6 till 12V 30 hästarsmotor

The "field coils" are basically wire wound around magnets called pole shoes. They are attached to the outside case of the generator. The spinning armature passes through the field coils to generate electricity. If you doubled the number of windings in the generator you would double its voltage(using thinner windings) This comes at a cost though, you can only get a fixed amount of amperage from a generator. Amperage is a product of the size of the generator(diameter) and the speed at which the coils pass through it.
The relationship between Voltage and amperage can be shown mathematically:
Amperage=Wattage/Voltage
A 6v (36hp)bug generator is 160 watts at 2500rpm
160W/6volts =26.6amps
160W/12volts=13.3amps
The 6V bug generator is severely limited in output already but to trade half of that isn't going to leave you with much.
Using a 12V regulator on a 6V generator isn't much better. See a generator isn't charging all of the time. Its only working when the regulator tells it to. The generator has a duty cycle based on its cooling efficiency. If it is working at full output all of the time it will overheat the fields and eventually burn up. Any added load will only hasten this. Since the whole reason to switch to 12V is to add brighter lights and more accessories this seems like a waste of time.   
The question I have is why do you need 12V?
Here are the three main points that I have heard:
1) a 12V lighting system is brighter for increased saftey
2) 12V system is more reliable.
3) 12V components are easier to buy at your local parts store.
These are good points but consider this:
1) Bulb brightness is determined by Wattage NOT voltage. A 6v bulb that is 55W is the same lumens as a 12v bulb at 55W
2) Although 6V has less ability to overcome resistance in an electrical system VW built their system to be 6V. A stock beetle has very little resistance due to Wire quality, short lengths and minimum number of connections. As long as you keep the system stock and CLEAN it will be perfectly reliable. In fact 6V bulbs use a larger filament meaning they are  more rugged and last longer than 12V.
3) With the advent of the internet you can have almost anything at your doorstep in just a few days, including halogen 6v bulbs comparable to modern 12v (http://www.snydersantiqueauto.com/searc … =0&y=0)
Check out this post for further details
http://www.thesamba.com/vw/forum/viewto … highlight=