Hi
I've just been reading this project with interest as I have converted two FS1E's to 12V in the last couple of years. The FS1E has a very similar circuit to the DT's, however I used a different method.
I wanted to run the lights on DC direct off the 12V battery as then you get full brightness even at tickover.
The problem is that the standard rectifier (and a C90 cub one) are the 'half wave' type with a single diode, this means that only half of the ouput of the generator can be used to charge the battery. This would mean the battery would not be charged sufficiently with the lights on (assuming the wattage of the bulbs was the same as before the conversion).
My answer was to use a rectifier/regulator of the 'full wave' type which are readily available on ebay for the larger Chinese bikes. Unfortunately the lighting/charging coils on FS1E's, DT's etc are usually earthed at one end. For a full wave rectifier to work this coil has to be de-earthed, so the reg/rect can be connected to both ends. The diagram below shows the circuit I used.
This does need some soldering work at the stator and some modification to the loom. However you do end up with a simpler wiring circuit. When fully installed I checked it out using a meter strapped to the tank, measuring current into or out of the battery.
I initially tried with a 35W headlamp (std is 18W), but the break even speed for charging was 44mph in top which is almost flat out. I settled on a 25W halogen bulb where the break even speed was 25mph in top. I used a dry sealed battery from screwfix and it's never needed charging in over a year.
The second fizzy I did, I fitted a whole pattern stator intended for a PW50 kids bike. This was to get CDI instead of points. I wired the lighting/charging in the same way as before, but this coil was more powerful and easily runs a 35W headlamp.
This was the reg/rect I used it's a 5 wire type. The 5th wire goes to a 12V feed from the battery that is only live when the ignition is switched on. Otherwis the circuit is as above. From memory the wire colours were:
Yellow = AC Input 1
Pink = AC Input 2,
Red = Battery positive
Green = Battery negative (earth)
Black = Battery positive but only with main switch on
http://www.petrolsco...r/category/411/
There are loads of similar units on ebay, but the useful information is usually lacking and it's not easy to tell the full wave from the half wave and the single phase from the three phase. The one above definitely works though and regulates at about 14.5V.
Hope that was useful.
Cheers
Mark C