# My 5hp Compressor Motor Slows and Stalls



## bobinyelm (Aug 15, 2020)

I have a nearly new compressor on an 80gal tank I built from a new Harbor Freight 5hp pump and a New Century 5hp motor (220v Single Phase). The unit has maybe 15 hours of run time and worked splendidly. It has a 105psi turn-on and a 140psi shut-off.

Now, when the motor comes on, it seems to start normally, but even at 110psi it slows and struggles, so I turn the pump control switch off to stop he motor so it won't "stall" which is seems like it will do because it starts struggling and slowing.

The unloader works find as you can hear the air escape as the unit controller is shut off. The motor seems to start normally and almost immediately starts slowing as it usually does when approaching as full 140psi but struggling much harder (down at only 110psi).

The compressor pump has full oil quantity and sounds normal as it spins. No bad mechanical sounds coming from anything.

The motor is not allowed to run long enough to get warm.

Where should I start?

Bob


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## stevon (Mar 5, 2019)

Bob,

I doubt your run capacitor on the new motor is bad but stranger things have happened. What motor drive pulley size did you pick? get a cheap ammeter and answer this question. What are the amps measured at 110 PSI? what is the target RPM specified by the pump for a 5 HP motor? Is the listing on the Century motor FLA 20 amps or more?

Stephen


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## stevon (Mar 5, 2019)

Cheap ammeter:






Test motor:





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Troubleshooting With Compressor Amperage


What should the amperage draw be of a compressor in which the nameplate says the RLA (rated load amperage) is 59.6, but the compressor is only pulling 45 amps? Is there a problem here? Do we need to change the compressor?




www.achrnews.com





Stephen


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