After purchasing a cheap Schwinn dynamo light kit I found the head and taillights to be of poor quality with the taillight bulb blowing only after 2 hours of use. You can't use the headlight without the taillight as that will cause an over voltage condition thus blowing out that bulb quickly. I ride after dark a lot so I thought the dynamo lighting system would save mounting costs for AA batteries for my Mag-Lite 3-watt LED flashlight. After looking for dynamo light systems on the Internet I discovered this link.
http://www.pilom.com/BicycleElectron...moCircuits.htm
After looking at the designs I thought there was too much complication involved in trying to use an unregulated AC power source with voltage and current sensitive LED's like the Luxeon 1 and 3-watt LED's. I thought it would be much better to feed the LED lights with a regulated power supply. Granted, using a regulated power supply is not going to be as efficient as the circuits shown but I did not want to burn out my LED's while miles from home in the dark. My main purpose was to build a robust and reliable power supply using the Schwinn bottle dynamo. I consequently designed and tested such a system.
I wanted the components to be easy to obtain and cheap. I consequently chose the 317-voltage regulator circuit. This adjustable voltage regulator has been around for many years and is still being used in consumer products. Everything for the circuit can be purchased in a Radio Shack store. Here is the circuit diagram.
I had a Mag-Lite 3-watt flashlight so that's what I wanted to use. It uses 2 AA batteries so the voltage regulator needs to prevent the voltage from exceeding about 3 volts DC. A combination of 220 and 330-ohm resistors provides a regulated 3.1 VDC no load output, which is close enough. A voltage reading of 2.5 VDC with the Mag-Lite flashlight loading the circuit is just fine. I drilled a small hole in the flashlight battery cap and used a section of fiberglass tent pole from a cheap tent to fabricate something to replace the batteries. Medical tape is used to hold it centered in the battery compartment.
Testing was performed on a bicycle with 700c wheels. I performed the test by getting out and doing a 30-mile run on an MUP (multi use path). The flashlight will start illuminating at 3 MPH pushing the bike but will not provide enough light to see where you're walking; oncoming traffic will be able to see the light. At 5 MPH riding on the bike the flashlight is providing the same amount of light as batteries that are near the end of their charge. At 8 MPH the flashlight is providing its maximum light output and is the same as fresh batteries. No problems were encountered with the flashlight, dynamo, or circuit.
This circuit will operate with hub dynamos as well, as the flashlight retains its on/off switch so no external switch is required. Here is a photo of the installed dynamo powered flashlight.
Note the use of an amber blinkie up front and a red blinkie is used as a taillight as well. Considering they run for 200+ hours on 2 AAA batteries each and don’t turn off when you must stop the bicycle it’s a safety feature you really need instead of depending on dynamo powered lights that quit when you stop.
The flashlight must be insulated and cannot short to the bicycle frame as this would short out the power supply. The reason for this is the dynamo is grounded to the frame so half the AC power provided from the dynamo is on the frame of the bicycle. All you need do it use a plastic clamp between the flashlight and handlebar solving that problem.