Have a look at the construction details of this Open Source Electric Bike Motor Controller. There are good circuit construction details and diagrams on the creators site.
More details are available on these pages:
"In brief the PicOx is a PicAxe 08M based digital Controller that performs an ADC of a Hall-effect throttle and an ADC of a Hall-based current sensor. These two parameters determine the “Mark” value of a 15Khz PWM signal that does the switching to the Output stage. At the end of the project the Controller can sustain 48V @ 75 Amps repeatedly for approx 5 second bursts and is really only limited by the In-Line breaker that cuts the supply voltage, though the entire system’s overall design objective is met reliably at 48V 50Amp operation…"
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