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How long do capacitors last?

The Shocker

The Shocker

Super Member
Apologize if this has been discussed ad nauseum, but I was unable to find this easily in a search...

How long do capacitors last on average?

I have a pair of Polk Audio RT-400 speakers that are circa 1997-98. Are they something that might be worth re-capping, or are they not old enough yet?
 
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How long they last might depend on how you define 'last'.
- still function as capacitors
- have not blown up
- measure to be still within 5% of initial specifications (and were they ever within 5% of specifications)
- measure to be still within 25% or initial specifications.

My amp manufacturer says to replace main electrolytics (I think mostly within power supplies) every 10 years but I believe that is due to expectation they will wander off spec rather than fail.

Steve
 
Film caps have no limit to their service life that I'm aware of. That doesn't mean that newer caps wouldn't be better than older caps, but that could be due to improvements in materials and processes.

Tantalum caps seem to be failure-prone; at least that's what I was hearing when I re-capped my dbx 118s.

Ceramic-disc caps don't seem to have a limit to the service life, but the new ones are half the size of the old ones, I guess that they've got improvements in materials and processes like film caps.

Electrolytic caps have about a 20-year service life, but I won't guarantee that they aren't wounded before that. Of course, cheap electrolytics may have a shorter life, while top-shelf electrolytics may go longer. And of course, any cap run to the limits of it's voltage or temperature rating is flirting with disaster.

Your Polks are ready for fresh caps.
 
42.271828182845904523536028747135266249775724709369995 years

I assume we're talking about electrolytic capacitors.

It Depends on the capacitor and its environmental conditions. Cheap capacitors sitting in some lines of Samsung LCD monitors failed after about 2-5 years. A quality capacitor in a good environment ought last about 15-20 years.

Some factors:
High leakage current.
Frequent charge and discharge cycles.
Excessive reverse voltage.
Application of voltages greater than the rated voltage of the capacitor.
AC voltage exceeding the limits of the capacitor.
Operation at temperatures exceeding the maximum temperature rating for the capacitor.
 
Have to pretty much agree with everything posted so far--so the answer is "there is no hard and fast" answer--it all depends--on a lot of different factors--type of cap, original tolerance specs, use, storage, abuse...and the list goes on. I have tested 50+ year old caps that spec'd just fine and functioned fine, but I have repaired failed boards on some TV's and DVD/BluRay players that were damned near new (part of that cheap Chinese "capacitor plague")--they somehow apparently acquired a design/formulation that wasn't yet perfected and just ran with it--not successfully--and I have worked on some of the inexpensive Chi-Fi gear (especially tube amps) where although they used good quality components, they were being used at or even (in some cases) exceeding their rated limits--YMMV.
 
bhunter said:
42.271828182845904523536028747135266249775724709369995 years
Click to expand...
Hey wait, my calculator won't take that many digits. I was going to translate that into the exact day and time but with that many digits, I don't know too many that have timepieces that can get that detailed. Plus there is the error on the front end of whether that time starts from build date or install date or purchase date. But I like the number. Accurate enough for me.
 
I first started recapping antique radios in the mid 1980's and was a bench tech for a while in the 1990's. Below is from my experience, YVMV

1. Electrolytic capacitors are the most failure prone, many going off spec after just a few years, or even earlier due to the nature of their construction. Anything over 20 years old, they can and should be suspect. They have a moist electrolyte material that, no matter how well sealed, will dry out eventually. Many computers, flat screens, DVD players, audio gear, etc. suffered from the capacitor issue of the mid 2000's as pointed out above. This seemed to have been resolved before 2010. These are usually easy to spot though, as they usually vent when they fail. That being said, I've seen many electrolytic caps in 50's and 60's gear, usually in metal cans, that still test well, even under load. Don't know if I would trust them though.
2. In oil, and paper capacitors are the next most failure prone. Most all in oil caps I've seen, mostly from sixties gear, were bad. Like nearly 100%. Paper are not much better.
3. Ceramic and Mica capacitors have a much longer service life. I have yet to see a bad ceramic, although I'm sure there are some out there. Mica capacitors used to always be good, but I've ran across some in 1930-1950's sets that have gone bad. Wafer mica caps in IF and RF transformers are starting to become an issue. The caps are inside the transformers themselves. These were common in 50's and early 60's radio circuits. This is a fairly new occurance for me. 20 years ago, I almost never came across a bad mica but it's not uncommon anymore.

In newer gear, especially gear built after 1980, many manufacturers seemed to install capacitors that were just rated for the circuit they were in instead of having a little voltage cushion. So there really isn't a lot of wiggle room when a cap starts to go bad. Also some caps, especially electolytics, may test OK until a rated load is put on them, then they fall apart.
 
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It should be said that "testing" a capacitor involves more than merely verifying the capacitance. A proper test also involves checking the Equivalent Series Resistance (ESR). ESR is an AC resistance, therefore it can be tested at various frequencies.

I have no doubt that there's more still to testing caps, I'm merely pointing out that even if it's capacitance is within spec, the ESR can be way high; which would interfere with proper device operation. As an example, a high-ESR cap in a loudspeaker crossover would reduce the volume level of the driver(s) it's connected to, even if the crossover frequency is unaffected.

The wonderful thing about film caps (aside from the longer service life as compared to electrolytics) is that the ESR tends to be a fraction of what a similar-capacitance electrolytic cap would have.
 
I just got a cambridge azur 740c cd player which is an 8-9 year old player. It has a bank of 10 very impressive looking 2200uf caps in it, of the 10 not one is within 20% a few have a very slight bulging top these measure around 1000uf, esr and vloss is also very high. Probably no way this thing would have worked very long, needless to say those all came out and it sounds better.
 
let me guess the caps were not from one of the respectable brands people usually talk about, over here?
 
They were marked Cambridge audio grade, white wrap with blue lettering. Very impressive looking but obviously crap. To out those in what was a very expensive player is criminal. All these things must be failing 10 years on.
 
Not sure if they're phoney or just cheap chinese caps, Cambridge stuff is made in china after all. I've seen caps do the same thing in other brands, seems like the power supply doesn't shut down but goes into standby, things heat up inside and they just don't last as long as they would if it was just turned off.
 
The Shocker said:
Apologize if this has been discussed ad nauseum, but I was unable to find this easily in a search...

How long do capacitors last on average?

I have a pair of Polk Audio RT-400 speakers that are circa 1997-98. Are they something that might be worth re-capping, or are they not old enough yet?
Click to expand...
Tough question. I just did a full rebuild on a 45 year old heathkit unit for a customer and the four high value polarized Nichicons (500uf & 1200uf) caps were still bang on for capacitance and ESR. The uf values on all four were within 5% of spec. In my experience replacing these could change the sound completely and possibly not in good way. Another factor is finding new caps of high quality, especially radials without spending $75 - $100. I did change some of the lower value no name caps as a few of those had drifted 25%+ (upward)
 
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