[SunRescue] exploding sun psus

[Christopher Byrne]

kebabthesheep Sent: Thursday, December 07, 2000 01:52

>Now I've never experienced a big psu blowing, and I don't want to again
>- 1300W of psu makes a big
>mess :(  It looks as if a capacitor failed, and took out some
>semiconductors.  Much ceramic
>shrapnel now being distributed throughout :-/
<snip>
>Capacitors are starting to become my least favourite electronic
>component


Man I have been there. Anybody ever seen what happens when a 5 farad
capacitor blows? No five pico-farad or micro-farad, 5 farad. It's pretty
damned impressive. That was in a very large, very old public address system,
and the smell and mess were pretty awful lemme tell ya.

Once I was working on the antennae for this multi-stage linear amplifier
amateur radio setup. The guy had an unregulated machine tool power supply
off of 220v mains going through a massive home built capacitor network. I'm
talking like maybe 50 barrel caps the size of coke cans packed into this
aluminum box. He thought it would protect his amp from voltage spikes et al
and allow him to transmit during slight power dropouts that were common to
his power grid. Well it turns out that the aluminum for the box was coated
with an anti corrosive substance that wasn't a very good grounding surface,
but Bob didn't know this at the time.

Bob also didnt know that the impedance of the amp setup was so mismatched to
his feed line that he burned the connectors. So here's this huge capacitor
network hooked directly to mains, with no load, and no path to ground.

The amateur radio operators and electrical engineers among us can already
see where this is going...

Bob of course realizes something is wrong and starts checking his
connectors. The whole time the amp is going full blast, the xmitter is going
full blast, and the caps are fully loaded, only he doesn't know it because
his reflectometer feed is at the antennae head end, at the opposite end of
the burned feed line. Anyway he finally gets back to the cap network, and
slightly unscrews the connector to reseat it...

The cap network, which was overpumped already, found this wonderful path to
ground through Bob's 80% saline solution body. The discharge was pretty
impressive to see, what with Bob flying 50 or 60 feet in one direction, and
the cap network 50 or sixty feet in the other. Thankfully he was all right,
minus a goodly percentage of the hair on his body and his shoes being
slightly melted. The cap network on the other hand was an interesting lump
of melted aluminum, sticky fluid, and grey dust.


Chris Byrne