# New start capacitor---wow!



## Tozguy (May 27, 2017)

My 2 hp capacitor start and capacitor run motor was sluggish starting so I replaced the start capacitor. Boy, what a difference. Either the original capacitor was cheap or it was very tired. Now the lathe gets going like a top fuel slingshot. I decided to change the run capacitor too so I can sleep better. Makes me wonder what the normal life expectancy of a 200 ufa and 35 ufa capacitor is.


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## Ulma Doctor (May 27, 2017)

the start caps fail much earlier than run caps, in my experience.
the life expectancy is in the order of years for most motors i have ever come across.


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## silence dogood (May 27, 2017)

Depending on quality, start capacitors which are bipolar electrolytic capacitor are suppose to have a shelf life of 2 to 5 years.  That is why I buy mine from a reliable vender.


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## darkzero (May 28, 2017)

That's interesting, I never would have thought to replace the caps as "periodic maintenance".

The start cap blew on my Chinese mill in like 6 months after purchase. The start cap was Chinese, the run cap was German. I replaced both, been years now & still running good.

My lathe is a few years older than my mill & it hasn't blown a cap yet. Has pretty much the same motor as my mill. I wondering if I should replace the caps now just for good measure?


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## Tozguy (May 28, 2017)

What would be the symptoms of a run cap that needs replacement?


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## Ulma Doctor (May 28, 2017)

darkzero said:


> That's interesting, I never would have thought to replace the caps as "periodic maintenance".
> The start cap blew on my Chinese mill in like 6 months after purchase. The start cap was Chinese, the run cap was German. I replaced both, been years now & still running good.
> My lathe is a few years older than my mill & it hasn't blown a cap yet. Has pretty much the same motor as my mill. I wondering if I should replace the caps now just for good measure?


I wouldn't recommend going to the trouble of replacing capacitors unless they are showing signs of weakness
i have a couple single phase motors that have the original caps from the 60's that still function correctly.
Changing a cap due to age alone is superfluous!



Tozguy said:


> What would be the symptoms of a run cap that needs replacement?


When a run cap is failing or has failed, the motor may lack power, run hot, and/or stall.
the run windings will consume more energy to run the motor as there will be an open in the windings where the run cap went


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## Tozguy (May 28, 2017)

Thanks Ulma, I'll keep my old run cap as a spare just in case those symptoms show up eventually with the replacement.
After noting the difference in construction of the new caps wrt to the 4 year old originals, I am glad to have changed them both. The new ones only cost 18$ each and are obviously made better. I would guess that the ones you have from the sixties are much better quality than the current ones on hobby budget machines.

Even so back in the old days of trouble shooting points ignition systems, the condenser was usually the first part to replace.


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## Superburban (May 28, 2017)

Is it true that sitting unused, is worse on a cap, then being powered up every so often. I read that somewhere, and make sure I power up my VFD's at least once a month.  Didn't think about the motor caps, I have several motors that have not seen power in years.


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## mksj (May 28, 2017)

Superburban said:


> Is it true that sitting unused, is worse on a cap, then being powered up every so often. I read that somewhere, and make sure I power up my VFD's at least once a month.


Yes, this is true of electrolytic capacitors only. They reform them, older electrolytic capacitors should be brought up slowly with voltage and not have any load applied to them for about 1 hour monitoring the current when possible, and then shutting them off for 24 hours as chemical change continue to occur. Some of the VFD manufactures have specific guidelines for powering up VFDs that have been sitting for an extended time, usually by more than a year. But you are correct, ideally turning them on once a month is advised.  
https://library.e.abb.com/public/cf...bd7be/Guide_for_capacitor_reforming_Rev_G.pdf
http://www.weg.net/files/products/W...vfd-capacitors-usareform-brochure-english.pdf

Heat and continued on/off cycling of electrolytic capacitors also leads to premature failure. That is why the start capacitors are usually the first to go, and why single phase AC motors with start capacitors do not do well with frequent start/stops. The start capacitors overheats and fails. They also have a finite life span, in my home AC compressors they get changed around every 5 years. Many VFDs also have timer counters that show the number of hours for different components and will give you an error code when they have reached a predetermined serviceable life. Electrolytic (and some non-electrolytic) capacitors often have ratings as to expected longevity based on temperature, voltage, etc, usually this is on the order of 1500-2000 hours at their rated maximum specifications. Although electrolytic capacitors do not like to be cycled on and off frequently, when left on all the time they will run warmer and the VFD timer counter is ticking down.


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## KBeitz (Oct 16, 2018)

I found the most capacitors fail because the manufacture uses alum. rivets to hook the capacitors
plates to the wire connection terminals and they corrode off.


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