Air Compressor Motor Problems

[carlr]

Picked up an Ingersoll Rand 80 gallon 5hp single stage compressor for cheap on Craigslist. I had to pick up a new motor and pressure switch. Wired everything up, flipped the switch to auto, and it filled the tank to about 120 PSI.
It's supposed to turn on at 105 PSI and off at 135 PSI.

I bled the air to about 50 psi and still it hadn't kicked back on. I've confirmed power is getting past the pressure switch, and to the motor. I never heard, saw, or smelt anything unusual around the motor when it kicked off, and the internal circuit breaker wasn't tripped. It was not unusually warm either.

Did I wire something up wrong?



> Circuit Breaker Panel (Red and Black wires to 30 amp double pole breaker. Bare copper wire to ground bus bar. White wire capped off.)
> To Pressure Switch (Red wire to line 1, Black wire to line 2, bare copper wire to ground screw, White wire capped off.)
> From Pressure Switch (Red wire to terminal 1, Black wire to terminal 2, bare copper wire to ground screw.)
> To Motor (Red wire to terminal 1, Black to terminal 2, bare copper wire to green ground screw.

Any suggestions?

 

[G_P]

If the motor ran fine and pumped up to 120psi then there is nothing wrong with your wiring. If the wiring was done wrong it would never have run at all.

Does the motor hum but not start?

You may have just been un lucky and got a defective motor. It ran for a while and then something failed internally and it died. Did the pressure switch cut it off at 120 or did it stop at 120 and the switch was still closed but the motor was no longer running?

 

[carlr]

Well right now I'm getting power in the wire between pressure switch and motor, though I never heard any humming of other noises after it kicked off.

Guess I'll just take it back and get a new one, I just wanna try to make sure the same thing won't happen again, if it was something on my end.

 

[scw1991]

What model is your pressure switch? The reason I ask is that they come in a variety of cut in/cut out pressure limits and amperage ratings.

If your motor runs, I'd say the culprit is the pressure switch.

 

[G_P]

Make sure the wire connections inside the motor are tight and secure. If one was left loose vibration could have caused it to come apart and that would stop the motor.

 

[scw1991]

Another culprit is the pressure switch is not adjusted correctly. The Square D Pumptrol models allow the user to make adjustments. If you raise the cut out pressure, then you also raise the cut in pressure.

 

[carlr]

Well I'm fairly certain the motor has failed.
Connections are secure.
I'm getting 240V between Red and Black (T1 and T2 on motor) wires.
120V between T1 and ground. 120V between T2 and ground.

I find it odd though it turned on, couple minutes later I flipped the pressure switch to OFF for a minute, then back to AUTO, just to make sure everything was working fine. It turned back on when I flipped the switch, and turned itself off at about 120 PSI. Wouldn't kick on after that.

Chalk it up to coincidence I suppose..

 

[scw1991]

Just to be sure, bypass the pressure switch completely.

I'm guessing that motor also has thermal overload protection as well, correct? If so, you would want to rule that out as well.

 

[bsaint]

What is the current draw on the old motor vs the current draw on the new motor? What is the RPM on the old motor vs the new motor?

That will tell us a lot.

 

[carlr]

Both old and new motor are rated at 21 amps, and 3450 RPM. Only difference is the old motor was for 3 phase power, new is single phase.

 

[bsaint]

Okay just making sure you replaced a real 5hp with a real 5hp. Strange how the old 3 phase motor was rated for the same amps as the new single phase motor. Usually 3 phase is going to be less current.

 

[RCStocker]

Have you tried running the motor by itself?
That should have been your fist test. Take the belt off and run it. The motor might have burned out. If it runs then I would say it is your pressure switch. You need to adjust it so it works for the pressure settings you want. They never come set properly. You make the adjustments with a screwdriver most of the time.

If the motor hummed then I would say you have a compressor problem and the release valve did not release the air on the intake line. Some compressors to don't have that divice.

If you look at the motor plate it should show you how to wire it properly. That should be a no brainer. Check your fuse or breaker. It might have blown and you are not getting any power. If all that fails go buy a new compressor. There are reasons they are sold cheap.

 

[C96]

Both old and new motor are rated at 21 amps, and 3450 RPM. Only difference is the old motor was for 3 phase power, new is single phase.

Okay just making sure you replaced a real 5hp with a real 5hp. Strange how the old 3 phase motor was rated for the same amps as the new single phase motor. Usually 3 phase is going to be less current.

bsaint, You are exactly correct. I would say this is where the problem lies.

According to the NEC, a 22 amp rated 3 phase motor @ 240 volt would be 7 ½ horse power.

I think the OP is installing an undersized motor. The 21 amp rating for the new single phase motor would be indicative to a motor with the “special” rating that is 5 developed horse power and NOT a true 5 horse power.

This compressor should also have a mag starter

I don’t think we are getting accurate information from the OP.

OP needs to check the actual pump specifications and install the correct motor / pulley configuration.

 

[carlr]

Hey my mistake, I pulled the old motor out and it was actually 9 amps at 230V.

Anyway I replaced the motor all seems to be working well.

Thanks for helping me solve this guys!