[Milsurplus] Electrolytics then and now

[jhhaynes at earthlink.net]

On Wed, 23 Aug 2006, Don Merz wrote:

> In the context of electrolytic caps, some of the worst
> junk ever made was made in the last 15 years for
> personal computers while, as this group can all
> attest, we routinely see cases where 40+ year old
> electrolytics still work fine.
>
There have been a couple of articles in IEEE Spectrum about counterfeit
parts, and in particular a bunch of counterfeit electrolytic caps used
in computers.  Back in my younger days we bought our parts from well-known
domestic suppliers who were often in the same city, or nearby, and there
was no question that what we bought really came from those suppliers.
Today the supply chain is much more convoluted and there are many more
opportunities for scam artists to substitute inferior parts.

Although even in the old days there was some of this going on.  I remember
when the radio-tv magazines had pages of ads from tube dealers
operating outside the official distribution channels.  And one of the
magazines ran an article about how some of these outfits would obtain
used and reject tubes and re-label them with counterfeit brand names.

Getting back to electrolytic capacitors, there is some progress from
time to time.  I went to an IEEE meeting a few years ago where the
speaker was from a company that makes variable-speed motor drives,
which consist of a rectifier turning line power into DC followed by
a variable-frequency inverter producing AC to drive the motor.
The speaker mentioned that electrolytic capacitors were one of their
reliability problems.  They had worked with their supplier and learned
that the supplier had not anticipated the kind of ripple current that
the rectifier-inverter application causes.  Excessive ripple current
was overheating the capacitors internally, leading to early failure.
The supplier came up with an improved design featuring much larger
terminal bolts, to conduct heat to heavy busbars, and with a 
threaded boss on the bottom to allow the capacitor to be attached
firmly to a heat sink.