mm ha escrito:

On Sat, 16 Dec 2006 08:48:44 +1100, Franc Zabkar
wrote:

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

Do the new ones put out 1.6 watts, which is what the back of the tv
says it uses on average? I have a spare new one.

Do even the old ones put out 1.6 watts?

- Franc Zabkar


If you are inclined to email me
for some reason, remove NOPSAM :-)


Well, 1.6 Watts at 6V is nothing more than 267 mA. (1.6V / 6V = 0.267
A) I would be greatly surprised to find a cellphone charger not able
to produce that amount of current. Check the mA rating of the DC
charger you want to modify, if it provides a *regulated* output of 6V
at 300 mA or more, you will be fine.

You want to find a charger who outputs nothing more than 6V, and 300 mA
or more. The TV will take the amount of power (consumption in mA) it
needs, meaning that a 500 mA power source will not damage it, because
the TV will only draw 267 mA from the 500 mA power source. Just be
careful of the voltage produced by the charger, because that´s a
critical paramater and it shouldn´t be higher than 6.6V or lower than
5.4V under any circumstances.

To close, the idea of the dropping resistor is an awful one. Why?
Because the 1.6 Watts consumption stated in the back label of the TV
probably is an average value, or a maximum one obtained only under
worst case conditions. The consumption power of a TV, radio, or
amplifier, is really a variable one. It will vary depending on how high
the speaker volume is, and even the screen content. For instance, a
white image will demand more power than a mainly dark one. So you
can´t really obtain a fixed voltage just using a fixed dropping
resistor if your load is a variable one. Even worse, as other posters
had previously stated, the DC voltage inside a car can go anywere from
12V to 14V or more. So now you have two uncontrolable variable
parameters: a) The voltage source, and b) The power consumption of the
TV.

Don´t risk frying your TV. It´s more worth having it fuly operational
than the cost of a proper DC regulated power supply.