[sdiy] Lifespan of Electrolytics?

[Steve Ridley]

RE: [sdiy] Lifespan of Electrolytics?
> What is the expected lifespan of electrolytics, 

Officially, as low as 1000 - 2000 hours for some types.!  Pause while that 
sinks in.  40 days continuous.  That's from manufacturers spec.  But that's 
a worst case, plus some pessimism thrown in to cover themselves.

In practice, things aren't as bad as the spec suggests.  These figures will
at maximum temperature etc, and the initial deterioration may be very minor.
The lifespan is largely determined by how the cap is used.

> and what are the effects of old and ageing ones? 

The first signs of ageing I know of are that the effective series resistance
(ESR) starts to rise.  A new electrolytic will typically have an ESR in the
range 0.3 to 2 ohms.  As the cap deteriorates, it can increase to
hundreds of ohms.  This isn't a big issue in most audio applications, but
in switched mode PSUs, TVs/monitors and anything that has to run at
high frequencies or deal with spikes etc, it can be a problem.  I'd expect 
ESR problems after 5 - 10 years, but have occasionally had trouble
after as little as three years.

My PC PSU died recently.  Only five years old and only used for an
hour or two per day.  Bad electrolytic.  Capacitance still measures OK,
but ESR around 15 ohm instead of 0.5.  It was right next to a heatsink,
so it got nicely cooked.  This is fairly common in my experience.  
Replace them with higher temperature ones if you can - they'll last 
longer.  85 deg C caps are the norm, but 105 deg C ones aren't much 
more expensive and should last longer.

Capacitance won't change very much at first, so a cap that is a 
complete dud in an SMPSU may have little or no effect at audio
frequencies.  I work with broadcast mixing desks which are usually
powered all the time.  The inside temperatures are often hot  enough 
that you can still just touch them without pain.  In those circumstances, 
caps start to show significant serious of capacitance after 10 - 15 years,
producing bass loss and phase shifts.

> Is it worth the trouble going through any old gear including synths that are 
> past, say, about twenty years and giving them a electrolytic overhaul?

Unless there are hot spots or reasons for the caps to fail prematurely, then
if one cap is bad, then the rest won't be too healthy either.  Caps are cheap.  
If you have time, I'd suggest replacing them.

> I just purchased a kit (of course) of an ESR meter that supposedly will find faulty caps 
> due to their high ESR reading.  Anyone here have experience with it? 

I use a Dick Smith ESR meter at work.  If you have to fix switched mode PSUs,
monitors etc, it's worth it's weight in gold.  You can test the caps in circuit too.
You need to know what value to expect, and having to look up the values is
a pain, but it's the only way and the tester has a look-up table on the front.  
It cost around £70 UK, so I guess that's around $100.  Ours get a lot of use.
There are a couple of other makes of ESR meter.  I have no experience of
them, but there are reviews of them on the internet.  Look for the Satcure
website...

Does that help?



Steve Ridley

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