Converging on a design for “cheap” bright bike lights

October 26, 2008

Relatively cheap, that is.I begin, with an upgrade to the lights on my son’s bike. The LEDs are mounted onto beefy chunks of aluminum that do triple duty as mounts, heat sinks, and (somewhat) light shields. Everything is bolted on, nothing needs to be removable, nothing needs to be recharged. It runs from a (cheap-ish) dynamo.

aluminum plate for rear, pre-drilling

aluminum plate for front, pre-bending, next to mounting bracket

bending front plate

old and new front plates, the new one is wider, for better heat sinking, and to shield rider’s eyes from light.

how to remove an epoxied LED: just bend the plate.
Note how thin the epoxy was on the backside of the LED

new LED(s) for rear taillight(s)

front view

cut enough wire to connect taillight to regulator

an abrasive puck is useful for roughing up the aluminum pre-gluing, and for making the edges not so sharp.

Soldering, sort of. This was my first attempt, I was trying to be methodical, but I gave up and did it free-hand (I’m pretty good)

Soldered and clipped

Trust, but verify. Be sure it’s right before you glue.

Collect all tools, parts, everything, because JB Kwik sets in FOUR MINUTES:


Taillight glued, clamped together hard. You want the thinnest possible layer of epoxy.

Headlight glued and clamped. Note that I clamped the old assembly, lens and all. I would not necessarily use JB Kwik for potting the lens; you might not have enough time, and you need to be a little careful to keep it off the lens.

Rear bolted on, wire routed.

Current regulator, in Altoids box (it’s way too large).
LEDs are wired in series.
From-Regulator red, to rear red.
Rear black, to to-front red.
From-front black continues straight on to regulator.
Heat shrink tubing on the soldered joints.

Dynamo, feeding Rectifier circuit

Rectifier circuit (already swaddled in tape, sorry)
red-black to regulator inputs leaves out the top.

The rectifier circuit uses parts that you can order from Digikey. It requires 2 Schottky diodes,


(or, cheaper, but minimum quantity 10)

1 24 volt Zener diode,

1N5359B DIODE ZENER 24V 5% 5.0W T-18

3 25V 1800 uF capacitors,


and (optionally) a ceramic capacitor or two.


Use standard 9V connectors to regulator, this allows you to use a 9V battery for quick tests, or a AA battery pack for backup/continuous lighting.

Circuit diagram, TBD. I am not confident that the voltage protection is sufficiently idiot-proof.

Front light, all bolted on.

Rear view.

Close-up of rear light. No lens necessary, you want that light visible from all directions and a big puddle on the ground, too.

This is a bigger bike, with bigger lights, running right at the hairy edge of what the regulator can do. Batteries help.

There are four LEDs, with two whites in front, in series, also in series with a parallel pair in the back. It is important to only parallel-wire similar LEDs — amber, orange-red, and red, can go in parallel, but not red and white. I am using orange-red because it looks red but is a hair brighter to the eye.

The two whites are in front, obviously, the yellow is under the front of the snap deck, and the orange-red is in back. Doing it like this cuts the tail light by slightly less than half, but it also reduces the forward voltage across the pair, which gives me slightly more margin from the regulator (every tenth of a volt counts).

Here’s another shot. The front lights use two different lenses, one flat and wide (16 by 50), other round and medium (32 degrees wide) to generally spread the light where I want it. I aimed the whole show just a hair below horizontal, so as to get light where I need it, but still be visible in front. I don’t know if the faux down-low glow really helps that much, or not, but it might be helpful if I ever have to work on the bike in the dark.

This is sort of what I see. You can sort of see how the two lenses superimpose, there’s a higher bump up of light, and the flat bit off to the sides, but really a lot, straight in front.

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