Electric Power & Utilities/Doerr Electric motor


QUESTION: I have a campbell hausfield air comp, ( old ) with a 5 hp doerr motor. MTR REF PR75394BD901 220 volt 1 ph, 1740 RPM  I can't read the run cap volts or mfd , its wiped off  I have checked it out and get no readings. I talked to Grainger, Campbellhausfield, and tryed a shop to fix it, Its a direct drive motor, What size MFD and volt can I use for a run cap ?


You could contact Doerr with the model # and ask them or a good electric motor repair shop SHOULD be able to provide you with the right one but they probably won't give you that information over the phone with out you bringing the motor in.


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QUESTION: Bob thank you, however Doerr is no longer in business, I have tryed 3 shops, but the motor is part of the comp, It uses the comp for a end plate.  Unless I take both the comp and motor they won't be able to run the motor. A friend of mine owns a repair shop, I went to him and once again he said I have to find out the MFD size, otherwise all he could do would  be guess. He would have to try diffrent MFD sizes and check the amp draw.  The comp weights about 700 pounds, make takeing it in very hard. You Sir are truly my last hope. Thanks again.


I found this on a search for what its worth:

"For Run capacitor-- 10-15 mfd for 1-2 hp, 20 mfd for 3 hp, max 40 mfd for 5 hp."

I found other information that seemed to support this general rule of thumb.

Try getting a few capacitors(used maybe) from your friend or Grainger and try them. See which one gives you the closest amp draw to "name plate" and the best performance.

BTW  Check the name plate on the motor. The uf capacity might be listed there.


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PV Electric Bob Mossman


Master Electrician licensed (29 years) 6165B Contractor in Closter New Jersey with 38 years total experience in Residential - Commercial - Industrial work. Emergency Service - General trouble shooting and repair work - Paddle fans - Kitchen & Bath exhaust fans - AC lines - Smoke detectors - Telephone lines - Cable TV lines - Computer network cabling - Exterior lighting - Recessed lighting - Security lighting - (200 - 150 - 100 amp service up grades) - Electric Heat - New circuits - New appliance hook ups - Back up generators - and more ! FREE ESTIMATES Fully insured 201-358-1552


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