Air Compressor Problem - Motor Stalls
Sparks Fergusson
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!
TonyS
> 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!
If it's a DC motor, maybe it needs new brushes?
Sansui Samari
I agree to check the brushes, if it's not a brushless motor. Does the
unloader bleed the entire tank off? If so, then the check valve is
probably bad. It could also be that your shutoff set point has self
adjusted back. Say your fill point is at 95 lbs, and your shutoff
self adjusts down to around 95 lbs, it can cause it to continuously
turn on and off. I had a compressor that used to do this to me for a
while, until I put a little locktight on the adjustment screw. It
could be just a worn out pressure switch as well. Maybe the spring
has become weak in it.
PeterD
Fergusson) wrote:
>
>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...
Bad pressure switch. The unloader is part of the pressure switch so if
it is being activated, the pressure switch is 'saying' that the
pressure is sufficient. Maybe it is just mis-adjusted.
>
>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.
Check the adjusting screws, and reset the cutoff back to 120 PSI.
Confirm the cuton is at 95 PSI.
>...
GregS
Check the line voltage while opperating at the motor.
I can do that stall with a long extension cord.
greg
GregS
Is it oiless ?If so, check the bearing.
greg
Bennett Price
and pressure switch are fine.
Sparks Fergusson
>On Mar 3, 9:13=A0pm, hates...@invalid.invalid (Sparks Fergusson) wrote:
>I agree to check the brushes, if it's not a brushless motor.
It's an AC induction motor, so no brushes. Could it be a capacitor
issue?
>Does the unloader bleed the entire tank off? If so, then the check valve is
>probably bad.
It's a combination check/unloader valve. I cleaned and lubricated it,
and it appears to be working fine. The tank holds pressure - the
unloader just vents the tube between the tank and the compressor.
>It could also be that your shutoff set point has self
>adjusted back.
Good thought, but the pressure switch seems to be functioning well. I
am getting around the problem by turning down the pressure below the
point where the motor stalls. But, that's only about 90 psi, which is
not as much as I'd like. Plus, the problem seems to be getting worse.
Thanks!
Sparks Fergusson
>On Thu, 04 Mar 2010 05:13:31 GMT, hate...@invalid.invalid (Sparks
>Fergusson) wrote:
>
>>
>>I'm having a problem with my 20 gallon, single stage electric air
>>compressor. ...
>
>Bad pressure switch. The unloader is part of the pressure switch so if
>it is being activated, the pressure switch is 'saying' that the
>pressure is sufficient. Maybe it is just mis-adjusted.
Actually, it's a mechanical unloader (combination check
valve/unloader, which I have already cleaned and lubricated.) It seems
to be working well.
>Check the adjusting screws, and reset the cutoff back to 120 PSI.
>Confirm the cuton is at 95 PSI.
The pressure swicth seems to be working fine. If I turn down the
pressure adjustment, I can get the contactor to turn off the motor
before it stalls, but that's only 90-95 psi or so. If I adjust it
higher, the motor is unable to turn the compressor if the pressure is
more than 95-100psi. It's definitely the motor stalling, not the
pressure switch opening.
Thanks!
Sparks Fergusson
Line voltage is OK, about 123 volts. It drops to around 121 volts when
the motor stalls. Voltage drop across the pressure switch is minimal
(less than a volt.) I'm not using an extension cord.
The compressor is oil filled, and has oil in it (although it is rather
old oil, come to think of it.) But, I can easily turn the compressor
over by hand and it feels like it's moving freely, with no excess
friction or binding.
Thanks!
Sparks Fergusson
>
>Compressor binding up.
I can turn it easily by hand, so it doesn't appear to be binding.
However, I don't have an easy way to check it when it's at full load.
Any suggestions?
Thanks!
Sparks Fergusson
>> Thanks!
>Do you know for sure that your gauge is correct? Maybe the compressor
>and pressure switch are fine.
Well, it's been working for a long time, but over the past few months
has been exhibiting the stalling issue.
