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RE: Attenuating the generator.

Posted by Pyramid (A) on July 25, 2016 at 13:39:46

In Reply to: RE: Attenuating the generator. posted by twystd on July 25, 2016 at 11:55:04:

The increase in voltage you are seeing is most likely a reduction in the voltage sag of your output. You can't really directly measure the back EMF, but it will manifest itself as an increase in effective impedance of the motor coils as the motor spins faster. Decreasing the voltage output at 81Hz will reduce the torque, but the torque will decrease with the higher speed even with the voltage held constant as there is less current flowing in the coils as the effective impedance increases.

I believe Mark Kelly posted somewhere that the approximate impedance of the motor coils = (coil resistance x forward voltage)/(forward voltage-back EMF). At zero speed, the output of the amp sees the DC resistance of the coils; as the motor increases in speed, the effective impedance will increase. If you want the motor to consume the same power at all speeds (and maintain torque) you will have to increase voltage with speed to compensate.

Going to 50Hz will require more power than at 60Hz. There's really no reason to do this unless you have problems with higher voltage at 81Hz.

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