DC is no more capable of raising the temperature of conductors than is
AC. If your cables are getting hot, they are simply too small for the
current drawn. Remember that current-carrying ability of a given
conductor is related to amperage, not to power. That's why the
electrical grid runs at 70,000 volts, the neighborhood distribution
lines run at around 7,000 volts, and your house feed at 230 volts. The
same wire can carry the same amperage at any voltage, although the lower
the voltage the easier it is to insulate.
But a 50W halogen at 12 volts requires over 4 amps, pretty much the same
as a 500W halogen at 120 volts, so it will need the same size conductor.
That's for a single bulb. Nine lamps at 50W is 450W which is 37.5 Amps
at 12 volts, the charts call for #8 wire for that load. I trust that
you're not using all nine lamps in one track fixture, they certainly
don't have internal conductors that can support that load.
Also note that excess heat suggests voltage drop. The rule of thumb for
incandescents is that a 5% voltage drop brings a 10% drop in light emitted.
It's reasonable to use a smaller conductor and allow some wire heating
for intermittent uses, the cables from car batteries to starters being a
good example. The task is done before an unsafe level of heat can be
generated. But conductors that are used for minutes to hours should not
heat up meaningfully.
Van
On 06/05/2011 5:20 AM, James Parker wrote:
>
> Since the lights are now running direct off the batteries, the cable
> will get hot -- it's transferring DC power, not AC.
>
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