I'm currently deployed to Iraq with the US Army and I'm working on hooking up an air compressor. I am not an electrician, but I have a little knowledge.

Here are the specifications:

Brand: Speedaire
Model: 1WD76
49CFM @ 175 PSI
15HP
208-230V/460
65A/60HZ/3PH


Pump speed: 1035
Pump model: 1WD22

We are trying to run the air compressor on a 30Kw generator that is producing 3PH 110V power at 60HZ. If my math is correct, it should take a little under 14KW to run this motor. This generator is plenty big enough to run this compressor.

Here's the issue: When the air tank is empty (no load on the motor) the air compressor runs great. It builds up the air tank to 175psi. and shuts down correctly. When the air pressure is lowered and the motor attempts to turn back on, it struggles to rotate at all. It may rotate a few times and then stops. We have taken the air pressure down to 75psi and the motor still will not start up.

We've also wired a 100A breaker in line with the compressor. This breaker blows when we try to start the compressor. Without the breaker in line, the compressor attempts to start, but turns really slow or doesn't turn at all when under a load. The data plate on the compressor says 65A, so I'm not sure why we are blowing a 100A breaker.

I've done a lot of reading and haven't found answers to my questions yet. Some of that may be that I don't know exactly what I'm looking for.

I have read that you can rewire some motors to get more torque out of them to handle heavier loads. The cover on the motor gives options to reconfigure the power rating for high voltage (460V) but getting this type of voltage isn't an option for us right now.

Any suggestions on this issue? Am I missing something simple? This motor came with the setup, so it should be large enough for the compressor. I guess my only real problem is that the motor will not start up under a load.

It sounds like your unloader valve is not working. Compressors will not start against full pressure. When they stop you will hear a hissing sound for a few seconds. This is the air pressure at the compressor outlet being vented. A check valve prevents the tank from venting. When the compressor starts there should be no pressure at its outlet and this unloading valve closes. This gives the motor a chance to get up to speed before it has to provide much torque.

I suggest that you not change the voltage settings.  As soon as the large starting load is presented to the generator, the exciter quickly shifts to maximum current, no matter where the voltage is set.  Changing the voltage or motor configuration will not make the generator produce more power than it does now.  The engine is probably the limiting factor.  If the generator needs adjusting, it will be adjustment of the stability control or the roll off control.  If either or both are set improperly for your circumstances it will decrease the ability of the genset to start loads that are a large fraction of the rated capacity.  Increase the stability and start the voltage rolloff at a higher RPM.  Read the manual.

Addition voltage under normal operating conditions will mostly serve to damage loads connected to the generator.

The electric motor will be most happy when the voltage to the motor lugs is exactly as the label specifies.  Either excessive voltage or reduced voltage will cause the current to increase.  The resulting current increases the heat load on both the motor and generator unnecessarily, reduces the capacity of the installation to carry additional loads and is the moral equivalent of pouring fuel on the ground.

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