air compressor motor (again)...

So, took my old motor apart, start/run switch seemed to be ok, but windings inside were black, so i think she's pooched... anyway, now to look for a new motor.

The old motor was a "5hp"... you know the ones, 220volts about 19 amps... motor is 3400 rpm, i only seem to get about 2 years work out of these motors... getting tired of replacing.

So looking for another motor to replace it, was wondering about a 1740 rpm motor (they always seem more expensive than the "same size" 3400 rpm motor), i know that the slower speed on the compressor will lower volume if the pulleys are not changed, but will it hurt otherwise. I already have a 60 gallon tank, and could add in another 60 gallon tank if i need for more volume (but longer recovery time), just wondered if it's worth the expense of the motor change?

Any other ideas? The compressor isn't used all the time, i'm not a commercial shop, just a farm one that uses air for tires, blow guns and impact wrenches mainly.

Links to better quality motors would be appreciated!!

Never heard of this type of repeating problem. Are you sure that you aren't getting some kind of voltage drop in the circuit after it starts running?

I would not change the RPM. That compressor was hopefully designed to run at the most efficient speed by the manufacturer.

If your motor says 19 amp @ 230v, that is not a 5 HP motor. More like a 3.5 HP. That was a common practice by compressor mfgs to put false HP info on their product. I think it has been outlawed, but you always go by the amp rating, not the HP.

I would look for a "compressor duty" replacement motor. They have more starting torque than a standard motor. If you have the original motor, or the manual that came with the compressor, look up the FLA of the motor. Find a motor with the same or more FLA. A TEFC (totally enclosed fan cooled) motor is a better quality motor, and it stays cleaner inside, especially if dust is a problem. You're going to be somewhat limited in selection, single phase 3400 RPM motors are not real common. A good source is Ebay or your local motor repair/supply company.

Once you get the motor and get it running, check the amp draw. Check it with the compressor under load, just before it cycles off. You don't want it to be over the rated amps on the motor. If it's over, check the voltage at the motor, check the wire size, make sure there is not more than about 10% drop below the name plate voltage.

If the amps are over, and the voltage is good, check the compressor. Be sure the valves, the air line, intercooler (if equipped) are free of carbon deposits. Check the crank bearings for wear, mechanical binding, etc. If it's still over amps, go with a smaller motor pulley.

I burned out my motor under warranty. Was doing a lot of sand blasting and it just could not take the almost continuous duty. Tractor Supply gave me kind of a run around, told me to take it to their designated repair shop. That guy just says, another one of them. They don't allow me to even try to repair them for warranty. He went on to say he had converted one or some to the lower speed much heavier, better motor and the price was not much different except for pulleys. After a little haggling, TSC got on the phone and Ingersoll Rand sent me a new motor. I am much more careful with it now and that was 7 years ago but don't use it as much either.

If it is in a shed away from the house you may have a voltage drop in the wiring.Easy to check with a meter. I agree with the pulley size change.

YUP you need sever use or constant run. Don't mess with junk.

It does sound like VD and exceeding the full load rated amps.

Go get an old heavy duty 5 hp. 1750 rpm motor and run your compressor with it. Even if you have to have it 'gone thru' first.
I did that about 16 yrs ago and have got along great , ever sense I thru away the little 5 hp, hi speed junker. Change the pullys , do not worry about it running the pressor a little slower, it will lower the CFPM , but very little.Your pressor will last longer.
I have a Vee 4 cyl compressor and a 60 gal tank , Am able to run all my air tools ok. I weighted my Baldor motor , it wts. 155 lbs, a handful to mount up on the tank. clint

As I've said before Buy 1 made for an air compressor, we found out years ago a regular motor will not last on a compressor.