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adapting 12vdc to 9vdc

  • Thread starter William Sommerwerck
  • Start date
W

William Sommerwerck

Jan 1, 1970
0
You don't want to use a resistor, because if you turn up the volume, the
change in current drawn as the sound gets louder and softer will "modulate"
the voltage.

You need a properly regulated supply to step the voltage down to 9V. I don't
know who makes one, especially of the capacity needed for a boombox.
 
C

Chas

Jan 1, 1970
0
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
 
C

Charlie

Jan 1, 1970
0
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

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.
 
M

mike

Jan 1, 1970
0
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.

Don't do that. It's wrong for a lot of reasons.
You need a regulator.
If you intend building something, make sure you understand this:
http://www.littelfuse.com/data/en/Application_Notes/an9312.pdf

Safest thing is to buy a car adapter.
 
C

Chas

Jan 1, 1970
0
Charlie said:
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.
.....< snip >
Thus a fully charged 6 cell battery is nominally 13.2 volts.
Charlie
Yes, that is what I always see about auto battery voltages....13+vdc.
Chas
 
C

Chas

Jan 1, 1970
0
Would you please share your schematic for the voltage regulator?
I would be most appreciative. . . . .Also, thanks for the guidance.
chas. L7912CV-Negative

http://www.ebay.com/itm/
2-Pcs-3-Terminals-1-5A-12V-L7912CV-Negative-Voltage-Regulator-/280803733057?pt=LH_DefaultDomain_0&hash=item416134ee41
.. . . .I'm curious...my first email to your address bounced...is it valid or
is my system messed up?
****************************
 
W

William Sommerwerck

Jan 1, 1970
0
Here's another possibility...

Buy an inverter that converts 12V DC to 120V AC. Then use an AC power supply
("wall wart") suitable for the boombox. It might even have its own built-in
AC adapter.
 
W

William Sommerwerck

Jan 1, 1970
0
I find that UseNet groups almost always suggest the most-complex and
most-difficult-to-implement solutions one can imagine.

There are three simple solutions...

1) Use rechargeable batteries. This won't be cheap, but the OP can operate
the boombox anywhere. This is an essentially fool-proof solution.

2) Find a 9V auto cord.

http://www.radioshack.com/product/index.jsp?productId=3812864

3) Buy an inverter and use the power supply that came with the boombox.

http://www.amazon.com/Wagan-EL2402-...2?s=electronics&ie=UTF8&qid=1326975432&sr=1-2
 
W

William Sommerwerck

Jan 1, 1970
0
Buy an inverter that converts 12V DC to 120V AC. Then use an
total waste of energy ...

WHY?

It requires no energy -- it's plug 'n play.
 
M

mike

Jan 1, 1970
0
Would you please share your schematic for the voltage regulator?
I would be most appreciative. . . . .Also, thanks for the guidance.
chas. L7912CV-Negative

http://www.ebay.com/itm/
2-Pcs-3-Terminals-1-5A-12V-L7912CV-Negative-Voltage-Regulator-/280803733057?pt=LH_DefaultDomain_0&hash=item416134ee41
. . . .I'm curious...my first email to your address bounced...is it valid or
is my system messed up?
****************************
Targus and Igo make universal car chargers. Can be had for $5 or so
shipped on ebay.
The problem is that they require special tips to configure the voltage
and the cheap ones come without tips.
But if you can design a regulator, you can open 'em up and add the
required voltage setting resistor and put the right plug on the wire.
 
K

Kripton

Jan 1, 1970
0
Would you please share your schematic for the voltage regulator?
I would be most appreciative. . . . .Also, thanks for the guidance.
chas. L7912CV-Negative

http://www.ebay.com/itm/
2-Pcs-3-Terminals-1-5A-12V-L7912CV-Negative-Voltage-Regulator-/280803733057?pt=LH_DefaultDomain_0&hash=item416134ee41 ..

. . .I'm curious...my first email to your address bounced...is it valid or
is my system messed up?
****************************

hi,
you must know how many amperes your boombox will draw from the battery ...
because if it draws 1 amp, and you must step down the voltage from 12v to 9v
you will have to dissipate 3W from the 78xx regulator
also a 7912 will output 12v, negative, and a 7809 will really outpout
9v positive what you need...
if it is too hot, you must then use a switching regulator
then it's cheaper generally to buy a ready made from ebay or dealextreme
hope this helps.

--
 
K

Kripton

Jan 1, 1970
0
Here's another possibility...

Buy an inverter that converts 12V DC to 120V AC. Then use an AC power supply
("wall wart") suitable for the boombox. It might even have its own built-in
AC adapter.

total waste of energy ...
--
 
W

William Sommerwerck

Jan 1, 1970
0
On 2012-01-19 12:31:10 +0100, "William Sommerwerck"
<[email protected]> said:
I'm not talking of human energy, but electricity energy ...
each time you convert voltage (12v->120V) then 120V->9V
you have power losses, that generate heat.
that means the energy if transformed into heat, useless and poor solution
for the planet ...
instead use a smps converter from 12vdc to 9vdc they exists
they are cheap, and the power losses are reducted to a minimum

I don't blame you for wanting to be green, but the energy involved is tiny,
compared to the energy the engine uses. For example, 20HP is about 15kW. Ten
watts (at worst) to run a boom box is nothing.
 
K

Kripton

Jan 1, 1970
0
WHY?

It requires no energy -- it's plug 'n play.

I'm not talking of human energy, but electricity energy ...
each time you convert voltage (12v->120V) then 120V->9V
you have power losses, that generate heat.
that means the energy if transformed into heat, useless and poor solution
for the planet ...
instead use a smps converter from 12vdc to 9vdc they exists
they are cheap, and the power losses are reducted to a minimum

--
 
S

Spehro Pefhany

Jan 1, 1970
0
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

Hey, this little device would probably have adequate capacity ;-)

http://www.nextag.com/Medela-9-Volt-Vehicle-595671550/prices-html?nxtg=4bf80a280508-548F46D24A00A4FA



Best regards,
Spehro Pefhany
 
R

Roger Blake

Jan 1, 1970
0
that means the energy if transformed into heat, useless and poor solution
for the planet ...

BARF! I for will not lift a finger to "save the planet." It doesn't need
saving, and if it did "reducing power losses" is not going to do the trick.

--
-----------------------------------------------------------------------------
Roger Blake (Change "invalid" to "com" for email. Google Groups killfiled.)

"Climate policy has almost nothing to do anymore with environmental
protection... the next world climate summit in Cancun is actually
an economy summit during which the distribution of the world's
resources will be negotiated." -- Ottmar Edenhofer, IPCC
-----------------------------------------------------------------------------
 
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.

PlainBill
 
G

gregz

Jan 1, 1970
0
Chas said:
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


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

This all reminds me of my boom box I built in the early 80s. I used car
parts and a gel cell, compatible with car charging systems, which can reach
16 volts. Picture does not show horn loaded drivers.
http://www.zekfrivolous.com/slidesandstuff/slides1/PICT0055.JPG

Greg
 
W

William Sommerwerck

Jan 1, 1970
0
I don't understand the problem. I have been using the 7809
etc. for years in the automotive situation without a single
failure. It's not exactly rocket science. :)

The problem is that the OP probably knows little about electronics, and is
likely to completely botch the project. He'll return to us asking for
troubleshooting help.
 
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