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Old 01-09-2011, 12:29 AM
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Default Starting Capacitor Questions

What are the most common causes of capacitor failure? Other than a manufacturing defect. I just had to replace the start capacitor for the circulation pump motor on my hot tub. The unit is all but brand new. I replaced the old one because the bearings in the motor were getting loud and the pump seals leaked. Having to deal with a pump failure in subfreezing temps is what I was trying to avoid in the first place. So this didn't make me too happy. The only event out of the ordinary was a power outage New Years Eve when the local grid overloaded. The pump didn't quit until this weds. I have the tub sitting on 2" of blue board insulation on the slab, extra fiberglass batting around the tub except in the section housing the spa pack and pump and 1/2" of closed cell poly foam for a spa blanket along with the cover to keep heat losses to a minimum. The tub only lost about 5 degrees in about 16 hours between finding out it wasn't running and getting it fired back up friday afternoon after work. I was pleased with that but, would rather not have to find out how long it takes to freeze up. As you can see from the pictures the capacitor let go with a pretty good pop. Given the fact they are fairly inexpensive should I keep another capacitor on hand or was this maybe just a freak deal?
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Old 01-09-2011, 12:39 AM
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What are the most common causes of capacitor failure?
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Old 01-09-2011, 08:45 AM
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Starting caps are intended for very low duty cycle use.they can get very warm if they are over cycled as could have happened during your local grid overload /power outage.
If they get warm enough they vent the excess pressure which reduces the amount of electrolyte in the cap. Eventually you get to see the insides of the cap.

Given the location and the effects of a failure I would consider remote mounting that cap in an easy access box.
inside a heated area if it is not too far away.
just be careful not to expose tub users to any possible contact with the wiring or capacitor box.

A friend has an outdoor tub 5 ft from his house. we buried a piece of 12 inch plastic culvert and ran the two pipes and the little air pressure switch hose through it.
now his pump heater and controls sit in a corner of his heated access mud room there is a good floor drain in that corner as well as a containment should it spring a leak.
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Old 01-09-2011, 09:21 AM
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Whitetrash, buy a spare capacitor and mark it to what it goes to, I have several spare capacitors that I have forgotten what they go to by now.
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Old 01-09-2011, 12:28 PM
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Thanks Terry and Dan, I will order a couple capacitors and keep them on hand. Putting the start cap in a remote box is a good idea. It could easily go in my crawl space. I was able to pull the capacitor off my old motor this time. One of the downsides of living in this town is it has no heavy industry whatsoever. I can get all the T-shirts and rubber tomahawks I want locally. But, any kind of industrial supply beyond a 1/4" cap screw is a 2-3 hour round trip to the valley.
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Old 01-09-2011, 12:56 PM
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Tim, have you checked ebay for replacement capacitors?
They're pretty cheap.
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Old 01-09-2011, 01:12 PM
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I think we had the mate to that cap on the air compressor we got last year. Brand new, but noticed an oily spot. Turns out the cap was leaky. The cap was not too well Hecho in Mexico.
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Old 01-10-2011, 04:02 AM
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As Terry said duty cycle.
Its not good to cycle them more them 20 times an hour, they build up heat and need time to cool off.
The starting switch disconnects the Start capacitor, usually in less then 2 seconds and most are not rated for not more then 6 seconds.
Once the motor is started and running they are essentially disconnected from the circuit.

Most of the higher value starting capacitors are, what is called Electrolytic capacitors.
These are filled with an electrolyte that can dry up over time and their capacity diminishes, they will not have enough power to start the motor.
So depending how well an electrolytic capacitor is made can effect its life and shelf life.

Electrolytic capacitors that have not been charged for over 5 years should be slowly brought up to their working voltage as the electrolyte has been known to settle, I have had caps blow out in an old 1949 TV when plugged in after setting to long.

If you over heat the electrolyte it steams up and the capacitor blows up like a boiler.

What I don't know is what will happen when a start cap is frozen like an out side machine.

-------------

The most common causes of capacitor failure is they dry up and the motor will not start, just hums. some motors will burn up if they don't have a built in overload protector.

As for the cap in your picture either the cap shorted out,
Or the motor did not disconnect the capacitor in less then 6 seconds, if something jams the motor the centrifugal switch can not get up to speed and disconnect the cap.

Assuming the motor you have has an OL protector.
An issue you may have is the ambient temperature around the motor may prevent the overload protector inside the motor from working properly.
OL's usually heat up to a certain temp then open up the circuit. if it's freezing out side the OL may not trigger fast enough.
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Old 01-10-2011, 06:57 AM
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When the cap actually fails and when it blows are most often not the same start cycle. If you are within earshot of a motor with a failing cap you will hear the distressed start sound. you then change the cap and all is well.
If the motor is unattended such as a pump or compressor motor you can get a blown cap no start as your first clue.

Anything (such as venting or drying up over time) reduces the real capacity and increases the effective series resistance (ESR) of a capacitor. The reduced capacitance lengthens the start cycle
The increased ESR increases the heat generated per second.
Eventually the cap either boils to where the vent is over come or the cap shorts internally.
The cap is normally in circuit at the time of rupture so there usually will be arcing effects visible at the separation points.
The freezing temperature for the electrolyte is well below the freezing temp for water.
The lubricant in the motor bearings will stiffens up and lengthen the start cycle resulting in exceeded duty cycle first.

As Gwiz said at lower temperatures the OL takes longer to operate so there is a nasty failure cycle at work in older motors.
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Old 01-10-2011, 10:26 PM
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Thanks again guys for the info. I checked out the E-Bay link you posted Rod and found one for $10.99 W/free shipping. That works for me and it'll come to my door. No chasing it down in the valley
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