Thread: Hot Capacitor

Check that the centrifugal switch is not stuck in the closed position (welded contacts).

The capacitor should only be used for a short period of time until the motor is up to speed (it is used to provide a second, out-of-phase, phase to the starting winding to get the motor moving in the correct direction).

Chris

watch the heat coz when they expode they do so with extreme gusto and spew loads of "stuff" all over the place

We are dealing with AC here polarity is not an issue, the capacitor should be non polar.

the capacitor should also be the correct size and rated for mains motor start.

depending on the motor configuration the capacitor may or may not stay in circuit.

indeed check on speed contacts.

unless you are absolutly competent in these matters it is wisest to call in a licenced electrical worker.

cheers

Originally Posted by soundman

We are dealing with AC here polarity is not an issue, the capacitor should be non polar.

the capacitor should also be the correct size and rated for mains motor start.

depending on the motor configuration the capacitor may or may not stay in circuit.

indeed check on speed contacts.

unless you are absolutly competent in these matters it is wisest to call in a licenced electrical worker.

cheers

I agree with soundman on this one

be very careful with the capacitor if by some chance it explodes be very careful with the swarf - the internal chemicals etc are usually extremely carconigenic. handle with care, do not breathe in any of the gases, wear rubber gloves and keep kids well away until the area is secure.
(no joke here guys)

What soundman said except you may want to take the motor to a rewind place and let them have a look, could be a bit quicker and maybe cheaper.
Just an option.
Motors are usually easy to remove.

Yeap, should be non-polar.

That unit most likely won't have a speed cut out switch for the start winding so the cap will have some load on it & will heat up.

You have to be sure that you have used a replacement that is correctly rated for the job.

Sometimes, replacing it with the exact same rated device is not right.
Some bits of gear are made for the 220VAC market & sold here in Oz where we often get upto 254VAC out of the mains socket.
Any 'mains' connected cap here in Oz needs to be rated to 400VDC to be safe.

Is it too hot to touch?

For all the above reasons, isn't there a capacitor cover in case the capacitor does explode?

Originally Posted by Cliff Rogers

Is it too hot to touch?

Close. But it was hot enough to radiate heat to about 50mm. I read the warning about their potential to explode and stepped away from it. Today I'll check that switch.

Thanks for the responses everyone. I did my homework before I asked and ran a search on threads in this forum. I'm ultra-careful with electricity and very quick to call in a professional when something is beyond me. This is not an urgent project: I have another drill press. It's more out of interest than anything.

I think that the important info that I gained from this is that once the motor's running the Caps should basically be out of action and shouldn't get hot. Is this right?

Originally Posted by Rossluck

...I think that the important info that I gained from this is that once the motor's running the Caps should basically be out of action and shouldn't get hot. Is this right?

Originally Posted by Cliff Rogers

...That unit most likely won't have a speed cut out switch for the start winding so the cap will have some load on it & will heat up.

Mine's a Rexon also and it does have a centrifugal switch.

Thanks again for the help. I took the motor apart this afternoon and the contacts were in such good condition that I didn't bother cleaning them. Instead I whipped out the replacement Cap and replaced it with another Cap I have. Problem solved. I ran the motor for half an hour, loading it occasionally, and it was as cool as a cucumber.

I do appreciate the frustration electricians must feel hearing of amateurs like me fiddling with stuff we don't know much about. But I am ultra careful, sometimes even wrapping the end of the disconnected cord around my wrist to be certain that I'm not fiddling with live stuff. I also have two in-line earth leakage circuit breakers and a "stand back and turn it on from a distance" attitude.

This did not, however, prevent me being lightly bitten while changing a welding rod this afternoon.

Thanks again.

Originally Posted by Tiger

For all the above reasons, isn't there a capacitor cover in case the capacitor does explode?

No, the cover is just to hold the electrolyte in and form some body, and to provide some shrapnel when it does let go
Generally the case is only a thin aluminium skin, even the little ones (5mm across by 10mm high) go off with one hell of a bang when hooked up asre about on a DC circuit (Cliff will remember those in Rad School )