Starter Capacitor for Garage Door Opener - What are the specs?

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Old 03-18-12, 12:34 PM
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Starter Capacitor for Garage Door Opener - What are the specs?

My Garage door opener stopped working and I know it's the starter. It hums for a second, then it stops. If I help turn it with my hand then it keeps going, so no doubt it's the starter.

My question is regarding the specs for the starter. The door opener is an old Genie. The bust capacitor reads 50-60 MFD 230 V. Why do I need a 230 V capacitor when the outlet is 120 V? Is it a safety factor? I've looked up prices, and a 60 MFD 230 V capacitor is about $20, but a 60 MFD 130 V capacitor is only a fraction of that price.
 
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Old 03-18-12, 12:48 PM
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It is possible that the capacitor is gone and is the easiest to check but is not the only thing that could cause your symptoms.
A bad starter switch bad start windings and low voltage are also possible.

When a motor starts the voltage across the start windings can momentarily go as high as 220 volts.
Although it is only for a second or so if you were to use a 120 volt cap the high voltage could cause arcing within the capacitor and poke holes in the foil.
Need to replace it with what came out.

Also, if the cost of a capacitor is a concern you could test it.
It is common for a capacitor to fail and have a visible indication.
A bulged relief cover or leaking oil in the connector end would give you some idea if it may have failed.
 
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Old 03-18-12, 01:14 PM
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Model number of the opener?
 
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Old 03-18-12, 02:24 PM
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It's a Genie Professional, with screw-shaft drive. I don't see a model number visible, and the previous owner didn't leave the manual.

I guessed it was the capacitor, because the hum definitely sounds like an inductive hum. But what you said made sense, so I tested the opener without the capacitor: the humming noise is the same, and it would start if helped. I also measured the the capacitance of the old capacitor, and it's down to 5-6 microF. There is no bulging, but some black dirt protruding from the bottom lid.
 
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Old 03-18-12, 02:47 PM
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Reason I asked.... I have a 20 y/o Genie Pro 82...and I had the same issue. Cap from an EBay seller for 1/2 the price of a local guy (who said it was a run cap, not a starter cap....uhhhh wrong?)...fixed it right up..
 
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Old 03-18-12, 02:57 PM
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Good point about start/run caps.
A 50-60 [email protected] volt will be a start capacitor.
Run caps are a much lower rating.

It is easier to test a cap with an analog meter but the procedure is the same with a digital meter.
Ensure that the cap is off the motor and discharged by shorting the terminals with a screwdriver.
Once discharged place one lead from a tester set at a low resistance setting firmly against one terminal on the cap.
When you touch the other lead to the cap one of a couple of things will happen;
If the needle rises and stays at a constant reading then it may be internally shorted.
If nothing happens it would be open and if it rises and then falls while holding the lead to the terminal it may be ok.

Sometimes you have to repeat the test because the rise/fall may not be that pronounced.
You do need to discharge with a screwdriver before each test attempt.
 
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Old 03-19-12, 07:41 AM
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Actually I found the same component from my local industrial-parts supplier for almost 1/3 of the retail price, relative to the garage-door-supply store. $9.78 vs $27.65 taxes included.
 
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