Lifespan of Capacitors

[W9TR]

Electrolytic capacitors are electrochemical devices, not purely electronic devices. Almost like a battery. Their lifespan is the limiting factor in most electronic devices today. A rule
of thumb based on the Arrhenius equation for temperature dependence of reaction rates is that electrolytic cap life halves for every 10 deg C rise in temperature. Applied voltage also impacts life but to a lesser degree.

So what actually happens, spec-wise?
The first thing that happens is Effective Series Resistance (ESR) increases. In power supply applications this increases the amount of ripple in the power supply’s output. Depending on the amplifier this may manifest itself as increased hum in the output. Or not. It depends on the amp topology.

Next the capacitance starts to decrease. This takes a lot longer. It will have a similar effect to increasing ESR.

 

[rbbert]

Ralph-Did you mean to say tube amp in the sentence I bolded?

Perhaps he meant that if caps in a SS amp were bad after only a few years then there is a problem somewhere (e.g., circuit design, manufacturing quality, "bad" cap from the get-go, etc)?

 

[mep]

Perhaps he meant that if caps in a SS amp were bad after only a few years then there is a problem somewhere (e.g., circuit design, manufacturing quality, "bad" cap from the get-go, etc)?

I'll let Ralp respond.

 

[puroagave]

maybe someone can explain this phenomenon, but Naim owners seem to LOVE recapping their gear every 10-yrs, its almost a fetish. I ended up spending a small fortune recapping all the stuff I owned, albeit some of it was Olive and Chrome bumper pieces but, on their 2nd, and 3rd recap! By contrast I took a Marantz 8b with orig. 50-yr. old PS caps in for a check-up and the tech said they were fine, not to touch them.

 

[Puma Cat]

maybe someone can explain this phenomenon, but Naim owners seem to LOVE recapping their gear every 10-yrs, its almost a fetish. I ended up spending a small fortune recapping all the stuff I owned, albeit some of it was Olive and Chrome bumper pieces but, on their 2nd, and 3rd recap! By contrast I took a Marantz 8b with orig. 50-yr. old PS caps in for a check-up and the tech said they were fine, not to touch them.

From a DFSS perpsective, this is because different design embodiments driving different functional responses can result in different outcomes for the "Design for X" quality attribute, durability. Durability* for a capacitor is the total lifespan of that circuit component used under the product's nominal operating condiitons. It follows that different types of caps used in different applications (e.g. a DAC, preamp, tube amp or a SS amp, for example) will have different specifications for Durability. Personally, I've owned gear where the electrolyte in an electrolytic cap has dried up and cap is now junk, and it's continued use can put the entire circuit at risk of failing.

OTOH, the Teflon caps C-J uses, because of the Teflon material used as the dielectric in their constructon, take a very long time to burn-in and will likely function nominally for decades.

*– as contrasted to Reliability, which is the time interval of component functioning nominally between service intervals).

 

[Puma Cat]

Electrolytic capacitors are electrochemical devices, not purely electronic devices. Almost like a battery. Their lifespan is the limiting factor in most electronic devices today. A rule
of thumb based on the Arrhenius equation for temperature dependence of reaction rates is that electrolytic cap life halves for every 10 deg C rise in temperature. Applied voltage also impacts life but to a lesser degree.

So what actually happens, spec-wise?
The first thing that happens is Effective Series Resistance (ESR) increases. In power supply applications this increases the amount of ripple in the power supply’s output. Depending on the amplifier this may manifest itself as increased hum in the output. Or not. It depends on the amp topology.

Next the capacitance starts to decrease. This takes a lot longer. It will have a similar effect to increasing ESR.

Excellent and informative post.

Thanks, Tom

 

[atmasphere]

Ralph-Did you mean to say tube amp in the sentence I bolded?

No. I probably should have said 'any amplifier' but I surmised that this was in a solid state amp amp- and in a solid state amp there's no good reason for a cap to fail in such short order since they should go much longer. Caps in tube amps usually don't last as long simply because tube amps are usually warmer environments. Our tube amps run pretty warm so we try to make sure there is good air flow around the caps to get as much life out of them as possible.

People are still running solid state gear made in the 1970s and caps back then were no-where as good as caps made today (unless they a counterfeits). So 8 years is just right out. That's going to make me really upset if we have any cap failures in our class D in anything approaching that time- we expect they will go 30 years with ease.