I guess the guage could be wrong, but I kind of know what 120psi
"feels like" and it's not getting up to what it used to, either by the
guage or by feel.
GregS
The compressor speed does not slow down normally, it just starts to
sound a bit different under load.
greg
Sparks Fergusson
>Current draw. 1/3 horse shouldn't draw more than 7 amps at 120 volts
>or 3.5 amps at 240 volts.
Nameplace current rating is 6.0 amps (I'm running on 120 volts.)
I measured about 5 amps at startup (0 psi) rising to close to 6 when
it stalls. When it stops turning, the current actually drops back
closer to 5 amps, then increases as the motor starts turning again.
The motor is also hot to the touch after pumping all the way up. I can
hold my hand on it for maybe 6 or 8 seconds. I don't know if that's
different from how it used to be, though.
Thanks!
Sparks Fergusson
>The compressor speed does not slow down normally, it just starts to
>sound a bit different under load.
It didn't used to, that's for sure. Now, it slows all the way to 0. :(
Alan Douglas
see if both run windings are actually connected? Perhaps a nut is
working loose on the terminal plate inside the motor.
Alan
Sparks Fergusson
>Can you disconnect the motor from the pump and run just the motor to
>measure its no load amps? And to see if it heats up with no load?
No load, it's drawing about 1.5 amps. It gets warm, but not as hot as
it was under load.
Sparks Fergusson
Hmm, you might have something, there! This motor is probably 15+ years
old, and has never had anything done to it. Could corrosion and/or
loose connections account for the lack of power? I can certainly try
cleaning and tightening anything I can get to.
Thanks!
AZ Nomad
>Thanks!
check the brushes and commutator.
William R. Walsh
You should check the pressure switch contacts to be sure they aren't
burned. If they look OK, check the wiring leading to the compressor.
Perhaps something is wrong there. (Be sure you shut the power off FIRST
or you could have a shocking experience.)
Failing all of that, I'd check to see if the motor uses a run capacitor.
If it does, the capacitor is probably bad.
William
Sparks Fergusson
>What kind of motor is this? I didn't see you mention that. A 1/3 horse
>induction motor should not draw 1.5 amps with no load.
It's some sort of GE induction motor. I have the model number, but I
can't find anything about it on the GE website or Google.
What sort of problems would high no-load amp draw suggest?
Sparks Fergusson
<newsg...@idontwantjunqueemail.walshcomptech.com> wrote:
>Hi!
>
>You should check the pressure switch contacts to be sure they aren't
>burned. If they look OK, check the wiring leading to the compressor.
>Perhaps something is wrong there. (Be sure you shut the power off FIRST
>or you could have a shocking experience.)
Pressure switch contacts look OK, and there's minimal voltage drop
across under load. Wiring looks OK, too.
>Failing all of that, I'd check to see if the motor uses a run capacitor.
>If it does, the capacitor is probably bad.
There is a capacitor, but I'm not sure exactly what it does. I don't
have a wiring diagram and can't find any info on the Manufacturer's
website (GE.) I'll try to check the capacitor as best I can.
Could a capacitor issue cause the motor to start fine, but not have
enough power when running?
Jamie
Bad bearings..
and if it's a single phase motor.. check the starter cap, if it
has one. most likely not much good any more..
Also, you may have a centrifugal switch in the motor that isn't
closing its contacts. Or, you could have an open winding!..
William R. Walsh
> Pressure switch contacts look OK, and there's minimal voltage drop
> across under load. Wiring looks OK, too.
Good to know. It never hurts to rule out anything particularly obvious. It
also would not hurt to check the wiring connections in the motor--are they
rusty, burned, loose or just bad? If the motor has a built in circuit
breaker, is it good? (A bad one could have burned contacts or start to open
up just enough when the load increases.)
> Could a capacitor issue cause the motor to start fine, but not have
> enough power when running?
If it's a "run" capacitor, yes. Starting is the hardest time for a motor,
and some of the air compressor motors I've seen have a dedicated start
winding (and cap) to give them a little more "kick" to get going. That
winding won't stand continuous operation, so it's taken out of circuit by a
centrifugal switch when the motor reaches a certain speed.
