Intro: Improved High Power LED Bike Head Light With Integrated Heat Sink
After scouring the globe for the right parts, the following is an updated version of my copper fitting based LED bike head light. See the original high power LED bike head light with integrated heat sink instructable for the details on the earlier version. The latest incarnation uses a cheaper and more full featured driver circuit, an in-line waterproof switch, a waterproof connector, a more elegant mounting solution, a more robust and waterproof enclosure, and gets your whites their brightest.
Step 1: Materials
The bill of materials for this light is more extensive than previous incarnations, but the result is an improved piece of kit.
1x ~1.25" long section of 3/4" copper pipe
1x ~1" long section of 3/4" copper pipe coupling
2x 3/4" pipe cap
1x ~4" section of 12GA solid copper wire
Gear for silver soldering
1x Cable with Trail Tech connector
1x Waterproof cable gland
1x 3-mode boost constant current driver
1x 2 Ohm resistor in 1206 or 805 surface mount size
1x LiFePo 6.4V battery pack
Misc wire for connecting driver to LED
Gear for electronic soldering
1x Rebel Endor star 3-up or 1x Cree XPG Indus star 3-up
1x Lens for Endor 3-up
1x 5/8" x 6" Velcro face strap
Step 2: Housing
Building the housing well is the key to a watertight and pleasantly distressed final product. Don't be afraid to drip solder, leave file marks, and otherwise individualize your light. Remember, bones heal, chicks dig scars, and the US of A has the highest doctor to daredevil ratio in the world. I don't know what that has to do with anything, but go nuts.
Similar to the last light project, you will need to trim down a pipe cap and drill holes in it to mount and wire the LED star. Leave a light shoulder on the pip cap protruding beyond the lens to protect it from damage, 2mm is fine.
The lengths of the 3/4" pipe and coupler section aren't critical. You'll need to have the smaller 3/4" pipe section stick out of the coupler enough to epoxy on the rear cap, about 1/4" is fine.
Take a section of bare 12GA solid copper wire and bend it up as shown in the photos using your hands, feet, and teeth or a handy pair of jewelers pliers. This wire will serve as the mount. Size it according to the handlebars on your application.
Test fit everything before soldering. Then deburr, sand, clean, and flux the LED pipe cap, the coupler section, the inner 3/4" pipe section, and the wire cleat. Use a clamp to hold the pipe cap and other tubes in place while you heat and solder. Balance the cleat on the top and solder it while the rest is still hot.
The back cap has to be the last to go on and can't be soldered since there are sensitive electronics on board at that point. You will want to drill a hole in the back pipe cap to hold the waterproof cable gland and trim the length of the pipe cap to match the amount of reveal you left on the 3/4" section of pipe. Depending on the size of the cable gland nut you might need to trim the nut or leave more pipe cap to get it to fit.
Step 3: Modify the Driver Circuit
The driver circuit I used for this light is much cheaper than the BuckPucks and has more features. The downside is that it is poorly made in China. Also, Chinese manufacturers have taken to sanding the identifying marks off of the IC's in their circuit boards from DX (I do not take your name in vain oh holy and almighty DX). I am not sure why they go to the trouble. I guess they figure that if they can whip up a knock off of the IC manufacturer's application example circuit from the datasheet then so can anyone else if they could just read the IC markings. But wait! They have cleverly sanded the markings off so you have to page through a few dozen datasheets to identify their circuit. They have obviously been to B-school and have heard the term "barrier to entry".
Ok, that is a long way of saying that I figured this out so you primitive screwheads don't have to. I mean, things with molecular structures and everything. The driver is based on the FP5138 (http://www.micro-bridge.com/data/Feeling-tech/FP5138_AN.pdf) boost driver.
The three modes on the driver are specified as 800mA on high, 200mA on low, and 400mA strobe. Since the "specs" on such products from DX are not very tight and seem to be in direct contradiction to the helpful formulas provided by the IC manufacturers, I went ahead and measured the currents myself. The measured currents are 1200mA on high, 250mA on low, and strobe just duty cycles high. Your mileage and circuit revision may vary. The currents are set via resistors which are difficult to reach and thus our task is to cut the two circular PCBs apart and swap the resistors and then solder the two boards back together. The smaller top PCB is the driver board, and the larger bottom one is the microcontroller that sets which resistor is being used via some transistors.
The resistor we are looking for was a stack of two in my boards, an 0.820 Ohm and a 4.7Ohm which gives 0.7 Ohms. This is the high resistor. The low resistor is a 2 ohm. I chose high to be 500mA and Low 250mA. This is to increase battery pack life and to cut down on thermal stress on the assy. To accomplish this, remove the 0.820 Ohm and 4.7 Ohm resistor stack and replace with a 2 Ohm resistor. See the picture. Solder the two boards back together and you are done.
Step 4: Put It All Together
Take the wires for the LED and solder them to the LED pads, thread them through the holes in the LED pipe cap and solder them to the driver circuit. You'll want to use a fairly thin wire so you can wind up the excess and insert it into the cavity. With the LED soldered up, use some jumpers to connect a battery to your driver circuit and briefly test to ensure that the LED lights as desired. To switch modes on the driver, you need to cycle the power. Make sure everything works before buttoning it all up.
With everything working, use the thermal epoxy to glue the LED to the bottom of the pipe cap. Be sure not to get the epoxy up onto the top pads since it is also electrically conductive. When that is cured, epoxy the lens in place on top of the LED star. Don't use the conductive epoxy in case it gets somewhere you don't want it. I use JB Weld in these cases. When the lens is cured in place, take some silicone sealant and seal the lip of the lens against the pipe cap to keep water from getting at the LED. Try not to get anything on the face of the lens, and if you do, wipe it up before it cures.
Mount the waterproof cable gland in the rear pipe cap, and thread the cable through the gland and tighten everything. The gland should come with an O-ring that seals against the housing, but if you lose this, use some silicone in there to seal it during assembly. Take the loose ends of the wires and solder them to the appropriate pads on the back of the driver circuit.
Next, take the driver circuit, wrap it in electrical tape and goop it up with silicone sealant and cram it into the housing. Let the silicone cure before gluing on the rear pipe cap. Now would be a good time for another system test prior to sealing. With everything functional, mix up some thermal epoxy and glue on the rear pipe cap, sealing your light forever.
To attach the velcro, measure your velcro strapping and cut to desired length. The idea is that one end of the velcro will be permanently attached to the light at the wire cleat and the other will wrap around the handlebars to the other section of wire cleat and loop back on itself to latch. Get everything ready and use some hot glue to fuse the end of the velcro around one end of the wire cleat. See pictures.
With your battery of choice (I chose a LiFePo battery as linked in the BOM) you are good to go.
Step 5: Final Thoughts
I hope the preceding has been helpful for those of you looking to build better lights than are commonly available on the market today. I'm in the process of adapting this design to the latest in high efficiency LEDs, which promise another 20% or so in performance. Good times. Feel free to contact me with questions or post to the discussion below.
I've also been approached by some folks who don't want to go to the trouble of building this light and wish they could buy one complete or failing that, a kit. Depending on the person and my bandwidth at the moment I have alternately obliged them or castigated them while buffeting them about the head. For those of you with similar ideas, feel free to contact me, although my prices are exorbitant.