Do you think my air compressor motor is shot?

[gonefishin]

So today i went to use my air compressor that has been sitting for 2 years. It started really slow. And didn’t act like it was running at full speed. It ran about 30 seconds and tripped the breaker. The motor smoked a little bit and was fairly warm. I took off the top cover. The black motor starting capacitor had leaked and is corroded. Then i looked at the windings. Do you think my motor is shot? Or should I replace the capacitors and see if it fixes it?

This is my quincy 4 cylinder 5 hp shop air compressor.

 

[wasted wages]

Windings look burnt,, it's toast.

( It's impossible to say positively without being there to look at it and without testing it with a meter.) but,,,

To test:

Unwire the motor at the leads, use an ohm meter to test between the wires going into the motor to ground on the motor base.

Any continuity reading on the meter will tell you if it's grounded out.


More than likely, the start relay or the centrifugal switch stuck on the motor keeping the start winding energized too long....
that's why it was running slow...it was bucking the phases.
Start winding overheated, grounded out and tripped the breaker.

(Again, without being there to look at it, can't
be one hundred percent positive.)

I doubt a start capacitor is going to do any good at this point.

 

[gonefishin]

Thank you. That’s kinda what i was afraid of...

I will go ahead and test it and see if it’s grounded out.

most of what you are seeing on the windings is dust though....

If you look closely at the picture you can see the very small wire or something that goes around the windings. It is melted. Not sure what that stuff is...

 

[rampage]

Any wire that is melted, open or has the enamel cooked off is not good. Be safe and replace the motor. My bet is that one of the wires in one of your coils melted and created an open.

 

[diesel4me]

It may be the pump was dragging and overloaded the motor--if it spins freely by hand (the pump) ,with the belt off,if its not direct drive,it should turn with no binding after the compression stroke..
Sitting that long may have let rust form in the cylinder(s) and put too large a strain on the motor...

I would think a fuse or breaker should have popped before the motor smoked though..most motors have a thermal overload built into the wiring that should re-set after it cools off enough..

If you smell that death of a ballast electrical stench then its a good bet the windings got cooked..once the enamel on the wires melts,its short circuit city..
Harbor Freight sells "lower priced" 5 HP motors...

I shop at the local scrapyard,its unreal how many perfectly good motors get cashed in for scrap...IF they are willing to let you go browsing,many I used to roam freely in are "off limits to customers" due to insurance regs now..sucks..flea markets and swap meets also are good places to score a large electric motor cheap..
All the old timers I knew who could rewind motors and rebuild armatures and long dead now..they were very reasonably priced .

 

[shady]

I'd replace the caps and try it again. The windings got hot, but I've seen worse running.
On Amazon you can get a red varnish insulating spray paint. If a new cap makes it run, pull it apart and HOSE it with that insulating spray. Let it soak in-between the windings real good.
I worked in a rewind shop for 4 years. We used the hell out of that stuff.

 

[diesel4me]

I used to buy the GE Glyptal enamel for motor windings at one of the motor rebuilder's shops to paint the lifter galleys on the Chevy V8's we rebuilt at one of the parts stores that had a machine shop..even back in the 80's it wasn't cheap!..

 

[shady]

The stuff I mentioned is about $15

 

[gonefishin]

So i pulled it all apart. First i checked and it’s not shorted to ground. And the motor leads are not open. it didn’t look like it was too burnt.

about half of the windings are dark colored and the other half look new... the nylon string looking stuff that goes around the windings is melted in a few spots.

do you think that capacitor could cause this? Or how do i test that centrifugal switch?

I thought about buying a cheap 5hp motor, but kinda hate to go from a baldor to something china made....

 

[shady]

The bad cap can do it, and the centrifugal switch can too. For the switch just make sure it moves freely and that the contacts are good.
The black cap starts it, and the switch takes the black cap out of circuit once it's up to speed.

 

[wasted wages]

lots of bare copper windings there....not a good sign.
It may have burnt "open" or phase to phase...
and not necessarily grounded.

how many wires are coming out of the peckerhead ? 3, 6, 9 ?

can you take a pic of the leads and the plate with the wiring instructions ?

