# Motor capacitor’s



## Roger123 (Sep 23, 2007)

Got a call today from the village I live in that one of their sewer pump motors was running high amps.
Went down to troubleshoot and I found a bad running capacitor.

Now I have questions about capacitors. 

Can a running capacitor go slowly bad or is it just good or bad?


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## CoolWill (Jan 5, 2019)

Yes, they can go from bad to worse. Both directions. They can slowly decrease in capacitance over time and depending on temperature conditions. They can go completely open or short as well. Replacement capacitance isn't desperately important so long as the value is within a reasonable range. Voltage should be equal or greater.

Small fan motors might need 5 uF (mfd), multihorse motors a few hundred uF. Most often, if it fits, it ships. But if you have to, it's better to go up rather than down.


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## 460 Delta (May 9, 2018)

They can and do lose capacitance over time. I have replaced them on fans that started slow or ran noisy and all went well. I have replaced a few in motors that were hard to start with new or sometimes slightly higher capacity units in particularly difficult situations like air compressors.


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## drsparky (Nov 13, 2008)

It's the capacitor plague!


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## micromind (Aug 11, 2007)

As others have stated, capacitors can go partially bad. 

If it's a run cap, make sure the replacement is also a run cap and not a start one. There's a difference. If a start one is in the circuit too long, it'll fail quickly (and sometimes catastrophically......lol).


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## MechanicalDVR (Dec 29, 2007)

micromind said:


> As others have stated, capacitors can go partially bad.
> 
> If it's a run cap, make sure the replacement is also a run cap and not a start one. There's a difference. If a start one is in the circuit too long, it'll fail quickly (and usually catastrophically......lol).


Fify


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## micromind (Aug 11, 2007)

MechanicalDVR said:


> Fify


Yes, come to think of it, the majority of the start caps I've seen that were in the circuit too long have indeed, blown up........


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## gpop (May 14, 2018)

I hate caps as its one of the few things that can test good with a meter yet still be bad.


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## frenchelectrican (Mar 15, 2007)

The capaiators can go bad slow or quick .,

There is no fixed rqte when they fail and it can happened at the worst time .,,

even the capacitor can be partal bad and still run but you need to test the capacitor to make sure they are +- 10% range anything out of the range is replacement time.,,

HVAC outdoor units are worst I get the call from time to time to replace it and they do come in combo verison so be aware of it.


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## MechanicalDVR (Dec 29, 2007)

micromind said:


> Yes, come to think of it, the majority of the start caps I've seen that were in the circuit too long have indeed, blown up........



Yeah, exactly....it' never like a terminal melts or something little.


Remember when they used to exoell PCBs all over?


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## Roger123 (Sep 23, 2007)

Thanks guys!

The motor was drawing close to 70 amps with no load. The maintenance guy pulled the motor from the well because most of the time high amps means some type of clog. 

BTW, overload was set at 24 amps, that's getting changed out soon. 

I check the voltage and it was in range, check for drop through the contactor and overload and found no significant voltage drop. Soon as I took the cover off the running cap I knew it was bad. Coincidentally this is the same motor that was reported to trip the breaker occasionally on start up. (another thread I started a little while ago)

New cap installed running amps when down to 12.5 under load.


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## Roger123 (Sep 23, 2007)

OK, second capacitor question:

Most of the well pump motors are single phase and during change out I connect the capacitor wire in the pecker head which is red in color. Where does it get connected to inside the motor? Does it get connected to the armature?


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## Roger123 (Sep 23, 2007)

micromind said:


> If a start one is in the circuit too long, it'll fail quickly (and sometimes catastrophically......lol).


Had this happen a few weeks ago. Maintenance installed 3 start caps before they called for help. All three blew up in there faces. There were shreds of paper on the ground.


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## CoolWill (Jan 5, 2019)

gpop said:


> I hate caps as its one of the few things that can test good with a meter yet still be bad.


With a DMM, you have to leave the probes attached for a good while to get a real reading. The meter is charging the capacitor and a 1.5 V AA cell in the meter can only do so much. At any rate, most of the time, if I read a capacitor and it stabilizes very near it's rated capacitance, it is rarely bad. If it reaches a peak and starts to fall, it's probably bad.


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## CoolWill (Jan 5, 2019)

Roger123 said:


> Had this happen a few weeks ago. Maintenance installed 3 start caps before they called for help. All three blew up in there faces. There were shreds of paper on the ground.


Like a confetti popper from the gas station.


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## frenchelectrican (Mar 15, 2007)

Roger123 said:


> OK, second capacitor question:
> 
> Most of the well pump motors are single phase and during change out I connect the capacitor wire in the pecker head which is red in color. Where does it get connected to inside the motor? Does it get connected to the armature?


The quick answer is if you have two wire pump the cap is at the motor head but once you get 3 wire verison then you will have a cap at the control panel which it usealy near the pressure switch loctation.

on three wire sub motors on single phase verison the red is start winding while the black is running winding and the two wire verison is combined at the motor head and it is sealed once they go to heck just replace the whole pump that is.

Just be aware of three wire pump some are three phase as well the sure fire way is ohm it out due start and run winding is different on ohm reading while three phase pump motors the ohms are pretty much the same phase to phase.


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## JRaef (Mar 23, 2009)

Secondary issue: there is no “armature” on a Squirrel Cage AC induction motor. There is a rotor of course, but it has no direct connection to any electrical source. Current flow in the rotor bars is “induced” via the magnetic fields in the stator across the air gap. 

Armature is a term for a rotor with windings on it connected by brushes or slip rings such as a DC motor, or on AC motors, a Wound Rotor motor, a Synchronous motor or a “Universal” motor (such as is used in small tools and appliances) which is actually a DC motor made to run on AC.


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