Re: Another DIY Light Question

"JJ" <piperjj@xxxxxxxxxxxx> wrote in message
news:7303c$43919a84$d826dfe9$6062@xxxxxxxxxxxxxx


.... (my buddy pointed out that my original choice for wiring is
> also not robust enough). Suggestions?
....


Your essential question is, "What guage wire do I really need?" To
"really" answer it, I (a degreed EE) would need to know the battery
voltage, length of wire run, and the allowable voltage loss in the
wire. However, you can get a workable solution more easily.

Regarding wiring, the required guage depends on current rather than
power. You have a 25 watt load, and if it required a 25 volt battery,
you'd need the wire to carry 1 amp of current. This can be done
reliably with very thin wire, as small as 30 guage if you can tolerate
considerable voltage loss. If it requires a 1 volt battery, the wire
would need to carry 25 amps of current. This wire would need to be
much heavier than 12 guage to minimize voltage loss, and is not IMHO
likely to be the right answer.

Conservatively you'll have at least 12 volts, so let's use that (I
don't really know the requirements for an MR-11). You'll then need to
carry 2.1 amps for at most 10 feet loop distance. For a 1/2 volt
loss, you then need a wire size 23 guage or larger (smaller guage
number). 24 guage is slightly too small.

So if you try some 23 guage wire and the light dims too much when the
battery begins to sag, try some heavier wire. 20 guage is easy to get
at hardware stores and would be safe in every respect. Also larger
wires are stronger than thinner ones, and hence would be a bit more
trouble-free on a bike.

I'd recommend you start with 22 guage zip-cord from the hardware store
and see if you like it. If the light output is too sensitive to
battery charge level, re-wire it with bigger wire. You'll find a
practical upper limit.

Good luck!

Another thing: halogen lamps are REALLY hot. I don't think you should
run one without protecting it from moisture, if it is not inherently
protected!

Ken




.

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