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PeterD
Guest
Sun Mar 07, 2010 3:02 am
On Sat, 06 Mar 2010 09:09:57 -0500, Alan Douglas
<alan_douglasat_at_verizon.net> wrote:
Quote:
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...
Alan Douglas
Guest
Sun Mar 07, 2010 3:00 pm
Quote:
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
Andy
Guest
Sun Mar 07, 2010 4:36 pm
On Mar 5, 5:44 pm, hates...@invalid.invalid (Sparks Fergusson) wrote:
Quote:
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.
Sparks Fergusson
Guest
Sun Mar 07, 2010 8:16 pm
Alan Douglas <alan_douglasat_at_verizon.net> wrote:
Quote:
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.
Sparks Fergusson
Guest
Sun Mar 07, 2010 8:19 pm
Andy <andrewkgentile_at_gmail.com> wrote:
Quote:
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).
malua mada!
Guest
Sun Mar 07, 2010 8:20 pm
On Mar 4, 11:35 am, hates...@invalid.invalid (Sparks Fergusson) wrote:
Quote:
Bennett Price <bjpr...@cal.berkeley.edu> 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.
Michael A. Terrell
Guest
Sun Mar 07, 2010 10:32 pm
Sparks Fergusson wrote:
Quote:
Alan Douglas <alan_douglasat_at_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, 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
Guest
Sun Mar 07, 2010 10:59 pm
"Michael A. Terrell" <mike.terrell_at_earthlink.net> wrote:
Quote:
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.
Quote:
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.
Quote:
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.
Quote:
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
Guest
Mon Mar 08, 2010 1:17 am
On Sun, 07 Mar 2010 08:00:01 -0500, Alan Douglas
<alan_douglasat_at_verizon.net> wrote:
Quote:
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:
Quote:
... 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
Guest
Mon Mar 08, 2010 1:18 am
On Sun, 07 Mar 2010 18:16:46 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson) wrote:
Quote:
Alan Douglas <alan_douglasat_at_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.
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
Guest
Mon Mar 08, 2010 1:20 am
On Sun, 07 Mar 2010 15:32:31 -0500, "Michael A. Terrell"
<mike.terrell_at_earthlink.net> wrote:
Quote:
Sparks Fergusson wrote:
Alan Douglas <alan_douglasat_at_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.
Quote:
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.
Quote:
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.
PeterD
Guest
Mon Mar 08, 2010 1:22 am
On Sun, 07 Mar 2010 20:59:24 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson) wrote:
Quote:
"Michael A. Terrell" <mike.terrell_at_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?
Quote:
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!
Sparks Fergusson
Guest
Mon Mar 08, 2010 3:00 am
PeterD <peter2_at_hipson.net> wrote:
Quote:
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
Guest
Mon Mar 08, 2010 3:04 am
PeterD <peter2_at_hipson.net> wrote:
Quote:
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/
Quote:
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
Guest
Mon Mar 08, 2010 3:08 am
PeterD <peter2_at_hipson.net> wrote:
Quote:
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.
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