mm wrote:
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.

Is that too high for a tv that is meant to run on 6.3? If so, I'll be
glad to make the resistor bigger and thus the voltage lower.

It also has provision for turning off the picture and only getting the
sound. I guess it would use less current then and I would calculate a
higher resistor to be needed. Maybe I should just use a resistor
substitution box and see at what resistance the tv works best? Or
should I buy a device made for this purpose. I have a spare cell
phone charger, but I don't think it wil put out a full 1.6 watts.)

Hi...

Just thinking out loud; wouldn't it be so much easier and so
much more practical to just pick up a nimh/nicad charger that
works off of 110 or 12 volts, along with 8 batteries, and use
one set while charging the other?

Take care.

Ken