Battery limits and BMS Board

matharpre

1 µW
Joined
May 27, 2022
Messages
1
Hello,
I am thinking about purchasing a 3000w ebike kit off of Amazon. It is specified that the motor supports a range of 48-72v, and that the controller is 80A. While looking at batteries I could use I ran into one with a 60A BMS. However, after asking the ebike kit's manufacturer they said I could only use a battery pack with a constant 80A rated discharge (which conveniently is made by them, has half the lifetime, the same capacity, and is more expensive). Doing simple math tells me that 72*60 gives me 4320 watts, which is way more than I need for the 3000w motor I have. Does this mean that I can use the 60A battery without worrying, or is there some issue I've overlooked?
Cheers :thumb:

The battery I want:
https://www.amazon.com/UPP-Offical-72V-Ebike-Battery/dp/B09NM7SSQZ/
The battery the manufacturer wants me to get:
https://www.amazon.com/Triangle-Battery-Electric-Bicycle-Conversion/dp/B0979383J3/
My ebike kit:
https://www.amazon.com/135mm-dropouts-48V-72V-Conversion-26inch/dp/B08R3X5D58/
 
If you use a battery that can't output as much current as the controller asks for, the battery will either shutdown (leaving you with no power), if it monitors current and can shutdown for that condition, *or* it will be damaged by excessive current draw from the controller during those demand times. Most commonly the BMS FETs overheat and fail, but the cells themselves can be damaged, especially since a common FET failure mode is shorted "on", meaning the BMS can now no longer protect the cells against overdischarge, etc. once they fail this way. If they fail open, then all power is shut off until you replace the BMS. (and then either replace the controller with an appropriately-limited unit, or one that is programmable to lower the limit to what the battery is designed to support).

The motor, regardless of what watts it's marked with, will draw power based on the load placed on it by your riding style, speed, and riding conditions and total rider/bike/etc weight. If the controller can output more power than the motor can handle, *and* the motor is used under conditions that ask for that power, the motor can overheat and be damaged if this goes on long enough or frequently enough.

See the reply I just wrote here
https://endless-sphere.com/forums/viewtopic.php?f=3&t=116310&p=1716989#p1716989
for someone else's system, for some more info and a link to a simulator that may help you figure out what you need to buy in order to make a system that can do the work you need it to.


matharpre said:
Hello,
I am thinking about purchasing a 3000w ebike kit off of Amazon. It is specified that the motor supports a range of 48-72v, and that the controller is 80A. While looking at batteries I could use I ran into one with a 60A BMS. However, after asking the ebike kit's manufacturer they said I could only use a battery pack with a constant 80A rated discharge (which conveniently is made by them, has half the lifetime, the same capacity, and is more expensive). Doing simple math tells me that 72*60 gives me 4320 watts, which is way more than I need for the 3000w motor I have. Does this mean that I can use the 60A battery without worrying, or is there some issue I've overlooked?
Cheers :thumb:

The battery I want:
https://www.amazon.com/UPP-Offical-72V-Ebike-Battery/dp/B09NM7SSQZ/
The battery the manufacturer wants me to get:
https://www.amazon.com/Triangle-Battery-Electric-Bicycle-Conversion/dp/B0979383J3/
My ebike kit:
https://www.amazon.com/135mm-dropouts-48V-72V-Conversion-26inch/dp/B08R3X5D58/
 
Back
Top