"easy" motor controller using audio amps?

[hummingbird]

Motor rotor induces a 'back emf' in the stator winding, thereby requiring way less current than the DC resistance of the stator would imply. This is the reason why there is a huge inrush current through a motor winding, when the motor starts - the back emf is absent at rest and slowly builds up as the rotor starts spinning...

Guess, you would likely encounter and tackle all design issues involved in a motor controller design from scratch. Will be fun to follow

[NiHaoMike]

You're better off starting from some large discarded UPSes. Or just get a surplus VFD (Variable Frequency Drive), which is already pretty much what you need!

[MazdaMatt]

Mike,

Please ellaborate on how an old UPS will help me produce a variable frequency and amplitude required to run a vehicle (bike, scooter, motorcycle, car, whatever).

Please show me a link to a DC-input 3-phase VFD for under $1000 capable of driving a few kW.

If my idea is totally fruitless i'll drop it. But please, ellaborate when you're telling me it isn't a good idea.


Hummingbird,

The huge inrush can apparently be avoided by driving the amplitude at the same factor as the frequency from the motor rating. Ie, if the motor is expecting 208V @ 60Hz, then when you're starting off at 0.6Hz you push 2.08volts, then when you're moving really slowly at 6.0Hz you push 20.8V, etc. Apparently deviation from this ratio allows you to control your torque for smooth take-offs and reasonable current at low rpm.