AC/DC
In this update about converting the VW Beetle, to 100% electric power, we look at the choice of electric motor.
eTrixie’s motor controller
Three-phase AC induction motors are almost the perfect machine!
They are lightweight, simple, efficient and close to maintenance free. They produce a rotating magnetic field in the motor case (stator) with magnets created by winding the wires in such a way to form magnetic poles.
The rotating magnetic field of the stator then induces a current, and magnetic fields in the rotor, which drives the shaft of the motor. The only real downside is the speed of the motor shaft is fixed by the frequency of the AC power supply and the number of poles in the stator winding.
But how can an AC motor work in a battery powered car?
Well, power electronics have saved the day! eTrixie has a Curtis 1238 650 Amp, 96 Volt motor controller. This critical component takes in DC power from the battery and ‘inverts’ it to output 3-phase AC power to the AC motor. But the real magic is that the power electronics can vary the frequency of the AC power supplied and so control the speed of the motor.
The combination of the motor controller and AC-motor together provide a near perfect combination.
The other thing the controller does is facilitate regenerative braking. I’ve added a transducer to the brake line which is connected to the controller so it knows when and how hard I’m braking. When the brake is pressed the controller will ‘reverse’ the function of the motor and will convert the rolling momentum of eTrixie into electrical power — the motor will become a generator and also help brake the car — free energy!
Master cylinder with the brake sensor inserted between the cylinder and the brake-light switch
Read more about the conversion:
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Electric certification in part one
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Power and brakes in part two
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Removal of petrol components in part three
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Flywheel and clutch upgrades in part four
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The AC induction motor in part five
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New Fuel in part six
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High Currents in part seven
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The Loom in part eight
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Keeping it cool in part nine
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Putting it all together in part 10 (including a video of the first drive!)
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Bottom balancing and battery management systems in part 11
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Getting the certification examination in part 12
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eTrixie the Movie! Video walk through
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A DIY EV in the real world in the final part
