Air Compressor Problem - Motor Stalls
in [Repair]
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From: Sparks Fergusson on 7 Mar 2010 13:19 Andy <andrewkgentile(a)gmail.com> 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).
From: Michael A. Terrell on 7 Mar 2010 15:32 Sparks Fergusson wrote: > > Alan Douglas <alan_douglasat(a)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.
From: Sparks Fergusson on 7 Mar 2010 15:59 "Michael A. Terrell" <mike.terrell(a)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. > 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!
From: PeterD on 7 Mar 2010 18:17 On Sun, 07 Mar 2010 08:00:01 -0500, Alan Douglas <alan_douglasat(a)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. > >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..."
From: PeterD on 7 Mar 2010 18:18
On Sun, 07 Mar 2010 18:16:46 GMT, hatespam(a)invalid.invalid (Sparks Fergusson) wrote: >Alan Douglas <alan_douglasat(a)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. |