Capacitor start electric motor failure

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  #1  
Old 02-02-07, 06:56 PM
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Capacitor start electric motor failure

I realize this may be the wrong section please advise if it is.

I'm about to crack open and old compressor motor to clean it in hopes to fix a problem. I'd like to offer symptoms of what's happening in order to maybe get hints on what to look at first.

I bought a used compressor mainly for the tank. But the only thing wrong with it is the motor so I figuredI'd take a crack at fixing it.

It's a 110v 1.5 or 2hp capacitor start motor. The capacitor looks new. Can I test it to see if it's still good with a multimeter?

When the motor is plugged in it hums an throws a breaker. It tries to spin the pulley seems to move.

I decided to test the motor under no load and removed the compressor pump belt. The motor started and spun but quicky threw a breaker again.

It was in a filthy environement and is extremely dirty so cleaning/oiling is the first thing I'm doing. Upon first inspection all the wiring tested good, the points for the centrifugal switch are very dirty but still seem to be spaced enough to prevent a contact.

The internal breaker never trips and appears to be ok.


EDIT: this is a single phase motor

RE-EDIT: It was plugged in a 20amp breaker circuit with nothing else on it. (my block heater plug outside)
 
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  #2  
Old 02-02-07, 10:42 PM
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You can test an electrolytic capacitor with an analog multimeter. Disconnect the leads and attach the multimeter on a high resistance range. The initial indication will be low resistance and then near infinity as the cap charges.

I haven't tried this with a DMM.
 
  #3  
Old 02-02-07, 11:37 PM
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If it started without a load, the cap is good. I'd clean and lube it.

Steve
 
  #4  
Old 02-03-07, 04:33 AM
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Originally Posted by Wayne Mitchell View Post
You can test an electrolytic capacitor with an analog multimeter. Disconnect the leads and attach the multimeter on a high resistance range. The initial indication will be low resistance and then near infinity as the cap charges.

I haven't tried this with a DMM.
It works with a DMM. Then switch to voltage and blead off the cap. The voltage should start high and move to and end up at zero.

Have spare batteries on hand. This process eats up the meters battery.
 
  #5  
Old 02-06-07, 01:18 PM
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I've given it a thorough cleaning will update tomorrow with the results.
 
  #6  
Old 02-07-07, 09:19 AM
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The motor is up and running thank you for your assitance. It's not lubricated yet though. I was going to use a dielectric grease? Is that ok? Which parts should be lubricated and which should not?
 
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Old 02-07-07, 12:05 PM
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I'm not sure anything should be lubricated. The only friction parts should be the armature end bearings and I might be wrong but I don't think they require lubrication.
 
  #8  
Old 02-09-07, 11:21 AM
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Originally Posted by Gotrek View Post
The motor is up and running thank you for your assitance. It's not lubricated yet though. I was going to use a dielectric grease? Is that ok? Which parts should be lubricated and which should not?
It depends on if they are bronze bearings or ball bearing. Bronze bearings are oiled with 10 or 30 wt non-detergent motor oil. Like what you put in a lawn mower not your car.

typically if the Cap is good then the pan switch is stuck either open or closed. A centrifugal weight switches the motor windings from start to run and the Cap just gives a short boost on startup (because of load) and then the switch disconnects the cap and puts the motor on the run windings when it get's to a certain speed.

You may have invertently unstuck the switch while taking it apart.

One thing to remember when putting it back together is end play in the shaft. With pan switch motors, end play can cause a failure to start if the rotating centrifugal weight doesn't contact the switch properly.
 
  #9  
Old 02-09-07, 05:24 PM
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There is no play in this motor at all (non detectable by me) I'ts operating well so far.
 
  #10  
Old 02-20-07, 08:24 PM
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Ok I must of goofed somewhere sorry to bump this up again. new question same motor.

I was refinishing the compressor tank (paint job) and took the compressor apart.

I decided to replace the electrical cord from the frayed 18 ga. it originally had to a 12 ga. 20amp 600v rated power cord I had lying around It's about 1.5 meters long to the pressure switch with another 8" from the switch to the motor. It's all running to a 20 amp dedicated plug to my fuse box there is nothing else on that circuit.

The motor still starts fine and runs for a while but after 5 mins or so (around 80psi in the compressor) The motor is really hot to the touch and starts to trip the breaker.

