motor start capacitor

Just look in the yellow pages for 'electric motors' or 'electrical wholesaler'. They are quite common.

You should have a local W.W. Grainger Company branch office. If not it can be ordered online at

and here is the info:

Stock # 4CU62 Motor Start capacitor, 64 UF @ 330VAC $8.32

An electric motor shop may also be able to sell you a replacement cap. Just bring the old one with you.

Excellent!!! We do have Grainger here, in fact they sponsor our local Minor League Baseball team. Thanks a ton, Ken.

Dan

So I've verified that the Lansing, MI grainger carries this capacitor and I can buy one on Tuesday. Woohoo!

In the mean time I've found that the motor will actually run fine provided I give it a nudge to get it started. I guess the whole purpose of the capacitor is to start the electric motor? How does that work? I don't actually understand how a single-phase AC current can turn a motor at all... since there's no rotating magnetic field.

Anybody know of a good reference on how an AC motor works?

Dan

The motor has two windings, one of them has the capacitor in series with it to give a phase shift with respect to the other ! Note if you want to reverse the motor apply power across the other side of the cap.

I--@@@@--- L2 I I L1---I Cap I I I--@@@@--- L3

--
Best Regards:
                      Baron.

Coincidence. It wasn't the grease.

Google for (permanent split phase capacitor motor).

Was that graphite grease? How much did you get on the motor/electrical contacts? Seems a bit strange!

Thanks for relieving my guilty conscience :-) I was beginning to suspect the same... though it's darned uncanny that it blew immediately after I greased the mechanical parts.

Once I disassembled the door opener, I realized the capacitor was hardly in a position to have gotten any grease on it. I looked up the service life of the capacitor and it's about 16k cycles... meaning it would last about 12 years if cycled 4 times a day (mom leaves in morning, dad leaves in morning, mom comes back, dad comes back). And it's definitely at least 20 years old.

Dan

It was white lithium grease. Not conductive. I use it on bearings in bicycles and lab equipment all the time, so I figured it would work fine on the garage door pivots and the bearings in the motor.

When I sprayed it inside the motor housing, I tried to carefully aim it only at the mechanical bearings, and NOT at the electrical contacts.

I agree that it's very strange, but the coincidence seems very unlikely. Although the capacitor was evidently nearing the end of its service life in any case (16k cycles).

Dan

I'm not convinced that it's a coincidence. If you really sprayed grease inside the motor, you may have gotten it on the contacts of the centrifugal switch that is supposed to interrupt the circuit to the start cap once the motor gets up to speed. If the start cap remains energized for more than the time needed to start, it will do exactly what you describe quite quickly.

So, at the very least, you should check the AC voltage on the start cap using a meter that reads only AC (not the DC omponent). It should go to

0 VAC once the motor is turning at normal speed. If not, you'll have to disassemble the motor and determine what's going on. And have your safety goggles on while doing it!

--- sam | Sci.Electronics.Repair FAQ:

Repair | Main Table of Contents:

+Lasers | Sam's Laser FAQ: | Mirror Sites:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

Unlikely they use such a motor - more likely a PSC motor with no such switch. Easy to reverse at speed and there is no great starting load.

Don't you hate when that happens?

That's a really good point, Sam. I have no idea if this motor has that type of switch or not. It's a Westinghouse 1/2 hp motor. Is the switch internal to the motor, or might it be external? If it's internal, then I really doubt I could have gotten any grease on it... but if external then I suppose there's a possibility.

In any case I'll buy 2 new caps since they're only $8.

Dan

It would be inside the motor, probably at the opposite end from the output shaft.

Someone else pointed out that he didn't think this was likely in a motor used for this application but rather a PSC motor. However, then you would have a motor run cap, not a motor start cap. I don't recall what the specs were for your cap.

--- sam | Sci.Electronics.Repair FAQ:

Repair | Main Table of Contents:

+Lasers | Sam's Laser FAQ: | Mirror Sites:

Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs.

I've seen a variety of those types of switches. Air pump driven, Magnetic Drag driven, bearing slip driven etc. all usually have a return spring or something to force the switch back into it's starting point again. Most common one's i've seen are magnetic and get pulled from the shaft when it's spinning. you might want to pull the back cover off the motor to make sure the mags still are there or have some life in them. Heat over time can kill them and thus not switch off the cap also, also a fused set of contacts don't help;

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Yea ! Like when you do a clean re-install on a computer, set it up just right........... then the hard drive fails !*@$"£@

--
Best Regards:
                      Baron.

Hi...

Might even be a simple centrifugal switch, in which case grease might be enough to bind it up.

Take care.

Ken

PS - REAL programmers use copy con.

:) i thought they used a numerical HEX entry key board!

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5