LED Lights
300 Lumen LED Bicycle Light

By Warren Beauchamp

I really like the Dinotte light, and the other new high power LED lights on the market, but they are all pretty expensive. After seeing the LED lights on instructables.com, I was inspired to build an LED headlight of my own for commuting.

I purchased some Luxeon II LEDs - two $5.11 ea (white) and one $5.01 ea (cyan). These are high power LEDs, are designed to run at over an amp, and put out over 100 lumens each. LEDs are finicky about how their power is supplied, and it not a good idea to just hook them up to a battery. LEDs come two way, either just the bare LED, or on a small circuit board. I opted for just the bare LEDs as higher power LEDs were available this way, and I figured I'd be able to pack more LEDs into the package that way.

To make it easy to run these LEDs, a circuit called a BUCKPUCK ($17.99 ea) is sold to allow several LEDs to be strung together and run with a single battery. LEDs run on about 4 volts, so sice I use going to string 3 together end-to-end (in series), I will need to hook up a 12V battery to the buckpuck.

I'd like to have these run for at least a hour. This buckpuck is rated at 1000ma (1A). The LEDs running at 4 volts and 1A ma will use 4 watts each. 3 LEDs at 4 watts = 12 Watts total.  12 Watts / 12V  = 1000 ma. So the battery I'm using would need to be at least 1000ma/hour. NiMh batteries are fine at this current, as they are rated at about 2000 ma/hr. Here are some NiMh batteries with tabs (about $20 for 12) to make them easy to solder together and a charger to go with them (about $26). Another option is Lithium Polymer batteries. Much lighter and smaller and more power, but about twice as expensive.
 

Here's the original schematic for my light. I decided to not have a high / low beam, and that I did not have room for the capacitor.

An LEDs main enemy is heat. Because of this I had to mount them to something that would either dissipate or sink a bunch of heat. This either means fins or a big chunk of metal. I scrounged through my metal pile and found some 1"x2" aluminum tubing, and thick L-brackets. 

11/30/08
I mounted the power switch, an indicator LED, and the power plug to one of the L brackets, and soldered up the wires to the buckpuck. Here are the buckpuck instructions.

Lead based solder. How retro.

Here's the non-blinding side of the light unit. Will everything fit?  
I soldered the LEDs together, then glued them to the second L-bracket with some JB weld. I cut up a mica power transistor insulator to insulate the back side of the LEDs from the bracket, as the LED instructions say that the LED back side is not electrically isolated. Fortunately the JB weld seems to be non-conductive. Hopefully it conducts heat...
Flame on! That's two white LEDs on the outside and the cyan one in the middle.

The LEDs are supposed to be focused mostly forward, but seem to throw light all over. This may actually be good for a bike light. We shall see.

After some drilling and tapping, and then the obligatory creative wire bending, it all fits without room to spare. It's a very nice tiny package.

The directions say to not touch the LED lenses, but I did, and they have some dust and stuff on them, so I will need to clean them well before I seal this end of the package with some clear Lexan or PETG.  

12/05/08
Now that I have this project almost completed, I learn that I could have made a brighter light for less money. Hmm. Anyway, the
Cree XRE Q5 emitters are rated for 228 Lumens at 1000ma, almost twice as bright as the lights I am using. The dealextreme.com site also has a Regulated LED driver that allows you to string two of these LEDs together for a total of about 400 lumens at 12 V. And for only about $20 in parts. Also nice are these lenses, which work well for bike lights. Wow. Don't forget the thermal glue. I see LED lights project #2 coming up quickly. 

Here's a 900 lumen single LED. Reflector Yeow!

 

12/28/08
I added a Lexan cover, hooked the light up to my 12V battery, and let it cook for a while. The block of aluminum does get very warm, but not hot.
I may add a heat sink later.

As noted above, These LEDs throw the light all over. Though they do light the area ahead of the light fairly well, it's not a great pattern for a bike light to be used to run at high speed in complete darkness. For that I should have used some lenses. This light will however serve well for it's intended use, which is not getting hit by cars during twilight commuting.

1/04/09
Rather than purchase a bunch of parts and try to build another light, I decided to buy one of the $20  Cree Q5 flashlights. It's 228 Lumens focused into a wide beam, and powered by a single rechargeable Li-Ion battery, which should give it about an hour's useful life. I also ordered the flashlight handlebar mount

1/30/09
I added the heat sink by roughing up the mating surfaces and gluing it with JB Weld.  I also adding bolt on mounting flanges to the bottom for mounting it inside the clear nose of my
practical commuter fairing.

I received the Q5 flashlights and 18650 Li-Ion batteries. They are very nice and bright and have a good focus pattern for cycling. Still waiting on the mounting bracket. Run time is only about an hour, but that's fine, I'm not running in the 24 hour Sebring races or anything...

How about a 900 lumen light?

3/21/09
While showing Tony the light, I hooked it up with reverse polarity, and toasted the buckbuck. Strange that they don't have protection built in to such an expensive device. I ordered and installed a new one, but this time I added a 3A power diode to protect it against polarity reversal. I also added the capacitor noted in the schematic above.

Here's the LED unit mounted in the fairing of my commuter e-bent. Next I need to wire it up.

   
   

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