The Stovebolt Site Forums The Shop Area The Electrical Bay 12V to 6V converter

I learned how to make one of these from another post here in the forums. It gave detailed instructions and a parts list from Radio Shack...

Ok... so I went to Radio Shack to get the parts...

They don't carry the 7806 or 7808 regulator.

They don't carry the 2N5881 transistor either.

Resistors, diodes, caps no problem.

Soooooo... I am trying another route...

Using a LM317T variable regulator with a potentiometer. the result should give me an ADJUSTABLE output range of 1.2V to 13.8V. Used in conjunction with a 2N3055 transistor, I should get up to 15 Amps of current capacity.

I will try to get it done today and will post my results. Once it is tested, I will post a schematic.

If it works, I may be interested in marketing the whole assembly. It seems like there is quite a demand for a 12V primary - 6V secondary power supply, and nothing commercially available.

Be sure you use a BIG heat sink to mount that transistor. Flowing 15 amps across the emitter/base junction will cause a deadly amount of heat buildup, unless it's able to dissipate the heat quickly. You might want to consider using two transistors in parallel to minimize the loss due to voltage drop, and share the load.
Jerry

Powerstream sells DC-DC convertors for only a little more than you will spend in parts and time. You may want to see if they have something for you. www.powerstream.com

If you are using parallel bipolar transistors you will need emitter resistors to ensure current sharing. Otherwise, you will have thermal runaway. If you really want to build it yourself, and you need more than a couple of amps, there are much better solutions (ie. DC-DC convertors).

The only thing that is still 6 volt on our truck is the gas gauge. I bought a regulated voltage reducer for it from JC Whitney - $17.99

What 6 volt device are you planning to retain when you switch to 12 volts?

I am planning to power my heater fan, fuel gauge, and distributor for now. I will be upgrading the disty to HEI soon, but for now, I keep burning up points w/12V.

I built it yesterday. It seems to work fine! I haven't gotten around to putting it in the truck yet so I don't know how it will work with the full load of the Disty and heater on it. I tested it with a couple of bulbs and it doesn't even begin to get warm. I will keep you updated when I put a real load on it.

For heat sinks, I used two pieces of 1-1/2 x 2-1/2 x 2-1/2" long aluminum angle. one for the regulator, and one for the transistor. connected by a piece of sheet PVC. The angle that the transistor is mounted to is +12V. The one that the reg. is mounted to is +1.2 to 13.8 low power. A third angle to mount it with is Gnd. The emitter is connected to a terminal strip which is +1.2 to 13.8V high power.

I have less than $10.00 invested in this thing, and it is an interesting enough project that, even if it doesn't make the final cut, is well worth what I spent.