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Potted electrolytic capacitor will last longer?

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Depends on the failure mode(s).

Potting should eliminate the seal leakage that comes from
vibration of the can against the leads.

Potting would be an additional egress barrier to electrolyte
vapor, at high temp.

Potting can lower can temperature if the cap is seeing a
lot of ripple current and airflow is nil, close-in.
 

Thanks, i noticed the philips xitanium led drivers quote lifetimes of 100000 hrs even though they have electrolytic capacitors in them.....thats over 30 years if used as a streetlight driver.
I think it shows that potting electrolytics totally solves the problem of short life times of electrolytics...the number one failure mechanism is electrolyte vaporising out of the can...and this cannot happen if its potted.
 

That argument is like saying a sealed water boiler is more efficient because the steam can't escape. It is only true if it doesn't explode instead!
In most cases, if vapors can't escape through the seal, they rupture through the top of the can instead.

Brian.
 

100 000 hours is possible for a 10,000 hour rated 105 deg C cap if it is run at 85C max.

En-phase make micro-inverters that have a 25 year warrantee, with 4 big electro's inside, fully potted internally...

certainly keeping the "good oil" inside the can is a good idea for long life if the can is not over pressurized as a result ...( i.e. kept cool enough)
 

Thanks, Interesting that you should say that…I’ve just found a lot of 20000hrs@105degc electrolytic caps on digikey.
It seems that electrolytic caps are getting better and better in terms of their lifetime?

I reckon soon the “guilty” wet electrolytic cap will not be blamed for poor lifetimes of electronics products?

20000 hrs at 105degC
http://nichicon-us.com/english/products/pdfs/e-uld.pdf
 

The wet electrolytic cap with the crappy rubber seal
that sells for a tenth the price of a reliable one will,
alas, always be with us. Because there's somebody
looking to shave BOM cost who either doesn't know
or doesn't care, and they are a customer for someone.
 

That argument is like saying a sealed water boiler is more efficient because the steam can't escape. It is only true if it doesn't explode instead!
In most cases, if vapors can't escape through the seal, they rupture through the top of the can instead.
Click to expand...
Thanks, i see your point...but i reckon that kind of slow , slow, vaporization which happens without building up pressure, but just eventually drys the 'lytic capacitor out after 4 years or so in a relatively hot environment will be stopped by having the capacitor potted?
 

I think if a 'hard' seal was the optimal solution, capacitor manufacturers would use a cheap resin 'bung' instead of a pliable soft one. It would be cheaper and easier to construct. I think there is more to it than simply 'drying out' although I am certainly no expert in electrolyte chemistry.

The key seems to be temperature, 105C parts seem to last longer than 85C parts even at lower temperatures. 105 and 85 are just reference temperatures the manufacturer uses when predicting life span but in reality, the operating temperatures and hence longevity have a continuous relationship.

It might be that some potting compounds have a thermal conduction that helps to cool the capacitors and certainly it help mechanical stability but I doubt it has any beneficial effect as vapor seal.

Brian.
 
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I think if a 'hard' seal was the optimal solution, capacitor manufacturers would use a cheap resin 'bung' instead of a pliable soft one.
Click to expand...
…Thanks, yes I see your point. What I suspect is that the manufacturers would like to seal the electrolytic capacitors up really tight, but they don’t because of the more severe explosion risk. But we think that if its possible to have the electrolytic capacitor enclosed inside a case, and then potted, then even if it explodes, the explosion isn’t going to fracture the case…….so I reckon this is why Philips have done it in their xitanium led driver.
 

Thanks,
Do these kind of snap-in electrolytic capacitors have a longer lifetime because they avoid the possibility of vibration damaging the seal and letting the electrolyte vaporise out?
The snap in ones all seem to have a much longer lifetime than the radial leaded ones.
MXC series snap in electrolytics…
**broken link removed**
 

Hi,

About potting of electrolytics:
I have heared ... (I can give no guarantee that this information is complete and 100% true)
... that in an automotive unit a company potted electronic components including electrolytic capacitors.
This resulted in early fails because the gas leaving the capacitor built a bulb (between capacitor and PCB) containing corrosive substances. This caused the solder joint to corrode and fail.
(My idea: maybe this was an acidentally bad combination with the potting compound)
With this failure they talked about "micro climate".

I personally have no experience in potting electrolytic capacitors.

Klaus
 
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Thanks, i see your point...but i reckon that kind of slow , slow, vaporization which happens without building up pressure
Click to expand...

Sorry, I beg to differ!!

A capacitor has losses due to dielectric (air core caps are the best) and in this case the electrolyte gets hot due to losses and with lots of organic solvent and water in the dielectric, it can take only so much of ripple current. It cannot live much above 100C because there is always some water there (rest are soap like salts and some organic liquid as a solvent).

Approx 15 deg reduction in oper temp will extend the life by a factor of two (just a rule of thumb) and if you can afford some head room you will play safe.

It is not good to pot electrolytic caps under any condition but I hope philips knows better.

It can dry out over time but the electrolyte has a consistency like tooth paste and if it dries out, it will not fail (no water there to build up pressure) but simply lose capacity...
 

The snap in ones all seem to have a much longer lifetime than the radial leaded ones.
Click to expand...

The sealing is better around the snap on pins ...
 
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Hi treez,

As this adds no technically useful content to the thread I assume I'll have yet more points taken off... But it is wisdom dressed up as humour.

I think Scott Adams describes a lot of things quite wittily/truthfully via Dogbert in the third cartoon strip down...

Tuesday January 23, 1996

"Did you know that if you put a little hat on a snowball it can last a long time in Hell?"
 
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