What happened to our compressor motor?

[candikid]

Our compressor made a deep humming noise for a second, followed by the fuse blowing. I put in a new fuse (old cabinet) and same thing happens again. The third time the humming noise last for about 2-3 seconds, before it becomes completely silent. Fuse is okay, motor and compressor block is spinning freely, and the terminal box looks fine. No loose wires and no burnt smell.

I have no idea where to go from here, so any ideeas would be greatly appreciated. Electric motors are just not my thing... Yet

Btw it's a 3-phase 5.5hp motor. I can add a picture if it's of any help.

 

[Gary S]

I'd start by checking for power on all three legs at the motor itself. If the motor starter has failed, it might no longer be sending power to the motor.
If one leg of power is missing, you will get a humming noise as the motor attempts to run on the other 2 legs, but after a few seconds, it will blow a breaker or fuse due to excess current draw.

 

[hofferwood]

Check for an open "overload". I have seen them open up, allow reset, but only pass two legs of power. Acts like a blown fuse---but they are good.
Like what Gary said

 

[wyliesdiesels]

Agree with the 2 guys above. Also, check for proper voltage(within 5-10% of spec). The starter contactors might not be fully engaging as well so take the starter apart and check the contacts, etc. Obviously make sure the power for the circuit is off AND tagged/locked out!

You can also check the resistance of the windings to see if there is a short or open/break in a winding. However, if the wire insulation in the windings is weakened but not completely failed, there could be an intermittent short. Unfortunately, the only way to test for this is with a megohm tester, which is different than a regular multimeter.

Good luck!

 

[Kevin C]

Make sure the un-loader on your compressor is working. The motor wont start the pump unless the pressure is bled off.

A brief power outage can cause this...Motor shuts off but the pressure switch has never cycled. When you try to re-start the motor its trying to spin up a pressurized pump.

Basically, any power interruption can cause this. If the compressor sits for a minute or so, the pressure bleeds leaks off past the rings.

A bad check valve will do the same thing.

 

[candikid]

Thanks for all your help guys! We will go on and check all legs for power to start off with. Kevin: the unloader, what is that? Being from Norway I unfortunately don't know the English term for all the compressors' parts

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[Kevin C]

Thanks for all your help guys! We will go on and check all legs for power to start off with. Kevin: the unloader, what is that? Being from Norway I unfortunately don't know the English term for all the compressors' parts

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These guy have a better explanation that I do...

http://www.about-air-compressors.com/unloadervalve.html

What Unloader Valve Does
Compressed air that is trapped over the piston when the compressor shuts off will be evacuated to atmosphere through the unloader valve, to prevent that compressed air pressure from adding load to the start up of the compressor motor, when the pressure switch again calls for air.

 

[candikid]

Ahh, good tip for sure! Haven't had time to go down there yet, but that will definitely be the first thing to rule out.

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[candikid]

It might be wise of me to add that the belts had fallen off the other day. I wasn't there, but I guess this can have caused the motor to run for a pretty long time. This was probably a week before it stopped working...

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[wyliesdiesels]

It might be wise of me to add that the belts had fallen off the other day. I wasn't there, but I guess this can have caused the motor to run for a pretty long time. This was probably a week before it stopped working...

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If the belts fell off, then the motor would be under no load and that wouldnt effect the motor, UNLESS the motor's duty cycle is low. Motors with high duty cycles dont mind running non stop. On the other hand, constant starting and stopping will kill a motor.