From that point the motor runs on a different set of windings. Since it
sounds like the motor runs fine up to a point where the load increases, my
money would be on a run capacitor or wiring/current delivery issue. The run
capacitor would serve to give the motor a little more kick when the load
increases against it.
Capacitors for electric motors are usually pretty cheap. I had a furnace fan
motor that would not start reliably and paid $7 and change for a new one. It
made all the difference in the world. They're certainly cheaper than
replacing a burned out motor.
William
Alan Douglas
>>see if both run windings are actually connected? Perhaps a nut is
>>working loose on the terminal plate inside the motor.
>
>Hmm, you might have something, there! This motor is probably 15+ years
>old, and has never had anything done to it. Could corrosion and/or
>loose connections account for the lack of power? I can certainly try
>cleaning and tightening anything I can get to.
None of the other suggestions I've read, fit the symptoms. First
would be low voltage to the motor under load, but you've already
checked that. The starting capacitor is out of the circuit when the
motor is up to speed. There's nothing left in circuit but the two run
windings, wired in parallel.
Alan
PeterD
And all those replies ignore the fact the unloader is operating (at a
wrong, low pressure) which certainly doesn't point an evil finger at
the motor at all...
Alan Douglas
>wrong, low pressure) which certainly doesn't point an evil finger at
>the motor at all...
>
Hmmm, yes, I think that wasn't in the original post so I missed it.
That would account for gradual deterioration too.
Alan
Andy
Motors don't generally fade away; they usually burn up. I don't see
how a motor would become weaker, especially an induction motor. There
are no parts to wear out other than the stator winding, which doesn't
fail gracefully. If it fails there will be an unmistakable stinky
cloud of white smoke. You probably have a thermal overload on the
motor, and that's what trips when the motor appears to stall. Based
on what I have read here, this is what I would check first.
1. Check the thermal overload. Remove it from the circuit, and find a
way to load it up with a known current until it trips. It should trip
after some time at 1.15 times the nameplate current. It generally
takes a long time, like several minutes, at that current. This will
be around 2x the motor FLA. If the overload trips before you reach
1.15x, then the overload is bad.
I hope this helps.
2.
malua mada!
I'd verify the gauge anyway.
Sparks Fergusson
The unloader is functioning properly, as far as I can tell. It's a
combination check valve/unloader. So, when the check valve is open, it
allows the high pressure air into the tank. When the check valve
closes, it vents the pump side to atmosphere.
So, then the motor stalls, the check valve closes and the unloader
part releases the pressure. When the presssure falls sufficiently, the
motor restarts and the cycle continues.
Sparks Fergusson
>1. Check the thermal overload. Remove it from the circuit, and find a
>way to load it up with a known current until it trips. It should trip
>after some time at 1.15 times the nameplate current. It generally
>takes a long time, like several minutes, at that current. This will
>be around 2x the motor FLA. If the overload trips before you reach
>1.15x, then the overload is bad.
I'll try to check it, but the thermal overloads I've dealt with in the
past usually don't reclose quickly. In this case, the motor stalls,
the unloader releases, and the motor restarts inside of about 5
seconds...and then the cycle repeats.
But, it's looking likely that I need to take the motor apart and
inspect the innards (or take it to a motor shop.) So, I'll certainly
check the overload(s).
Michael A. Terrell
It shouldn't. The unloader is supposed to open when the motor first
starts, to let it come up to speed. Since the motor is stalling, you
either have a bad pressure sensor, or the run capacitor has lost some or
most of its capacitance. The pressure sensors deteriorate with age, and
the calibration goes to hell.
The capacitors have to pass a lot of current, and aren't made to last
forever. They are AC electrolytics to keep the size and cost within a
range you can afford to build and sell a product. A film capacitor
would be quite large, and can caost more then a new compressor.
Some compressors have two capacitors. One in the start circuit, and
the other in series with one of the run windings to provide the required
phase shift.
--
Greed is the root of all eBay.
