High Power LED Bike Head Light With Integrated Heat Sink

For those of us traveling by non-motorized conveyance (bicycle e.g.), visibility is important in both forenoon and post-twilight conditions. The best way to ensure such visibility is through the use of excessively bright lights, of which the latest light emitting diodes (LEDs) are the acme. The following account will detail the process of building an LED based head-light capable of of more than 500 lumens of output using about 6W of electrical power. For comparison, this is the same output as a typical 45W halogen bulb.

The high powered LEDs used for this Instructable are very efficient, putting out 80-90 lumens per watt, compared to typical incandescent and halogen bulbs. However, they still generate a lot of heat and the lifetime of the LED will be adversely affected by high junction temperatures. Therefore we want to get the heat away from the LED through ensuring good thermal contact with the LED board, high thermal conductivity in all materials, and good coupling of the thermal energy to the surrounding medium (air). The LED star board used for this project has three LEDs on it and has a metallic backplane that is isolated from the LED electronics. This is a good thing. The rest of the LED head-light is built out of copper fittings from the local hardware or home improvement store. To complete the project you will need:

Parts:
Luxeon Rebel Endor star 3-up LED
Endor star lens
Buck Puck constant current LED driver
3/4" Copper Pipe Cap
1" to 3/4" Copper pipe reducer fitting
Waterproof connector of your choice (I use 2 position automobile trailer connectors)

Supplies:
Conductive epoxy (thermally or electrically)
JB Weld or similar high strength epoxy
RTV silicone or epoxy for waterproofing
Silver solder and flux
emory paper for cleaning copper

Tools:
hacksaw
drill and bits
file
propane blowtorch
vice
hammer
sandpaper

The first step is to cut most of the 3/4" section off of the reducer fitting. In the BOM picture you can see that I started this cut before took the picture. In the picture below you can see the completed cut next to the 3/4" cap. The most important thing is to make sure that the surface is flat and square so that the cap can be soldered on with a watertight joint.

Once you have the cut flat (test fit the cap a few times until you have it right) use the emery cloth to sand the surfaces that will come in contact with solder. This includes the area on the reducer around the cut you made and the back portion of the cap. Sand them until they are bright, no need for too much effort.

With the pieces clean, place them together into a vice to hold them during soldering. Make sure there are no flamable materials around, and try not to do this job in sandals. Don't ask, just trust me. With the pieces in the vice, apply paste flux around the joint and the fire up your torch. You can see in the pic the parts in the vice, sanded and fluxed and ready to solder. Make sure everything is square and straight before soldering.

The trick to soldering copper pipe is to apply heat away from the joint and wait until the metal is hot enough at the solder joint for the solder to flow into the joint. Or so I have been told. I am no good at soldering pipe, and this piece is too short anyway, so go ahead and blast the part around the joint. Once the metal is hot enough, remove the torch and quickly apply the solder to the joint and let it flow. If you don't apply enough heat, or the joint is too dirty, or the flux is all burned off, or the gap in the joint too big, the solder will not flow and coat and fill everything. Keep trying.

Eventually you should get something like the pictured joint.

I find that often I add so much solder to get it to fill the joint that I end up with a thick drip of solid solder on the bottom of the joint. Go ahead and file this down if so desired.

We also need to cut the front cap shorter to match the lens height. Using the lens as a guide, cut the front 3/4" cap to size as shown. File the cut flat and square and test fit the lens. The lens should sit flat on the inside face of the cap and have some amount of the copper cap sitting proud of it as a lip to protect the lens from impact and scratches. See pics.

If you noticed, the Buck Puck is square and too big to fit in the 1" diameter section of the body. Never fear. The trick here is to form the back section so that the electronics just fit inside. I used a small chunk of aluminum held in a vice as a form (see pic) and pounded the rear section square with a hammer. Take your time and test fit the Buck Puck occasionally. Once you have the fit, go on to the next step.

If this is to be used on a bike, then we need a method of mounting to the handlebars or similar. I prefer the o-ring method used by cyclo-computers, and that is what I will present here. I used the section of 3/4" copper pipe that I cut off of the reducer to make a band for mounting the light. To do so, I cut the ring, bent it out, formed the ends in the vice to turn upwards and hold the o-ring and then filed some notches to help hold the o-ring in place. It makes more sense when you see the whole thing mounted in the last step.

To attach the bracket, I of course soldered it on. To make this easy, I drilled and filed out a square in the middle of the strap to allow a good solder joint between the bracket and the body. I added some other holes for reduced weight. Oh and they surely function as much needed speed holes.

Be sure to clean the copper before soldering, and hold the two body pieces in the vice like we did on the first soldering step. If you don't and the body gets too hot then the solder joint holding the whole thing together will melt and the whole thing will fall apart. Which would suck. Holding the bracket in place while soldering is a challenge. I used a pair of pliers to hold the bracket while I heated everything up, set down the torch, and picked up the solder and started applying it while holding the bracket in place as best I could. Once the solder melted and wetted everything, I carefully let go of the bracket and let the solder solidify. There must be an easier way, I leave that exercise to the student.

With the lens and LED compartment cut to size and the bracket mounted, test fit the LED. Using a fine pen, mark two spots in the Endor star cutouts. You will drill holes here to allow the wires to come through from the electronics compartment. Keep the holes small to make them easy to seal after the wires are through and the LED mounted.

