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Air compressor not restarting

David said:
Well I tried the compressor again today and it tripped at just over 100 psi with the door wide open. So something is very wrong with the thermal switch.
I tried to pull the end bell and there's no way I can get it off. Can't get a bearing puller in because there's no room for the arms and I'm afraid that cast aluminum end bell is going to break.
Tomorrow I'll pull the motor of the compressor and either take it to a shop or spring for a new one at Princess Auto for $229 :(
Click to expand...

I am not entirely certain if your motor design is a little less service friendly than most but here's a YouTube video I found that shows the typical way a single phase AC motor should come apart (2:00 - 7:00 min. portion):

Single Phase AC Motor Disassembly Video
 
@David - I've never had any difficulty removing end bells without a puller. At most it required a few love taps at the seal with a plastic or rubber mallet to break the seal.

Nonetheless, I can imagine that this might not always be the case.

If you are contemplating a new motor or a motor rebuild anyway, you have nothing to lose by using a chisel or wedge to break the seal.
 
I'm off today so I hope to tear compressor apart.
Yesterday was a bit of a bust as my planned one hour motorcycle ride turned into three hours, two of which were sitting in traffic watching the fuel gauge go down and the temperature gauge go up.
 
David said:
I'm off today so I hope to tear compressor apart.
Yesterday was a bit of a bust as my planned one hour motorcycle ride turned into three hours, two of which were sitting in traffic watching the fuel gauge go down and the temperature gauge go up.
Click to expand...

What!!!!

Doesn't that silly bike have automatic start/stop on it?

Btw, the US EPA has officially announced that they are killing that stupid requirement. Only about 30 years too late!
 
Pulled the motor off the compressor. Thermal switch is a sealed unit so no way to tell if it's burnt or what not inside.
Calling around to see who has one.
Troy Electric to the rescue!
 
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Well blast. They didn't have the switch. Nor can they identify a replacement because the part number off the original switch is meaningless.
Off to Princess Auto.
 
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Yeah we tried that at the shop. They had 15 or so examples of the Klixon brand, none had the mounting ears, all were $130+. The sizing worksheet for the Klixon switches is quite involved and specifically says that it is not possible to select a Klixon protector based on horsepower, amperage or nameplate data.
In the end, I decided to just stick a new motor on it. WEG branded motor with warranty.
 
David said:
Pulled the motor off the compressor. Thermal switch is a sealed unit so no way to tell if it's burnt or what not inside.
Calling around to see who has one.
Troy Electric to the rescue!
Click to expand...

O-L.PNG


Took the above from the first link. Once the switch is out of the motor you could carefully test it's function with a heat gun, thermostat, and meter set to ohms.

Edit: Without knowing the your motor's thermal switch exact ratings but using the ratings above as a rough guide - "120F open and close at 745F (+/- 5-12F)".
 
Elektrishun said:
View attachment 66627

Took the above from the first link. Once the switch is out of the motor you could carefully test it's function with a heat gun, thermostat, and meter set to ohms.

Edit: Without knowing the your motor's thermal switch exact ratings but using the ratings above as a rough guide - "120F open and close at 745F (+/- 5-12F)".
Click to expand...

Whoops - I think I see the problem now...



Should be "close at 74F"
 
David said:
It states 17.x A
On start-up it should pull that many but not more if all is right?
Click to expand...
Incorrect, it will pull much higher current for a short time while the motor is coming up to speed, 80A (wild guess). However depending on the response time of the meter you won't see it, you need a C.T. And scope to see that transient current.

I made a little circuit for my 5x6" bandsaw that is supposed to help prevent destruction of the worm gear when the blade jams. When the blade jams, the worm gear can start acting like a knife shaving off the leading edge of the driven gear. My little circuit detects increased current and trips the motor off. When starting, the circuit is disabled while you push the start button. A sensor detecting motion on the saw's motor driven wheel would be a worthwhile improvement.
 
So yes? - and we are assuming induction motors right?

Unloaded starts are also an order of magnitude less onerous than loaded starts - any sort of tool versus a pump compressor etc. Which is why those load valves exist
 
All this talk made me take a look at my own compressor.

It's a small upright 20 gallon air compressor with a 120 volt motor. Purchased it from COSTCO about 15 years ago.

First time starting today in a 22 Celsius room with an empty tank. The start current was 30 amps. Within 2-3 seconds the current dropped to about 11 amps and stayed close to that for the duration.

Let the pressure build to about 50 PSI and shut it off. Waited a few seconds, turned it back on, and start current was 28 amps. Within 2-3 seconds it dropped to 11 amps. As the gauge neared 100 PSI the current gradually increased to about 12.6 amps. Manually shut it off at 100 PSI. Max pressure before auto shut-off is 125 PSI.

Fortunately both the thermal overload switch and capacitor are available for a reasonable price on Amazon.
 
Elektrishun said:
All this talk made me take a look at my own compressor.

It's a small upright 20 gallon air compressor with a 120 volt motor. Purchased it from COSTCO about 15 years ago.

First time starting today in a 22 Celsius room with an empty tank. The start current was 30 amps. Within 2-3 seconds the current dropped to about 11 amps and stayed close to that for the duration.

Let the pressure build to about 50 PSI and shut it off. Waited a few seconds, turned it back on, and start current was 28 amps. Within 2-3 seconds it dropped to 11 amps. As the gauge neared 100 PSI the current gradually increased to about 12.6 amps. Manually shut it off at 100 PSI. Max pressure before auto shut-off is 125 PSI.

Fortunately both the thermal overload switch and capacitor are available for a reasonable price on Amazon.
Click to expand...
Thanks for testing and reporting. Lots of good information in this thread for future troubleshooters.

I'm now curious what the actual resistance is of the start and run windings of David's motor?

I was going to try and estimate what the start current would be with a 150 vs. 178 uF start capacitor.

Xc (can be thought of as the resistance of the start capacitor) is 17.7 Ohms for 150uF and 14.9 Ohms for 178uF.

Somewhat meaningless without knowing the start winding resistance and how long it takes the motor to get up to speed and the actual trip characteristic of the thermal cutout. However the other evidence tells us that this combination is operating very close to the trip threshold so every extra amp, a bit higher ambient temperature a weak cutout or possibly a combination of all of the above is likely the thin margin between everything is fine and dandy to WTF why does my compressor not start.

One would hope that the Sanborn engineer calculated or tested what happens if the capacitors are both at the high end of their specified tolerance while the thermal cutout is on the sensitive side of its tolerance and the ambient temperature is at the maximum specified?

Don't be so sure. Or if that engineer did, that a bean counter later decided that this new (untested) capacitor or thermal cutout has roughly the same specifications but costs 10c less can save us x $ a year.

At the end of the day some fraction of those consumer priced compressors fails early often for a 10c cost saving at the factory. More often it's just a case of we can't get part X from manufacturer Y they are out of stock until Z so an alternative part is found and used without testing to keep production humming along. By the time the problem is detected via warranty repairs it's too late.

The alternative is to pay the big bucks for something like a Quincy that uses a top drawer motor with plenty of margin in the first place.

Says the cheap ass with a used Sanborn under his steps;-)

A part of me still regrets not making the four hour round trip drive to Kingston for that lightly used and well priced Quincy that was on Kijiji a couple of years back.
79EB2B75-0DA4-4DFF-A277-DE24FA3420CA.jpeg
 
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