Checking run capacitors

[Steve Wright]

I work with a guy who checks run capacitors as a part of his routine maintenance. If it is supposed to be 20mfd and his checker say 17mfd he say es it is bad and replaces it.

I know this falls out side the 10% tolerance but my question is, is his checker that accurate?

I have always been taught that on a run capacitor if it is not shorted, open, or grounded it is OK.

I know there are homemade and other line voltage testers that can accurately test for capacitance but a hand held with three volts. I just do not know?

What do you guy think? Does anybody have any factory data on this?

Thanks Steve

[chillin out]

Hi steve
So long as whatever he is using to check the capacitors is accurate then he is probably doing right (or wright ..lol).
Things like these can cause comps to fail premature. (or be condemed unduly)

[Steve Wright]

Thanks chillin out

I guess that im relly not sure if his $100.00 meter is right or are there other things like temperature that could affect the reading?

[Greg W]

I changed countless motors with run caps fitted, I would say the run cap accounts for about 5% of failures.

I will add that only an inspection of the poles will determine what caused the fault.

[dan wong]

many capacitor check good at static condition (not hook up). But capacity change under load. long ago I attended a seminar the instructor show us a few capacitor checked good at static condition, but capacitant change drastically under load, He call it "dynamic capacity check". I can not find that diagram now, anyone here familiar with what I am talking about? can you post that diagram?