Single phase motor problem

[fizzy]

It has been so long since I did anything with single phase motors I have forgotten the basics!
Went to use my Eagle surface grinder. First time I tried it the speed was rather low. I thought it might have needed a pulley change.
Tried it again yesterday. Wouldn't start - just sat there making a loud humming noise. I gave the wheel a flick. It did start but ran extremely slowly and didn't sound too healthy.
Any ideas? Everything turns freely by hand with no power.
Possibly the large capacitor or the centrifugal switch?

 

[carbon]

Usually if it just hums the capacitor is at fault. They can be checked with a dmm with a capacitance range.

 

[fizzy]

Usually if it just hums the capacitor is at fault. They can be checked with a dmm with a capacitance range.

It looks pretty rough and could be as simple as the wire hanging off - it's just dangling
Would that explain the low top speed when I first tried it?
Seemed about half of what it should be.
I think someone converted it from 3 phase though so might need a different pulley or a higher speed motor.

 

[Dcal]

Could be almost anything but the main culprits, in no particular order, would be the capacitor/s, the centrifugal switch, the windings and the supply / switch gear.
If it's converted to single phase from a 3 phase motor it is likely it doesn’t have a centrifugal switch and the start capacitor will need to be switched in and out by some other means, e.g. by hand or a timed relay?
It could also be that the start capacitor is not switching out which can cause oveheating and running issues.

Post below on how I went about finding the fault on my slow or non-starting compressor motor.

Stuff you have fixed today

faulty self adjusting caliper.... here's the caliper with the air can removed. and the top cover off and the offending item removed from the big chunk on metal that it sits in. the cause? the top circlip is missing (with the relevant seal) so there is no effective spring pressure. a new...

www.mig-welding.co.uk

 

[MetalMonkey]

Sounds like classic symptoms of a duff capacitor. Is it cap run or cap start?

 

[fizzy]

I will have to move the grinder and check it properly.
Looks like a single phase newish motor in there but can't see it properly.
Would rather 3 phase as I have it in my warehouse anyway.