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Run Cap subsitution question. Two vs. one
by LarryC - 05/13/22 08:43 PM
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Joined: Jul 2004
Posts: 785
L
LarryC Offline OP
Member
Greetings all.

Had a factory smoke leak at the motor for my air compressor. 7.5 HP WEG single phase motor 240 volt. A start cap decided to leave home and splattered itself all over the inside of the motor junction box. After cleaning out the mess, I checked the bearings and centrifugal switch. All good. I had a local motor shop megger the windings. All good. So I assume the cap failed with age and heat. No significant change with the mechanical load as far as I can tell. Motor is 14 years old.

I decided to replace the start and run caps. Line voltage is usually around 240 when I check it and the caps were rated for 250. I decided to be a bit more cautious and I ordered 330 V caps to replace the existing ones. Of course, no good deed goes unpunished and now I am cramped for space in the box.

The existing run caps are two 30 u in parallel and I was wondering if there was any reason not to replace them with a single 60 u cap.

Thanks

Joined: Jul 2004
Posts: 9,687
Likes: 10
G
Member
Electrically it should work fine. I have played some strange capacitor tricks to get the AC going until I could get a new one. I have rooted around in my junk box looking for a bigger capacitor cover.


Greg Fretwell
Joined: Jul 2004
Posts: 785
L
LarryC Offline OP
Member
My concern is whether the single cap will develop problems because of heat dissipation issues. Two caps, half the current, a quarter of the heat generated, assuming same internal resistance. I am now thinking of staying with dual run caps and just up the sizes of the start caps since they are in the circuit for a much shorter time.

Am I overthinking this?


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