In article ,
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.

That is a crude method - far better to use a voltage regulator. The
output voltage may go too high under certain conditions - like standby -
if you use just a resistor as that voltage is load dependant.

Like all these things it's probably cheaper to buy a ready made one.

--
*If you think nobody cares about you, try missing a couple of payments *

Dave Plowman London SW
To e-mail, change noise into sound.