Jim
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This is my second phase converter. I disassembled my my first phase converter because it did not have enough power to supply my Hobart CyberTig welder.
The second one has not one, but two idler motors: a 10 HP motor and a 7.5 HP motor. They are started in a clever arrangement: first a 10 HP motor starts with capacitors labeled 1-3 connected. These capacitors act as starting capacitors. Then a second motor starts with the capacitors connected to legs 2-3. This creates a balanced system that has low noise, proper voltage balance, and good voltage stability under load.
See this this excellent article on making homemade phase converters.
I used an enclosure from a defunct Ferrups UPS, two used 3 phase motors, and a Allen Bradley size 2 starter for the 10 HP motor.
A few years later, I added a special mode to my 3 phase compressor, that would permit it to act as a third, additional idler.
