Electric bike question

[sutton sailor]

A non electrical mechanic friend of mine is trying to build an off road electric bike. After he had assembled it he has this problem. With it fully charged when he rides it and accelerates, he tripped out the 16A circuit breaker. He up rated the breaker to 20A but it still trips out. Also the battery quickly discharges. I tested the no load voltage of the output from the battery pack which was 78.8V
The motor is a Risun 48 - 72 V, 3000 - 5000 watts. the cells are 3.7V, and I am told there are 50 cells. Assuming they are all used that could only make up 10 banks of 5 cells = 18.5V, or 5 banks of 10 cells = 37V, or 2 banks of 25 cells = 92.5V. Non of these alternatives match with the motor requirements. Can the forum please advise?

 

[duncan99210]

Given that the motor is 3000 watts, it’s hardly surprising that the batteries run down quickly. My electric assisted bike has a 400 watt motor, gives me more than enough assistance for trail and road riding and the battery lasts for up to 40 miles with the maximum level of assistance - a good deal further if you set it a bit lower.
As to the breaker tripping out, if you take 3000 watts at 48 volts, that gives you a current of 62.5 amps (if I’ve got things the right way round) so not surprising that the 20amp breaker is tripping.

 

[LiftyK]

Pedelecs forum is a great U.K. site to get help on electric bikes.
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