tom_eaton said:
is there a way you could do the design for a 3 phase circuit? i'm a bit confused as to how you could do it.
Here is an untested version for a 3 phase circuit. I have shown the opto-isolators separated on the diagram to make it easier to read.
IC1 is a TL431 or equivalent. The battery voltage is smoothed by R4 and C1. The voltage is divided by R5 and R6. When the divided voltage is above 1.25, IC1 turns on and turns on the opto isolators.
When the opto isolators are on they stop the SCRs from turning on by bypassing the gate current.
However, the circuits shown elsewhere in this thread would seem to be more suitable for 3-phase generators. The internal inductance of generators is so large that they can be considered constant-current supplies, so no damage is done by shorting them. The only reason that I built a circuit like this was that shorting the generator effectively shorted the directly lit headlight, run straight from the generator, not from the battery. Any motorbike with a 3-phase alternator won't have a directly lit headlight.
If anyone is thinking of increasing the voltage on a small motorbike with a directly lit headlight, it is worth remembering that the current, not voltage is set by the coil design. If you chose a headlight of a higher voltage, but the same current, the generator should light it OK.
I had a 1984 Honda CG125, which had a dreadful electrical system. Honda should be ashamed of what they made. It had magneto ignition, a directly lit headlight and no voltage regulator. The battery only powered the brake light, indicators and neutral light, and the battery was in effect used as a shunt regulator.
I fitted electronic ignition, and used the magneto coil as an additonal generator coil. That gave me enough power to run the side and tail lights from tha battery. I fitted the regulator that I showed the circuit for. I changed the battery to 12V.
On the headlight, it used to be a 25W 6V bulb, with a 5W 6V tail light. The total was 30W at 6V which is 5A. I changed it to a 60W 12V headlight which was also 5A and was lit very well from the existing generator. It was rather dim at tickover, where the low voltage became more important than the constant current at high revs.