Air Compressor Problem - Motor Stalls

[Sparks Fergusson]

Is that ther right Part #? Does it have some dashes inbetween the
numbers and letter like most Ge motors do?

No dashes. That's what's printed on the motor nameplate.

Is it wired for 120?

Yes.

 

[David]

....

The voltage to the motor is never interrupted during the stop/start
cycle. Above a certain psi (about 95), the motor starts bogging down
and eventually stops. This occurs even if I bypass the pressure switch
and attach the cord directly to the motor leads. Then, after the
unloader vents the pressure, the motor will restart.

I had a somewhat similar set of symptoms with my compressor. Spent a
while trying to figure out what was wrong.

The problem turned out to be that wasps had plugged up the air input
holes with mud. Cleaned out the mud and away she went

David

 

[Sparks Fergusson]

The problem turned out to be that wasps had plugged up the air input
holes with mud. Cleaned out the mud and away she went

Darn mud daubers! Not the issue with mine, though.

Thanks!

 

[Jeffrey D Angus]

...
The voltage to the motor is never interrupted during the stop/start
cycle. Above a certain psi (about 95), the motor starts bogging down
and eventually stops. This occurs even if I bypass the pressure switch
and attach the cord directly to the motor leads. Then, after the
unloader vents the pressure, the motor will restart.

Is it an oil-less compresser? They are VERY sensitive to
both ends being lined up correctly. The through bolts loosen
under vibration and the ends shift slightly. Re-align them
and that should solve the problem.

Jeff

 

[[email protected]]

I'm having a problem with my 20 gallon, single stage electric air
compressor. It's acting like the motor is underpowered - it pumps up
to about 95 psi ok, but then the motor stalls. The unloader bleeds the
pressure off, the motor restarts, runs for a couple of seconds, and
then stops again...repeat...repeat...

It worked fine for years (The pressure switch would shut it down at
about 120 psi) but over the past few months, it's gotten worse and
worse, and now will only make about 90-95 psi before the motor stalls.

I cleaned and lubricated the compressor itself, and it spins freely
and doesn't appear to be binding or otherwise have excessive friction.
The check valve/unloader is working and the piping is all open and
clear.

It seems like the electric motor (1/3 hp) just no longer has the oomph
it used to. It starts up fine, no humming, no smoking, no bad smells,
no clunks. It just doesn't seem to have enough running torque to
handle the load like it did before.

Anyone have any ideas?

Thanks!

After reading all the posts, several things stand out. The most
significant: There is no excessive current draw when the motor stalls.
By all the laws of physics, that is flat out impossible. There are
two explanations (well, three, but I'm assuming you aren't making this
up). The first is slippage at the belt, motor pulley, or rotor.
Given the knowledge you have exhibited, I say that can't be the
problem; it's pretty hard to miss the fact that the motor is spinning
but the belt is slipping.

That leads to only one conclusion: The actual voltage to the windings
is dropping. Possible causes are a bad thernal overload protector,
bad run capacitor (some motors hide the starting capacitor inside,
while the run capacitor is in a cupola on the side), or a corroded
terminal so only one of the paired windings is used.

All of these possible causes result in a lot of heat generated at
one small point EXCEPT the single winding and the bad run capacitor.
The single winding explanation is unlikely because it would not
deteriorate gradually. That leaves the bad run capacitor.

PlainBill

 

[David]

On Thu, 04 Mar 2010 05:13:31 GMT, [email protected]
(Sparks
Fergusson) wrote:
After reading all the posts, several things stand out.
The most
significant: There is no excessive current draw when the
motor stalls.
By all the laws of physics, that is flat out impossible.
There are
two explanations (well, three, but I'm assuming you aren't
making this
up). The first is slippage at the belt, motor pulley, or
rotor.
Given the knowledge you have exhibited, I say that can't
be the
problem; it's pretty hard to miss the fact that the motor
is spinning
but the belt is slipping.

That leads to only one conclusion: The actual voltage to
the windings
is dropping. Possible causes are a bad thernal overload
protector,
bad run capacitor (some motors hide the starting capacitor
inside,
while the run capacitor is in a cupola on the side), or a
corroded
terminal so only one of the paired windings is used.

All of these possible causes result in a lot of heat
generated at
one small point EXCEPT the single winding and the bad run
capacitor.
The single winding explanation is unlikely because it
would not
deteriorate gradually. That leaves the bad run capacitor.

PlainBill

There is one more possible cause: Some or all of the
windings on the rotor that are supposed to be shorted are
open. An induction motor works because windings on the rotor
are shorted to induce the field needed to turn the rotor.

David

 

[Baron]

David Inscribed thus:

There is one more possible cause: Some or all of the
windings on the rotor that are supposed to be shorted are
open. An induction motor works because windings on the rotor
are shorted to induce the field needed to turn the rotor.

