Air Compressor Problem - Motor Stalls
in [Repair]
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From: PlainBill47 on 18 Mar 2010 14:55 On Thu, 04 Mar 2010 05:13:31 GMT, hatespam(a)invalid.invalid (Sparks Fergusson) wrote: > >I'm having a problem with my 20 gallon, single stage electric air >compressor. It's acting like the motor is 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... > >It worked fine for years (The pressure switch would shut it down at >about 120 psi) but over the past few months, it's gotten worse and >worse, and now will only make about 90-95 psi before the motor stalls. > >I cleaned and lubricated the compressor itself, and it spins freely >and doesn't appear to be binding or otherwise have excessive friction. >The check valve/unloader is working and the piping is all open and >clear. > >It seems like the electric motor (1/3 hp) just no longer has the oomph >it used to. It starts up fine, no humming, no smoking, no bad smells, >no clunks. It just doesn't seem to have enough running torque to >handle the load like it did before. > >Anyone have any ideas? > >Thanks! After reading all the posts, several things stand out. The most significant: There is no excessive current draw when the motor stalls. By all the laws of physics, that is flat out impossible. There are two explanations (well, three, but I'm assuming you aren't making this up). The first is slippage at the belt, motor pulley, or rotor. Given the knowledge you have exhibited, I say that can't be the problem; it's pretty hard to miss the fact that the motor is spinning but the belt is slipping. That leads to only one conclusion: The actual voltage to the windings is dropping. Possible causes are a bad thernal overload protector, bad run capacitor (some motors hide the starting capacitor inside, while the run capacitor is in a cupola on the side), or a corroded terminal so only one of the paired windings is used. All of these possible causes result in a lot of heat generated at one small point EXCEPT the single winding and the bad run capacitor. The single winding explanation is unlikely because it would not deteriorate gradually. That leaves the bad run capacitor. PlainBill
From: David on 18 Mar 2010 16:58 <PlainBill47(a)yahoo.com> wrote in message news:vrs4q59ejbb3o71mmtejt53subrukq6vg1(a)4ax.com... > On Thu, 04 Mar 2010 05:13:31 GMT, hatespam(a)invalid.invalid > (Sparks > Fergusson) wrote: > After reading all the posts, several things stand out. > The most > significant: There is no excessive current draw when the > motor stalls. > By all the laws of physics, that is flat out impossible. > There are > two explanations (well, three, but I'm assuming you aren't > making this > up). The first is slippage at the belt, motor pulley, or > rotor. > Given the knowledge you have exhibited, I say that can't > be the > problem; it's pretty hard to miss the fact that the motor > is spinning > but the belt is slipping. > > That leads to only one conclusion: The actual voltage to > the windings > is dropping. Possible causes are a bad thernal overload > protector, > bad run capacitor (some motors hide the starting capacitor > inside, > while the run capacitor is in a cupola on the side), or a > corroded > terminal so only one of the paired windings is used. > > All of these possible causes result in a lot of heat > generated at > one small point EXCEPT the single winding and the bad run > capacitor. > The single winding explanation is unlikely because it > would not > deteriorate gradually. That leaves the bad run capacitor. > > PlainBill There is one more possible cause: Some or all of the windings on the rotor that are supposed to be shorted are open. An induction motor works because windings on the rotor are shorted to induce the field needed to turn the rotor. David
From: Baron on 18 Mar 2010 18:01 David Inscribed thus: > > > <PlainBill47(a)yahoo.com> wrote in message > news:vrs4q59ejbb3o71mmtejt53subrukq6vg1(a)4ax.com... >> On Thu, 04 Mar 2010 05:13:31 GMT, hatespam(a)invalid.invalid >> (Sparks >> Fergusson) wrote: >> After reading all the posts, several things stand out. >> The most >> significant: There is no excessive current draw when the >> motor stalls. >> By all the laws of physics, that is flat out impossible. >> There are >> two explanations (well, three, but I'm assuming you aren't >> making this >> up). The first is slippage at the belt, motor pulley, or >> rotor. >> Given the knowledge you have exhibited, I say that can't >> be the >> problem; it's pretty hard to miss the fact that the motor >> is spinning >> but the belt is slipping. >> >> That leads to only one conclusion: The actual voltage to >> the windings >> is dropping. Possible causes are a bad thernal overload >> protector, >> bad run capacitor (some motors hide the starting capacitor >> inside, >> while the run capacitor is in a cupola on the side), or a >> corroded >> terminal so only one of the paired windings is used. >> >> All of these possible causes result in a lot of heat >> generated at >> one small point EXCEPT the single winding and the bad run >> capacitor. >> The single winding explanation is unlikely because it >> would not >> deteriorate gradually. That leaves the bad run capacitor. >> >> PlainBill > > There is one more possible cause: Some or all of the > windings on the rotor that are supposed to be shorted are > open. An induction motor works because windings on the rotor > are shorted to induce the field needed to turn the rotor. > > David Thats a possibility, I've seen open rotor bars on induction motors. Sometimes they arc at the break and leave burn marks. -- Best Regards: Baron.