I wired it the same as it was originally (sure you did )

The only thing "new" is the new pressure switch (the old one was broken and I was running power right to the motor and shutting it off when the compressor was full) I was even using the same 12ga power cord listed above.

EDIT. In case it matters (I'm sure it does)

It's wired like this. Ground to the switch housing, From the plug-->>white to the L1 on the switch Black to L2 on the switch, T1 goes to Line 1 on the motor and T2 to Line 2 on the motor.
 

Last edited by Gotrek; 02-20-07 at 08:49 PM.
  #11  
Old 02-21-07, 07:31 AM
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If you can borrow one you may want to check the motor with a meger. Sounds like you may have a partial short to ground. If you have an amprobe I'd also watch the amp draw as it runs. Frankly it may be time to give the motor last rites. Sometimes a motor can be revived by "baking" the stator if moisture is the problem but it may need rewinding.
 
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Old 02-21-07, 11:17 AM
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You're probably right. I was also thinking of the possibility that the start circuit is not disengaging as it should. this would lead to overheating would it not?
 
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Old 02-21-07, 12:06 PM
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Originally Posted by Gotrek View Post
You're probably right. I was also thinking of the possibility that the start circuit is not disengaging as it should. this would lead to overheating would it not?
That would cause heating for sure.
 
  #14  
Old 02-21-07, 01:58 PM
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You're probably right. I was also thinking of the possibility that the start circuit is not disengaging as it should. this would lead to overheating would it not?

yes this is one of very common failaure on single phase motors [ but when running light or no load it will not affect but it will draw more current that all ]


Merci , Marc
 
  #15  
Old 02-21-07, 03:22 PM
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Originally Posted by french277V View Post
yes this is one of very common failaure on single phase motors [ but when running light or no load it will not affect but it will draw more current that all ]


Merci , Marc
Merci Marc, ta raison le moteur devient chaud seulement apres avoir rejoin 80 livres de pression quand il doit force un peu. Ca doit etre ca car il deviens plus chaud vers l'arriere que l'avant proche de la switch qui detache le circuit de demarrage.

Originally Posted by joed
That would cause heating for sure.
Yep and Like I just told Marc above I suspect this is what's happening as the motor only gets hot when the load becomes harder (around 80psi and it blows the breaker around 100psi) It runs fairly cool up to 80psi.

What puzzles me is it was fine when the switch was by passed. But I did have a problem with the starter contacts being dirty as in my original post. I'll crack it open once more but likely replace it.
 
  #16  
Old 02-21-07, 04:04 PM
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l'ok i ont une question pour vous demander qu'est le commpressor est huile moins de type ou type standard de piston ? ?

la raison pour laquelle parce que si le roulement ou la douille est porté hors d'elle surchargera le moteur

tellement un de la manière deux qu'elle échouera sur celle-ci


translated to engish speaking peoples here ;


ok i have one question to ask you is the commpressor is oil less type or standard piston type ??

the reason why because if the bearing or sleeve is worn out it will overload the motor

so one of the two way it will fail on this one


Merci , Marc
 
  #17  
Old 02-21-07, 04:38 PM
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You're not french speaking are you Sorry the name was misleading.

The compressor pump is a splash oiled piston type with new oil. The pump itself is almost new.

I did a quick test and let it get hot and unplugged the motor. Even 5-0 mins after the unit was unplugged it was still getting warmer and warmer this indicates to me the capacitor is still releasing it's energy into the circuit. I'm pretty sure there is my problem

thanks everyone.
 
  #18  
Old 02-21-07, 04:49 PM
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Gotrek;

yes i do speak in French and i am oringally from Paris France

let you know there is few diffrent verison of French i genrally speak either European French or Quebec French but unforetally i haven't speak Bayou French so i am kinda little lost on that with their phrase


anyway let us get back on the point for a min

genrally when you shut down the motor most of the time the capaitor will bleed down thru the winding or have built in bleeder it will effect for few min

you may have to test it both cold and hot set up with capaitor but quick warning if you want to test the capaitor when it is hot make sure you short out the cap leads other wise you can get nasty jolt from it but i dont have the specfics for the excat number to tell you because i left my chart in the shop

Merci , Marc
 
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