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PSC Motor Capacitors

PSC Motor Capacitors

PSC Motor Capacitors

I should mention that am in the UK so 240v.
We run small linishers for light production and also teaching- these have been 100% reliable until the last month. We unpacked and set up a brand new one and the belt jammed, a student left it on but stalled for a few minutes. We let it cool down and it seemed to run fine. But on listening closer we realised it now buzzes as it runs - and seems to get hot quicker. This is not bearings as as soon as it is turned off it spins down quietly again. Is a PSC with 12 UF capacitor, windings are roughly 10, 20 ohm.

I thought little of this until I started a project that involved trying to get this motor to run backwards ( I started with another silent running one). - not possible electrically as I couldn't split the common winding, so I reversed it in the casing. Unfortunately this meant spinning the switch and it wasn't symmetrical and shorted something when I first closed it. This blew a fuse but when everything was put back more carefully the motor still ran- except it is identical now to the buzzing one.

If I disconnect the capacitor on either, it will normally stall but will spin up and run either direction and silently- I haven't dared run them long enough to see if they get hot. Windings are identical on both off these damaged machines and I can detect no short to earth. If I put the capacitor wires together it is incredibly noisy and runs at about 1/4 speed. Didn't risk that for long.

My thought was the capacitor- but these test our OK, I replaced with a similarly rated ( no identical ones available at short notice)this makes no difference.

Does anybody have any idea what I have done and if it can be repaired? Motor casing says 370 w , 230v , 2.4a , 50hz, 2800 rpm, PSC S1 F INS , 12 UF 440V

RE: PSC Motor Capacitors

"Spinning the switch"? Did you mean a centrifugal switch? If so, it is NOT a PSC motor, it is a Capacitor Start motor. Different animals. If it is a Capacitor Start / Induction Run (only one capacitor), then my guess is that in running it jammed, the centrifugal switch welded shut, meaning the capacitor is never taken out of the circuit.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: PSC Motor Capacitors

"Spinning the switch"? Did you mean a centrifugal switch? If so, it is NOT a PSC motor, it is a Capacitor Start motor. Different animals. If it is a Capacitor Start / Induction Run (only one capacitor), then my guess is that in running it jammed, the centrifugal switch welded shut, meaning the capacitor is never taken out of the circuit.

I think I should have been clearer- the only way I could get the motor to reverse was to strip it and rebuild it with the shaft reversed in the casing. The on/off switch is on the casing so this has to be spun / turned 180 as well. I am confident it is PSC; I found no centrifugal switch inside and it has PSC printed on the casing.

RE: PSC Motor Capacitors

The more I read up on this the less ideas I have-
1. It seems like if you have the wrong ( or damaged) capacitor then you can get noisy running as the windings aren't properly energised 90 deg out of phase. Yet every one I have tried is within spec.

2 If I disconnect one lead of the capacitor the motor runs quietly- this means I can rule out bearings or anything mechanical, I hope it means I can rule out frying the windings as well?

3. If I connect the capacitor leads together it runs very roughly and slow, but doesn't buzz. Not sure what that means, other than don't do that.

Instinctively I am still looking at the capacitor but can't find anything wrong with it. I have tried powering the windings directly to see if the switch was at fault, but it was a slim hope anyway I think.

Any ideas? At the moment I am tempted to run it with one lead of the capacitor disconnected as this seems to run the smoothest, starting by hand is no issue in the short term- or is this a really bad idea?

would it help to attach a video, if that is allowed ? the sound is pretty distinctive I would have thought- in that when searching youtube videos I haven't heard anything like it.

RE: PSC Motor Capacitors

Try adding a bunch of info to this post, maybe that will jar a few neurons lose around here.

A picture of the motor.

A picture of the motor plate.

A picture of the capacitor.

A picture of the wiring block if there is one.

Use the

above to post them directly into the thread.

Hopefully 1000 pixels wide or less.

Keith Cress
kcress - http://www.flaminsystems.com

RE: PSC Motor Capacitors


Thanks for the reply!

Hopefully not too huge. These are all I have at the moment. Can get some of the whole machine later on, can I attach a video of it running?
Last one of switch shows a sheared stud, this I guess happened on Assembly at the factory but hadn't caused any issues until I turned the switch 180 deg, and shorted something which caused the problems on this motor.

Have phoned the factory that made these and they say they no longer produce these motors, so that avenue is closed.

RE: PSC Motor Capacitors

Un-flip the motor and see if it fixes itself.

RE: PSC Motor Capacitors

Lionel - I probably will flip it back at some point to get it back to spec, but sadly I am confident that isn't the issue, It did run quietly after I flipped the rotor but before I flipped the switch and shorted it, also I have an untouched one that now makes the same noise after being left stalled but on for s few minutes.

RE: PSC Motor Capacitors

If you are using motor starting capacitors, then throw away the motor starting capacitors and buy motor run capacitors.
Costs a little more but worth it.
Comparing the performance with the cap in the circuit and with the cap shorted, your capacitor may be failing.
If a motor starting cap is used for running duty, you can expect early failure.
"Why not the best?"
Jimmy Carter

RE: PSC Motor Capacitors

Waross - My first thought was cap. I bought a replacement that tests at 12.5 uF, the two originals come in at 12 uF. The new one sounds identical to the old ones. It is possible it is not the right sort as you suggest but I doubt it would fail the first second it was switched on and still test the same?

I realize now that to make it run quietly - dusconnecting one lead on the cap is actually just disconnecting the higher resistance winding. Will running it from just one winding damage it in any way? I guess the power must be reduced, but in practice it is OK

RE: PSC Motor Capacitors

If you want to disconnect the capacitor, use an electronic starting relay.
These are use on single phase hermetic compressors in place of the centrifugal switch.
Find them at a refrigeration supply house.

"Why not the best?"
Jimmy Carter

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