[sdiy] old epoxy-sealed electrolytic capacitors

[Roy J. Tellason]

On Monday 28 August 2006 08:05 pm, anthony wrote:
> So I have a BUNCH of neat-looking epoxy-sealed electrolytic capacitors that
> I have taken out of a number of devices over the years. They're in the bin
> of unusable parts because >>>as everyone knows<<< electrolytic caps don't
> last forever. But I was wondering if epoxy-sealed units had a good chance
> of reliability in spite of great age. I have read that epoxy-sealing is
> more expensive and these units are considered higher quality units
> (although I wouldn't want to use large ones in a power supply should there
> be a fault somewhere!).
>
> I know it's folly but they LOOK so cool. I suppose I could pepper circuits
> with dummy caps for show but no go.
>
> Then there's the whole other issue of all of the cool old Sprague Atom caps
> that I have and can't use.
>
> Oh and what about tantalum caps? I just realised that I don't seem to
> recall ever reading about the usable lifetime of tantalum units and have
> always just assumed their life was as indefinite as that of a ceramic cap
> provided proper polarity was observed and ratings weren't exceeded. Does
> the cap generate the tantalum pentoxide dielectric during use like an
> aluminum electrolytic or is it prepared during the manufacturing process? I
> always assumed the latter because Ta caps look nothing like Al
> electrolytics in construction.

I salvage a LOT of parts,  and in terms of bulk probably have more 
electrolytics than anything else.  Also a fair amount of tantalum caps, and 
lots of other stuff.

Years ago I ran into a problem with some really old stuff,  but a cap checker 
I bought at the time got the bad stuff weeded out,  and I've not run into a 
problem since then.  I think that the common perception of electrolytics 
having little or no scrap value is very much over-rated.

Though I wouldn't turn down an ESR meter if one came my way.  :-)

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
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