High Power LED Bike Head Light With Integrated Heat Sink

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Introduction: 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.

Step 1: Bill of Materials

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

Step 2: Solder the Body

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.

Step 3: Cut Front Lens Space

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.

Step 4: Form the Electronics Compartment

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.

Step 5: Install Mounting Bracket

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.

Step 6: Install the LED

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.

Step 7: Install the Lens and Electronics

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.

Step 8: Rig It Up and Get on the Road

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.

Step 9: Test Shots

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.

Step 10: Updated Design

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.

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    158 Discussions

    You might want to add some kind of heat-sink, It will cool off easily with the wind

    1 reply

    The whole assembly is the heat sink, hence the copper. Works great.

    You might want to add some kind of heat-sink, It will cool off easily with the wind

    Hi, I am building a battery powered LED torch with 4X1.2V 1200mA batteries, and 3X3W LEDs I am trying hard to find a driver which could do the job of connecting them together

    the LEDs I have are,
    LED, HIGH POWER, 5000K, 70CRI, 275LM
    Series: LUXEON TX
    LED Colour: White
    Luminous Flux @ Test: 369lm
    Forward Current @ Test: 1A
    Forward Current If Max: 1.2A
    Forward Voltage @ Test: 2.86V.

    could you please help me what should be the specifications of the driver??

    3 replies

    First, I'd recommend looking at the latest Instructable I've done on these bike lights:

    https://www.instructables.com/id/Improved-high-powe...

    Based on your parts, you will have a 4.8V battery pack, and with 3 LEDs in series a forward voltage of 3x2.86@1A = Vf = 8.58. This means you need a boost type driver capable of outputting your desired drive current. Here is a boost type driver that may work, it is only rated down to 5V input so you might want to increase your pack size to 5 batteries and 6V. With 4.8V and 1200mAh you only have 5.8Wh which means that at the 800mA drive current of the linked driver you will only get about 45 minutes of run time assuming the driver won't drop out of regulation at 4.8V input.

    Many thanks for the info

    and I have made a mistake the batteries are 2100 mAh (not 1200 mAh)

    would you still think i should include more batteries??

    The runtime will be better with the 2100mAh, but the voltage is still low for the driver I linked to. If you can find a driver that will work, go for it as is. You are looking for a boost type driver which are typically made for flashlights. There are many out there on dx.com but the array is bewildering and I don't have the time to find one for you. Good luck.

    check it out..... I used an Epoxy mold that allows for side lighting... or 180 degrees of light.
    https://www.instructables.com/id/Bike-Light-2011/

    Hi Jon, I finished the Housing....just have to add thee electronics now :-) Thought you might like to see pictures..... More pictures to come when it's all together. Thanks again for all the help. -Mike

    Light1.jpgLight2.jpg
    5 replies

    Wow, looks nice. I wonder if there is enough material and surface to adequately cool the LED. I would consider reducing the drive current from 800mA to around 500mA by changing out the resistor on the board. No way to know for sure until you try it and see how hot the housing gets. I know that mine gets really hot (barely can hold your hand on it) at 700mA if you are standing still but does OK when riding and is getting some convective cooling. Yours looks like it has more thermal mass to it, but similar surface area. Let us know how it goes. -Jon

    Hi Jon, I just figured I'd post an update on my light. I've been running it for about 9 months now with no problems at all. It's been completely reliable so far. I get at least 2 hrs of light with a full charge out of it and have yet to run it dry. As far as the heat is concerned.... The extra thermal mass seems to make a huge difference for my light. It barely get's hot at all! Just slightly warm. If you remember, I'm only using 2 of the 3 LED's on the board. because of my battery selection I did not have enough voltage to drive all 3 LED's. (7.2 V 3300 MAh Nimh) That being said, I am running them dangerously close to 1000 mA so they are pushing a lot of light. so far so good (knock on wood) Regarding the optics, I also think the beam is a little too wide for my trail riding. on the other hand my buddy has a light that is too narrow. I definitely need something in the middle of the two. Well, I was googling for new optics since LED supply had no new offerings and I came across this: http://www.luxeonstar.com/Carclo-18-Deg-Tri-Lens-With-Holder-p/10507.htm At 18 deg, I think it may just be the sweet spot I'm looking for. I ordered 2 and will let you know how it goes. -Mike

    never mind on the 18 degree lens. It will ONLY fit on the the luxeonstar boards. you will have to purchase their 3-up board in order to use that lens. it does not fit on the LED supply board. different LED spacing :-(

    Glad to hear that everything continues to work well. Thanks for the tip on the optics, I have been looking at doing a Cree XPG star based light that will have a 16.4 degree optic. I agree that for trail riding the rebel 3-up optic that LED supply sells is too wide, but for city riding and visibility it is great. Keep up the good work. -Jon

    Thanks, I thought about machining some fins into it but didn't have the time. I guess I could still groove it if I need to. or attach a heatsink to the top. I also added screws to hold down the Star so I don't have to pot it just in case I burn it out and need to swap it. I am going to put some heatsink grease under it to help with the thermal transfer. Which resister would I need to change?

    I've made this and I like it.  Easy to make and use.  Very simple mounting.  The only thing I did not like was the light itself.  Not knowing I got the one you suggested and it just does not do it for me as far as a good beam.  I will be making another to be helmet mounted using this led.
    http://ledsupply.com/creexpg-w417.php
    When I talked to a person at LED supply, he told me this was their latest and greatest and has a few different selections for optics.  I've done a dual mount side by side using these and they are very good.  Using your design I've also done side by side tubes Bike mounted I call my Double Barrels using these
    http://ledsupply.com/luxeon-leds.php
    I like these also because of the selction of optics I get a better beam.  Thanks for your design and I look forward to making more
    One other thing I did was to mount my Buck puck on the battery housing which sits in a top tube bag near the handle bars.  No reason for that except not confident enough to square out the end of the tube.  CS

    1 reply

    I've been working on a design with the CREE XPG, it looks like a great LED way better (30% or more) than the Rebels.  The optics choices for the XPG star are also great as you discovered.  The XPG and optics are a little smaller than the Rebel stars and will make centering and sealing a little trickier, but worth the upgrade.

    Thanks for trying these out and check out my newer design (still about 9 months old) below for a cleaner looking housing. 

    https://www.instructables.com/id/Improved-high-power-LED-bike-head-light-with-integ/

    Good detailed instructable.
    IMHO the soldering processes are a bit difficult & I suspect the junction temp may be right on the limit ,although even if it should cut the life by 80%, I suppose that's no matter really.
    Problem as always is getting a conducting medium to get the heat away & I am not keen on conducting epoxy.
    I wish you could hurry the update, I bet you have some real improvements to show us.

    1 reply

    Barring getting the Rebel LED chips and building your own heat sink and PCB combo, the star boards are the only game in town.  Do you have any ideas?  I've got no data to show that the LED junction temp is too hot, and have seen no failures.  That said, the light has less than 1000 hours on it.

    If you look at the thermal conductivity of stuff that you could realistically put between the PCB/star and the heat sink there is not a product out there that is better than a conductive epoxy.  Conductive epoxies contain conductive particles, and outside of Aluminum Nitride and diamond, the best thermal conductors are all electrically conductive.  The difference between a thermal and conductive epoxy is the amount of solid filler.  The electrically conductive epoxy is loaded past the so-called percolation threshold and therefore has reduced resistance (both electrical and thermal).  The advantage of the isolated backplane of the star board is that you can use a conductive epoxy which has a higher solids content and therefore higher thermal conductivity.

    BTW, the new doc is up.