Date: Fri, 10 Oct 2003 14:58:48 -0400
Reply-To: David Beierl <dbeierl@ATTGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Beierl <dbeierl@ATTGLOBAL.NET>
Subject: Re: Short Fused about plastic fuses
In-Reply-To: <19a.1b67c318.2cb827ed@aol.com>
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At 11:19 AM 10/10/2003, George Goff wrote:
><< But you'd be amazed at how complicated fuse
>design can really be. Ultimately they are compromises. >>
>
>You wanna fight? Circuit breakers are compromises! A properly designed
>fused system assembled from quality components is an example of the
>highest order
>of refinement.
Those statements don't contradict each other -- you can't have it all in
either situation, any more than with a boat. Voltage drop, heat load,
sensitivity to ambient temp, interrupting capacity, voltage capacity, surge
capacity, minimal-overload characteristics, short-circuit characteristics,
time-delay, fast-blow, physical size, cost... Gets *really* interesting
when you need high interrupting capacity with DC. My dad spent some time
at MIT around '50 doing research on a fuse that would interrupt 100,000
amps at nominal 600 VDC -- I don't believe he succeeded, but the submarine
community certainly wanted one since that's what they ran their boats
on. Pretty sure Bussman has one now with really interesting-looking
multiple elements with a dendritic structure, made of silver and buried in
sand -- I recall reading an article describing it in early '80s. Side note
-- I don't know what the available current is on the ?5,000 volt? street
power lines, but I was a few hundred feet from one when a breaker
opened. This breaker had a Jacobs-Ladder-type arrangement to snuff the arc
by making it longer and longer, and it took several seconds to accomplish
this. Meanwhile it made a noise like the alarm buzzer from hell, really
astoundingly loud, as the arc kept re-establishing itself with opposite
polarity. Didn't get to see it as I wasn't line-of-sight, too bad.
Jorge, in my experience the blower draws 12 amps on high setting and the
16-amp fuse is marginal in that circuit. I suggest re-routing the blower
high speed to a new fused 16-amp circuit, controlled by a relay driven from
the high position on the switch. I predict your problem will vanish at
that point.
david
"Transistors fused against the worst
Protect the fuse by blowing first."
--
David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"
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