Date: Fri, 10 Oct 2003 12:55:22 -0800
Reply-To: Jack <john.cook58@VERIZON.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jack <john.cook58@VERIZON.NET>
Subject: Re: Short Fused about plastic fuses
In-Reply-To: <5.1.0.14.2.20031010123614.027dd348@pop1.attglobal.net>
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Informative note, David. I remember running across sand filled fuse
cartridges in the 50's or 60s and found out later that it was an attempt to
increase arc length. Also, some designs use various techniques to reduce
flying shrapnel when the fuse explodes. But that high power stuff scares
the beejezus out of me. I can't even imagine interrupting 100,000 A. I'd
be very happy to be a mile away when something goes wrong. //Jack
On 10 Oct 2003, at 14:58, David Beierl wrote:
> 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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