Air compressor motor amps

[bigtiller]

I bought a used Coleman 20 gallon air compressor and need help with the amperage requirements for powering it with a generator. Can you see on the label how many amps are required at start-up and run?

It looks to me that it wants 102 amps at start-up. Is that possible?

 

[SPYDERLK]

Yes. Locked rotor Amps are stated as 102. That is very brief, but it takes a good sized gen to hold voltage to nominal and it drops immediately, foiling startup. This drop means no torque. The compressor loads almost immediately as it spins up and it stalls. If your tank is dead empty ... maybe, but I think you are going to need at least a 10KW to start it otherwise -- and NOT an inverter gen because they want a balanced load to actually give their nominal rating.

 

[404nouser]

Yes it says locked rotor is 102.
But a 20A breaker should hold for it.
The way inductive loads pull power is different than resistive loads.
I would much prefer a breaker tripping than letting a motor pull LRA for more than a couple of seconds.

 

[MichiganIron]

Yes it says locked rotor is 102.
But a 20A breaker should hold for it.
The way inductive loads pull power is different than resistive loads.
I would much prefer a breaker tripping than letting a motor pull LRA for more than a couple of seconds.

Compressor motors are usually capacitor start motors. The start capacitor provides the locked rotor amperage for 1-2 seconds so the motor can provide the necessary starting torque in a compressor application. The capacitor shuts off 1-2 seconds after start up (at rpm) and the motor runs on the rated run amperage under load. This allows a 120v compressor motor to start up and run off a 20amp circuit.

 

[RandyT]

LRA is 102 but motor tag states volts 120 amps 15 hz 60 just below the top of the tag. The issue with trying to run it off a generator is most outlets on gensets are limited to 15 amp breakers with no delay. So it doesn't matter is most cases how big the generator is rated the outlets are the limiting factor.

 

[404nouser]

On a DC supply a capacitor will supply voltage stability to reduce voltage sag from a surge in supply or load.
An AC system uses a capacitor to delay the wave to supply a second waveform thus providing the ability to start rotation from a standstill on a single phase motor.
After the motor is rotating a single phase will keep it going

 

[34Willys]

There should be 1 or 2 humps on the housing where the capacitors are located.
Have you plugged it in to house power and tested? I wouldn't use a generator for the first run.

Patrick

 

[caver]

220-221 whatever it takes.

 

[WinterDeere]

I just love watching electrical threads on this forum.

Listen to 404nouser, he sounds like he actually knows his stuff. The capacitors have nothing to do with supplying LRA, nor do you even care what LRA is, it's a mostly-useless number for the end user.

A single-phase motor is like a bicycle with one pedal. As 404nouser already implied, the capacitor provides some phase shift to the current applied to a secondary winding, temporarily adding that all-necessary second pedal to get the first off bottom-dead center. Once rotating, it can be switched out, as is the norm on most inexpensive "capacitor start induction run" motors. You can ride a bicycle with one pedal, as momentum carries it past the bottom-dead center "stall point", it's only starting them without a second pedal that's a real problem.

All intersting, but none of this has anything to do with your original question of running the compressor off a generator. Your biggest problem with this motor is that it's only a 120V single-voltage motor, with no option to reconfigure for 240V. Attaching this load to any split-phase 240V generator is going to load one leg very heavily, which will cause neutral to "float" in that direction, and cause output voltage on that leg to drop accordingly. This is not good.