Air Compressor HELP

[novaboy009]

Well, the bearings in my air compressor electric motor appear to have died. The motor is going immediately to overload protection/blown breaker. After fiddling around with the pressure switch, pressure relief valve, etc, I've narrowed it down to the motor. This was a used Craigslist special - 60 gallon, 7 (peak) hp Porter Cable compressor. It was used in a wood shop and appears to have some mileage on it.



Motor specs:



I'm in the process of a full blown restoration on my Nova, with the body stripped to bare metal. I'm trying to complete the build before August due to the arrival of a new baby. Budget needs to be constrained due to investments in the car project and (obviously) family spending coming up. I'm going to paint in my shop, so I need a compressor that will run an HVLP gun. I prefer electric to air powered sanding tools, so that isn't a big concern at this point.

1) Can I use a harbor freight special "3 hp" motor on this compressor?

http://www.harborfreight.com/3-horsepower-compressor-duty-motor-68302.html#.UxczJM68ZXo

It specs at 12.25 Amps vs the original 14 amps. They both run at the same rpm and I could reuse the pulley from the original motor.

2) If I want a Baldor/Eaton/Century motor, I'm probably $300 in and I should go get a new similar compressor for $450 (Husky/Kobalt/Cambell Hausfield knock offs).

3) I can use my dad's fairly large Craftsman oilless compressor. I think it's around 30 gallons (33?) and probably has enough juice to spray a car in pieces if I take my time.

4) I could ask around about getting it rebuilt, but the last time I asked our local place to rebuild an old electric motor for my '47 Craftsman bandsaw, they came back with a $350 quote.

What would you do?

Kev

 

[TAMPAGT07]

Don't cheap out on a motor....Get a Baldor if you can afford it....I'm done with cheapo motors...

 

[katy]

Offhand, I would suspect that the (starting) capacitor has failed.
What makes you think that the bearings have failed? They usually start to make noises before they give out completely.
Have you removed the belt and tried running it like that? Have you tried turning the motor by hand, w.the belt off?
Permanently lubricated bearings, as it says on the motor label, are typically good for 25,000 hours.
If it is the bearings and everything else is OK, you can replace the bearings.
Forget about getting it rebuilt, that cost way more than a new one.

 

[Davefr]

As long as the windings aren't fried, motors are easy and inexpensive to rebuild yourself.

Replace the bearings, caps and clean it up and it'll probably perform like new. (Cost approx. $50)

Based on my experience, the problems with motors are listed in this order from common to rare:

1. Bad capacitors
2. Dirty centrifical switch contacts
3. Wiring problems
4. Bearings, lack of lubrication, filthy dirty inside, loose end caps (rotor/stator alignment).
5. Open/shorted stator windings

#1-4 are easy, #5 means replace it after you test the ohms.

 

[A_Pmech]

Agreed with katy. If the bearings have indeed failed, simply replace them.

If the motor bearings are smooth and offer little resistance, either the start switch has issues or you need a new start capacitor.

None of these things will cost you over $20.

 

[novaboy009]

The motor sounds like poop when it spins around - kind of clunky - and there's a lot of resistance when turning. The pump spins nice and free with the belt off. The compressor would work on and off before the motor finally quit turning on at all. For awhile I could let the compressor sit for a long time and it would start, now it immediately shorts out no matter what, even with the belt off.

I don't know the first thing about electrical motors. If there is a bearing that's dead (likely the case here), wouldn't the shaft it rides on also be too worn (I'm thinking like a crankshaft or cam bearing)?

Kev

 

[bsaint]

56Z frame 7 hp rofl. I love when they rate motors on inrush current. The motor is toast. Dont bother with an expensive motor as its probably not worth putting on that machine. Get something from Harbor Freight to get yourself done. Then go out and buy an Emglo or Rolair.

 

[sberry]

I don't know if yur motor is toast but started hearing a funny noise in mine a couple weeks ago, 14$ for 2 new bearings.

 

[Davefr]

The motor sounds like poop when it spins around - kind of clunky - and there's a lot of resistance when turning.
Kev

Either something has come loose inside or the bearings are shot.

Either pull the end caps off to inspect or buy a new motor. It's kind of hard to diagnose unless you start taking it apart to inspect.