This is an instructable to show how I converted a cheap headlamp from Harbor Freight Tools into a semi-powerful headlamp for my bicycle.
Originally I was using a flashlight I had mounted on the top of the handlebar but it was not providing enough illumination, and since it is now getting darker earlier in the day, I decided it was time to upgrade the light for safety purposes.
My primary goals were to increase my ability to see when riding in the darker parts of the day, become more visible to traffic, and of course, use whatever materials I have on hand and limit the cost of the project.
I began with a high power LED I had from a while ago, I believe it was a 3 watt but it could be a one watt as I purchased it long ago. I also decided to use an RC car battery I had mainly because it was the weaker of the two batteries for my RC car, it had an output of 7.2v at 5000mAh so it can last quite a while and it is rechargeable.
I grabbed an old headlamp I got from harbor freight tools more than 5 years ago for the housing and main unit.
Like my previous instructable, I prefer a lower profile look that compliments the bicycle and doesn't look cluttered and awkward. So I purchased a water bottle and cage that complimented the colors of my bicycle to house the battery. Plus when I decide to upgrade my rear flashing light in a future instructable, I will use the same water bottle to house all the electronics to keep things waterproof and maintain the sleek look of my bicycle.
Step 1: Step 1: Mounting the Headlamp on the Bicycle
You will notice wires coming out of the headlamp already because I started the project before deciding to do an instructable. I apologize but nothing to do but go forward anyways.
One thing I didn't like about having the flashlight mounted on the handlebars was the fact that the light projected was not in line with the bicycle, and while this may be a small issue, I would prefer a light that is projected in line with the center of the bike. This is why the headlamp was ideal.
I was able to mount it to the stem using a total of 4 zip ties and keeping in lined up in the center of the bicycle. This also has the added bonus of allowing me to adjust the angle of the beam weather I want it shining higher or lower very easily.
The back of the headlamp had a grippy foam padding that kept the unit secured to the stem/handlebar cross piece.
Once the headlamp was mounted, I removed the actual lamp part of it from the base that was mounted to the bicycle. It was held in by a bolt and nut.
Step 2: Step 2 : Removing Old Components
Like I said earlier, I started this before taking pictures so on this step use your imagination.
There was pretty much a tiny lamp in here connected to metal terminals and fastened with screws. I removed everything and I placed solder on the exposed metal terminals that led to the battery compartment. These points of contact will be later used to connect the LED to the circuit.
I proceeded to install wires to the points of contact. The green wire corresponds to the cathode (-) of the LED and the red wire will go to the anode (+).
These metal terminals came in handy because they allowed me to use the battery compartment for electronics without me having to run wires or drill any holes. It also was already wired with a pushbutton switch to open or close the negative terminal which would later be connected to the LED. It saved me from having to install a switch of my own.
Step 3: Step 3: Preparing for the LED
I cut a hole in the reflector to allow for the led to sit inside of it. I cut it with a small hobby saw (tiny hack saw) and carved away a semi consistent circle using an x-acto knife. You may notice the hole is too big but that is okay.
I proceeded to use the aluminum housing of a broken flashlight to create a heatsink for the LED. Weather it is necessary or not, I didn't want to risk damaging the LED because I was too lazy to put a heatsink on it. I simply cut the housing length wise with tin snips, flattened the piece and cut it down to a manageable size.
After the heatsink was cut, I attached it to the LED and reflector, and soldered the leads to the LED. Once that was done I closed the LED area up.
Step 4: Step 4: the Electronics...Sorta
I say electronics but what I mean is the resistor.
I tried making a complex LED driver with transistors but the truth was, I was unable to get my current output to be higher than 50mA, which was making a not very bright light. So I went simple and used a power resistor.
Normally I would order stuff from Mouser or Jameco but I didn't want to wait and I only needed one resistor, so I went a picked up one from RadioShack. I really don't like doing that because their components are marked up like 400% and I really don't want to support a practice like that but I did it because I didn't want to wait. I actually commute to work on my bike and the light needed to be done by the end of Sunday. So necessity forced my hand.
Since the pack came with two 10ohm resistors, I decided to wire them in parallel to give me a 5ohm resistance, however it proved to be too little resistance. It was putting out about 800mA of current which was wonderful because the light looked like it belonged to a semi-truck but it was putting out almost 4 watts of power which would destroy my LED. I ended up removing one of the resistors and went with the 10ohm resistance giving me 310mA which is still bright but its under the safety threshold on the LED.
I didn't take a picture of the single resistor wired to the insides so just use your imagination.
After the resistor was in place I was able to drill a hole to run the wiring that will go to the battery powering the lamp. I sealed it all up and called it good. The resistor fit nicely inside the battery compartment.
Step 5: Step 5: the Battery Connector + Wire Management
Now that the headlamp was pretty much done, I remounted it back on the base and began the process of attaching the battery connector to the headlamp wires.
I decided to make my hole in the lid of the water bottle because it would be the easiest to replace should I decide to use the water bottle as a water bottle in the future.
Once I made the hole, I pushed the headlamp leads through and soldered the wires to the battery connector. Then I fixed the power wires to the frame using a combination of black and clear zip ties.
Step 6: Step 6: Finishing Up
At this point everything was done and secured. The last thing to do was place the battery in the water bottle and power up my new bicycle headlamp.
It all worked and gives off a nice amount of light. much more than my previous light source and this one is rechargeable.
The last picture was taken at a distance of around 20 meters and although the camera cant pick up the illumination well, it is 10x better than what I had before + it is more visible.
I hope you enjoyed my project and thanks for looking.