Compressor Motor Fault?

[Andrew2007]

Hi

I got myself a large air compressor with supposedly a faulty motor, the seller was told by an electrician that the motor needed to be replaced but I thought it would be a good idea to test it out myself before committing to buy an expensive replacement.

It's a 3 Hp 230V AC motor single phase, you can see in the photo that the neutral wire that's connected to the 16A breaker has overheated.

The capacitor checks out okay with my multimeter and inside of the breaker look's okay too.

I've bought a cheap insulation tester, obviously not as good as what an electrical engineer would use but adequate for what I'll be using it for, I've tested the insulation resistance at 20°C between each of the three coil wires and ground, when testing at 500V DC the insulation resistance intially would be about 400 MΩ and go up to 1000 MΩ after 5 second's and 2000 MΩ after 7 second's which is the maximum the meter will read.  I know these number's should be temperature corrected to a higher temperature as the motor temp will rise when running, I read somewhere about 120°C but even so they appear to be well within what's acceptable.

I can only think that this connector on the breaker has overheated as the result of a bad connection, is the motor faulty?

Any idea, thanks?

[tppc]

I can only think that this connector on the breaker has overheated as the result of a bad connection, is the motor faulty?

I think it's a bad connection too.

If you short the blue wires, does the motor run normally?

If you can start the motor by manually turning the shaft, then replace the large white capacitor.

[Andrew2007]

I haven't tried to run the motor yet as wanted to check everything first, I forgot to say that the capacitor appears to be okay as I checked it out with my multimeter which reads capacitance.

Everything looks okay inside the 16A breaker but I can just connect the blue wires together to be 100% sure.

[soldar]

To me it looks like the faston connector was loose and overheated. I would try repairing it and then testing the equipment.

[cvanc]

It has the appearance of a classic case of localized heating caused by a loose connection.  I think your motor might be OK.

[Andrew2007]

I tried it yesterday and the motor does run, I'll get it connected to the compressor pump shortly and see how it performs under load. 😁

[soldar]

Those faston connectors when they start to heat up soon deform and go into a spiral of death.  You  should make sure they are tight  and make good contact.