New LED Bike Light
After much time & effort my new bike light is complete. Here’s a quick peek:
More photos are in the Gallery.
The two LEDs are Cree XR-E bin Q2 power LEDs and are driven with a BuckPuck 1000mA regulated power supply. This takes care of any fluctuations in the battery voltage as the cells discharge. I’m using four Lithium Ion cells in series, giving me 14.8V and 2.1Ah. Four cells were chosen because my previous light was three Cree XLamp 1W LEDs in series and I needed a higher drive voltage. I’d get away with three cells now, but I’ve all ready bought the batteries and charger. The optics are Ledil CRS rectangular lenses, one being an oval and one being a smooth spot. These mount to the LEDs with double sided tape. Q2 LEDs are good for around 160 lumens at 1000mA, so the light is around 320 lumen total. Cree have released Q5 bin LEDs that give 250 lumens at 1000mA, so if I was building the light now I’d be able to get 500 lumens total!
8W of LED is sometimes too much, so I have used a double pole switch (Apem 5649A with waterproof boot) to short out the spot LED when the switch is in the up position. There are two positions: up is oval only, middle is both off and down is both on. Battery power is supplied through a Switchcraft EN3 panel plug. Using a plug means that the lead from the battery ends in a socket, which reduces the chance of short circuits. The plug locks down with a bayonet lock, so it won’t vibrate out. The plug and socket are sealed to an IP68 rating which should cover any storms that Brisbane can deliver.
Mounting a home made light on the bars can be tricky. My last light ‘borrowed’ the mount from a Cateye light, but I couldn’t find any more of the headlights to butcher. Chain Reaction Cycles in the UK sell spares for the Light & Motion bike lights, including a light mount plate and a handlebar mount. These provide a very solid connection.
The body of the light is rectangular section aluminium from Bunnings that is meant to be used for making tables. It is black anodised and nice plastic end caps are made that bung up the ends. The tube is 25mm x 25mm, so almost a perfect match for the 23mm x 23mm Ledil lenses. It proved very hard to find 50×25 box section aluminium with a thin enough wall, so the 25×25 was a godsend. Cutting it square was a challenge, but I got there with a jigsaw. A drop-saw with a metal cutting blade would have been ideal, but was too expensive to buy for a little project like this.
The LEDs are mounted onto 8mm thick squares of aluminium, which are screwed into place on two sides into the tubing. Thermally conductive epoxy was used to glue the LEDs to the plate, and to fix the plate to the inside of the tube on the sides that were not screwed down. It is important that heat be carried away from the LED module as easily as possible. The light runs quite cool with both LEDs running, but I haven’t done a temperature rise test yet. To keep rain out the front of the lenses are sealed against the aluminium tube with silicone sealant.
The light has been used a few times now, and has survived rough Brisbane roads (on 23mm tyres at 110 psi) so I’m quite happy with the result. The batteries should last between 4-5 hours with both LEDs on, and 10h with the oval only.