Sparks Fergusson
> It shouldn't. The unloader is supposed to open when the motor first
>starts, to let it come up to speed.
An electric unloader, yes. This is a mechanical one, integrated with
the check valve. It is working as designed.
> Since the motor is stalling, you
>either have a bad pressure sensor, or the run capacitor has lost some or
>most of its capacitance. The pressure sensors deteriorate with age, and
>the calibration goes to hell.
The pressure switch is OK. It is not what is stopping the motor. The
contactor never opens and the motor is receiving full voltage through
the stall cycles. The capacitor could certainly be the issue, though.
> The capacitors have to pass a lot of current, and aren't made to last
>forever. They are AC electrolytics to keep the size and cost within a
>range you can afford to build and sell a product. A film capacitor
>would be quite large, and can caost more then a new compressor.
Indeed. This motor is probably 15-20 years old, so I can easily
believe the capacitor may be at fault. I'll have to disassemble the
motor and check it as soon as I get a chance.
> Some compressors have two capacitors. One in the start circuit, and
>the other in series with one of the run windings to provide the required
>phase shift.
I only see one capacitor, so I'm assuming it's in the starting
circuit. I don't have a wiring diagram, and GE has no information on
it's website for this motor.
Thanks!
PeterD
From the original post that started this thread:
>... 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..."
PeterD
Your checkvalve has a small copper tube to the pressure switch, right?
That's the unloader, which is also the small valve on the pressure
switch. Read my original response on adjusting the pressure swtich.
PeterD
<mike.t...@earthlink.net> wrote:
>
>Sparks Fergusson wrote:
>>
>> Alan Douglas <alan_do...@verizon.net> wrote:
>>
>> >>And all those replies ignore the fact the unloader is operating (at a
>> >>wrong, low pressure) which certainly doesn't point an evil finger at
>> >>the motor at all...
>> >>
>> >
>> >Hmmm, yes, I think that wasn't in the original post so I missed it.
>> >That would account for gradual deterioration too.
>>
>> The unloader is functioning properly, as far as I can tell. It's a
>> combination check valve/unloader. So, when the check valve is open, it
>> allows the high pressure air into the tank. When the check valve
>> closes, it vents the pump side to atmosphere.
>>
>> So, then the motor stalls, the check valve closes and the unloader
>> part releases the pressure. When the presssure falls sufficiently, the
>> motor restarts and the cycle continues.
>
>
> It shouldn't. The unloader is supposed to open when the motor first
>starts,
Typical small compressors the unloader opens when the pressure switch
activates and shuts off the compressor. This releases all pressure on
the compressor head, allowing the motor to start when pressure drops
down to the cutin PSI.
> to let it come up to speed. Since the motor is stalling, you
>either have a bad pressure sensor, or the run capacitor has lost some or
>most of its capacitance. The pressure sensors deteriorate with age, and
>the calibration goes to hell.
IHMO it has not been said that the motor is stalling! A stalled motor
(called locked rotor) will cause input current to swing sky-high,
usually tripping the breaker, making a hell of a noise, and is very
obvious.
PeterD
Fergusson) wrote:
>"Michael A. Terrell" <mike.t...@earthlink.net> wrote:
>
>> It shouldn't. The unloader is supposed to open when the motor first
>>starts, to let it come up to speed.
>
>An electric unloader, yes. This is a mechanical one, integrated with
>the check valve. It is working as designed.
>
>> Since the motor is stalling, you
>>either have a bad pressure sensor, or the run capacitor has lost some or
>>most of its capacitance. The pressure sensors deteriorate with age, and
>>the calibration goes to hell.
>
>The pressure switch is OK. It is not what is stopping the motor. The
>contactor never opens and the motor is receiving full voltage through
>the stall cycles. The capacitor could certainly be the issue, though.
So the original post is incorrect then? WHich is right, this or the
other one? Is motor current high when the motor stalls?
Sparks Fergusson
>So the original post is incorrect then? WHich is right, this or the
>other one? Is motor current high when the motor stalls?
