Crikey - an alternator? Automotive alternators typically have 6 poles, which delivers 60 Hz at 1200 RPM. You would need to go to 8000 RPM to get 400 Hz, or a bit more than 133 revs per second. That's really humming along.
When I was younger, and found a tank gyro about 3" in diameter, it needed 115 VAC 3 phase. I found an electronic 28 VDC to 115 VAC 400 Hz that was single phase. A capacitor to the third phase wire would spin it up after you started it by hand. The motor doesn't care if the excitation is sine or square. There is a bit more heat dissipation from the harmonics in the square wave, but nothing to worry about in a small motor. If you are a purist, as many list members are, you could build a six step inverter to cut down on the harmonics. To be practical, divide 10 MHz from a GPS disciplined oscillator (which is necessary to be talking about this in this group), use a transistor to switch any available DC into a suitable audio transformer, and resonate it to 400 Hz with some caps. There was a time when I'd have killed for that kind of souvenir from a Northwest aircraft, but now I just sit back and read about it with fading interest. Bill Hawkins _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.