[rescue] Slightly OT: Bad Cap Saga
idylukewild at yahoo.com
Mon Aug 18 09:45:38 CDT 2008
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
] 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
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