trying to understand battery sizing w/controller amp output

[mocles]

How does a Rad Rover 6 with an upgrade kit(35amp) perform when the battery discharge rate is probably only about maybe 20 to 25 amps? I'm lost on how you size a battery with the controller output. Does the battery discharge rate have to equal at least what the controller outputs?

 

[biknut]

If your BMS max current is less than your controller current you run into problems hitting the BMS current limit. The battery's BMS limit needs to be the same or higher than the controller current limit.

 

[mocles]

If your BMS max current is less than your controller current you run into problems hitting the BMS current limit. The battery's BMS limit needs to be the same or higher than the controller current limit.

How would one know the bms limit of a stock battery unit from factory?

 

[biknut]

How would one know the bms limit of a stock battery unit from factory?

If the factory doesn't tell you, you have to guess. Factory battery's usually won't have a BMS much bigger than necessary to get the job done. Assuming 48v, and 750w motor, the bike would need at a bare minimum, 750w divided by 48v = 15.625 amps. Based on that I would guess maybe a 25 amp bms.

 

[mocles]

If the factory doesn't tell you, you have to guess. Factory battery's usually won't have a BMS much bigger than necessary to get the job done. Assuming 48v, and 750w motor, the bike would need at a bare minimum, 750w divided by 48v = 15.625 amps. Based on that I would guess maybe a 25 amp bms.

So back to my original question....how does the radrover with 35amp controller not overheat the battery?

 

[biknut]

So back to my original question....how does the radrover with 35amp controller not overheat the battery?

Either you're just putting around not drawing much current, or your BMS is big enough to handle it.

 

[mocles]

Do you think most bikes have at least a 10amp buffer?

 

[biknut]

Do you think most bikes have at least a 10amp buffer?

Factory bikes, I would hope so.

 

[mocles]

Okay okay.. I have a dual motor e-bike right now that's supposedly 2,000 w split between the two wheels. It's got a 22.4 amp hour battery with a 50 amp discharge rate and it has two 25 amp controllers running the front and back motors. Would it be safe to get a controller just for the front motor that is 10 amps greater?

 

[biknut]

Okay okay.. I have a dual motor e-bike right now that's supposedly 2,000 w split between the two wheels. It's got a 22.4 amp hour battery with a 50 amp discharge rate and it has two 25 amp controllers running the front and back motors. Would it be safe to get a controller just for the front motor that is 10 amps greater?

I don't think it would be particularly unsafe, but you might run into a problem with the BMS cutting off power if both motors max out at the same time for more than a few seconds. The only way to know for sure is to try it and find out. If you have Bafang motors, and install a KT controller, mine allow you to adjust the controllers max output, so if there is a problem you could make adjustments.