[VAC] Re: Why Car & Trailer Battery to Univolt?

[Dr. Gerald N. Johnson, electrical engineer]

Marc, what you need is one really big car battery (or two in parallel)
and then the trailer battery on the isolator. What the makers used to
ship for battery wasn't enough to run the headlights four hours or the
glove compartment light a week. They do better now, and with the
computer control the computer can detect lack of motion and turn off the
lights. My plain '98 F-150 does that for the dome light.

I did know of an Oldsmobile with a confused computer that would turn the
headlights on when parked in the garage though and kill the battery. So
the owners had to remember to turn off that automatic feature when
putting it away for the night.

The logic for a headlight warning gadget isn't complex. All it has to do
is detect ignition off and lights one, might be as simple as a 12 volt
buzzer and a diode wired between those two circuits. Should be low
current else the engine might not stop when turning the key off unless
or until the lights were turned off.

Gerald J.



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