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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
Comments: To: THX0001@AOL.COM
Comments: cc: Jorge Osorio <josorio@ATLAS.KENNESAW.EDU>
In-Reply-To:  <19a.1b67c318.2cb827ed@aol.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

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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