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Discussion Starter #1
I have a really perplexing problem with an older air compressor. The compressor is an old 2-stage Saylor Beall 80 gallon with a 240v 5HP Dayton electric


When the compressor is plugged in, the motor starts and begins to turn the compressor pump, but then trips the circuit breaker right away. I have checked

the current with an AC clamp meter, and the motor is drawing a peak of 213 amps on startup with the belts hooked up to the compressor.

I have tried unhooking the compressor from the tank so that the compressor head cannot build up pressure. This did not change my results. I still tripped

the breaker with the tank unhooked.

If I remove the belts so that the motor is not coupled to the compressor head, the motor will start and run fine, but does make a lot of noise like the

bearings may not be in the best shape. When I remove power to the motor, the motor keeps spinning for a LONG time. As the motor spins down, there is a

point at which I hear a click and the speed decreases quite suddenly. It's almost as if there is a brake inside the motor that kicks in at this point.

When I hook the belts back up after running the motor by itself as described above, I can start and run the compressor successfully one time. The

compressor will run until it reaches the cutout pressure and then shut down. After this one successful run, I cannot start the compressor again without

tripping the breaker.

There are three capacitors on top of the electric motor. One is a 25MFD oval cap, and the other two are round 1070MFD. I have tested these with the

capacitance function on my AC clamp meter, and they all test OK.

I would greatly appreciate any help, as I am really stumped with this.


Motor Info.jpg


18 Posts
Many motors draw that kind of amps (especially at startup), it just depends how big the motor is.

Did you check the motor windings? Maybe 1 is broken and it runs on only two. You can easily check it with a simply multimeter.

You could also measure the insulation resistance (should be i the megaohms) of the motor windings, that's a common failure. But you need a special high-voltage meter for that.
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