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I have an aging Compressor that started malfunctioning last year. It would fill the tank to partial pressure (~25psi) and then the motor would stall (without electrical straining noise) and periodically spin for a few revs then stall again and repeat indefinitely. Initially I thought it was the pressure switch but I looked inside and that can't be it so now I conclude it is the large Motor Run capacitor (I don't see a start cap) 130uF CBB60 type. I'm interested in the failure mechanism, Does this match a typical pattern, is it just High ESR limiting motor current? Why didn't the motor sound like it was trying to spin, what cut the power?

I just ordered the cap ($16), I'll confirm the fix later

https://www.harborfreight.com/8-gallon- ... 68740.html
Similar to this one but older with some design differences.

i had an intermittent motor before, turned out to be a broken winding..luckily i was able to fix it..
Are you able to peer into it while it is running ? maybe you might be able to see it sparking or something..
compressors do vibrate a lot..

Oh, ,I also remember a brushless generator that did the same thing, one time it would generate,, next time it wouldn't.
one day in frustration i fed heavy power into it backwards and then i finally saw the culprit. the armature sparked.
when i finally examined it, turned out to be a shorted winding to ground.. it was the 1st few turns at the start of the winding.
So I wound up rewinding that 1 pole on the armature. luckily it was just a 2 pole armature.
but it works like a champ now.

Hmmmmm.............

Shorts in the windings, huh.....
I would see that on Flyback Transformers.

One solution I found was to get some corona dope, then thin it out with paint thinner till it's consistency was almost that of water.
I would then take the transformer and dip it in the corona dope, letting it work its way in to the windings.
Then pull it out, let it dry, then do another dipping.
Normally I'd have to do this at least four times, to insure that the exposed wires were completely sealed.


Signed: Janitor Tzap

I replaced the capacitor, the motor runs longer but there is still an issue. While now it can pump the tank up to ~90PSI, it can't quite make it to 125 to activate the pressure switch. The symptom is the same, it runs until it appears to not have enough torque to push the piston then it stalls. Once I find my Kill A watt meter, I can confirm that it is drawing current while stalled even though it is quiet (I did see a wisp of smoke, so I expect it is getting hot in the windings, probably getting worse in the process). I'll look for an easy fix or a shorted winding but considering the replacement cost, I'm not going to tear down the motor and try and rebuild it. I wonder how much I can get for it at the recycling yard

Is it really stalling or is the internal thermal protector opening the circuit? A continuity test will tell that with a quick test. When the motor and air flow stops, the windings may still smoke for a while so maybe that's what you see. Quite possibly the motor was marginal from the beginning, not uncommon with discount store units, and the motor took a beating, overheated, and the windings increased in resistance. Higher resistance, means less current, and less energy. At the top pressure is where the hard work comes and since it cannot make it, it labors inefficiently, the motor heats the windings, and they increase even more. The old dog chasing his tail syndrome! I doubt it has shorted windings, since it is at least running. Usually a winding short makes the motor growl and it pulls way too much current and trips the motor protector. You need to check the current draw to get some solid data.

You might consider setting the pressure switch lower and just use it at the lower pressure if you can, until all the smoke comes out. Then do whatever you need to do. Unless you have a pile of used motors it is likely not worth the cost to repair or replace the motor.

I had a generator that eventually could not carry the load of our well pump starting even though the engine was running as usual. The output was down more than 15% with the engine maxed out. Since it ran fine for lower loads it found a new home!

I agree with LEMP as for the thermal protector tripping from overheating.
maybe perhaps you can put a fan on the motor to help cool it.
if not shorted, then it can be possible that the windings are just worn out. copper windings can loose their umph when they have been dogged for so long. I bet a lot of them cheap motors are slightly under-rated.

I'm not too much a fan of dry compressors..the teflon compression ring wears out too fast, and then they are noisy as hell..
i'd love to have me an oil type of compressor one day.. I think i'll buy me one whenever my current freebie 20Gal dies.
right now it works just fine.. just noisy..lol

I'm scrapping that compressor. It has oil in the pump, it never went dry but may have begun break down, I never replaced it. For some reason the motor stall torque has gone way down. I did change the cap but stopped short of replacing the pressure switch when I observed it could not pump more than 50% PSI as normal using the dial to measure. it was like the pressure against the piston exceeded the motor torque at this point. The thermal protection did kick out and back in again, that's what was causing the motor to cycle on and off but never getting many rotations before it stalled and overheated again. It could be used for light duty blow off but really its junk for recycler next opportunity.

I'll get a new one as soon as I actually need one. I have some painting coming up but don't really need it for that. It was awkward to store anyway

does this motor have a centrifugal switch for the start phase ? it could be faulty..have seen some that wouldn't open the start phase..the over current would be activated by that..or if the switch wasn't closing to kick in the start phase,, and the run phase was being overloaded.
and other issue could be a shorted coil winding.

or ( if i read right ) you said the compressor runs,,but will only pump up to 50psi before it stalls ?
Do you know the current draw at all when it's running ?
are you using an extension cord? ( if yes,,,then try a heavier cord, at least 12Ga or better ) I had a guy give me a compressor because it stalled on him all the time, because he was using an extension cord that was too small, and it too would stall at a certain point. so he got mad and gave it away..Then bought another one, only to have the same issue.. I told him his issue..I told him to either get a stronger cord or a longer air hose and plug the compressor directly into the shop...

my last test was on a solitary 20A outlet with a 3 foot run the main panel, no voltage drops there

My bet is damaged coil, shorted or open, who cares at this point. Darn, I just realized I forgot to put it on the curb Wednesday with the other metal junk, he can have it next time.

do you know how many amps it's drawing before it quits ?
It sounds like a possible shorted winding too