Alex Wetmore is always busy with something…

I played with building my own headlight back in November, and just got back into it last Saturday and yesterday. I think I’m done with such projects for now and I’m using this blog entry to document what I’ve done so far.

What I’ve built

I built this headlight yesterday (click for an annotated slideshow showing the construction):

It looks nice, but this is a very basic light with no standlight. The brightness and beam compare well to a Niterider MiNewt USB-Mini headlight. This is good, but not as nice as the brightness on most commercial headlights.

In November I spent a lot of time experimenting with standlight electronics. Thanks to a lot of help from the CandlePowerForum I came up with a circuit that works pretty well:

Here is how the circuit works:

• Therectifier is the circle on the left and turns the AC generated by the dynamo into Vcc (positive) and ground.
• Most of the power runs from Vcc through the LED (D)and back to ground.
• When the supercap (C, marked 10F) is discharged some power ispulled off to charge it. The LM317L is a simple voltage regulator that regulates the output from therectifier down to 2.1 volts (the maximum that the dynamo supports).
• The ZXCS310 is a LED driver thattakes the power from the supercap (0.8 volts to 2.1 volts)and boosts it up to the power needed by the LED. Using this driver let me get all of the possible power out of the supercap and gave a runtime of around 8 minutes.
• There is a bug in the drawing, the other side of L should go to Drive, not a mystery 4th pin on the ZTX618 transistor.
• A more optimal design also has a transistor which watches for Vcc to drop to 0 and then disables the Shutdown pin on the LED driver. This makes it so that the LED driver isn’t running unless you need the standlight (the dynamo isn’t running).

I did a lot of playing with space layout and got a layout that would fit on a 2″ by 1″ board. I never did end up building that board.

I also built a housing for a LED headlight. It would use the same circuit, but 3 LEDs instead of 1. The housing is about twice the diameter. It looks like this:

The wall thickness on that housing is too thick (to make it possible to use screws to secure the front and back). It weighs a lot more than commercial headlights. The idea with this one is that one LED would be the standlight, and the other two would always be on. It should have been brighter than the commercial headlights.

Headlight Beams

All of these headlights use symetricspot lenses as on most battery headlights (like theNiteRider MiNewt series). I don’t like that beampattern too much because if they are aimed high enough to see far down the road then they also blind oncoming traffic.Most commercial dynamo headlights use an asymetric beam whichis brighter at the top than the bottomand which has a sharphorizontal cutoff. That is similar to a car or motorcycle headlight and does a really nice job of lighting up the road in front.

Peter White has a long post with photo comparisons of headlight beams. The Super Nova E3 is a headlight with a spot beam (you can see that it is lighting up the trees and the brightest part isn’t the farthest) while the eDelux is a headlight with an asymetric beam.

The “right” beam is a subjectopen to debate, but I personally prefer the beams of the commercial headlights such as the Schmidt eDelux or B&M IQ Fly. The optics for such beams are hard to reproduce in a home workshop because there aren’t easily available lenses for them.

My Conclusions

I think I’m done experimenting with building my own headlights. Here is why:

• It takes me about 4 hoursand $15-$20 in parts to build a headlight roughly as good as the $60 Planet Bike one, only it doesn’t have the standlight. Most of this time is machining time to build a housing. I don’t think that time/cost tradeoff makes sense.
• Building a headlight that is as light, compact,and reliable with the same features as a commercial headlight takes even more time. It is difficult for me to do surface mount electronics with custom boards at home,and those are the features that make the commercial electronics so small.
• I can’t build a headlight at home with a beam that is as good as the IQ Fly ($92). The IQ Fly is my baseline for a good dynamo headlight.
• I don’t need a highlight brighter than the eDelux or IQ Cyo. I actually don’t want a headlight brighter than that, I personally don’t think that brighter is always better. I think the best reason to build LED headlights at home is to get the super bright spot beams that are useful when mountain biking.
• It’s distracting me from my main fabricationgoal this winter (building a bike frame).

I have another project which will use my remaining LEDs (I’m building solar powered lighting for our shed). The supercaps that I bought will be useful in taillights (which I do enjoy making).

If anyone wants to buy my LED optics just let me know. I have 6 L2 OPTX (including adapter lenses) and 3 L2 OPTX 3 that I probably won’t be needing.

It’s too bad that there aren’t commercial standlight circuits for homebuilders. There are tons of tiny driver circuits available for home builders who want to make their own battery powered headlights.