Electric Skateboard

[Suladan]

Hiya, I am currently 15 years old and am taking a GCSE in electronics. I will be building an electric skateboard, and for this will require a PWM circuit to drive my motor. I've built some test circuits using 2 x 555 timer, and another one using a Pic chip, but these have all been used with fairly small voltage motors. The motor I'm looking at is a 36 volt 27amp 800 watt electric motor. I was wondering if anyone could help me make a circuit or link me to any premade circuits. I have seen lots of PWM circuits, but nothing powerful enough to drive this motor.

On a separate note I was wondering how hard it would be to charge the batteries when going downhill. Would this require a very complex circuit, and once again could you link me to any premade schematics.

Thanks
Denis

 

[Externet]

A search for 'dc motor speed control schematic' yields dozens of results. Wheelchairs are good donors of parts. Larger motors just need larger mosfets driven by the same basic circuitry.
Do it in stages, tackle the regenerative feature after you succeed with making it run.

Later you can also work on a handheld wireless control for it, and implement a step-on safety switch, so as if you disembark (-read fall-), that 1HP propelled skateboard will not rocket to break several ankles at a distance.
Miguel

 

[Hero999]

The circuit to drive a 27A 36V motor isn't much different to the circuit used to drive a 6V 2A motor.

You need to replace the driver transistor with a MOSFET with a VDS >45V and can easilly handle 27A, e.g. IRF3415 or IRF45N06, use one with as low on resistance (RDS) as possible and put it on a suitably rated heatsink with an insulating pad.

The 555/PIC needs to be powered from a lower voltage which can be derived using an LM317 voltage regulator. Make sure that the voltage driving the gate is high enough to allow 27A to flow; there are graphs on the datasheet which will help you determin the minimum voltage required.

It probably isn't worth charging the battery down hill because you need a boost converter to increase the voltage generated by the motor to above the battery's voltage which can be complecated, expensive and the amound of energy you get bace isn't much.