I have a 5 hp 3 phase industrial air compressor with 90 gallons of capacity. I built with Bill Cosby a crude 10 hp 3 phase rotary converter. I want to wire it so that the rotary phase converter will only run when the compressor runs to save power. I also want to have it wired, so that I can run it constantly when I add a lathe to the shop. I've made a basic wiring diagram, but I am not sure if it is correct. Or if there is a better way.
Can someone look over the diagram and give me advice?
-Adam Prince
Crisp Line Metal
View attachment 107170
Your diagram looks like you have the basics thought out.
Give the RPC time to come up to speed, and then engage the air compressor motor.
With the HP rating of your RPC, I would have expected to see a magnetic starting circuit, but you may have left that out for simplicity.
Based on your diagram, when you disengage the start capacitor, the RPC is up to speed and the run capacitors are already charged and engaged.
You could eliminate the timers entirely by using a NO/NC relay as part of your starting circuit.
You could set the system up to close the circuit to a magnetic motor starter on air compressor at the same time as you disengaged the start cap.
My limited experience with air compressor circuits is they usual have a pressure activated relay that starts and stops the motor based on tank pressure.
This provides the switch gear large enough to handle the motors starting current.
If you use a set of timers on the legs between the compressor and the switch, they will need to be rated for the full voltage and starting current of the motor.
It may be more cost effective to add a magnetic starter to the circuit and use one smaller timing relay or a NC/NO relay to control it.
You also won’t have the issue of supplying the air compressor motor with single phase power should one timer fail.
My limited experience is big timers are not cheap or all that common, but motor starters are not hard to scrounge up second hand.
I have also noticed that many starters and relays can be disassembled and reconfigured easily from NC to NO.
Just thoughts, not instruction.