Note: There are six cutouts on the star, three of which need to be clear for the legs of the lens to sit in. When drilling holes for the wires, you need to pick two cutouts that are not next to each other, leaving a cutout between them for the lens legs. I did not do this, as you can see in the pics and had to drill three holes total.

Once you are satisfied with the holes, feed the appropriate wires up from the Buck Puck and electronics compartment and solder them to their corresponding pads on the Endor star. Try to keep the height of the wires low so that the lens will sit correctly, and be sure that the pads are not bridge or the wires shorted to anything, including the back metal of the Endor star. See pic.

With the wires soldered on, test the system by applying power to the Buck Puck briefly. Don't run the LED long or it will be damaged since it is isn't on a heat sink. If everything is 5 by 5, then mix up some of your conductive epoxy and epoxy the LED in place at the back of the compartment as shown. If you are using electrically conductive epoxy (higher thermal conductivity) be sure to keep the epoxy away from the top of the Endor star and the exposed wires and pads. Let the epoxy set overnight. While it is curing, you want to keep pressure on the LED star so that it stays as tight to the metal underneath as possible to improve thermal transfer. I used a rolled strip of cardboard in contact with the star outside of the LEDs and applied pressure with some rubber bands. Try not to touch or scratch the LEDs lens domes as this will impact their performance significantly due to increased internal reflection and thus heat buildup and junction temperature.

Once the LED epoxy has cured, epoxy the holes you drilled in the back of the copper cap with JB Weld or similar. Make sure they are well sealed. With the same epoxy, dab some in the cutouts on the front side LED star to hold the legs of the lens. Don't put in too much or it may squeeze out and get on the LEDs or lens. With the epoxy in place, insert the lens. Using masking tape or similar hold the lens tight and flat to the back of the LED housing while the epoxy cures.

Once the lens and wire sealing epoxy is cured we can install the electronics. Coil the extra wire as needed and check your fit. Using silicone RTV (room temperature vulcanizing) sealant or caulk or even epoxy fill the gaps around the Buck Puck in the compartment so that the electronics are both held in place and the cavity made water tight.

One thing, the RTV produces acetic acid during cure (the distinctive smell of curing silicone caulk) which etches copper and can impact the adhesion of the sealant to the copper. Epoxy is a better but messier choice. I went with RTV since I didn't think I was going to use this underwater and because the epoxy would be a permanent, irreversible step.

Similarly, caulk or seal or epoxy around the top edge of the lens to seal the LED side from the elements. I used a silicone RTV again, and if it fails will go to a liquid nails type adhesive/sealant. Be careful to keep whatever you use off of the lens face.

With everything sealed up and glued in place, solder and shrink wrap on your preferred connector on to the power wires for the Buck Puck. Then glue on a strip of rubber or foam on the bottom curved portion of the bracket to protect the paint on your ride and to improve the grip of the light on the handlebars. The benefit of the o-ring mounting style is that you can quickly remove your light when you park it in theft-able areas. The limitation of the o-ring mounting style is that it isn't very rigid. Thus if the ride is really rough or the o-ring too loose the light can shift around. If you find that to be the case, you can use zip ties to put it on more permanently or modify the bracket to have a screw and clamp. See pic below for my mounting method. The world is your oyster.

Possible future improvements:
1. Add a magnetic reed switch inside the electronics cavity to allow water-tight on-off function. My bike electrical wiring harness has its own built in waterproof switches for the various functions so I left a switch out of this design, you can modify as needed.

2. Use a buck puck with dimming and external control to add a flashing and dimming mode. There is plenty of room in the electronics cavity for a small PCB to switch and dim the light. I figure with 500 lumens, no flashing is needed. Besides, I have a xenon flasher on the back that is plenty adequate.

3. More cooling surface area. I have found that the whole copper body gets pretty hot under continuous 700mA operation when not moving through the air on a ride. I would estimate it gets in the neighborhood of 120F, which is hot but not burning you hot. This means that the LED junction temperature is much hotter, but since Ihave not seen noticeable light output dropoff I don't think the junction temperature is too high. In order to improve this, I would fold some thin copper strips and solder them to the outside of the body before adding the LED and electronics.

This step just shows some various comparison tests for light output and beam pattern. The first set is in my basement, with the camera set on a fixed 1 second shutter time and distance to the far wall of 25 feet. The first photo is the scene illuminated by a bare 60W incandescent bulb in the ceiling. The second shows the same scene illuminated only by a 10W narrow (15 degree) spot halogen bicycle light that I built. The final pic is of the scene illuminated only be the LED bike light detailed in this instructable. It is clear that the output of the LED light is much greater. However the ability of the LED to put light in a specific spot is not clear. The optics need some work if a spot type light is desired. I plan on taking some outdoor beam shots when the weather is a little more cooperative. Stay tuned.

DATELINE MARCH 29, 2010, 11:40PM CDT:    I've made some significant changes and improvements to the design in the past year or so.  See the attached pics for a sneak peak.  I am working on a writeup for a companion instructable that details the new design.  Stay tuned.

DATELINE APRIL 12, 2010, 11:40PM CDT:    The new writeup is completed and posted.