Electronics, Lighting, & Gadgets - Ultra cheap Dynamo LED headlight project.

Let me start out explaining the reasoning for this project. I purchased a cheap dynamo light kit for $7.20 at Target. I didn't expect much and didn't get much! The bottle dynamo it's self is ok but the head and taillight were pretty much junk. I ran it as is out of the package for about 2 hours before blowing the taillight and if I had kept on going without switching to my backup flashlight the headlight bulb would have burned out soon after. I called the LBS and replacement bulbs were $5 each! I would have spent more on replacement bulbs plus spares to carry than I really wanted to. I thought about it and decided to experiment a little. I had a $1 store flashlight utilizing LED's. I scrounged up a bridge rectifier rated at 100 volts and 1500mA, 16 Volt 100uF electricrolitc capacitor, 7805 5-volt regulator, 20-ohm resistor, and a terminal strip. I proceeded to assemble and solder everything together to make an unregulated AC to regulated DC power supply. I hooked it up and checked it for proper operation. I was guessing the LED's in the flashlight were standard high brightness types and would like to have 3.6 volts by 20mA run through them. I hooked up my voltmeter and read 3.55 volts on the LED's no mater how fast I turned the crank. It did not take much wheel speed to get the LED's to illuminate fully. I subsequently put it all together and affixed it to the bike for a nighttime run. I did 30 miles in slightly less than 3 hours with no problems from the dynamo or home brew LED headlight. I was thrilled! The modified LED flashlight is slightly brighter than the headlight supplied with its 6 volt 2.4 watt bulb at full brightness. This required a speed of at least 12 MPH. The LED headlight attains full brightness at 4 MPH! I can even push the bike while walking and get enough light to see with the LED light. I can't tell you what speed as I was going as I was pushing the bike up a steep hill and the Cyclocomputer would not even register that speed. Needless to say I was stoked! Granted, the light produced is nothing like that available from battery powered lights but it's enough to safely navigate a very dark MUP without resorting to the backup flashlight and consuming it's batteries. I'm planning on upgrading to a 1-watt LED headlight that should produce much more light than the $1 store flashlight. I'll also be using much more efficient electronic parts for the next dynamo to LED power supply. I expect the new light to draw more power from the dynamo and so more speed to start producing light, but it will produce much more light than what I am getting now.

Here is a photo of the electronics and flashlight with its "guts" showing.
http://i143.photobucket.com/albums/r154/n4zou/guts.jpg
And here is the assembled and ready to roll photo.
http://i143.photobucket.com/albums/r154/n4zou/assembeled.jpg

I'll be using the information at this link to build my 1-Watt LED headlight.
http://www.pilom.com/BicycleElectronics/DynamoCircuits.htm

Another thing to try: you can now buy replacement bulbs for flashlights made of superbright LEDS. Some of the older, earlier headlights for bikes are fine candidates for bulb replacements.