About life of Electrolytic capacitor

[alok1982]

Hi!

I am using a electrolytic capacitor as a bulk capacitor in my power supply design (using flyback topology).

As I know life of my power supply depends on this Electrolytic capacitor. As this capacitor is inversely proportional to the temperature.


I have some queries;

1) What happens to this cap when it comes to its end of life i.e. what is the status of this capacitor; it opens, shorts, bursts etc?

2) Also, temperature will affect life of this cap when it’s working. But if it’s not working i.e. circuit is not working and present in high temperature, that time also caps life degrades?


Waiting for your replies.


Thanks!

 

[Nigel Goodwin]

By FAR the most common capacitor fault is going high ESR, so that's what likely to happen. High external temperatures will also shorten their life, although not as much as when running with high external temperatures.

I would suggest using a high quality capacitor from a good manufacturer, and pick a low ESR and 105 degree one.

 

[schmitt trigger]

In some instances, this increased ESR is accompanied with increased self-heating, which causes the capacitor's can to bulge out.
In extreme cases it could burst.

 

[dr pepper]

The life of a cap is longer if the applied temp and voltage are lower than its rating, but that only goes so far.
You can predict cap life via the manufacturers datasheet.

 

[crutschow]

Also derate the voltage rating at least 25%.

 

[kubeek]

The life of a cap is longer if the applied temp and voltage are lower than its rating, but that only goes so far.
You can predict cap life via the manufacturers datasheet.

Exactly, but even for very long life caps like 20000h at 125°C the curves that show you how long it works at better conditions usually stop at around 10 or 15 years. Beyond that it is anybody´s guess, which is why it is very hard to use electrolytics in devices that should have say 25 year long lifetime, such as in railway safety applications.

 

[alok1982]

So, after 20000h, the electrolytic in cap get dries? It acts as continuous i.e. short?

 

[Nigel Goodwin]

So, after 20000h, the electrolytic in cap get dries? It acts as continuous i.e. short?

No, as they age they go high ESR and eventually open circuit, it would be unusual for them to go S/C.

 

[JimB]

So, after 20000h, the electrolytic in cap get dries?

Be aware that the drying out process is gradual.
It is not a case of :
19990 hours - full spec capacitor
20010 hours - dead capacitor

The degradation may start around 10000 hours (best guess).

JimB