On Fri, 15 Dec 2006 21:09:04 -0500, mm put
finger to keyboard and composed:

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?

The majority of mine are switchmode PSUs based on an MC34063 IC (I
also have some linear supplies).

The application circuit on page 7 of the MC34063 datasheet shows a
5V/500mA design example:
http://www.onsemi.com/pub/Collateral/MC34063A-D.PDF

In a typical car charger you will need to recalculate R1 and R2 to get
the desired output voltage.

FWIW I've adapted one of these chargers to supply 7V to a 12V fan in a
DVD player.

If you are worried about the load dump problem being discussed
elsewhere in this thread, then you might like to place a transorb or
transil (transient voltage suppression diode) across the 6V output.
However, I suspect that a SMPS of this type is largely immune to
supply transients (due to the series inductances). You may still want
to add the diode for overvoltage protection in the event that the IC
fails.

- Franc Zabkar
--
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