The Rezistor Headlight

jstept's picture

The Vespa 50S Special originally had a 6V 15W headlamp. The old lens was partially obscured with overspray from past rattlecanning, but the previous owner gave me a brand new headlamp when I bought the scooter from him.

In any case, I wanted to switch to more efficient LED lighting and run it at 12V, so I bought five MR11 LED lights on eBay. I think these are intended to be replacments for the halogen spotlights commonly used in low-voltage lighting systems that you commonly see with exposed wires. Each of them is a cluster of 19 LEDs emitting "cool white" light, as opposed to the warmer yellowish light of halogen and sodium incandescents. I'm hoping the brighter white will produce a more distinctive effect and help make the scooter more noticable. Each MR11 is rated at about 0.78W, so the entire headlamp should draw less than four watts. I think this is a big improvement over incandescent.

headlight_parts_1.jpgheadlight_template___lens.jpg

First I spent a while rubbing the lens of the old headlamp with paint thinner to remove the spray paint. Then I sawed off the back end of the curved reflector and found a spider that had died inside. The five MR11 lamps just fit inside what remains of the reflector and the front lens. I cut a piece of black acrylic plate to about the size I needed to mount the lamps, then created a template to help me align the lamps on the acrylic. I drilled a hole for each of the lamp leads, used JB-weld to attach the lamps to the acrylic, then wired them all together in parallel. Then I epoxied the acrylic plate to the lens with some bits of plastic scavenged from an old wireless mouse transmitter.

headlight_template_lens_plate.jpg

I had originally planned to use the bottom three lamps as the low beam and the top two to be the high beam, but I abandoned this scheme to simplify both the alignment and the wiring. Also, I figured that for an urban vehicle, the primary function of headlamp is to make you more visible, with the illumination of the road in front of you being of secondary importance. Plus, I'm pretty sure that Oregon doesn't require a high beam on vehicles.

Interestingly, I didn't need to pay attention to the polarity of the leads for these lamps, which is not usually the case when working with LEDs. The internal wiring of the lamps seems to include a diode to allow current to flow in both directions.

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Overall, I'm pleased with the results. Each of the lamps produces a fairly concentrated spot, and I did a fairly good job of aligning them all, but the lens spreads out the light somewhat. There is an adjustment screw in the bottom of the headset with which I can aim the light higher or lower. I think it will still be pretty visible and a big improvement over the old lamp.

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Hey,nice work. You've given me a few ideas for my next bike light project. I'm pretty convinced Led's are the way to go. I'm also pretty keen on the idea of modulators as a safety/being seen feature http://tinyurl.com/ysvg7o though I don't have any direct experience of them yet.

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