Here is a really good tech manual from WEG electric motors, everything you ever wanted to know about 3 phase motors. This should keep you entertained for a few hours
http://ecatalog.weg.net/files/wegne...f-electric-motors-50039409-manual-english.pdf
OK, onto the problem. Let's break down what I did:
First the latest drawing
I am highly confident that the system is wired as above.
None of the caps have been switched in yet.
The VFD is set to coast to stop
The output relay in the VFD energizes CR2 on reaching operating speed.
The VFD run command is dropped out by CR2 and
C2A and C2B contractors supply the power to the idler motor are energized by CR2
EDIT: I should note that the system was tested with light bulbs prior to connecting the idler motor.
Assuming there is something weird going on between the 0.5 HP pony motor and the 15 HP idler motor. The idler motor should have enough torque to twist the tiny flex coupling into a pretzel even running on single phase. That doesn't seem to be happening. Even if the 0.5 HP pony motor were operating at full torque, in the opposite direction, the idler still should have more than enough power to overcome that and the VFD would trip out due to overcurrent, it's set at 2.2 amps.
Changing wiring combinations and pony motor rotation has no effect on the outcome.
Trying to start the idler outside of the system would be a bit hard, and electrically would really be the same because I would still be connect to the same breaker panel.
Feedback from the pony motor to the VFD? Maybe that's possible. Haven't been able to run it long enough to find out. If that's the case, I can fix that.
The only thing that really makes sense to me it that the idler motor is bad, it came out of a known broken air compressor said to have a fried brain, but that is somewhat indeterminate. It could be that the motor failed and that's what took down the system. Unless there is some revelation in the next few hours, I'm headed to the motor shop in the morning.
I suspect there will be a new idler motor in my future
I'm still open to suggestions