Phase converter started making terrible noise

Hey all,

I went to turn on my rotary phase converter in my wood shop and it made a terrible loud buzzing/grinding noise. I obviously turned it off immediately. It was working fine this morning so I'm wondering what could have gone wrong so suddenly. I'm in the US. It's DES electric phase converter with a Lincoln electric motor. 10 HP, 220 V. Do I need a new motor/phase converter? Should I just call an electrician? Or is this something I can try to diagnose myself?

Thanks in advance for any advice you can offer.

I think you will find the problem in the potential relay not taking the start caps out of the circuit.

That sound is likely the motor single phasing. Three phase motors sound terrible when doing that. You likely have a blown capacitor. See if any have a burn mark on one. My RPC you could leave the start caps engaged if you were starting a heavy load. There was no automatic throw out mechanism.

Just an idea. https://m.youtube.com/watch?v=SiF2OnNTQDo

Yup, single phasing. Could be a bad start cap, bad potential relay (not pulling the start caps), or a bad contact or loose wire on the start contactor. I spent a few months starting mine by manually holding in the start contactor until I noticed one of the relay wires was hanging close, but not actually attached to the relay.

Well, the idler is ALWAYS "single phased"..... but maybe you mean the unit was not starting ? Do you know if it was actually turning? If it was turning at more than a very slow rate, the start circuit was likely at least trying. If it sat and buzzed, without any significant turning, then that is a slightly different issue.

Sitting and buzzing indicates start circuit not cutting in, or a bad start cap, relay not closing, loose wire, etc.

Starting, but somewhat slower than ot should, can indicate the capacitor is undersized....if there is just one, it is partly failed, if there are several, then some of them may be bad or disconnected. Sometimes a similar thing can happen if the start circuit does not disconnect, which would point at a relay problem...

My phase converter has an undersized potential relay that is failing.

When I attempt to start the converter and the potential relay was stuck open (start capacitors never in circuit) it makes an absolutely terrible noise and the motor only barely starts to rotate.

The run capacitors may or may not be enough to get the motor to rotate and may even be enough to start the motor, though it will sound terrible and take much longer and risk damage to the motor.