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Old 1st Apr 2024, 12:46 pm   #1
vinrads
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Default Motor start capacitor value.

I have just decided to refurb this half horsepower motor it appeared to be running on the start winding, the capacitor checked OK for value but leaky on volts test, it looks like 65uF/75uF, tried a 10 uF motor capacitor which seems to run OK, it's drawing just over three amps ran it for half an hour all OK, do I leave it in?

Thoughts please. Mick.
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Old 1st Apr 2024, 2:30 pm   #2
wave solder
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Default Re: Motor start capacitor value.

With single phase motors, the best way is to check the current when the motor is under load, too small a capacitance and the current increases, too large a capacitance and it also increases. Motor capacitors often have a built in discharge resistor which may cause the capacitor to show as leaky when tested. 10µF is a bit small, usually it would be 16-25µF for that size of motor.

Last edited by wave solder; 1st Apr 2024 at 2:39 pm.
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Old 1st Apr 2024, 6:16 pm   #3
John_BS
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Default Re: Motor start capacitor value.

I'm assuming that this is a capacitor-start motor: can you hear the centifrugal switch click shut as it runs down?

If that's the case, a 1/2HP motor will require c 60uF to 80uF - too small a value will give poor starting torque. The cap and winding are only rated for about 8 seconds (max) starting time, so it's important that the centifrugal switch is operating.

John
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Old 1st Apr 2024, 10:15 pm   #4
Uncle Bulgaria
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Default Re: Motor start capacitor value.

I second ensuring the capacitor is being switched out of circuit. You can do it with a continuity check while spinning the motor with a drill or something. I just had a 3hp one fail and take out a winding, and new ones are not cheap!
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Old 2nd Apr 2024, 9:23 am   #5
vinrads
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Default Re: Motor start capacitor value.

Thanks for all the info, when I checked the motor with a 10mf capacitor I noted the current on start up which would be just over 10 amps after a few seconds it dropped to 3 amps this would suggest that the centifrugal switch is working ok . I have ordered a new 60mf capacitor . Mick.
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