[Healeys] BN2 80/100 W bulbs on the PL700 tripod headlights....

[Richard Ewald]

I think you need to go back and do a bit of math.
2 100 watt light bulbs is 200 watts total load.  Divide 200 watts by 13.5V
(system voltage with the engine running) gives you a amperage draw of not
quite 15 amps (14.81) for both headlights on high beam.  The rule of thumb
for fuses is they should be roughly 1/3 higher rating than the expected
load.  One 20A fuse would cover both headlights.  A fifty amp fuse is too
large and would be the automotive equivalent of a penny behind the fuse.  In
other words, using a fuse that large in the system would give you a system
where the wiring would melt to protect the fuse.
Also why 4 25 amp relays?  Kinda overkill isn't it?  If you want to run a
relay, I would suggest getting a highbeam/lowbeam relay from a fairly modern
car.  The headlight step relay from say a Volvo 240 would work perfectly and
would handle the current draw.  Easy to mount, simple to wire, and
waterproof.  What's not to like?  If anyone goes that route, I can supply a
wiring diagram for the relay.
Rick

On Wed, Feb 2, 2011 at 3:55 AM, Oudesluys <coudesluijs at chello.nl> wrote:

> You need thicker gauge wires */and/*  heavy duty lamp connectors, and
> better wire the lamps through 4 25A relays (high beam/dip, L&R). The
> feed wire to the relay is best directly from the battery and should be
> able to handle at least 50A. Also include a 50A fuse.
> Kees Oudesluijs
> NL
>
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> of coudesluijs.vcf]
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