 

[gonefishin]

There are 3 wires from the peckerhead. Motor is single phase.
I’ll try and get a pic in the morning. Heading offshore tomorrow afternoon

 

[wasted wages]

We are talking about the wires actually coming out of the motor - correct ?

Use the ohm meter, and read the resistance between the 3 wires.. use a scale that will give you an ohm reading not just continuity..

IE: 6.7 ohms

They may be labeled C / S / R on the wires, or on the motor nameplate by number...

read between C and R
read between C and S

C is common
R is run winding
S is start winding

This will tell us if the windings are still good.

 

[gonefishin]

Thank you! I will test that in the morning.

and yes there was 3 wires going into the motor after the overload in the junction box

 

[gonefishin]

I was wrong. There is 4 wires and labeled with numbers red 8, blue 1, black 5, and white/yellow with no label.

Then on top where the capacitors are there is 1 white and 1 black for each capacitor.

the blue and black wires are tied together in peckerhead along with 1 hot wire from the pressure switch.

they other hot wire is tied to a yellow wire. From there it goes to overload.

Overload has 3 connections. 1 from hot yellow. 1 yellow that goes into motor. And 1 brown wire labeled j that hooks to the red 8 that goes into motor.

Red wire that goes into motor ties in where the silver capacitor black wire hooks up.

 

[shady]

lots of bare copper windings there....not a good sign.
It may have burnt "open" or phase to phase...
and not necessarily grounded.

how many wires are coming out of the peckerhead ? 3, 6, 9 ?

can you take a pic of the leads and the plate with the wiring instructions ?

I don't see any bare copper in there...

I do see that the start winding has blackened. Which means it got hot, but that's it.

An ohm reading on a single phase motor isn't going to tell you much. Unless you had ohmed it before this incident.
On a 3 phase you can check them against each other. But with a single any 2 you pick will give you different results.

 

[Chevy305]

Have you checked the capacitor with the meter?

 

[Fordum]

Been watching this, I wanted to jump in but been having some health issues. Mostly not being able to breathe. But I think I've got a handle on it right now.
But, if you don't get a reply to a question, just be patient.
No way to tell if the start windings are bad from the pictures. If they are not shorted to ground, then that is about the only thing you can test with your equipment.
But, I have seen some a lot more burnt than that that ran just fine.

First thing, replace the starting cap. If its leaking, its bad. With it bad, the motor will either not start at all, or never get up to full starting speed.
That weight and springs that should be on the back end of the motor shaft works the switch. Lift the weights against the springs and make sure the washer looking thing moves smoothly.
Look at the board at the end of the motor with the two arms with nylon pads on them and make sure the contact is making contact.
When the shaft gets to a certain speed, the weight swings out, and the washer releases the two arms and opens the contacts. This takes the start cap out of the circuit and lets the motor run on the run cap.
The run cap usually will not show any obvious signs of failure. If one if the contacts is leaning to one side, then its bad because an internal fuse has blown.
But, not all of them will do that.
You can test the cap with your meter to a certain extent. Disconnect it, carefully short across the contacts. Do not do this if the motor has just finished running.
Put the meter across the contacts on ohms. You should see a very low reading that will quickly ramp up to open circuit as the cap charges.
Since that is a small value cap, it will charge up quick. A digital meter might not catch it.
I doubt that the windings got that hot that quick. With the start cap leaking, it has probably been having problems starting for a while before you put it up.
As the cap weakens, it takes longer and longer to get up to speed, and the windings get hotter and hotter.
I would check the switch, make sure its working, replace the start cap, and see what happens. If the run cap is bad, it will usually run, but not cleanly and will make noises.
Given the price of a new motor, a new start cap ranging from $5 to $11 depending on where you buy it, is a good gamble.

 

[JoshHefnerX]

Those contacts on the centrifugal switch that can get corroded and cause problems. emery cloth cleans those up.

 

[fordsucks!]

If the cap popped/leaked - it is bad! Doesn't mean that's your only problem, but caps are about $10. Start there. If motor is causing cap to blow, then it's time for new motor.

be careful handling those caps - when loaded up, they are strong enough to kill you. Make sure you discharge!