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From: (no name) (no email)
Date: Mon Sep 17 2007 - 07:56:19 EDT
Steve--Sounds like you have a short in the system, probably in the wiring. If
you pull the lamps out, you can check for a short in the system with an amp
meter. A short will probably not be detectable with the lamps in because the
combined resistance of the lamps in parallel is less than the resistance of
each lamp itself, which means less than 1 ohm. That's pushing the precision of
most amp meters. If you just installed the light into the circuit, the first
place to look is at the ends of the wires, including any splices. My best
guess is that you've got bare wires touching somewhere. Unless there is
something shorting out the lamp holders (unlikely) or unless the lamp failed by
shorting instead of opening (very unlikely), there is not much in the system
other than the wiring. Dave
David Sill
Via Bella
Quoting Steve Wight <>:
> Achhh so many questions!
>
> The first, that blew in about a minute, was 15amp. My spares were too
> large to fit in that fuse holder, so I replaced the fuse holder, then
> blew a 20, then a 25. (none slo-blo) There are 2 lamps on the circuit,
> in parallel, nothing else. The control side has its own fuse.
>
> Thanks!
> Steve
>
> wrote:
> > Steve--The resistance is almost right. It has to be low if you're going to
> > draw 8 amps in a 12 volt system. 12 v/ 8 1/3 a= 1.44 ohms. Fuses don't
> blow
> > because of resistance, except indirectly. They blow because of excessive
> > current. So the question is why is there excessive current and is it
> > changing? To answer those questions, we need to know several things:
> >
> > 1. Were all the fuses the same or was the first one a slow blow fuse, the
> > second medium, and last two fast blow fuses? Fuses are designed to open at
> > different rates for different applications.
> >
> > 2. What size fuses are you using?
> >
> > 3. Is the lamp the only thing on the fuse or are there other loads?
> >
> > 4. Is the relay on the same fuse as the lamp? The relay signal is a
> control
> > signal that controls the power to the lamp. If they are both on the same
> > fuse, then a shorted control side of the relay could draw excessive amp.
> If
> > that is the problem, you need to check the control wiring when replacing
> the
> > relay because that wiring is not likely intended to carry the amount of
> > current necessary to blow the fuse.
> >
> > This is just to get a start.
> >
> > David Sill
> > Via Bella
> >
> >
> >
> > Quoting Steve Wight <>:
> >
> >
> >> Got a new 100w halogen, but it blows fuses. Thought I found my problem
> >> when my meter showed VERY low ohms on the light, but 100 W / 12 V = ~8
> >> amps, and if P = I^2*R still, then R = ~ 1.4 ohms ??? This just seems
> >> very very low. The first fuse took about a minute to blow, the second
> >> about 15s, the next two instantly. Does a relay fail like that? (the
> >> switch feeds a relay which feeds the light)
> >>
> >> Steve
> >> Fales, 'Gulli'
> >>
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