Compressor problem

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haklesup
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Compressor problem

Post by haklesup » Fri Feb 14, 2020 10:19 am

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.

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dacflyer
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Re: Compressor problem

Post by dacflyer » Fri Feb 14, 2020 12:11 pm

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.

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Janitor Tzap
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Re: Compressor problem

Post by Janitor Tzap » Sat Feb 15, 2020 9:42 pm

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

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haklesup
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Re: Compressor problem

Post by haklesup » Mon Feb 17, 2020 11:06 am

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

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Lenp
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Re: Compressor problem

Post by Lenp » Mon Feb 17, 2020 7:08 pm

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!
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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dacflyer
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Re: Compressor problem

Post by dacflyer » Thu Feb 20, 2020 8:00 pm

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.

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