A friend of a friend of mine asked me to build a rear bike light that would be better than anything he could buy (for a budget of $45). So I set out to build this light and I thought I might as well try to help anyone else out there that want to do a similar project. He rides road but there is no reason you cant light up the trail with this light too. He also wanted to go a little different from the traditional red rear light so I used cree's xre blue leds. Ill try my best to walk you threw what I did and what you can do with a few basic tools.
Also it had been brought to my attention that blue might not be legal in some areas (still checking if they are in my area). If they are not you can always use crees red xre led(make sure you check in your area before buying your leds so you dont waste money). It cost the same amount and puts out roughly the same amount of light.
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Step 1: Tools and Materials
The tools needed here are very basic:
screw driver drill press (although a hand held drill and a steady hand will do just fine)
heat gun (a hair dryer will work too, If you don't have one just borrow you girlfriends/ boyfriends, if you don't have one of those then a heat gun can be bought online pretty cheap and comes in handy more than you think)
Just a little plactic adhesive (or hot glue if you want, I just normally don't like to use it for permanet things)
2x CREE XRE led (I got blue, $6 each on ebay)
2x CREE 3 watt led driver ($10 for two on ebay)
2X lens for cree leds ($2 ebay)
2x Lithium ion batteries 18650, I pick 1500mah but you can use whatever (you can get some online fairly cheap but I just happened to hove some from another project but will probably cost you $15)
A alumimum case for the leds and batteries (I got one on ebay that was just the right size for $7)
A dc-dc buck for the charger ($5 ebay)
A 12 volt 500ma transformer (I also have one lying around, really anything from 6.5 volts to 30 volts will do)
2x copper pipe plugs (2 bucks each at home depot)
Some type of battery connectors, the ones I got on ebay for 2 dollars
One on off switch (also had laying around but one 2 dollars on ebay)
One lipo protectiong circiut (very important so you don't ever overcharge or discharge your batteries) $3 ebay again (you would think they sponsored me the way I keep talking about them but there just had the best prices)
also a plastic case for the charging circuit (any old thing will do, remember we are on a budget) free!
Step 2: Builting the Guts of the Light
The circuit is very simple and I have a picture of the actual lights cuts and the wire diagram. You must have a lipo protections circuit though if you want your batteries to last and not catch fire. I used some 22 gauge wire I have laying around (these leds only draw at max 1 amp each).
Step 3: Buildign the Housing
The case I got off ebay just need some holes drilled into it and it was pretty much ready to go. I borrowed my dads drill press to make it easier but its not necessary.
You need to drill two holes in the back fro the clamp mount (stole it from a crappy 5 dollar light). For each copper plug with an led inside it you also need to drill 2 mounting holes for the leds to be screwed into the aluminum housing. You also need two small holes for the wires. You need to drill one hole on the top plate for your switch and two holes on the bottom plate for your charging wires.
Once you screw the leds to the copper pipe plug and the housing (with thermal compound under both the led and the copper plug (where it has contact with the Aluminum housing). This is a important step to insure there is good heat sinking. once attached you will use the plastic adhesive to secure the lens to the led.
Step 4: Building the Charger
This is a really simple quick summary to building a lithium battery charger. There are really good instructables that give better detail but pretty much you just need to solder your dc transformer wires to the input side of the dc-dc buck converter and the output side to the battery connector you bought. Using a multimeter set the voltage to 4.2 and the constant current to 1-1.5 amps(this will insure long lasting batteries and will charge in 2-3 hours).
Step 5: YOUr Done... Almost
Now just shove everything(being sure to insulate the top of the battery to not short out on the case, I used some rubber pieces I had) in tot he case and solder the final wires and test it out. This particular set up will last on full power for about 2 hours on full power and 20 hours on low power.
well, if you have any questions be sure to let me know and ill do what i can to help explain my processes or help with an any other project you are working on.
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