Arcing Centrifugal Switch

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Old 11-12-11, 05:48 PM
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Arcing Centrifugal Switch

I have a 1/2-horse capacitor-start motor that one day began to send out a slight burning odor when starting up. As I expected, the contacts on the centrifugal switch turned out to be pretty grubby, so I cleaned up the points, filed and polished them, and put the motor back together. Now they don't smell burnt, but they arc a lot and stutter. I'd replace the whole switch (if I can find one-- the motor's about 50 years old) but would like to know for sure that the switch is the problem, and not just a symptom of something more serious.

Thanks for any suggestions anybody may have.

LFMiller
 
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Old 11-13-11, 09:56 AM
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Motors are not my area of expertise but it could be a sign of a bad starting capacitor (if fitted) or perhaps a bad coil. You can replace the centrifugal switch with a starting relay. If this is a motor that would be fairly expensive to replace I'd check with a motor repair shop. The smaller shops can be quite reasonable in costs.
 
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Old 11-13-11, 07:23 PM
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Have you checked the end play of the rotor? Too much (over 1/64) will cause the centrifugal switch to act up. Shim it with a fiber washer and it should be fine.
 
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Old 11-14-11, 07:52 AM
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Thanks, guys. I'll check out both suggestions. It seems Westinghouse parts are going to be hard to come by, so hopefully the shim will put things back on track; or if not, a hard-start relay. (If I have to replace the whole motor, I'll still have no gripe with the universe, since I snagged this puppy off the side of the road .)
 
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Old 11-14-11, 10:41 AM
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It is not a "hard-start" relay, but simply a starting relay. It takes the place of the centrifugal switch.

I seriously doubt that excessive end play is the problem. Motors have an "electrical center" and anytime the windings are energized the motor will assume the electrical center unless physically constrained. The problem COULD be not enough end play or a sticking centrifugal switch caused by an accumulation of grease and dirt.
 
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Old 11-14-11, 09:21 PM
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I added the "hard-" on the strength of looking up "starting relay" on Grainger: hard-start relays for 1/2 hp motors from $16, cheapest non-hard relay $60 and that's on clearance at 50%. Would a hard-start relay be inappropriate in my definitely not-hard-start situation (direct drive into a 30:1 reduction gearbox with nearly no load)?

What I'm going to try first is re-reconditioning the centrifugal switch. I didn't fully dismantle it the first time and so may have missed some grunge build-up or pitting.
 
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Old 11-15-11, 10:25 AM
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No, more like one of these, Prices start around $20.

http://www.electrica.it/file_pdf/electrica_rva.pdf

UMSR-50 Universal Motor Starting Relay from ICM Controls, North Syracuse, NY | Proudly Made-in-America

http://www.sensata.com/download/4cr.pdf

http://www.servorecambios.com/recamb...lixon_2cra.pdf

You could just use a timing circuit to de-energize the starting winding after a second or two (an open-on-delay relay) or you could even use an additional normally-open pushbutton switch to momentarily connect the starting winding if the motor is in a manually started application anyway. Lots of possibilities depending on the application.

As I stated before, it could just be a bad starting capacitor (assuming it even has one) or it could be a damaged starting coil. If it is just a fractional horsepower motor you found along the road and not a special mount on a machine AND you can't find a problem with the centrifugal switch the best thing might be to simply send it to the recyclers.

One more thing, did you check that the centrifugal "governor" (for lack of a better name) moves easily on the motor shaft and doesn't have any missing or broken springs? It could be there is nothing wrong with the switch itself and it is the actuator that needs some TLC.
 
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Old 11-16-11, 05:53 AM
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Thanks for the tips and info. I'll post a report when I get this thing sorted out.
 
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Old 11-17-11, 05:47 AM
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Given enough time, my powers of observation and analysis may actually cut in. In case there's someone else out there with a Westinghouse 309P821C Frame H56Y motor, or similar, here's a long story made short:
1. This thing's a two-speed. If one speed shows a problem, try the other speed (brilliant, huh?)
2. Both speeds use the same centrifugal switch. So if the other speed runs fine, there's no problem with the capacitor or with the capacitor-bypass function of the switch.
3. However, that same switch also controls the relationship between the high- and low-speed windings, such that low actually uses the high-speed windings for starting until the routing function of the centrifugal switch changes the path.
4. Make sure you know which speed is working. Don't necessarily believe the markings on the control box, because it may be miswired (mine was.)
5. If low runs but high doesn't, I'm stumped (because of #3 above.) If high runs but low doesn't, I'd say there's either a problem with the routing function of the switch, or possibly something serious with the windings.
Step 5 is where I'm at. Since high runs and that's what I need, I'm not going to experiment further, for fear of making things worse. (Seems I just needed a hard-start device for my brain.)
 
 

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