[tcb] 6 Volt Power Supply

  • From: Will Wood <evilscientistboo@xxxxxxxxxxxxx>
  • To: tcb@xxxxxxxxxxxxx
  • Date: Sun, 12 Aug 2007 17:05:11 -0500

I know this is technical and it's Sunday but it is VW/Bus related.  

I'm finally done.  Too much "On the road" of late has put this off
for a week or so.  I thought I'd share with you this little hobby
circuit I implemented.

Anyway, I found this URL 

http://www.ford-trucks.com/article/idx/8/040/article/6_To_12_Volt_Conversion_Guide_.html

and read how this circuit could be used as a 6V power supply for
automotive purposes.  I've been a "tinkerer" with electronics for years
but it hadn't occurred to me to use an audio amplifier transistor to
drive the power load for something like this.

With most of us running 12V conversions there are still some 6V things
we need to run: old radios, gauges, wiper motors etc.  The problem is
most of the commercial items, volt a drops etc. Aren't the greatest.
So, anyway I read up on this schematic and design and saw a couple of
opportunities.  I've modified it by adding a lower power amplifier, a
2N3005, in front of the 2N5881.  The problem is as power increases
through the amplifier transistor it increases the load on the base
connection.  In the case of the 2N5881 up to 7 amps.  This isn't good
for the 7808 voltage regulator which is only rated at 1 amp.

The 2N3005 acts as a proxy for the 7808 by taking on up to 7 amps of
load for the base connection of the 2N5881.  I will tell you that the
circuit is capable of 200 Watts of power output but that generates a 
lot of heat in the two amplifier transistors.  I've clipped the output
with a fuse to 10 Amps or 64 Watts maximum (The Vout for the circuit is
6.4VDC).  I would think with this board you could go to 15 amps but
beyond that I'd need a bigger heat sink and larger wire.  The whole
sheet of aluminum is the heat sink.  I've also included an indicator LED
to let me know the circuit is working.

If you were running a gauge or something that drew less than 1 amp at 6V
you could use a 7806 with the two capacitors.  This could be soldered
together in a small package and wired just behind what you're trying to
power.  All of these parts can be found at Fry's or any other stocked
electronics shop.  Radio Shack doesn't count!  The components were about
$12 not including the fasteners and aluminum.  I had all the rest of the
wiring and connectors already.  I've packaged it so it can be mounted
under my parcel tray.  

Just think, all of that "crappy" 6V stuff hanging around is now useful
once again.  I'll let you guys know how my 6V two speed wiper motor
works out.

Here's some pics.

http://s22.photobucket.com/albums/b313/EvilBus/6volt/?action=view&current=6vpowersupply.png
http://s22.photobucket.com/albums/b313/EvilBus/6volt/?action=view&current=6vpower2.jpg
http://s22.photobucket.com/albums/b313/EvilBus/6volt/?action=view&current=6vpower1.jpg





Other related posts:

  • » [tcb] 6 Volt Power Supply