How do you test the capacitors? And how do you safely discharge them?

by Jim Richardson
(Hillsboro)

I have a Porter Cable oil free compressor (mdl#CPF-6020-1) that pops my dedicated 20 amp 110v breaker as soon as you turn it on. The motor turns over about 2-3 times and then trips the breaker. The piston moves freely by hand so I am thinking it could be a bad start up capacitor?

So how can I test a capacitor and how do I safely discharge it before testing? Or if you think this is caused by something else, please make suggestions.

Thanks,
Jim

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Bill says....

Jim, I am still looking for a safe way to discharge and test capacitors for business and for the DIY compressor user. No luck so far.

Does it exhibit the same symptom when starting with an empty tank? If so, your diagnosis is likely spot on.

Bill

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Sep 04, 2011
contd.
by: Jim

I took the motor to an electric motor shop and they tested both capacitors as good. BTW they discharge them by just shorting across the terminals with a screwdriver.
The motor ran fine for them on the bench and again for me when I got it home on my bench.......but then there was no load on the bench. But when I reinstalled it on the tank and it had to pump air into the tank it would once again barely start and then pop the 20 amp dedicated breaker....I also tried a different curcuit and it again pops the breaker. So I have to conclude that once under load the motor draws too many amps. It only drew 8 amps running on the bench under no load.

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Jim, thanks. I know about the discharging capacitors by shorting the terminals. I'm not going to tell folks to do that because they could do themselves an injury if they are not careful. I'm looking for a safe way to do it. It is too bad that your motor test people wouldn't test the motor under load. I think your motor may be failing and it's manifesting when it's trying to run against load. Make sure the check valve into the tank is working properly. If your intake or pressure valve is seized, that might be an issue causing this too.


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THERMAL RESET SWITCH

I HAVE A 5 HP SINGLE PHASE 230V COMPRESSOR THAT THE THERMAL SWITCH KEEPS CUTTING OFF. IT JUST STARTED DOING THIS TWO DAYS AGO IT HAS HAD BEEN WORKING FINE AND DOES NOT SEEM TO BE OVERHEATING. i AM IN A REMOTE LOCATION AND I NEED TO GET THIS BACK UP AND RUNNING ASAP. CAN I TEMPORALLY BYPASS THIS SWITCH

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Bill says...

If you have a heat problem and you bypass the cut out, then the heat will destroy the components that the thermal switch is designed to protect.

Can you bypass the thermal switch? I'm sure you can. Can you afford the greater damage repair bill that will likely be the result?

Cheers,

Bill

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