If memory serves me (and it doesn't always), at the specified specific
gravity of a lead/acid cell for automotive use is the nominal voltage is2.2
volts.

Thus a fully charged 6 cell battery is nominally 13.2 volts.

But, of course, in the automotive world the battery is only used for
starting unless the engine is off. When engine is running the voltage
available to the vehicle's electrical system is determined by the alternator
and its associated regulation system.

A decent voltmeter is a handy way to check your own particular situation.

Charlie

wrote in message
...
On Jan 18, 4:55 pm, "Chas" wrote:
I plan to use a ''boombox" in my vehicle because the existing sound device
is defective and next to impossible to remove.
My boombox uses 6 AA batteries...would it be safe to just run a plug from
the 12v cig lighter to a power plug on the boombox? I imagine I will need
some sort of voltage reducer. Anyone got any ideas on how one could build
such a reducer. I am fearing such a device may induce noise.
. . . . .I am of an understanding that 1.5v batterys are acutally 1.2v. Is
this correct? If so, I could run the 12v car voltage to 10 AA batterys and
then tap off six batterys....
Else, if the AA's are truly 1.5 volts then run the 12v car power to 8 of
the
AA's and tap off 6.
any help would be greatly appreciated.. . . chas

AA batteries (regular carbon or nickel metal hydride) are 1.4 to
1.5V, NICAD AA batteries are 1.2V. So you need to drop 14V to 9V.
14V because that is the actual voltage of a car system whenever the
engine is running,12V is the nominal battery voltage when the engine
is not running.

You need to determine the current drain of the device in order to
figure out what value of resistor you need to put in series with the
14V to drop it to 9V. You need to drop 5V, the value of the resistor
needed is R=V/I where V=9, I=current drain in amps.