stray voltage? circuit problems

[tim vadas]

I've got two outlets in my workshop ceiling on one 20 amp circuit. I installed them before closing up the ceiling and finishing the space. They seemed fine once installed, measured 120V where it should have, etc. I only regularly use one outlet, the first in the loop, for a Jet air filter, which has a 3 speed motor. The unit works fine, powers on, runs, timer works, etc. However, the motor will hum occasionally when the unit is turned off. I haven't done a ton of troubleshooting because i don't have the time. All i've done so far is open up the first outlet, measure voltages across wires (the read what they should), retwist and wire tie all the connections, and it still isn't fixed. I checked the neutral at the breaker box and it seems snug.

Do you think it could be the circuit board of the air filter unit? I suppose the easy thing to test is plug it into another circuit and see if it hums; i'll try that tomorrow. If that shows that the problem is the circuit, any reason why i may get stray voltage on the neutral that could lead to the motor humming? Any other problems you could think of? I'm just looking to minimize my troubleshooting time. Thanks for any suggestions.

[Ken Fitzgerald]

Tim......something has to be applying power to the motor for it to hum.

I would use an appropriately sized extension cord on a different circuit and see what you get.

What makes your believe you are getting stray voltage on your neutral?

[Thomas Hotchkin]

Tim
You might want to keep it unplugged until you find your problem. Dirty switch? Tom

[Kevin W Johnson]

I'd be more inclined to think it's in the filter unit itself. If the control board is easy to get to, look for cracked solder joints, etc. You may need a good magnifying glass to look it over.

[Ken Fitzgerald]

Kevin....I agree and if it hums when hooked to another circuit in the shop, that will prove it. Then he can begin to troubleshoot the filter control board.

[tim vadas]

You're all right, it was the filter unit. I plugged it into another outlet and still a hum. I took the circuit board out and looked it over. It's a pretty basic board. I didn't notice any cracks, nothing burnt, etc. Maybe this is too much trouble than it's worth, but any tips on troubleshooting the circuit board? It's almost $100 part with shipping.

[John Coloccia]

You're all right, it was the filter unit. I plugged it into another outlet and still a hum. I took the circuit board out and looked it over. It's a pretty basic board. I didn't notice any cracks, nothing burnt, etc. Maybe this is too much trouble than it's worth, but any tips on troubleshooting the circuit board? It's almost $100 part with shipping.

Is there a transformer in there? If I had to bet, I would bet the transformer is humming.

[Matt Meiser]

Is there a transformer in there? If I had to bet, I would bet the transformer is humming.

If its one with a remote, probably, but the one on my Delta is pretty small because it just has to power a small circuit board.

I'd open it up (might just need to remove the filters) and unplug the motor from the board and see what you get too.