put our Heads Together
Join Date: Jun 2003
Location: southeast pennsylvania
Bikes: a mountain bike with a cargo box on the back and aero bars on the front. an old well-worn dahon folding bike
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I can try to help.
Short answer to your question - yes, I think so.
What you need to know is how your battery will behave if your controller "asks" for 50 amps. If you ever go up to full throttle, it's likely your controller will "ask" for the full 50 amps if it's designed as a "50 amp, at peak current" controller.
Many LiFePO4 batteries have a current limit feature built in to the battery management circuit at "2C" meaning you multiply the amp hours by 2 to get the amps it can put out. Batteries from ebikes.ca, LiFeBatt, DeWalt, and a couple others, may be able to tolerate much higher current than that.
So your battery might be limiting itself to 40 Amps. This is probably fine - I think your battery won't blow a fuse. I think it'll just send out 40 Amps and no more if it gets "asked" for more than 40 amps, or else it'll cut out when you ask for more than 40 amps and come back on when you unplug it.
One thing you should be aware of is that to get the wattage (power) that a motor+controller combination are consuming, you multiply the controller's Amps by the Volts. So 36V times 50A = 1800 watts as "peak" power. Motors are often rated in terms of "continuous" power which is less than peak power, but it's usually something like 66% of the peak power, which would be 1200 watts in your case.
If you never use "full" throttle while your bike is moving very slowly, you might never go above 40 amps anyway.