The guys that have posted have lots more experience and smarts than me about it. I've only built one, two different ways, three if you count the one I let the magic escape out of
.
I learned a couple of things that I don't recall being directly mentioned so far.
There are 2 different types of capacitors, "start" and "run". A start is usually one of those black round, lighter, ones with paper insulation. They have higher MFD numbers on them and kick the motor into motion, but can't cool well and won't last long at all if run constantly.They are the ones usually found under the cover of single phase motors, to kick your compresser or whatever into motion. Then there's run capacitors that are usually metal, oil filled, cans. They can run constantly and are used where you balance the legs, or create a phase with capacitors. The number of capacitors doesn't matter, their rating and your needs are what determines the number. I have some in the barn that I havent tried yet that are large, have a low mfd number, and I got a box of them when a local factory shut down. In theory I think it should just take more of them.
Somebody told me once that the British slang for capacitor is "tank", that worked for me. The first converter I made used a pair of starts to get it rolling and a bank of runs, that were connected to one incoming phase and the missing leg. It stored power from the line and dumped into the missing phase of the motor when it came around (I ain't no electrician
). That's a static phase converter and has no Idler motor. It only makes a portion of the nameplate HP though.
The next one used starts to get an idler like yours running and a couple of runs to balance the legs. I made up a harness with several slip on spade connectors and kept trying capacitors till it seemed to meter evenly the best I could get it.
A book I have suggests the idler be twice the hp of the motor being run, but goes on to say you can often stretch that. I'm stretching it a bit, a 5 running a 3 and nothing gets hot. I've also read somewhere that Delta windings work better than star wound motors.
