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An Electric Motor question
plentywahalla - 2/12/13 at 10:56 AM

This is a question for those of you who know these things, its all a black art to me!

I have a 230 volt ac 600w capacitor run motor on a pump.

It stopped running and just humms. That usually means that the capacitor has blown so I replaced the 15 microfarad capacitor and tried again. Same result it just hums and when manually spun in correct rotation, nothing!

The odd thing is than when I take the capacitor out of circuit so each set of windings is powered directly, and give it a spin it runs perfectly. With the capacitor in circuit, nothing. I have tried putting the capacitor in series with the other set of windings and giving it a spin (backwards) I still get nothing.

My understanding is that a capacitor run motor works by creating effectively a 2 phase supply by the capacitor creating a delay in the second set of windings. If so the above shouldn't happen.

Any answers?

Ashley Jenkins - 2/12/13 at 11:12 AM

I would test continuity/resistance of starter winding. It sounds like it might be open circuit hence why when spun manually the motor will run

big-vee-twin - 2/12/13 at 12:06 PM

Check the centrifugal switch, probably burnt out.

David Jenkins - 2/12/13 at 02:14 PM

quote:
Originally posted by big-vee-twin
Check the centrifugal switch, probably burnt out.


That was my first thought... or maybe dirty contacts.

There used to be a useful electric motor rewinding company on the Hythe in Colchester. They gave me a lot of help a long time ago when I needed new bearings in a motor - might be worth a quick look in yellow pages to see if they're still around.
(found them - they've moved - Colchester Rewind & Repair, Moss Road, CO3 0LE)

plentywahalla - 2/12/13 at 02:35 PM

quote:
Originally posted by big-vee-twin
Check the centrifugal switch, probably burnt out.


Its a capacitor run motor, there isn't a switch.

MikeRJ - 2/12/13 at 03:56 PM

Sounds to me like the main winding could be open circuit. By removing the cap and connecting mains directly to the capacitor winding, you would get it to run (with low torque) but it wouldn't be self starting.

Have you checked both windings for continuity with a multimeter?

[Edited on 2/12/13 by MikeRJ]

big-vee-twin - 2/12/13 at 06:47 PM

Capacitor motors have a centrifugal switch to switch the cap and start winding out of circuit once it's up to speed.

plentywahalla - 2/12/13 at 07:07 PM

quote:
Originally posted by MikeRJ
Sounds to me like the main winding could be open circuit. By removing the cap and connecting mains directly to the capacitor winding, you would get it to run (with low torque) but it wouldn't be self starting.

Have you checked both windings for continuity with a multimeter?

[Edited on 2/12/13 by MikeRJ]


You're right .... I opened it up and there was a break in the wire to the main windings. I soldered it back together and the motor starts and runs fine now.

What fooled me was that I assumed it was running at full torque when spun up manually. It wasn't ... after I had fixed it it leapt off the bench and onto the floor!

Thanks Mike

Richard