----- Original Message -----
From Dave O'Neill <dave_oneill138 at hotmail.com>
To: <rob@thomasr.greatxscape.net>; <spridgets@autox.team.net>;
<midgetspriteclub@listbot.com>
Sent: 17 November 2000 00:34
Subject: Re: Amps?
> What rating fuses?...that depends on how you are wiring the car! Are you
> using a 2-way or 4-way fuse-box or are you fusing each circuit separately?
> Work out the wattage of each item connected to each of the fuses and -
using
> Ohm's law - you can then work out the current drawn. Allowing a safety
> margin you can then select a suitable fuse.
> 66 amp wiring seems a little excessive for your headlamps as 2x130watt
bulbs
> will only draw 21.66 amps!!
>
> Dave O'Neill
> Solihull, UK.
Wires won't burn out though and I'm told that the thicker wires will
'consume' less current than thin ones due to their lower resistance, thus
increasing the brightness of the bulbs. Since I only got a D at A-level
Physics, I can't be sure if this is right. The fuse box runs 8 'blade'
fuses and I have wired the car to represent the 1500 Midget loom with extras
such as an electric fuel pump, radio, washer pump for the screen, interior
lights, boot lights, bonnet worklights, Ignition kill switch, "steal my car
and you'll find the footbrake operates the horn, you thieveing bastards"
switch etc.
Now school was a LOOOOOOONG time ago and I can't remember how to best work
out the fuse rating for a given circuit. Do I need to connect the wiring up
to bulb and then measure the ohms between the battery live terminal and the
far side of the bulbs? How about when you have side lights with 2 bulbs??
I think that an extra 50-100% on the rating is advisable to keep it from
smoking the wire. Can I simply assume no ohms for the wires/switches and
calculate the ohms across each bulb and add them up?
How about I just say 17 amps for everything? Naw, after all this
work/expense I want to do it right.
Post script:-
Measured the ohms accross a bulb. 3.0 ohms for the brake light and 1.1
ohms for the tail light. They are marked 21w and 5 w, which with 12 volts
should give........err.....no, that doesn't work out right. V=IxR so
12v=Ix3ohms. I=4amps. W=IxV so W=4x12. That makes 48 watts when it is
marked 21 watts. What am I missing?
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