I measured about 5 amps at startup (0 psi) rising to close to 6 when
it stalls. When it stops turning, the current actually drops back
closer to 5 amps, then increases as the motor starts turning again.
Sparks Fergusson
>Typical small compressors the unloader opens when the pressure switch
>activates and shuts off the compressor. This releases all pressure on
>the compressor head, allowing the motor to start when pressure drops
>down to the cutin PSI.
On this compressor, the check valve/unloader is completely separate
from the pressure switch. The unloader is similar to this one:
http://www.amazon.com/Control-Devices-CA121A-Unloader-Check/
>IHMO it has not been said that the motor is stalling! A stalled motor
>(called locked rotor) will cause input current to swing sky-high,
>usually tripping the breaker, making a hell of a noise, and is very
>obvious.
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.
Input current does not swing sky-high, though, nor does the breaker
trip, nor is there a hell of a noise. It definitely comes to a dead
stop, though.
Sparks Fergusson
>
>From the original post that started this thread:
>
>>... 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..."
Yes, those're the symptoms.
Alan Douglas
So it stalls first, then the unloader bleeds off pressure at the
compressor and allows it to restart?
I'm puzzled, but at this point I would disable the switch and unloader
and see if the compressor runs up to 120 as it used to.
You said the motor current is only 5 or 6 amps when it stalls?
Locked-rotor current for a 1/3HP motor should be much more than that,
at least 30 amps (I haven't looked it up). You're sure it's getting
full line voltage at that point? I don't see how it could be.
Alan
PeterD
Fergusson) wrote:
>PeterD <pet...@hipson.net> wrote:
>
>>Typical small compressors the unloader opens when the pressure switch
>>activates and shuts off the compressor. This releases all pressure on
>>the compressor head, allowing the motor to start when pressure drops
>>down to the cutin PSI.
>
>On this compressor, the check valve/unloader is completely separate
>from the pressure switch. The unloader is similar to this one:
>http://www.amazon.com/Control-Devices-CA121A-Unloader-Check/
>
The URL above is 'dead'...
This is probably what you are trying to point to:
>>IHMO it has not been said that the motor is stalling! A stalled motor
>>(called locked rotor) will cause input current to swing sky-high,
>>usually tripping the breaker, making a hell of a noise, and is very
>>obvious.
>
>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.
So the motor actually stalls, and there are no sounds (humming, etc.)
from it?
>
>Input current does not swing sky-high, though, nor does the breaker
>trip, nor is there a hell of a noise. It definitely comes to a dead
>stop, though.
A most interesting set of symptoms... Motor stalls to locked rotor, no
significant current draw, odd...
How 'hot' is the motor? Is it possible the thermal cutout is tripping
(at too low a temperature, perhaps?)
PeterD
Well, he did say (in another post) he's bypassed the pressure switch
for a test run, and the symptoms persist. I think he's got a high
resistance point in the wiring too, but I'm not sure where.
Maybe monitor voltage at the motor terminals might give a clue.
As Alan says, locked rotor should result in very high current/power
draws. It is very noticable, and unless the compressor is on a circuit
that is vastly overfused result in a blown fuse/tripped breaker almost
immediately.
Can you (the OP) post specicifications from the motor's name plate,
and the compressor assembly? FWIW, no compressor has a fractional HP
motor, most are motors rated at 1 to 3 HP on small compressors.
Michael A. Terrell
Sparks Fergusson wrote:
>
> I only see one capacitor, so I'm assuming it's in the starting
> circuit. I don't have a wiring diagram, and GE has no information on
> it's website for this motor.
Don't assume. What is the capacitance? Some small split phase
motors only have a run capacitor. The fact that the current only rises
slightly indicates a bad capacitor or a poor connection to one winding.
GregS
I don't think GE is making the motors anymore, and thats why you can't
get info. Either test the cap or replace it. Its probably a run cap.
greg
Wild_Bill
already, induction motors don't get tired or exhibit lower power output with
age.
You don't state some of the most essential info.. namely, the brand name and
model number of the air compressor, and the size and type of air pump.
The complete info listed on the motor label should also be included.
