On Thu, 14 Dec 2006 23:05:16 -0500, mm put
finger to keyboard and composed:

I have a 2 inch Sony Watchman tv that runs on 4 AA batteries. I want
to use it in the car during a trip this spring.

Is it better to buy a "power supply" that plugs into the cigarette
lighter and generates 6 volts, OR

to run it with 4 batteries, measure the amperage, calculate the
effective resistance of the TV, and then make my own power supply that
plugs into the cigarette lighter, that would consist of a plug, a
jack, a wire and a fixed resistor. The resistance of the resistor
would be the same or nearly the same as the calculated different of
the tv.

My experience is that fully charged AA batteries are usually 1.56
volts x 4 = 6.3 volts, which is exactly half of the resting voltage of
fully charged car batteries, 12.6 volts. I won't be watching tv when
the car is running, but maybe I would sometimes run the car to charge
the car battery, or even to warm the car** Then, iirc and I can
measure it to be sure, the voltage goes up as high as 13.2, half of
which is 6.6. Also, the label on the back of the tv says that it
uses, on average, 1.6 watts, but I will measure its current current
use and not rely on that.

If you are looking to do this on the cheap, then I'd modify a mobile
phone car adapter/charger. But then I have dozens of them.

- Franc Zabkar
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