new project: a generator-driven LED headlight
May 1st, 2008 | Published in general | 7 Comments
I’ve been tinkering with this for a couple of weeks now, off and on, and finally have a working model. Here ’tis:
There are several places online with plans to build various versions of this, including great schematics, but of course i had to do it a little differently. Most of the plans call for using aluminum for the housing, which is light and a great heat conductor (the 3w LEDs get hot), but i liked the idea of a copper housing instead. The other main difference is that most of the examples i found were glued together with thermally conductive epoxy. This is good from a heat-transfer standpoint, but it’s expensive glue, and i wanted to be able to open and repair the light if necessary.
The electronics were fairly easy; a 3 watt LED ordered online and a full-wave rectifier bridge from Radio Shack. That’s really it – just the wiring and power connector. The case was harder, because i didn’t want to permanently glue it together and had a hard time figuring out an easy & cheap way to thermally connect the LED base and the housing. That’s still a potential weak point, but i’ll just have to use it and see how fast it dies. Here’s the light on the bike:
The housing is repair connector for 3/4″ copper. It’s a slip fit over 3/4″ copper tube, and the LED and optics fit inside nicely. I soldered a short piece of 3/4 tube inside the repair tube to serve as a shoulder for the LED to rest against, then the lens sits on the LED, then a bead of silicone to seal the front. The rear is a small cabinet pull with the power jack installed, held in place by rubber o-rings. The mount is temporary until i can figure out something better. I originally just used a big o-ring, but it kept moving down with each bump.
The light pattern is a spot, and i may construct a shield to cut it off lower. A sort of visor with reflective inside surface might be useful to light the road close-up. I didn’t have a cyclometer on the bike when testing tonight, but it’s giving a steady beam at probably 3-4 mph, so it’ll be useful even for climbs, maybe even offroad.
My original design was for a 2-LED light with two copper tubes joined side-by-side, but i had serious problems getting that case built as originally planned and reverted to this simpler design. I still like the idea of a double light and will probably gut this version to build that once i work out the case logistics. I also sort of like the idea of having it sealed shut with solder, waterproof like plumbing, but that’s unlikely given the number of vital parts made of plastic.
update: web references & credit – these are a couple of sites i found to be the most help in this project, along with several posts to the iBOB list and lots of google searching:
Jim G’s master list of project links
Schematics
http://www.luxeonstar.com – source for LED, lenses and holders
The LED is a white Lambertian Luxeon III star – the newer Cree LED is apparently brighter, but the Luxeon was just easier to figure out what to order (it seemed like the Cree was also more expensive, but perhaps not). Optics are the L2 medium 15° lens for Luxeon LEDs. Since finishing this version 1 model, i’ve gotten some additional information on adding a standlight function, and will modify this one with the right capacitor once i find one. The 2-light version will use one 5° and one 15° lens for better beam coverage.
May 1st, 2008 at 11:39 pm (#)
You’re a damned genius. Now to use the excess heat to drive a steam generator that can power your GPS.
I finally developed that roll of film. Two of the images look pretty good. I ruined the rest.
May 2nd, 2008 at 10:10 am (#)
What LED and what optics are you using?
May 2nd, 2008 at 11:16 pm (#)
I used a Luxeon III and L2 lens. The Cree XR-E is brighter i guess, but the Luxeon is fine, and was easier to figure out ordering. In my non-scientific testing so far, this light seems about as bright as a Lumotec halogen lamp. I bet the dual Lux version ends up plenty bright, and different lenses should give better beam pattern.
May 26th, 2008 at 3:48 pm (#)
You have captured simple elegance.
You should get a picture with your bike outside the Ordway Music Theatre. The design resonates.
The Cree XR-E works at slightly different voltages so getting it to work with the simple circuit is a little trickier. The Luxeon seems to match up very well with generator [dynamo] output.
I have a similar set up made with an aluminum tube and a copper cap pressed in. My attachment point is in the drops of the bars with a double p clamp with a long spacer to put the light in the space between the bar and the front bag. That lets me adjust the focal point on the fly.
I am working on a second setup powered by 4 aa batteries to go on the other side as a backup / standlight.
November 22nd, 2008 at 4:37 pm (#)
How do you make sure the LED is not overloaded? Are you using a 6 volt 3 watt generator? I understand that the LED is about 3 watts? How is the wattage determined? I’m new to this stuff.
November 24th, 2008 at 12:33 pm (#)
I’m not an electrical engineer or anything, but as i understand it the LED’s tolerance is well within the range of output for a standard 6 volt, 3 watt bicycle generator. It seems to be one of the rare examples of standardization in the industry.
Not ALL LEDs would work in this sort of direct setup, but it’s easy to do some searching online to see what other people are using. There are a handful of different models that work fine.
April 2nd, 2009 at 8:39 pm (#)
I wanted to comment and thank the author, good stuff