We can't see it from where we are.
Forget the capacitor.. the motor is starting normally, so the cap isn't the
problem.
A mechanical failure in the motor may be contributing to the overload. The
motor bearings may be worn out, they're likely to be sleeve bearings in a
1/3 HP motor, and not replaceable, but all hope is not lost if the motor
shaft isn't scored.
FWIW, sleeve bearings can wear to the extent that the rotor begins to rub on
the stator segments (lots of friction and excess heat).
If the bearing surfaces aren't completely wiped out, re-orienting the end
bells of the motor may provide better bearing surfaces. If the bearings are
the sleeve type, and haven't been oiled regularly, it's likely they would be
worn or damaged.
I can't positively explain why the motor isn't already destroyed, or why the
circuit breaker isn't tripping.
It's very likely that the overloading of the motor is related to air
pressure from the tank resisting movement of the piston in the pump, if the
pump is a piston-type pump.
Normally on small air compressors, tank pressure is isolated from the piston
by a check valve at the tank fitting.
Additionally, (in a piston air pump) there are likely to be reed valves in
the head of the air pump that would separate the cylinder from the outlet
fitting (the tubing constitutes a manifold in air compressor nomenclaure, if
the unit doesn't have a separate part designated as a manifold).
If the air intake is restricted (or choked off from a clogged filter as many
small air compressors only have a piece of wool felt filters), this may
contribute to more load on the motor.
Many piston air pumps have oil lubrication in the pump's case. If the oil
becomes very dirty or the level is inadequate, bearings, the pison and
cylinder can be damaged, resulting in excess friction until a full failure
takes place.
It's possible that the motor's thermal protector is responding to high
current, and if this is the case in this particular situation, it's the
reason the circui breaker hasn't tripped, and likely saved the motor from
destruction.
It's fairly obvious that the restarting actions described are the result of
a self-resetting protective device.
With the power cord unplugged, and the belt removed from the air pump (if
it's a piston-type pump), the pumping action can be checked by placing a
finger over the outlet fitting and briskly turning the pump pulley by hand.
The pump's basic operations of intake and compress/ouput can be observed
with this fairly simple test.
Some of the same conditions included above may pertain to diaphram-type air
pumps, although many diaphram types are direct drive, where the motor and
pump are a single unit, which may make checking the pump's basic operation a
little more difficult.
--
Cheers,
WB
.............
"Sparks Fergusson" <hate...@invalid.invalid> wrote in message
news:4b8f3f2a...@news.eternal-september.org...
>
> 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...
>
snippage
>
> Anyone have any ideas?
>
> Thanks!
PeterD
Additional comment. The five amps draw is perhaps normal for this
unit, as it appears to be a 240 volt setup. I was thinking it was 120
volt (US) but I appear to be wrong there... <g>
Sparks Fergusson
I can't read the markings on the cap without taking the motor apart.
But, thanks to everybody's help, it looks like that's the next step.
I'll definitely replace the cap and otherwise clean, lubricate, and
tighten as appropriate.
Thanks!
Sparks Fergusson
>This is probably what you are trying to point to:
>
>http://www.amazon.com/Control-Devices-CA121A-Unloader-Check/dp/B000LB7PBK/ref=sr_1_1?ie=UTF8&s=hi&qid=1268055829&sr=8-1
Sorry, yes, that's the one.
>So the motor actually stalls, and there are no sounds (humming, etc.)
>from it?
Yes, it actually stalls. There's not super loud humming. There may be
some motor noise, but it's hard to hear over the sound of the
unloader.
>A most interesting set of symptoms... Motor stalls to locked rotor, no
>significant current draw, odd...
>
>How 'hot' is the motor? Is it possible the thermal cutout is tripping
>(at too low a temperature, perhaps?)
Well, it does get warm. It gets warm when running with the belt off,
too. When it goes into it's stall cycle, it's definitely warmer than
that. I can put my Mk I hand on it for about 8 seconds, which says
it's hot, but not super hot.
Sparks Fergusson
>So it stalls first, then the unloader bleeds off pressure at the
>compressor and allows it to restart?
