This simple circuit allows a 12V battery pack (10x nicads in the bike seat stem) to be charged via a bike generator. The generator is rated at 3W and with this voltage multiplier circuit provides about 200mA at about 15km/h. A 12V system was chosen because it allows the use of a car horn (get noticed)!
Was previously running 6V 3W globes in series provides adequate lighting and they last more than six months - now using an old car phone charger and changed the output voltage to be suitable for a 3watt LED - the rear light is now 2xred+1xFlashing LED in series
3watt LED driver was made using an old mobile phone car charger - see typical circuit based around the MC34063. Just need to find the feedback resistor in the circuit (R2 in this case) and adjust that for the LED drive voltage (typically 3.6volts). The input can be 9-24volts.