Next message: Steve Wight: "Re: lv-ab: spotlight"
Incandescent bulbs have much lower resistance when cold, their true
resistance can only be measured while operating. (So 1.4 ohms is normal in
use, actual measured resistance with a meter will be LESS.) You need a
clamp on meter to measure the current. It is possible the relay is wired
wrong or that the lamp draws more than expected. If there is some voltage
drop to the light, it WILL draw more current, due to the nature of
incandescent bulbs. I suggest a bigger fuse. Also, every boater should
have a clamp on DC current meter. Most clamp on meters do only AC, but some
also do DC, $50-60 @ Sears.
----- Original Message -----
From: "Steve Wight" <>
To: <>
Sent: Sunday, September 16, 2007 8:56 PM
Subject: lv-ab: spotlight
> 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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