Air Compressor Problem - Motor Stalls
in [Repair]
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From: Alan Douglas on 7 Mar 2010 21:56 >> >>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. 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
From: PeterD on 8 Mar 2010 08:54 On Mon, 08 Mar 2010 01:04:59 GMT, hatespam(a)invalid.invalid (Sparks Fergusson) wrote: >PeterD <peter2(a)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: http://www.amazon.com/Control-Devices-CA121A-Unloader-Check/dp/B000LB7PBK/ref=sr_1_1?ie=UTF8&s=hi&qid=1268055829&sr=8-1 >>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?)
From: PeterD on 8 Mar 2010 08:58 On Sun, 07 Mar 2010 21:56:03 -0500, Alan Douglas <alan_douglasat(a)verizon.net> 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. > >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 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.
From: Michael A. Terrell on 8 Mar 2010 11:58 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. -- Greed is the root of all eBay.
From: GregS on 8 Mar 2010 12:24
In article <4B952CC7.28373A3B(a)earthlink.net>, "Michael A. Terrell" <mike.terrell(a)earthlink.net> wrote: > >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. 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 |