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From: (no name) (no email)
Date: Sun Sep 16 2007 - 23:01:57 EDT
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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