Let me start with this: I love biking at night. Everything from the empty streets to the cool air keep me biking into the night. But my quick setup of a LED flashlight pipe-clamped to my stem was not cutting it. I needed more power. I needed a true headlight.
And so was born my second LED lighting project. It totaled about $150 after several trips to the hardware store and a custom water bottle battery pack. 1300 lumens is about the total output of the LED star, the actual output through the lens will be about 10% lower. It is still comparable to both of my car's headlights combined and, even when under-driven, is plenty bright for any biking needs.
Fun Feature - The b2flex board is capable of flashing the LED in a strobe pattern at full strength with an effect similar to a police dazzler. NOT recommended for biking. Blinding muggers and spontaneous rave parties, maybe.
CREE XPG R5 3-up star
3-up Carlco Optics
Arctic Alumina Adhesive (Note: Needs to be the ADHESIVE)
CPU Heatsink I choose this on based on size and a radial design for looks, Personal Choice.
B2Flex LED driver To save money one could use a buckpuck from LEDSupply, I wanted the extra features.
2.5mm Plug (I reused some broken headset cords)
Off-mom-on button: Any will work as long as you can easily push it.
Any 3mm or 5mm LED, low power.
Handlebar Mount Be sure to measure your own handlebars to get the right size.
Lexan - At least 3x3 Square, any thickness
1 inch PVC slip plug
Aluminum bar -at least 1" wide, 1/8" thick
-4 10-36 thread 1 1/2" machine screws with fitting locknuts and washers
-4 small machine screws, max 3/8" long
-A 1 1/2" x 1/4" machine bolt, hex head with matching nut.
1x Female Tamiya Connector
1x Male Tamiya Connector
14.4v Battery Pack The size is only dependent on budget.
Double-Conductor Cable: I used a old lamp cord
Cheap Water Bottle- Bigger than battery pack
Optional - 3" heatshrink
The battery pack is only NiMH due to the cost of starting a lithium setup from scratch. If you have a 4-cell charger, a lithium pack would be the cheaper (and lighter) route.
Step 1: The Driver enclosure
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The driver, the b2flex driver, really is a cool little bit of engineering. Sporting a micro controller, the driver has several sets of configurations for applications like automotive, cycling, camping, and general use. I am in no way affiliated with TaskLED, the driver is just a huge step above the standard buck constant current drivers. But with the added features comes added complexity which I've addressed to varying extents.
First, the mounting holes for the board and holes for wires were drilled out. I then used machine screws and nuts to clamp the board down. Nylon screws and nuts should have been used but it is what I had on hand. No matter what method you use, be careful on how tight you secure the board. The Inductor on the back is brittle and cracked when I tightened down on it.
The interface holes include LED power, the 2.5mm jack, status LED, and battery connection. Sizes will of course vary depending on what cabling and status LED you use. An 1/8" drill will get you pretty far though. To keep wires short, I soldered connecting wires after the board and components were mounted.
To follow my order, install both the 2.5mm jack and the status LEDs without the board installed. Hotglue works for the LED and the jack should be panel mount i.e. clamp right to the enclosure. I had to use a scrap jack and JB weld it in.
Next begin to install the battery connector and the LED leads. For all board soldering, a flux pen is essential. Use a pencil tip iron and carefully begin to add the connections to the board. Connections should be labeled and easy to figure out; consult the b2flex manual if you are confused.
A final bit of hot glue for the battery and LED leads for strain relief finishes the enclosure. Two holes in the corners opposite the closure screws will be used to mount the enclosure to the heatsink.
Step 2: The Heatsink and LED Assembly
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Because of the LED exceeding 10W, a major heatsink is used to keep the LED as cool as possible. A radial CPU heatsink was used for its cost and attractive look. I wanted to keep a radial style to the whole light and this one fit the bill perfectly. Any CPU heatsink should be enough but even mine became toasty after a while.
