wrote in
:

On Sat, 21 Jan 2012 01:48:39 -0800 (PST), spamtrap1888
wrote:

On Jan 21, 1:04*am, Rheilly Phoull wrote:
On 1/21/2012 6:41 AM, spamtrap1888 wrote:







On Jan 20, 2:26 pm, wrote:
On Thu, 19 Jan 2012 10:07:50 +0800, Rheilly Phoull

*wrote:
On 1/19/2012 6:55 AM, 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

Just search for "three terminal regulator" until you find a
circuit for the 9volt one. This is a very simple circuit and
easy to build, I have had such in use for years in my vehicles.
You can build it in a small diecast box which would be strong
and act as a heat sink for the regulator.

Rheilly P

To expound on this idea, the xx1084 family of regulators would be
ideal. *Specifically, the AP1084TL-U adjustable regulator.
*Datasheet:http://www.diodes.com/datasheets/AP1084.pdf. *It's
capable of putting out 5A and has thermal shutdown.

The parts list is simple - An AP1084TL-U, 2 ea 100µF, 25volt
caps, a 120 ohm and a 750 ohm 1/4 watt resistor, the die cast
box, and an insulator - the tab of the AP1084 is at the output
voltage.

One problem with using this part is the risk of destroying it as
soon as you start the car: The absolute maximum supply voltage is
only 12V, and the alternator puts out more than 13VDC.

The 7809 has a max input of 40v from memory.


I'd use a 7809 myself, but the part with the low abs max Vin
recommended here was a AP1084TL-U.
No one mentioned putting a string of silicon diodes in series to lower
the voltage. Unlike a resistor, the voltage drop would be reasonable
fixed. But, no fancy parts, capacitors, etc are required. Sort of
crude, but why wouldn't it work? 7 diodes would drop approx 4.2 volts
bringing 13ish down to 9ish. Or, maybe 8 diodes to be safe. 13.8 down
to 9. Just wondering why no one mentioned the possibility. Heat
would have to be handled, but no worse than a three terminal regulator
and the heat would be spread across all 8 diodes.


forward voltage drop of a diode varies with current through the diode.

--
Jim Yanik
jyanik
at
localnet
dot com