Date: Mon, 9 Sep 2002 20:58:14 -0700
Reply-To: Jack <john.cook58@VERIZON.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jack <john.cook58@VERIZON.NET>
Subject: Re: Headlight upgrade questions
In-Reply-To: <Pine.SUN.3.96.1020909220021.2712B-100000@grex.cyberspace.org>
Content-type: text/plain; charset=US-ASCII
On 9 Sep 2002, at 22:04, David Brodbeck wrote:
> On Mon, 9 Sep 2002, Jack wrote:
>
> > But an even more fundamental purpose of fuses is to prevent fires,
> > regardless of wire size. Can there be a fire without drawing enough
> > current to damage the wire? You bet! The probability of that happening
> > can be reduced (but not eliminated) by reducing the fuse size to the
> > minimum necessary.
>
> If you're gong to worry about this, I have something more serious you may
> want to think about. A careful look at the wiring diagram in my Bentley
> seems to indicate that, at least on my '82 Diesel, much of the wiring has
> no fuse protection at all! This includes the fuel solenoid and 'ignition'
> switch circuit, and the entire instrument cluster. They're all wired off
> the battery side of the fuse panel. I wonder if putting in a master
> fusible link would be a good idea?
Could be. At least to minimize the unprotected circuits. I'd guess that
as long as the fusible links are reliable & don't cause problems of their
own, it could be a good mod. to make. But perhaps there's historical data
that says the unprotected circuits rarely if ever cause problems. I don't
know. As always, there will be trade-offs between risk, reliability and
cost. Automotive electrics is not my specialty, so I'll defer further
comment.
> > Someone on this list, a month or two ago, described a situation where he
> > discovered a defective wire terminal connection in his vanagon (fuse
> > block?). The crimp connection was bad (high resistance) and was heating.
> > Ifirc, it was getting close to where it could have started a fire. The
> > circuit fuse had not and may not have blown until after a fire was
> > initiated (and a true short developed), but by then the fire may have been
> > self-sustaining.
>
> I don't think a fuse will save you there, until something serious starts
> to happen. The high-resistance connection, even as it heats up, will
> cause *lower* current than usual to be drawn. The fuse will think
> everything is peachy-keen.
Possibly. Depends on how long it takes for the carbonization or
ionization current paths to reach a ground (or unintended loads) and to
begin creating a shunt current (as opposed to a series current). That
shunt current is what will take out the fuse, hopefully before a self-
sustaining fire has developed. The closer the fuse is to the normal load,
the quicker it will go. But you're right, there's no guarantee.
[David, are you a ham? (I'm guessing N8SRE is your call, but I've been
out of it so long, I'm not sure.)]
//Jack Cook (W6SGA)
'85 GL Original owner
>
> _ _
> __ _ _ _| | | | David M. Brodbeck (N8SRE) Ypsilanti, MI
> / _` | | | | | | +-----------------------------------------------------
> | (_| | |_| | | | @ cyberspace.org
> \__, |\__,_|_|_| "The VW camper is a brilliant invention -- it's like a
> |___/ Swiss army knife for the road... It's the stealth RV."
> -- Wayne Curtis
| 
