This is a lightweight trail running headlamp. My runs are usually 1 hour or less, so my design goal was to make a light that has a good compromise between being lightweight while having the brightest 1 hour runtime. Honestly, a lightweight 18650 headlamp (such as the H03 or the Nitecore lookalike I reviewed) works for trail running, but I became obsessed with creating an optimized light for this purpose.
Since the battery capacity in part determines the 1hr brightness and it is a significant part of the total weight, choosing the cell size was the first decision in making the light. I considered 14500, 18350, and 18500. The light weight of 14500 and 18350 were appealing, but the capacity drop relative to 18650 was a bit more than I wanted. The Panasonic NCR18500A was a good compromise at 2000mAh and 32g.
I used the same Frankenstein strategy that I used to make my trail running flashlight last year. I had another of the skywolfeye cheap zoomies that I used for the main battery tube and tailcap. For the right angle head I cannibalized part of the head from a cheap trustfire AA light. It is flipped around so the internal threads for the pill are now the threads for the bezel/reflector retaining ring on the headlamp.
For this build I was considering literally every gram. I thinned the walls of the battery tube mainly using a Dremel to save ~5g (I was keeping close track of this but I forgot the numbers because this was several months ago). I shaped the head piece for a nice fit and used JB weld to attach it.
The construction of the shelf was an important consideration to insure adequate heat removal. The shelf had to have a curved surface that closely fit the inner surface of the battery tube. Below, first I had an idea to use a hole saw to cut some sections of 1/4” Al because the saw ID was close to what I needed, but there was too much slop in the saw and drill press so the pieces ended up with too small a radius.
The next idea, which worked pretty well, was to mark the desired shape on a piece of Al, cut off the big chunks using a mitre saw, then finish it up with hand filing and sanding. Shown below.
I used a 5000K SST20 for its compromise of output and throw. The reflector down below is an OP reflector from the trustfire light. I wanted max throw, so later I got a smooth reflector from KD that I got to fit in there.
I adhered the shelf with arctic alumina.
Mounting and grounding the driver was another challenge. There was not really an option for a threaded retaining ring, and there was no separate threaded battery tube to tighten and make contact with the driver (like on emisar lights) so making reliable electrical ground contact was not straight forward. I decided to use a press fit. To do this I made a shelf from thin Al and adhered to the tube with arctic alumina. Then I soldered some wires to the edge of the driver board and filed them so they would make a tight contact fit in the tube. (I got this idea from a post from djozz some years ago) I also sanded the inside of the tube in that area to remove the anodizing.
For the driver I used a 17mm qlite driver with 5x 350mA 7135. I installed a attiny85 and made some RC filtering additions required for the 85 to run well. It’s running anduril with custom modes instead of a ramp.
Here is a picture of how the switch is mounted. I then made a rubber switch cover using bicycle inner tube. The tailcap was made as minimal as possible, with the thin Al cap adhered to the threaded part with JB weld.
However, I finally reached the limits of JB weld’s abilities. The bond with Al is good, but there is just not enough bonding area here and the cap came apart from the force of screwing down. I reinforced the area with thin nylon fabric and epoxy. I first tried using fiberglass, but the glass fibers are too stiff to conform well to that sharp right angle.
To reduce bouncing/discomfort of the light on my head, which was the objective of this build, I believe the flashlight weight, rather than the light+strap weight, is the important thing to consider. The final weight of just the light is 21g for a complete weight of 54g with 18500. This is a 40% reduction compared to my H03 with 18650.
I hope you enjoyed the pictures and thanks for looking!
