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Attenuating the generator.

Well a pot would work, of course you'd have a 3 gang one to deal with. There is also a possible impedance issue to deal with. The generator has a DC offset. The way I approached the problem was to use DC blocking caps on the three outputs. I also had a problem getting the output levels attenuated to get the generator outputs (too much voltage) in the range that worked with my amps, and the eventual output voltage to the motor. I was worried that the impedance of the amps, the attenuating resistors, and the caps could impose phase shift, and possibly affect the efficiency of the motor, due to power factor problems.

The way I went about that is to figure the amps input impedance (3k3) plus the attenuating resistor (5k6) for a total of 8k9 impedance each phase. Since the lowest frequency I was going to pass was 50hz, I went down a decade to avoid phase shift, and solved the cap value for 5hz. That comes out to about 3.58uf, so I'm using 3.3uf caps on the outputs. Not sure all that is really necessary, but decided to do it anyway, doesn't seem to hurt.

twystd


Edits: 07/21/16
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