12 Volt Conversion

A Technical Report from the Hinterlands

Here's how to change a 6 volt VW into a 12 volt VW. Of course, you have to have a 12 volt generator or alternator and a 12 volt regulator.

REGULATOR AND GENERATOR The regulator must be securely fastened to the firewall (or some such place). In 12 volt bugs it is located under the rear seat for some reason. The regulator has 4 connections other than ground. They are

In addition, a ground wire (brown) should be run from the case of the generator to the base of the regulator where it is mounted. Try to maintain the color code so you don't get confused when you have to change the generator on the road in Cedar City, Utah.

STARTER The 6 volt starter will work with 12 volts until you crank it for too long. Unlike the generator, the starter has no provision for cooling, and running the 6V starter with 12 volts results in twice the expected power dissipation (although it spins twice as fast). But this means heat. When you replace the starter with a 12V unit, you MUST ALSO REPLACE THE FLYWHEEL. The 6V flywheel will work for a while (maybe) until that time when you have to get the pregnant wife to the hospital or get to court before 3:00.

WW MOTOR Some folks put a resistor (1 ohm or so) in series with the WW motor to drop the voltage to an acceptable level, but the resistor has to be able to dissipate a great amount of heat:

  V=IR           voltage = current times resistance

  12 volts = I * 2 ohm
  6 amps = I     looks like 6 amps in this example

  Pd = VI        power dissipation = voltage times current
  Pd = 12 * 6
  Pd = 72 watts  and it looks like the 1 ohm resistor should
                       be rated for 72 watts, anyhow
If you leave the 6V WW motor as is, you'll notice it runs real fast for a minute or two and then smells like something burning.

When we got the Clubhouse (65 II), the WW motor was fried this way, and we couldn't locate a replacement motor. But interestingly enough, the WW frame and transmission assembly from a 77 bus matched the 65 frame exactly in the distance from wiper shaft to wiper shaft, although the holes through the body for the shafts had to be enlarged to 3/8". Unfortunately, the 77 WW motor was much too large to fit between the shelf and the dash. But the good news was that a Super Beetle motor, much smaller than the 77 bus motor, bolted right up to the 77 bus transmission, and that's the way the Clubhouse is to this very day.

WIRING HARNESS Don't even think about replacing the wiring harness.

  Pd = V * I              work = voltage times amperage
  Pd12 = I12 * 12v        work under 12 volts = 12 volts
                                      times 12V amperage
  Pd6 = I6 * 6v           work under 6 volts = 6 volts
                                      times 6V amperage
  Pd12 = Pd6              and the work is the same either way,
  I12 * 12v = I6 * 6v     and
  I12 = I6 / 2            12 volt current is half the
                                      six volt current
The wires for 6V are much heftier than the wires for 12 volt. This is because the 6 volt system - to perform the same work - uses twice the current as the 12 volt system. With 12 volt devices in place and a 12 volt power supply, the old wire is more than sufficient to handle the current.

Note, however, that this does not apply if you are leaving the old 6V starter in the car. That starter will spin twice as fast meaning that the power dissipation is doubled. So the same amount of current at twice the voltage is coursing down the wire when the starter is activated. We've never seen a burned starter wire from this, but it is a theoretical possibililty.

BULBS The 6 volt bulbs sure are bright at 12 volts for a little while, and we are measuring in seconds here. Remember to replace the bulbs in the instrument panel as well. It would be a shame to burn out the oil pressure warning light, eh?

AND WHY BOTHER Just a personal note.

Kevin changed Flaming Moonbeam (66 II) BACK to 6 volts because he was having trouble starting the engine and you can always jump the 6 volt vehicle from a 12 volt battery. I personally like the 6 volt systems better than the 12 volt, and unless there is an over riding reason for changing to 12 volt, would recommend staying with 6.

As an example, there are plenty of 6 volt gas heaters, but 12 volt units are as scarce as brains at a Richfield Village Council meeting.

In the case where the engine is being replaced with a newer one and the charging system will be 12 volt, my advice is to put another 6 volt battery under the back seat, run the car off one of the pair but charge both in series from the 12 volt source.

           6 V battery           6 V battery
            ________              ________
           | +    - |            | +    - |             common
+----------|-o    o-|-----+------|-o    o-|------------ ground
|          |________|     |      |________|
|                         |
12                        6 
volts                    volts

You will end up with the best of both voltage worlds and the expense and difficulty is much less than a conversion. And on that cold Winter morning when you have to get to work and the car just won't start ... why you've got the 6 volt gas heater and the 12 volt CD player going while you jump the car from the 12 volts of batteries you've got right there under the back seat already. Hoo hah!

Back to the Junkyard

c 1997 Air Cooled Volkswagen Junkyard formerly of Richfield, Ohio http://www.acvwjyro.com "Where Advice Is Always Free"(216)659-3638 This story may be distributed only if it is not altered in any way and is distributed freely without charge.