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!

[]
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?

On Mar 3, 9:13*pm, (Sparks 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!

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.

On Thu, 04 Mar 2010 05:13:31 GMT, lid (Sparks
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.

...

In article , lid (Sparks 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?


Check the line voltage while opperating at the motor.
I can do that stall with a long extension cord.

greg

In article , (GregS) wrote:
In article ,
lid (Sparks 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?


Check the line voltage while opperating at the motor.
I can do that stall with a long extension cord.

greg

Is it oiless ?If so, check the bearing.

greg

On 3/3/2010 9:13 PM, Sparks 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!
Do you know for sure that your gauge is correct? Maybe the compressor
and pressure switch are fine.

Sansui Samari wrote:

On Mar 3, 9:13=A0pm, (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!

PeterD wrote:

On Thu, 04 Mar 2010 05:13:31 GMT, lid (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!

(GregS) wrote:

In article , (GregS) wrote:

Check the line voltage while opperating at the motor.
I can do that stall with a long extension cord.

greg

Is it oiless ?If so, check the bearing.

greg

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!

Meat Plow wrote:

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!

Bennett Price wrote:

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.

In article , lid (Sparks Fergusson) wrote:
Bennett Price wrote:

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.

The compressor speed does not slow down normally, it just starts to
sound a bit different under load.

greg

Meat Plow wrote:

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!

(GregS) wrote:

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.

Assuming it's a 120V/240V motor connected for 120, can you check to
see if both run windings are actually connected? Perhaps a nut is
working loose on the terminal plate inside the motor.

Alan

Meat Plow wrote:

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.

Alan Douglas wrote:

Assuming it's a 120V/240V motor connected for 120, can you check to
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.

Thanks!

On Fri, 05 Mar 2010 03:13:01 GMT, Sparks Fergusson wrote:
Alan Douglas wrote:

Assuming it's a 120V/240V motor connected for 120, can you check to
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.

Thanks!

check the brushes and commutator.

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.)

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

Meat Plow wrote:

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?

"William R. Walsh"
m 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?

Sparks Fergusson wrote:

Meat Plow wrote:


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?
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!..

Hi!

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

Assuming it's a 120V/240V motor connected for 120, can you check to
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

On Sat, 06 Mar 2010 09:09:57 -0500, Alan Douglas
wrote:

Assuming it's a 120V/240V motor connected for 120, can you check to
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

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...

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.

Alan

On Mar 5, 5:44*pm, (Sparks Fergusson) wrote:
Meat Plow wrote:
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?

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.

On Mar 4, 11:35*am, (Sparks Fergusson) wrote:
Bennett Price wrote:
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.

I'd verify the gauge anyway.

Alan Douglas 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.

Andy wrote:

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).

Sparks Fergusson wrote:

Alan Douglas 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, 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.

"Michael A. Terrell" 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.

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!

On Sun, 07 Mar 2010 08:00:01 -0500, Alan Douglas
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.

Alan

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..."

On Sun, 07 Mar 2010 18:16:46 GMT, lid (Sparks
Fergusson) wrote:

Alan Douglas 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.


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.

On Sun, 07 Mar 2010 15:32:31 -0500, "Michael A. Terrell"
wrote:


Sparks Fergusson wrote:

Alan Douglas 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.


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.

On Sun, 07 Mar 2010 20:59:24 GMT, lid (Sparks
Fergusson) wrote:

"Michael A. Terrell" 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?


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 wrote:

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.

PeterD 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-Device...nloader-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.

PeterD wrote:


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.