Air Compressor Problem - Motor Stalls

Mon Mar 08, 2010 3:56 am   

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

Mon Mar 08, 2010 2:54 pm   

On Mon, 08 Mar 2010 01:04:59 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson) wrote:


The URL above is 'dead'...

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



So the motor actually stalls, and there are no sounds (humming, etc.)
from it?


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?)

Mon Mar 08, 2010 2:58 pm   

On Sun, 07 Mar 2010 21:56:03 -0500, Alan Douglas
<alan_douglasat_at_verizon.net> wrote:


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.

Mon Mar 08, 2010 5:58 pm   

Sparks Fergusson wrote:


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.


--
Greed is the root of all eBay.

Mon Mar 08, 2010 6:24 pm   

In article <4B952CC7.28373A3B_at_earthlink.net>, "Michael A. Terrell" <mike.terrell_at_earthlink.net> wrote:

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

Mon Mar 08, 2010 9:44 pm   

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.

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" <hatespam_at_invalid.invalid> wrote in message
news:4b8f3f2a.47238118_at_news.eternal-september.org...

Mon Mar 08, 2010 10:05 pm   

On Mon, 08 Mar 2010 08:58:34 -0500, PeterD <peter2_at_hipson.net> wrote:


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>

Tue Mar 09, 2010 6:32 am   

zekfrivo_at_zekfrivolous.com (GregS) wrote:


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!

Tue Mar 09, 2010 6:37 am   

PeterD <peter2_at_hipson.net> wrote:


Sorry, yes, that's the one.


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.


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.

Tue Mar 09, 2010 6:42 am   

Alan Douglas <alan_douglasat_at_verizon.net> wrote:



Yes, that's correct.


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.


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!

Tue Mar 09, 2010 6:57 am   

PeterD <peter2_at_hipson.net> wrote:


Yes, bypassing the pressure switch doesn't make any diffence. You may
well be right about a high resistance point.


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.


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.


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.

Tue Mar 09, 2010 1:55 pm   

On Tue, 09 Mar 2010 05:57:35 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson)wrote:


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

Is it wired for 120?

Wed Mar 10, 2010 3:00 am   

Meat Plow wrote:


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


Yes.

Tue Mar 16, 2010 2:45 am   

In article <4b944c36.5653699_at_news.eternal-september.org>,
hatespam_at_invalid.invalid (Sparks Fergusson) wrote:

....

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

Tue Mar 16, 2010 6:33 am   

David <postings_at_REMOVE-TO-REPLYconfidential-counselling.com> wrote:


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

Thanks!