Series parallel??

Discussion in 'Electronic Basics' started by steamer, Jul 29, 2005.

1. steamerGuest

--Here's the situation: I've got a small vehicle that uses a 6v
battery for starting. But I need a 12-v supply to run some auxiliary
lighting stuff. What I'd like to do is add a second 6-v battery in
parallel with the first one, so that the engine will "see" 6v when it's
started and so that the alternator will charge them both. But I'd like
to have the batteries output to the lighting controllers in series, so
that the controllers "see" 12v. Is there a way to do this? Any pointers
appreciated..

2. Tom BiasiGuest

Hi,
The batteries would have to be isolated with large diodes.
Circuit similar to a voltage doubler circuit.
Tom

3. MochueloGuest

I would not use two batteries. Use a boost converter to generate 12 V
from the 6 V input.

4. John LarkinGuest

I did this once for a young lady who bought a Porsche with a 6-volt
system, and then bought a fancy 12-volt da-da-la air horn. She wanted
to make an entrance at a picnic in the new porsche, tooting the horn.
So she had her new Porsche air-freighted in from Germany and drove it
over to us with the air horn for installation.

We added a Honda 6-volt battery and a DPDT relay, so when she pressed
the horn button we switched the batteries from parallel to series and
powered up the horn at 12 volts. Of course, the Honda battery doesn't
charge when the 12-volt load is energized, which was fine in this
case.

There's no way to wire batteries to be in parallel and series at the
same time.

John

5. rayjkingGuest

Hi,

You may not want to do this but by using two IR2110'S and 4 fets and a
toroid with two wires bifilar wound . Connected as you would a push pull,
center tapped 6 to 12 volt converter and replace the two diodes with two
fets. This must be driven with a 40 to 50 % on each half cycle. You now have
a synchronous rectified voltage doubler that is bi-directional and if a 12v
charger is applied to the 12 volt output you will also charge the 6 volt
battery.

I have built such a device for a friend to add a 12v battery to a triumph
motorcycle because the 6v batteries are no longer made. The 6v charger
charges the 12v battery and the electrical system is all 6v. Above I used
the 555 timer and 4013 to divide by two and give a symmetrical output.

Ray