Intro: Over 7000 Lumen Bike Light
This hack is for those that like night riding or want to get into it (it's great, never too many people and nice and cool) but think that those 300 lumen lights just don't cut it and don't have the cash for a 1000-2000 lumen lighting system (they can be like $500 - $1,000 dollars, yikes). Even with 1000 lumens, it's just not enough plus some of those systems out there can only last about 2 hours at max power.
There is hope though, with this slightly overdone bike light I built for my mountain bike. The light you see featured in these pictures I made myself and it has a max of 7,000 lumens on high with a battery life of 2.5 hours, while it can do 3000 lumen's on low power for over 6 hours. The light is made of 6 cree xml u2 LEDs mounted to a copper and aluminum heat-sink to keep its 60 watts nicely dissipated. To power this light I built a 150 watt-hours lithium polymer battery pack all in-closed in a extruded aluminum case. I built the case so it can easily attach to any standard water battle cage (you can see on my bike the water bottle cage just happens to be on the bottom of the frame, that's just how GT decided to do there full suspensions those years). The weight of the light and the battery and all the wires come out to just under 3.5 pounds (with the battery being the fatty at 2.9 pounds). I also hooked up a few other cool things like rear red lights and a power level indicator so you know when you have to charge it.
The charging is done with a lithium polymer balance charger for rc cars and helis that I bought just for the light (cost me 30 bucks on ebay). I ended up building the whole thing for about $150 (would only have been $100 if i would have built a battery pack half the size). For those who know high power LEDs have to be run at constant voltage and current to make them last (these are guaranteed to last 50,000 hours). So I have 3 parallel dc-dc converters with a 93 percent efficiency regulating them to put out 20 watts, 40 watts or full power of 60 watts to make just over 7000 lumen's of light, but the lenses I used are 92 percent efficient and I am getting about 6600 usable lumens.
To put this in comparison a standard headlight of a car gives 1000lm while a D2S Xenon metal halide arc head light you can buy gives you about 3000lm (so double that and that is what I hit the trails with). I can't imagine much more power being useful or very easily created (running this amount of power gives you a problem with heat dissipation which made me do a lot of testing to get a good rough design) but I think I will keep trying. I will give a detailed description on the parts i used and how to build the light.
18 li po 2200 mah batteries. I got them for 3.33 each on hobby king
random lenths of 18 gage wire.
3 2s lipo battery protection circuits found on ebay
1 aluminum case
2 automotive kill switches
3 dc-dc converters found on ebay
aluminum and copper pieces for heatsinks
assorted chip heatsinks for dc-dc converters
3 20 amp schottky diode for dc-dc modulation
2 push button switches for rear light and power indicator
1 6s power level indicator found on ebay for rc helis
2 high amperage rc power connectors
battery insulation tape
2 22 gauge 6 series lipo charging wire extenders (like 2 bucks each shipped on ebay)
Heat shrink tubing
I-max B6 lipo charger bought on ebay for $35 shipped
6 cree xml u2 leds
6 75 in. copper end caps
1 75 watt heat sink for cpu ($8 at fry’s electronics)
Heat sink compound
Small brass screws found at hobby store
4x4 copper plate at least 0.060 in.
Some kinda mount for the light im going to use a bottle mount I found on ebay for 3 dollars
6 lenses for the leds (found on ebay, im using 2 9o, 2 45o and 2 60o lenses)
2 12 volt leds strips (meant for automotive purposes)
Vip ties to hold it down
Step 2: Building Process
The build process is kinda long and can be a little tricky if you do not have experience with electrical systems or know about heat transfer. I will continue to add steps to make it as easy as possible to build your own light but please let me know what parts you need help with the most and ill work on them first.
I will continue to check the comments for questions and answer them as best I can.
once again, If you have any questions on what I did please ask. I spent some time with the heat dissipation issue (that you will have trying to run 6 cree xmls at full capacity for an extended period of time).
I also make these kinda light systems for friends, family and colleges and can build you a light if you cant make one your self (it is a little tricky, I assume thats why they cost so much but mine cost much less and are brighter and last longer)
Step 3: Temperature Management
If you are going to have light system this powerful you will need to pay very close attention to your heat dissipation method. I had to go through a few prototypes before I found one that I was happy with. Here is a bit of nerdy heat transfer info you want to know.
There are three way to dissipate heat and they are with conduction, convection and by radiation (no median for heat transfer required). Unless you have a temperature difference of about 100 degrees Celsius then the effects of radiation are minimal (being that the equation has the temperature to the 4th power). Heat transfer by conduction is in our case going to be much higher than that by convection (this is due to our material selection and properties of air). The copper is there to evenly spread the heat from the leds because copper is a very good conductor of heat (about twice as good as aluminum). The reason we didn’t make the whole heat sink out of copper was for cost and weight (copper is very dense and expensive compared to aluminum). I have pictures of one of the test runs I did with free convection (no wind or movement of air) and one with forced convection using a fan pushing air at 7-8 mph (speeds easily seen on a mtb).
The max operating temperature (at full power of 60 watts) given on the manufactures website for the leds is 150 degrees Celsius at the junction between the aluminum pcb bored and the copper heat sink plate. I have a small hole drilled into the copper plate behind the right top led so I can put a thermocouple in and measure the junction temperature. The max temperature (which seemed to level off and reach its max value after 45 minutes) of the free convection was 137 degrees Celsius. This is at okay levels (although still too high for my liking) for the light and the mount but not something you want to touch. I am okay with this though because I will never use my light and just let my bike sit there (although if I did there would be no harm to the light or bike but you might burn yourself). With the forced convection test the max temp reached at the junction of the led and the copper heat sink plate was 57 degrees Celsius. I also did a ride with the thermocouple hooked up for an hour and recorded a max junction temperature of 47 degrees Celsius running at full power. This is a fine operating temperature (just warm to the touch). I did all the testing with a k-type thermocouple with a rated accuracy of 0.5 degree Celsius.
This was the testing I did to make sure my initial calculations were correct (you always want to test it out because sometimes your calculated value can be quite off). I have since gone on 5 night rides using the light and I check the temp with my hand (I know not very accurate) and it is never more than slightly warm.