Re: [CAD_CAM_EDM_DRO] Cheap Power Supply was Re: low cost drivers

In a message dated 31-May-02 19:57:33 Central Daylight Time, asdf@...
writes:

> Thanks.... that's hard to pass up! Does anyone know where to buy surplus
> caps?

RC: Someone else "in here" will have to answer that one for you, as I
don't buy "surplus caps" every few days. But, warning! An electrolytic
capacitor of the kind we are talking about here (larger than 1.0 µF, 50 WVDC)
is "wet" inside. Yep, there's yellow goop soaked in tissue-paper between
aluminum "electrodes" made of heavy foil all rolled up like tape on a reel.
And the "chemistry" of all that is such that it will last for a few years and
work amazingly well, and some, particularly those made for computers and
aerospace will REALLY amaze.

BUT, that "goop" is not as mild and non-corrosive as distilled water, and, it
gets suddenly hot and creates "instant steam" if the polarity is reversed for
a few seconds (or less, depending on many factors), and if you've never seen
a 10 millifarad capacitor explode, blowing yellow goop all over the room and
other expensive gear and eyes, you haven't lived!

So, "surplus" often connotates "...that old inventory that's been tucked
way-back on the rear of those shelves in the back-room so long that no one
still working here even knows if they are stolen merchandise or not". And
such "gets older and older" until such point as some brilliant summer-worker
says, "Hey! I bet we cold sell that to the surplus market for even more than
we PAID for it. After all, those old electrolytics are over 20 years old!"
An old electrolytic and "look just fine" until you mount it in an enclosure
you have been working on for weeks, and when ready to test, BOOM! Yellow
[deleted] all over things! And this stuff is conductive, and if you don't
get it off those just-etched laborously-produced one-of-a-kind PCB's you just
did, the logic on those will begin to do very strange things and untoward
syntax will begin to pervade your vocabulary, and...

I.e: Be very, very careful when being tempted to design new/expensive stuff
with "surplus" electrolytics!

Jan Rowland, OLD Troll who has had yellow sticky stuff on his fingers and
face (but not eyes! GOOD point about wearing cheaters!)


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