Yes, that's correct.
>I'm puzzled, but at this point I would disable the switch and unloader
>and see if the compressor runs up to 120 as it used to.
It's a mechanical unloader, integrated with the check valve, so
disabling it would be difficult. However, it's pretty obvious that the
unloader only opens after the motor stalls when the check valve
closes.
>You said the motor current is only 5 or 6 amps when it stalls?
>Locked-rotor current for a 1/3HP motor should be much more than that,
>at least 30 amps (I haven't looked it up). You're sure it's getting
>full line voltage at that point? I don't see how it could be.
There's definitely no current spike when it stalls, nor does it trip
the breaker, dim the lights, etc. Is it getting full voltage? It is at
the point the motor leads connect to the pressure switch. I can't
easily measure any closer than that because the leads run into the
motor and there's no easy way to get to them, especially when it's
running. But, it looks like I need to disassemble the motor and check
things out inside, so that'll be the next step.
Thanks!
Sparks Fergusson
>Well, he did say (in another post) he's bypassed the pressure switch
>for a test run, and the symptoms persist. I think he's got a high
>resistance point in the wiring too, but I'm not sure where.
Yes, bypassing the pressure switch doesn't make any diffence. You may
well be right about a high resistance point.
>Maybe monitor voltage at the motor terminals might give a clue.
I can't easily get to the internal terminals. The closest I can
measure is at the pressure switch, and the voltage looks fine there.
>As Alan says, locked rotor should result in very high current/power
>draws. It is very noticable, and unless the compressor is on a circuit
>that is vastly overfused result in a blown fuse/tripped breaker almost
>immediately.
It's on a standard outlet circuit with a 20A breaker. It hasn't
tripped. Nor have there been any of the signs that you mention for
high current draw.
>Can you (the OP) post specicifications from the motor's name plate,
>and the compressor assembly? FWIW, no compressor has a fractional HP
>motor, most are motors rated at 1 to 3 HP on small compressors.
1/3 HP is what's on the nameplate. These days, it would probably be
rated at 1 or 2 "marketing HP" :-)
The compressor itself has long lost it's label. But, it's a single
cylinder reciprocating, belt driven compressor with about a 20 gallon
tank, a 3 inch pulley on the motor and a 9 inch on the compressor.
The motor was made by GE, and is labeled:
Model: 5KC42JG391AX
Volts: 115/230
Ph: 1
Amps: 6.0/3.0
HP: 1/3
HZ: 60
RPM: 1725
It's running on 120 volts.
Sparks Fergusson
>On Tue, 09 Mar 2010 05:57:35 GMT, hate...@invalid.invalid (Sparks
>>Model: 5KC42JG391AX
>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
hate...@invalid.invalid (Sparks Fergusson) wrote:
...
>
> 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
--
“Egotism is the anesthetic that dulls the pain of stupidity.”
Frank Leahy, Head coach, Notre Dame 1941-1954
Plain...@yahoo.com
Fergusson) wrote:
>
>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
<Plain...@yahoo.com> wrote in message
news:vrs4q59ejbb3o71mm...@4ax.com...
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
Thats a possibility, I've seen open rotor bars on induction motors.
Sometimes they arc at the break and leave burn marks.
--
Best Regards:
Baron.
Plain...@yahoo.com
wrote:
I've never seen that, but it is definitely a possibility and would
also explain the symtoms.
PlainBill
David
<Plain...@yahoo.com> wrote in message
news:q6e7q5daqoilfbm0c...@4ax.com...
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
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
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
Am I missing something?
Jeffrey D Angus
>> It ran, but wouldn't start.
>
> 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.
911r...@gmail.com
> 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!
pf...@aol.com
> Just replaced a "run capacitor on my 5 H.P. Champion compressor that was having a similar issue...All is well now.
This will very most likely be the problem. The motor is an AC induction motor, no brushes. But the run capacitor is critical to proper torque. And, if you are already in there and the happens to be a start-cap, do that one too.
Peter Wieck
Melrose Park, PA