Air Compressor Problem - Motor Stalls

Thu Mar 04, 2010 9:09 pm   

Meat Plow wrote:


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!

Thu Mar 04, 2010 9:12 pm   

zekfrivo_at_zekfrivolous.com (GregS) wrote:


It didn't used to, that's for sure. Now, it slows all the way to 0.

Thu Mar 04, 2010 10:24 pm   

On Thu, 04 Mar 2010 20:09:31 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson)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?

Thu Mar 04, 2010 11:30 pm   

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

Fri Mar 05, 2010 2:05 am   

Meat Plow wrote:


No load, it's drawing about 1.5 amps. It gets warm, but not as hot as
it was under load.

Fri Mar 05, 2010 4:13 am   

Alan Douglas <alan_douglasat_at_verizon.net> wrote:


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!

Fri Mar 05, 2010 5:13 am   

On Fri, 05 Mar 2010 03:13:01 GMT, Sparks Fergusson <hatespam_at_invalid.invalid> wrote:

check the brushes and commutator.

Fri Mar 05, 2010 4:37 pm   

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

Fri Mar 05, 2010 4:39 pm   

On Fri, 05 Mar 2010 01:05:35 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson)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.

Sat Mar 06, 2010 1:44 am   

Meat Plow wrote:


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?

Sat Mar 06, 2010 1:47 am   

"William R. Walsh"
<newsgroups1_at_idontwantjunqueemail.walshcomptech.com> wrote:


Pressure switch contacts look OK, and there's minimal voltage drop
across under load. Wiring looks OK, too.


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?

Sat Mar 06, 2010 2:59 am   

Sparks Fergusson wrote:


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!..

Sat Mar 06, 2010 8:29 am   

Hi!


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.)


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

Sat Mar 06, 2010 3:09 pm   

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

Sat Mar 06, 2010 6:01 pm   

On Sat, 06 Mar 2010 00:44:32 GMT, hatespam_at_invalid.invalid (Sparks
Fergusson)wrote:


Suggests possible bad bearing, insulation on windings breaking down,
bad start/run capacitor, bad centrifugal switch, bad connections where
windings attach to start/run devices and line voltage. Find a place
locally that repairs motors. Most communities have somone who does it
and they should be willing to have a look at it for a few bucks.