It will work for awhile but I wouldn't. Maybe if you disciplined yourself and
occasionally swapped the two, you could get away with it but if you forgot when
you swapped them, after a period of time you'd unbalance the capacities and
damage one of them (guess which one?).

Here's a cute little board.

It's a switcher rated for over 1 amp. Its output can be fixed from 2.5 volts to
9 volts with a change of only one resistor, and an input range from about 7
volts to 20 volts. Under my test circuit, with 6 volts out, I  loaded it with
1.2 amps, and with an input voltage of 13 volts, it draws about 500ma. With an
input of 7 volts it drew about 750ma and with a 16 volt input, drew about
300ma. The switcher chip and the inductor were "barely" warm to the touch. I
came across about a dozen of these boards. I sawed them off a production board
from a run of video monitor cards in a notebook type computer for police cars.

http://www.pic101.com/pix/P9030001a.JPG

The unit is quiet too! I had an AM radio sitting next to it and heard no noise
or squeal until it dropped out of regulation below 6 volts input. I would like
to lay out a new board for them for a bunch of projects I'm working on and also
make them available to anyone on the list if interested in them. Contact me off
list if you're interested.
Rick

Pic Dude wrote:

> Funny you should mention this.  I'm in a similar situation
> trying to get +5V and +/-12V for a PC.  For the +5V signal,
> I'm wondering why I can't use 2 6V gel cells in series and
> pull the voltage off only one for the 5V signal (using an
> LDO).  I've been trying to find out what happens when
> charging 2 unequally-charged batteries in series.
>
> Cheers,
> -Neil.
>
> > -----Original Message-----
> > From: pic microcontroller discussion list
> > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jim
> > Sent: Tuesday, September 03, 2002 2:28 AM
> > To: PICLIST@MITVMA.MIT.EDU
> > Subject: [EE]:Better regulator
> >
> >
> > Hi
> >
> > I have a lcd tv and a dvd player I want to run on a 12v battery.
> > Like from my van battery or a 12v gellcell.
> > The dvd runs on a 12v wall wart rated at 1a.
> > The lcd tv runs on 6v@ 1a.
> > I have built a simple circuit using a 7812 & 7805 and it works fine
> > the tv works good on the 5v and draws .7a But these regulators get so hot
> > they must be wasting alot of energy are there better regulators I
> > could use
> > in this app? the gellcell's I have are rated 12v @ 5ah/20h And I
> > don't think
> > it will last very long driving these loads.
> >
> > Thanks for any input
> >
> > James M
> >
> > --
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> >
> >
> >
>
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