First, the heatsink went through some prep work. The thermal paste was scrapped off and cleaned with rubbing alcohol. I decided to go a step further and polish the part of the heatsink I will mount the LED to. While there are arguments for and against polishing (aka lapping) I felt the finish was terrible on the heatsink and some time spent with 400 and 800 grit sandpaper yielded a better surface. Using the 'wrong' side of the heatsink didn't help the finish either.
Carefully solder on the LED leads from the driver enclosure. Higher temps can be used, the star will try to dissipate the heat quickly and possible damage the LEDs. Don't get frustrated and let the star cool off between joints.
Clean both the top of the heatsink and the bottom of the LED star with rubbing alcohol. Then mix together a small amount of the thermal adhesive. Apply a small amount to the center of the heatsink and press the LED star in place, trying to center the best you can. The lens should then follow shortly after, pushing down as far as possible. Some sort of clamping method must then be used such as weights. While a junk bin is one option, it is best to look for books or some other weight that is less... volatile. Consult the Alumina adhesive manual for detailed (and slightly snarky) instructions.
At this time, use the excess thermal adhesive you just mixed to attach a piece of scrap aluminum to the gold square on the b2flex board as a heatsink. To create a larger mass, cut a square with a small tab on one side and fold the tab over onto the face of the square. This impromptu heatsink is necessary to drive the led at the full 1500ma for any length of time. Place a small dab of the adhesive on the gold square and press the tab of the heatsink onto this. Because a heatsink this size is a little more than needed, a stable connection is all that is necessary. Don't worry about clamping too much. Just make sure the heatsink is not touching any exposed contacts of the driver board.
After an hour, the weights can be removed and tested with a voltage source between 14 and 25v. Don't worry, the light should be dim unless you have already messed with the current set point. Default is 350ma, severely under-driving the LED star. This will be greatly remedied after construction.
Step 3: The Battery
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As I said before, a lithium setup would be much better for this application. But without the money for specialty chargers, I really had no choice but to use NiMH. If you have a lithium setup already, the b2flex driver features voltage warning and cut-off set points to protect lithium packs. If interested, consult the b2flex manual.
The battery I used was a Tenergy 14.4v NiMH battery. The closer the battery is to the drive voltage of the LED star + 1.7v, the more efficient the driver will be. No guideline is given by TaskLED for 3 LEDs, so assume more than a 1.7v margin. In picking your own battery, just stay away from NiCd batteries. They are not suited vary well for this project.
First, I enclosed the battery in 3" heatshrink. This is optional and slightly over-kill, I just had the heatshrink left over from a laptop battery project. Other coverings include glass-reinforced tape and even duct tape if you do not care to get this battery back. Wire was then added to the existing leads to extend it, I added about 4 feet of scrap lamp cord that I marked the ground conductor on.
The enclosure was made of a cheap sports bottle from my local bike store. A constriction in the middle was cut out leaving the body and top. Foam padding was cut and inserted around and at the bottom of the bottle and the battery was fitted inside. The tip of the bottle was drilled out and the cord was fed through. A knot in the cord adds strain relief and silicone was added to provide some water-resistance. The top and bottom were simply glued together with silicone, pop-rivets or some mechanical fastener would be much safer.
Last, the male connector was soldered to the end of the lamp cord, completing the battery pack.
Step 4: The Mount
Aluminum bar stock was used to make a simple bracket to which the heatsink and driver enclosure is mounted to. The stock is 1"x1/8" aluminum, available from Lowes. My first attempt at measuring, cutting, and bending resulted in far too small of dimensions. Your results may vary but I ended up bending and cutting as I went, starting from the center and working out. Cut a 12" section to start out with and mark the center. I then centered the driver enclosure an this, angling it diagonal to the bar (see the photo). The mounting holes drilled earlier were then transfered to the bar stock and drilled.