From: PlainBill47 on 19 Mar 2010 13:49 On Thu, 18 Mar 2010 15:58:38 -0500, "David" <someone(a)somewhere.com> wrote: > > ><PlainBill47(a)yahoo.com> wrote in message >news:vrs4q59ejbb3o71mmtejt53subrukq6vg1(a)4ax.com... >> On Thu, 04 Mar 2010 05:13:31 GMT, hatespam(a)invalid.invalid >> (Sparks >> Fergusson) wrote: >> After reading all the posts, several things stand out. >> The most >> significant: There is no excessive current draw when the >> motor stalls. >> By all the laws of physics, that is flat out impossible. >> There are >> two explanations (well, three, but I'm assuming you aren't >> making this >> up). The first is slippage at the belt, motor pulley, or >> rotor. >> Given the knowledge you have exhibited, I say that can't >> be the >> problem; it's pretty hard to miss the fact that the motor >> is spinning >> but the belt is slipping. >> >> That leads to only one conclusion: The actual voltage to >> the windings >> is dropping. Possible causes are a bad thernal overload >> protector, >> bad run capacitor (some motors hide the starting capacitor >> inside, >> while the run capacitor is in a cupola on the side), or a >> corroded >> terminal so only one of the paired windings is used. >> >> All of these possible causes result in a lot of heat >> generated at >> one small point EXCEPT the single winding and the bad run >> capacitor. >> The single winding explanation is unlikely because it >> would not >> deteriorate gradually. That leaves the bad run capacitor. >> >> PlainBill > >There is one more possible cause: Some or all of the >windings on the rotor that are supposed to be shorted are >open. An induction motor works because windings on the rotor >are shorted to induce the field needed to turn the rotor. > >David > I've never seen that, but it is definitely a possibility and would also explain the symtoms. PlainBill
From: David on 19 Mar 2010 14:09
<PlainBill47(a)yahoo.com> wrote in message news:q6e7q5daqoilfbm0c7aarr47lcv3stka6k(a)4ax.com... > On Thu, 18 Mar 2010 15:58:38 -0500, "David" > <someone(a)somewhere.com> > wrote: > >> >> >><PlainBill47(a)yahoo.com> wrote in message >>news:vrs4q59ejbb3o71mmtejt53subrukq6vg1(a)4ax.com... >>> On Thu, 04 Mar 2010 05:13:31 GMT, >>> hatespam(a)invalid.invalid >>> (Sparks >>> Fergusson) wrote: >>> After reading all the posts, several things stand out. >>> The most >>> significant: There is no excessive current draw when the >>> motor stalls. >>> By all the laws of physics, that is flat out impossible. >>> There are >>> two explanations (well, three, but I'm assuming you >>> aren't >>> making this >>> up). The first is slippage at the belt, motor pulley, >>> or >>> rotor. >>> Given the knowledge you have exhibited, I say that can't >>> be the >>> problem; it's pretty hard to miss the fact that the >>> motor >>> is spinning >>> but the belt is slipping. >>> >>> That leads to only one conclusion: The actual voltage >>> to >>> the windings >>> is dropping. Possible causes are a bad thernal overload >>> protector, >>> bad run capacitor (some motors hide the starting >>> capacitor >>> inside, >>> while the run capacitor is in a cupola on the side), or >>> a >>> corroded >>> terminal so only one of the paired windings is used. >>> >>> All of these possible causes result in a lot of heat >>> generated at >>> one small point EXCEPT the single winding and the bad >>> run >>> capacitor. >>> The single winding explanation is unlikely because it >>> would not >>> deteriorate gradually. That leaves the bad run >>> capacitor. >>> >>> PlainBill >> >>There is one more possible cause: Some or all of the >>windings on the rotor that are supposed to be shorted are >>open. An induction motor works because windings on the >>rotor >>are shorted to induce the field needed to turn the rotor. >> >>David >> > I've never seen that, but it is definitely a possibility > and would > also explain the symtoms. > > PlainBill PlainBill: I once saw a fractional HP induction motor on a fan had problems starting in a certain position. After moving the rotor a bit, it would run. There was one open winding on the rotor. The open was visible on the side of the rotor and applying a significant amount of solder cured the problem. There can be a lot of current in these shorted turns on a loaded motor. David |