I need help designing a circuit for an electric bike

Thread Starter


Joined Apr 5, 2015
Hi guys,

I need help or need someone to design me a circuit. Here are the requirements that I am looking for:

I want it to take a reading of current consumption and adjust a PWM output (from 1000ms to 2000ms, like to operate a servo) to keep the current at or below a set value. It would have a PWM input (from a servo tester, again 1000-2000ms) to give me somewhat control over the speed of the bike, but no matter what I do it will stop increasing the PWM if the current gets above a set amount.

To give a bigger idea of what it will be doing, it is going on an electric bike. It will be put in series between the servo tester PWM out and the ESC (electronic speed control for RC stuff) PWM input. I am able to control the ESC using the servo tester and adjust speed accordingly, but if the circuit sees the current go above, say, 60A, it will simply stop increasing PWM even if I keep moving the servo tester. The circuit is designed to prevent overheating and failure of the ESC due to excessive current draw (especially during full power acceleration or climbing hills), because it is a $200 ESC and I would really not like it to burst into flames :)

It would be even cooler if it could get a reading from a temperature sensor and if the temperature got above a set value (say 80C) it will limit the current to only 30A until the temperature is back to 50C or lower.

Ideas? :)


Joined Jan 18, 2008
A block diagram would be helpful. Some points to consider, if I read your requirements correctly:
1) Servo pulses are 1.0 to 2.0 ms. Your values are 1000 times longer.
2) Current limiters on PWM controllers are quite common. Why not just buy a controller with one built in. That would be cheaper than paying someone to design and build your proposed unit. Have you searched for what is commercially available?
3) Addition of a temperature shut down should be easy and is also probably available on some controllers.
4) What is your budget for this project? At what voltage, current, and PWM frequency does your present device work?.