Follow the diagram to mark and make the bends. Think ahead and keep in mind the layout of your vise, make sure you can clamp where you need to for each bend. To make a bend, clamp the bar stock firmly in a vice so that the bend point is where the top of the vice jaws meet the bar stock. Then hammer the bar stock in the direction of the bend until a tight, 90 degree angle bend is formed. Repeat for all bends.
Unless you are some blacksmithing wizard, the sides will not end up exactly where you want. As long as the driver fits and the ends make a gap around 3/4" of an inch, the bracket will do. Trim the end so that they match up and are about 5/8" long. Next drill the 1/4" hole on each end for the mounting bolt
Now to mount the driver to the heatsink. Pass 2 small machine bolts and washers (i believe 10-36 and 1 1/2" long, cut to size) between the heatsink's fins on opposite sides into the holes drilled in the bracket. Put the driver in place and pass the threads through the mounting holes drilled in the enclosure. Using locking nuts, tighten the bolts until everything is snug. Replace the cover on the enclosure.
Step 5: LED enclosure
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As this light will be used on a bicycle in adverse conditions, a cover for the LEDs and lens is recommended. A 3/4" PVC pipe cap fits the LED star and lens nicely. A small machine lathe would clean up this step considerably but if that applies to you, you most likely would know how to adapt the instructions yourself.
Drill a 3/4" hole in the center of the cap and sand the fitting until the total depth is the same as the height of the lens and LED star. Next, cut a small notch in the bottom with a knife to fit the leads to the LED star. Do a test fit and sand to make sure the whole thing fits.
Next, place a small square of lexan over the fitting and drill 4 small holes, screwing in small machine screws as you go. Try for a square arrangement if possible and measure it out if it concerns you enough. Once finished, sand down the lexan to fit the profile of the fitting. Remove the lexan plate and add a very small bead of clear silicone around the edge of the fitting. Screw the plate back on, taking care to incrementally tighten the screws so that the silicon spreads evenly around the fitting. Remove any excess and place over the LED lens. I later clamped this cover to the heatsink using the same bolt and washer method used for mounting the heatsink to the bracket.
Step 6: The Remote
The remote is still the weak point of this build only because of money constraints. Pressure-activated switches are used on laser sights for firearms and would work perfectly with a 2.5mm plug soldered on the end. Else, any momentary switch will do as long as you can comfortable mount it and use it. I hid the small switch I ended up using under the rubber hood on my brake/shifter. Firm pressure to the area activates the switch fairly reliably without too much change to my grip on the handlebars.
Of course this step can be skipped by mounting a switch to the enclosure and cutting out the 2.5mm jack. If that works for your riding style (maybe mountain bikes) I would recommend skipping the external remote.
Step 7: Mounting it to the Bike and Setting the B2flex
To mount the light assembly to your bike, first clear a small place on your handlebars for the universal clamp. Then screw down and tighten the clamp until very snug. A turn or two of electrical tape on the handlebar can increase friction a bit more if it is a problem. Feed the 1/4" bolt through the top of the bracket, a washer, the universal mount, another washer, and then the bottom of the bracket. Tighten the nut until the light becomes difficult to swivel. A locknut can be used if you do not plan on taking the light on and off. I later made a hand-held mount for the light so I stuck with a standard nut.
Programming the b2flex is pretty simple so long as you have a reliable remote. My setup ended up with the following:
-1500ma Drive current
-UIB2 with Trimode
-L1 at 500ma
-L2 at 1200ma
-L3 at 1500ma
I really recommend you to read through the manual and pick out your own settings. There is a huge amount of flexibility to fit whatever needs you have.
Step 8: The Conclusion
So that is my 1300 lumen bike light. There are many things you can do to make it you own and even better. Most of all, it desperately needs a cutoff shield so you are not blinding car drivers. But beyond that, enjoy your LED bike light much brighter and cheaper than most bike-specific lights. If replaceable lenses are important, the LED cover could easily function as a lens holder as long as no adhesive is allowed to fill the alignment holes in the LED star.
Have fun, be safe, and enjoy the night.