[rescue] Slightly OT: Bad Cap Saga

[Luke Goembel]

I build electronic devices that are 
meant for use in space. In a vacuum 
environment, electrolytic caps are 
not allowed because they leak/explode 
when in vacuum. I suspect they wouldn't 
be allowed because of their notoriously 
short lifetime even if they didn't 
explode in vacuum.

It turns out when I try to get an 
electrical engineer to design 
a circuit and then give the guidelines 
for building space flight hardware, 
the "no electrolytic caps" guideline 
can be very hard to follow. Electrolytic 
tend to have a huge capacitance per 
unit volume. Substitutes, if a 
substitute is even available, tend 
to be much bulkier and more expensive 
than the equivelent capacitance 
electrolytic. In my experience, 
there just isn't an off-the-shelf 
non-electrolytic for high capacitances. 

By all accounts electrolytics suck! 
They are a short-lived component. 
All this talk about planned obsolescence 
or lack of ethics in electronics 
manufacture aside, there is a gold 
mine to be made for anyone that comes 
up with a workable substitute for 
electrolytic caps. The demand for 
such caps in space flight hardware 
alone would be significant. As it 
is now, we go to great trouble to 
work around the 'no electrolytic' 
rule. Hopefully we will see some 
improvement in large value capacitors 
someday. I hate them. When I have 
laboratory electronics built, I 
demand "no electrolytics" even though 
they won't be in a vacuum. I've 
restored a number of old electronics 
[see, for instance, my post 
http://www.nextcomputers.org/forums/viewtopic.php?t=145
] simply be replacing the electrolytics. 
Clearly, electrolytics are the week 
link in many consumer electronics 
and have been for decades. In fact, 
I recall that in restoring old 
television sets from the 40's it 
is reported that replacing all the 
old 'paper' capacitors with new ones 
is often all it takes to get 60-year 
old electronics running again!

The bits posted about the bad formula 
for the electrolyte are very interesting. 
Even with the 'good formula' electrolytics 
are amazingly sucky! What irony that 
someone has made a sucky product even 
suckier!