This is the schematic of my new bicycle dynamo circuit.
Presently I am using a Bottle type tire driven dynamo. This circuit is suitable for use with hub dynamos as well. Circuit description is as follows.
Dynamo: 6-volt AC, 3-Watt standard bicycle dynamo. May be hub or tire driven types.
Bridge rectifier circuit consists of 4 1N5818 Schottky type. This type of rectifier diode has lower voltage drop across the junction making them a little more efficient than standard rectifier diodes.
Headlight: I used a Seoul Z-power U-BIN high power LED in a Luxeon 10X30 optic holder and lens. This produces a beam pattern much like a vehicle headlight. The 470mF capacitor filters rippled DC for the LED giving a little more light output and reducing low speed flashing. The capacitor should be rated for at least 16 volts. The Seoul Z-power U-BIN can be driven with up to 1 amp without damage. This allows direct connection to the bridge rectifier with no harm done as most dynamos produce about 500mA at speed. The Pioneer E-generator is capable of 770mA, which is still safe for use with a Seoul or Cree high power LED.
S1: Switches dynamo power for either the headlight or the USB circuit. You canít power USB devices like a cell phone or GPS unit and the headlight at the same time. S1 allows switching between one and the other or center off if your using a hub dynamo. With this circuit you can leave a USB powered device connected to the USB connector and batteries allowing you to power and or recharge the device until they become discharged while using the headlight. This allows switching the headlight on while traveling through a tunnel without needing to disconnect a USB device from the USB connector.
Ni-MH batteries regulate both voltage and current providing safe filtered power for any device plugged into the USB connector. The batteries must be solder tab types with no possibility of loose connections.
Recharging: If the circuit batteries become discharged they may be rapid recharged at full current from the dynamo. Simply disconnect any Devices connected to the USB connector. Youíll need to calculate how much time is required to recharge your batteries. This information should be available on the battery package. If using typical AA rechargeable batteries you will need to recharge them about 3 hours at 500mA. The chances of you being able to maintain speed with no stops are very low. Trying to keep up with recharging time is also hard to do even with a watch. Just let your cycle computer take care of that for you using the trip time function. It stops and starts timing as you stop and start cycling. Just reset the trip time and stop rapid recharging with the trip time reaches 3 hours or your batteries require. Recharging most USB devices is very easy as most have a battery level meter. Simply unplug it from the USB connector and check the level.
Some of you will note the absence of a taillight. Considering how cheap blinkies are and batteries run for 200+ hours I simply did not feel the need to try and power one along with the headlight.
Here is a photo of my headlight.
This one is made from Bamboo