David

Thats a possibility, I've seen open rotor bars on induction motors.
Sometimes they arc at the break and leave burn marks.

 

[[email protected]]

There is one more possible cause: Some or all of the
windings on the rotor that are supposed to be shorted are
open. An induction motor works because windings on the rotor
are shorted to induce the field needed to turn the rotor.

David

I've never seen that, but it is definitely a possibility and would
also explain the symtoms.

PlainBill

 

[David]

I've never seen that, but it is definitely a possibility
and would
also explain the symtoms.

PlainBill

PlainBill:
I once saw a fractional HP induction motor on a fan had
problems starting in a certain position. After moving the
rotor a bit, it would run. There was one open winding on the
rotor. The open was visible on the side of the rotor and
applying a significant amount of solder cured the problem.
There can be a lot of current in these shorted turns on a
loaded motor.

David

 

[GregS]

I've never seen that, but it is definitely a possibility and would
also explain the symtoms.

PlainBill

With all the talk, I would have liked to hear the final answer to
the story. Is the compressor working yet. Its
been a long time.

greg

 

[Sparks Fergusson]

With all the talk, I would have liked to hear the final answer to
the story. Is the compressor working yet. Its
been a long time.

Um...can I phone a friend?

Ok, here's the status. I have disassembled the motor. I have found the
following:

* The windings appear to all be in good shape. I don't see anything
obviously open or burned.

* The bearing surfaces are all in good shape.

* The contacts of the centrifugal switch are badly carbonized. I will
clean those up before reassembly.

* I have ordered a replacement start capacitor. I don't have a
capacitor tester, but for $5, why not just replace it, eh?

* The thermal overload tests OK (dead short,) but I can't easily test
it under load.

* The rotor showed no evidence of hitting the stator and appeared
undamaged.

I will clean all the connections before reassembly, although all
looked fairly good already. I'll also measure to make sure I have good
continuity through all the windings. Hopefully, that should get things
going again. Thanks to everyone for their help and suggestions.

I'll post another update when I get it all back together.

Thanks!

 

[PeterD]

Um...can I phone a friend?

Ok, here's the status. I have disassembled the motor. I have found the
following:

* The windings appear to all be in good shape. I don't see anything
obviously open or burned.

* The bearing surfaces are all in good shape.

* The contacts of the centrifugal switch are badly carbonized. I will
clean those up before reassembly.

* I have ordered a replacement start capacitor. I don't have a
capacitor tester, but for $5, why not just replace it, eh?

* The thermal overload tests OK (dead short,) but I can't easily test
it under load.

* The rotor showed no evidence of hitting the stator and appeared
undamaged.

I will clean all the connections before reassembly, although all
looked fairly good already. I'll also measure to make sure I have good
continuity through all the windings. Hopefully, that should get things
going again. Thanks to everyone for their help and suggestions.

I'll post another update when I get it all back together.

Thanks!

Sounds good, please give more updates as you go along. Maybe it was
the start switch contacts that you mention.

 

[Sparks Fergusson]

The main problem is that the motor is being overloaded. As mentioned
already, induction motors don't get tired or exhibit lower power output with
age.

It's taken longer than I hoped, but I have finally put my air
compressor motor back together and it's working again!

To review, over time, the compressor had developed a problem of the
motor stalling before it reached full pressure.

Bearing in mind everyone's suggestions, I took the motor apart and
found that the bearings looked good, there was no sign of rotor/stator
contact, and the internal wiring and connections looked OK. The only
obvious problem was somewhat burned contacts on the centrifugal
switch.

Unfortunately, as I was taking it apart, I broke the voltage selector
switch, and that's what's taken me so long to get around to fixing.

Finally, with some JB weld and spare circuit board material, I managed
to glue the switch pieces back together.

I then cleaned and reseated all the internal connectors. I measured
all the windings for continuity or shorts (they looked good.) I
installed a new start cap, lubricated, and reassembled the motor.

It ran, but wouldn't start. After disassembling it again, and some
careful bending of the centrifugal switch, it was starting and running
smoothly.

Then, the moment of truth, I put the pulley and belt back on and fired
it up. As I carefully watched the pressure gauge, I kept adjusting the
regulator upwards. I ran it up to 140psi, and there was no sign of
stalling or even slowing down! Success!

I then adjusted the regulator back down to 120psi and buttoned
everything back up.

So, thanks to one and all for your help and suggestions. I'm back in
business!

 

[William Sommerwerck]

It ran, but wouldn't start.

Am I missing something?

 

[Jeffrey D Angus]

Am I missing something?

Yeah, you can yank the pulley to get the motor turning, then
it runs. But it won't start turning on it's own.

Jeff