery when the controller draws too much.
==Watts==
Voltage * battery Amps = Watts. Watts are your power. In fact it takes 745.7watts to make one horsepower. While voltage determins your absolute max RPM, without more watts you won't go any faster unless you where limited by the motor reaching its max RPM before you ran out of watts.
==Amp Hours==
Amp hours are how many amps your battery can give for one hour. For example if it was 10 amp hours, it could give 10amps for one hour, or 20 amps for 30 minutes, or 5amps for 2 hours. You might be mistaken into thinking that amp hours are equal to range, but that is only true for a given voltage as watt hours are the true unit of energy storage.
==Watt Hours==
Watt hours are Amp hours * Voltage. They tell you the true power capacity of a battery. In fact you will often find electric vehicles energy efficency expressed in watt hours per KM or mile. (wh/km or wh/mi). For a very rough idea, you can assume about 10wh/km for very slow riding at 25kph or below on flat ground, 20wh/km for fast riding up to 45kph or on slightly hilly ground, and up to 40wh/km for very fast riding at up to 60kph or on very hilly ground.  Exact figures vary greatly but this gives you a rough idea.
==C Rating==
Cells have what is known as a C rating, this is basically how quickly they can be discharged, with 1C being the current needed to fully discharge the cell in exactly 1 hour. You can calculate the peak discharge current by multiplying the AH rating and C rating hence for a 3.3Ah cell, 1C would be 3.3A and take 1 hour to discharge at that current. For a 2.5Ah cell, 1C would be 2.5A and also take one hour to discharge. a 2.5AH cell at 2C would fully discharge the cell in 30 minutes and at 5A current, 4C is the rate that would fully discharge the cell in 15 minutes at 10A for a 2.5AH cell, and so forth.


Note that the C rating is only the maximum you can safely draw from the cell, if you only draw at a lower current the cell will take as long to discharge as a lower C rated cell of the same Ah value
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]

Revision as of 08:31, 13 September 2023

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 (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.

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. LG M50LT datasheet, from batteryspace, Simplified datasheet of M50LT, courtesy of Batemo.de

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