[sdiy] electrolytic cap degradation over time ?

[Harry Bissell Jr]

The 105 degree cap is probably better... however the
reason for the 105 degree rating should be considered.

Most electrolytics rated for 105 degree operation are
specified for high ambient temperatures... and more
importantly, high ripple currents.  These caps are
most
often specified for applications like switching power
supplies, and are designed to have lower self
inductance
(if possible) and low equivalent series resistance
(ESR).

These parameters cause a great deal of the heat
generated in a capacitor.

The problem with the CD player capacitor 'may' be
related to an incident where an employee of a Japanese
capacitor electrolyte manufacturer jumped ship with
the
formula for several water-based electrolytes.

Unfortunately... he was not aware of some stabilizing
compounds that were supposed to be added to the mix,
and
a large number of the Taiwanese 'clone' capacitors
began
to fail after a short time.  Quite a scandal...

I have just seen (for the first time) a failure
related
to an old electrolytic. (meaning it was the root cause
of the failure, not a side effect).  I would not
change caps just because they are 'old'... but in some
marginal designs it could be a prudent thing to do...
ESPECIALLY
if they are in switching power supplies.

H^) harry

> 
> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl] On Behalf
> Of
> Peter Blackett
> Sent: den 29 februari 2004 19:27
> To: synth Diy list
> Subject: [sdiy] electrolytic cap degradation over
> time ?
> 
> Hi,
> a question for those knowledgeable people on this
> list .
> I've been looking at an Arcam cd player about ten
> years old
> .
> the problems with it are that one output channel is
> low in
> volume and lacks bass .
> so I opened up the case and found after looking at
> the
> circuitry that one of the  electrolytic caps in one
> output
> channel has lost value .
> ( it measures about 10% of what it should do ).
> I know that its a problem with degradation over time
> , but
> are there any pointers that I should look at for
> replacement
> caps ?
> are 105degree rated caps likely to last longer than
> the 85
> degreee rated caps ?
> I'm assuming this is why a lot of caps are needing
> changing
> in synths and their power supplies .
> regards Peter
>