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OT: 1ph motor hums

I recently bought a brand new Leeson 5 hp (20 Amp, 230 V) 1 ph "Compressor Duty" motor off Ebay. I made a quick test to see that it works correctly before I put it on the shelf awaiting other parts to finish my new compressor, and it sorta does. It starts fine, and seems to run well, but it makes a very loud hum, like a winding or core is loose inside. It also seems to get a bit hot pretty quickly. I thought that perhaps the start switch was not disengaging, but you can hear the centrifugal weights flip in and out as it starts and stops, and if you push the switch collar (the insulated collar around the motor shaft that moves when the weights fly out) in with a screwdriver, the switch opens up, as measured with an Ohmmeter. OTOH, it does not "snap" open, and the contacts don't open very far at all. Should this be a "snap action" switch, or just a pair of spring loaded contacts? Does anyone have a suggestion as to how to test dynamically that the start switch is opening up with the motor running? Thanks.

Yeah, I know. It hums because it doesn't know the words. :-)

Reply to
Bob Chilcoat
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Power it up so it hums. Then snap the power off momentarily then back on. While it was off, did the hum stop? If so, it's a bad motor and you got ripped off.

GWE

Reply to
Grant Erwin

Reply to
Don Young

I had simular symtoms on a smaller motor that I was running off an inverter. This was on a CNC key machine I used in a service truck. The unit worked fine when I ran it off line current but when it was plugged into the inverter the solid state relay that controled the motor would pulse on and off when it should have been off so when I metered the voltage going to the motor it would read about 35V.

This the motor did not like and eventuly burned out ne of the wires inside.

I rigged a mechanical relay that I could use in place of the solid state relay and that did the trick. The guy at the mtor shop said that if you run a motor below the name plate voltage you will cause it to overheat.

Perhaps the first thing you should check is if the voltage is high enough. Your extension cord might be too long or too thin and this would cause a voltage drop.

Reply to
Roger Shoaf

I don't think it's quite as clear-cut as this. A good single phase motor will vibrate less with the power switched off because the pulsating magnetic field inside disappears. Single phase motors naturally vibrate more than three phase motors, so this motor might be fine. It sounds like the switch is okay - the centrifugal switches I've seen do not have a rapid "snap" action and the contacts only open a few millimetres. If you switch on the motor in a dark room you should see a brief flash from the contacts as they open. I had a single phase motor which seemed to get very hot (almost too hot to touch) when unloaded. I found another identical one to test, and it did that same. I also measured the increase in winding temperature using the change in resistance, and it was much less than I expected. It was just the way the motor was designed.

If you hold onto your motor while it's running, is it uncomfortable to hold due to the vibration?

Chris

Reply to
Christopher Tidy

Could the field windings be hooked up wrong. I once wired up a 110/220 motors windings wrong and it hummed. Fixing it fixed the hum. Karl

Reply to
Karl Vorwerk

Reply to
EdFielder

try opening the motor and disconnecting the start windings, then power it up and spin the shaft by hand (or better, spin it as fast as you can by hand, then apply power, and it will lock in and run - if it does'nt hum with the start windings disconnected, you have a problem with the windings or the switch.

Reply to
william_b_noble

Reply to
Grant Erwin

Thanks, William. I'll try that.

Reply to
Bob Chilcoat

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