PSC motor capacitor trouble

[ericaustin]

I'm ttrying to run a 1/12 HP AC Permanent Split Capacitor motor rated for 3450 RPM at 115 V / 60Hz using a 100 MFD run capacitor rated for 125 V at 60 Hz. The motor says it needs a 98 MFD capacitor.

I used a start cap and the motor ran smooth, cool, fast, and quiet until the capacitor began to fail. The cap got hot, boiled and sprayed some oil and smoke out of the top. This is actually typical and expected if you energize a cap too long that is designed for only intermittent energization, such as a start capacitor.

Later I ran the motor with a 100 MFD run cap and instead of the cap failing, the motor now gets exceedingly hot and runs noisy, and a little bogged down.

Why would a run capacitor rated at only 2 MFD over the spec cause such a dramatic degradation in motor performance. What are some possible solutions or tests to correct this problem?

Thanks.

[Al_The_Man]

That seems to me to be a huge value for a run capacitor for a 1/12 HP motor.
Are you sure of the value, typically I would expect well under 10µf.
Al.

[ericaustin]

It might be too large. I found one post in some other forum from a guy with exactly the same motor...he was trying to make it run but didn't get as far as I did. I think he said his needed a run cap valued at 9.8 MFD. I checked the stamp on my motor's case and it says 98 MFD. Maybe it should be 9.8 and the decimal is gone or missing.

Anyway I started and ran the motor with a start cap valued at 86-108 MFD. It started and ran the motor great until I failed the cap. The motor did not heat up and runs really smooth and quiet. Then with the 100 MFD run cap...which is physically about half the size of the motor...I ran the motor and it overheats and runs noisy and seemingly a bit slow or bogged down, with no attached load.

So are you suggesting that I should try a 9.8 MFD run cap and see where that takes me?

Thanks.

[Al_The_Man]

Originally Posted by ericaustin So are you suggesting that I should try a 9.8 MFD run cap and see where that takes me? Thanks.

I would expect it would be more like the correct value.
It should not hurt the motor to try it briefly, as long as it has not already been damaged.
Al.