Air Compressor Problem - Motor Stalls

check the brushes and commutator.

Hi!

You should check the pressure switch contacts to be sure they aren't burned. If they look OK, check the wiring leading to the compressor. Perhaps something is wrong there. (Be sure you shut the power off FIRST or you could have a shocking experience.)

Failing all of that, I'd check to see if the motor uses a run capacitor. If it does, the capacitor is probably bad.

William

What kind of motor is this? I didn't see you mention that. A 1/3 horse induction motor should not draw 1.5 amps with no load.

It's some sort of GE induction motor. I have the model number, but I can't find anything about it on the GE website or Google.

What sort of problems would high no-load amp draw suggest?

Pressure switch contacts look OK, and there's minimal voltage drop across under load. Wiring looks OK, too.

There is a capacitor, but I'm not sure exactly what it does. I don't have a wiring diagram and can't find any info on the Manufacturer's website (GE.) I'll try to check the capacitor as best I can.

Could a capacitor issue cause the motor to start fine, but not have enough power when running?

Bad bearings.. and if it's a single phase motor.. check the starter cap, if it has one. most likely not much good any more..

Also, you may have a centrifugal switch in the motor that isn't closing its contacts. Or, you could have an open winding!..

Hi!

Good to know. It never hurts to rule out anything particularly obvious. It also would not hurt to check the wiring connections in the motor--are they rusty, burned, loose or just bad? If the motor has a built in circuit breaker, is it good? (A bad one could have burned contacts or start to open up just enough when the load increases.)

If it's a "run" capacitor, yes. Starting is the hardest time for a motor, and some of the air compressor motors I've seen have a dedicated start winding (and cap) to give them a little more "kick" to get going. That winding won't stand continuous operation, so it's taken out of circuit by a centrifugal switch when the motor reaches a certain speed.

From that point the motor runs on a different set of windings. Since it sounds like the motor runs fine up to a point where the load increases, my money would be on a run capacitor or wiring/current delivery issue. The run capacitor would serve to give the motor a little more kick when the load increases against it.

Capacitors for electric motors are usually pretty cheap. I had a furnace fan motor that would not start reliably and paid $7 and change for a new one. It made all the difference in the world. They're certainly cheaper than replacing a burned out motor.

William

None of the other suggestions I've read, fit the symptoms. First would be low voltage to the motor under load, but you've already checked that. The starting capacitor is out of the circuit when the motor is up to speed. There's nothing left in circuit but the two run windings, wired in parallel.

Alan

Suggests possible bad bearing, insulation on windings breaking down, bad start/run capacitor, bad centrifugal switch, bad connections where windings attach to start/run devices and line voltage. Find a place locally that repairs motors. Most communities have somone who does it and they should be willing to have a look at it for a few bucks.

And all those replies ignore the fact the unloader is operating (at a wrong, low pressure) which certainly doesn't point an evil finger at the motor at all...

Hmmm, yes, I think that wasn't in the original post so I missed it. That would account for gradual deterioration too.

Alan

Motors don't generally fade away; they usually burn up. I don't see how a motor would become weaker, especially an induction motor. There are no parts to wear out other than the stator winding, which doesn't fail gracefully. If it fails there will be an unmistakable stinky cloud of white smoke. You probably have a thermal overload on the motor, and that's what trips when the motor appears to stall. Based on what I have read here, this is what I would check first.

1. Check the thermal overload. Remove it from the circuit, and find a way to load it up with a known current until it trips. It should trip after some time at 1.15 times the nameplate current. It generally takes a long time, like several minutes, at that current. This will be around 2x the motor FLA. If the overload trips before you reach

I hope this helps.

I'd verify the gauge anyway.

The unloader is functioning properly, as far as I can tell. It's a combination check valve/unloader. So, when the check valve is open, it allows the high pressure air into the tank. When the check valve closes, it vents the pump side to atmosphere.

So, then the motor stalls, the check valve closes and the unloader part releases the pressure. When the presssure falls sufficiently, the motor restarts and the cycle continues.

I'll try to check it, but the thermal overloads I've dealt with in the past usually don't reclose quickly. In this case, the motor stalls, the unloader releases, and the motor restarts inside of about 5 seconds...and then the cycle repeats.

But, it's looking likely that I need to take the motor apart and inspect the innards (or take it to a motor shop.) So, I'll certainly check the overload(s).

It shouldn't. The unloader is supposed to open when the motor first starts, to let it come up to speed. Since the motor is stalling, you either have a bad pressure sensor, or the run capacitor has lost some or most of its capacitance. The pressure sensors deteriorate with age, and the calibration goes to hell.

The capacitors have to pass a lot of current, and aren't made to last forever. They are AC electrolytics to keep the size and cost within a range you can afford to build and sell a product. A film capacitor would be quite large, and can caost more then a new compressor.

Some compressors have two capacitors. One in the start circuit, and the other in series with one of the run windings to provide the required phase shift.

An electric unloader, yes. This is a mechanical one, integrated with the check valve. It is working as designed.

The pressure switch is OK. It is not what is stopping the motor. The contactor never opens and the motor is receiving full voltage through the stall cycles. The capacitor could certainly be the issue, though.

Indeed. This motor is probably 15-20 years old, so I can easily believe the capacitor may be at fault. I'll have to disassemble the motor and check it as soon as I get a chance.

I only see one capacitor, so I'm assuming it's in the starting circuit. I don't have a wiring diagram, and GE has no information on it's website for this motor.

Thanks!

From the original post that started this thread:

Your checkvalve has a small copper tube to the pressure switch, right? That's the unloader, which is also the small valve on the pressure switch. Read my original response on adjusting the pressure swtich.