Wednesday, July 8, 2009

Underbike Lighting - Construction Details

How to get the fun and safety factors of the Down Low Glow (DLG) without spending too much? Here's what worked for me.

LED Ribbon

A couple of years ago a colleague heavily into car audio (and thus close to the boy-racer scene) recommended a then-new product - waterproof led ribbon - that has finally started turning up on TradeMe. Turns out that ribbon strips are super easy to use. They can be cut every few cm (3 leds on mine) and have clear soldering pads which are easily exposed by trimming a couple mm off the plastic casing. (It felt like cutting through a firm gummy-bear, but without the guilt factor.) Each block is wired in parallel to the others, so you can cut or append with ease.

Each block has the necessary resistors etc., so you just need to hook up a 12V power source such as a lead-acid car battery. If you put the power through the wrong way they just do nothing, rather than blowing up. Finally, the self-adhesive backing which they all seem to come with worked really well.

Few electrical safety precautions are required with low current 12V dc. You can just pinch the wires together between your bare fingers for testing, for example. I did put in a fuse to make sure that the battery couldn't be shorted, and built some basic weather protection.


I bought 1m of green ribbon, pre-cut into 2x50cm strips and wired on one end, and two 30cm offcuts of red. All fully waterproof, so long as you seal off the ends after soldering on your wiring. I chose green as it was the brightest colour available from my supplier.

The red off-cuts were super-cheap and I thought some extra rear visibility wouldn't hurt. They were an older, dimmer model (leds get brigher ever day, it seems) but that was okay as they face directly at drivers and the blinky served for initial long-distance visibility. Conveniently their black presentation was more suited to exposed placement than the green strips.

My friend, Glenn, lent me a spare neon car tube and two sealed lead-acid batteries. One never charged back up, so awaits the next hazardous waste collection, but the other is working sweetly. It should give me about 5 hours, but isn't in perfect health and I'd be happy with 2. Frankly, I rarely ride for hours in the dark - mostly commuting, not the PBP. I charge the battery with a Battery Doc which I bought when I had a motorbike.


I exposed the other end of each green strip and soldered on the wires from a red strip. To provide weather protection I put shrink-wrap over the connection. There was never much space between the end of the strip and the first led, and wrap wide enough to fit over the strip didn't shrink enough to really grip the wires, but it seems to be working okay. I tried putting wrap on the 'open' ends of the red strips, to seal them off, but it didn't stick so well without the wire and I left it off.

Then I peeled off the backing tape, wiped down the mounting surfaces, and stuck each pair down. Simple as that. I put electrical tape over the 'open' red ends, to seal them and to hold that end down. I wasn't sure if the ribbon would adhere to the tubing, but the tubes are fairly wide and it seems to be working. The green strips had shrink wrap forcing up both ends of each strip, but was placed under a flat surface and seems to be gripping well.

The blue neon went on the down tube, just taped on. This light is possibly illegal, as NZ car lighting regulations require that you can't directly see cosmetic lights. (That's partly why I put the green ones underneath running boards, not just on the rear wing tubing, although they'd soon enough get crunched against a curb if I put them there.) The tube is pretty heavily frosted, so I'm not worried that it will blind a driver or anything, and who knows exactly what regulations apply to bikes.

I brought the three sets of wires, from front neon and left and right green/red pairs, to a single point on the frame near where the battery would go. Then I taped it all down - not super beautiful, but effective enough.

Battery and Circuitry

I built a simple case out of coroplast for the battery. I'd wanted some experience with this material, and learned a few things. The lid has no fastening, but sits pretty snugly around the base. I built the base taller than the battery, so that there was room to put in the wiring. It took a bit of practise to figure out how much allowance to make for the curvature/thickness of bends in the board.

The base box is held together with packing tape and has no overlapping surfaces. Very basic, but not much required either. The lid has overlaps, and I found that I got a strong join by cutting off the inner surface of the overlap and applying hot glue. Probably didn't need to cut off the inner surface, but that way the overlaps are flatter. I had read about 'welding' the plastic with a soldering iron, but couldn't make that work.

I wanted to be able to to swap out the battery pretty easily, so have connected to it using alligator clips. First thing connected to the positive terminal is a fuse, then there is a switch toggling between connections to the leds and the charger. The negative line just joins directly to those two connections.

Both sets of connections come out the back of the box, threaded between the lid and base. I put one extra loop of wire around the cable-ties holding the box on the frame, just to keep my options open, then soldered the wires from the battery box to those from the lights. Passing the charger connection above the cable tie seems to have kept it away from the tubing and prevented banging.

Now I plug my bike in every day when I get home, like I used to do with my motorbike. (The main charger unit sits on the rack of a Raleigh 20 which hangs from the carport roof in the forlorn hope of refurbishment.)


Overall, I'm stoked. The light cushion is nice to ride on and I feel more visible on the road. Too soon to say if I get more road space, but I've had some positive feedback from passersby.

The neon is good for side visibility, but isn't as bright as I might like. It takes about the same power as one of the green strips, so is less efficient (no surprise). I could perhaps replace it with some leds, but would probably still want to diffuse the light in some way. I don't know that the green leds throw out as much light as the DLG, but then I could always add more leds. Not for a while, though.

So far I've spent NZD$80.20, but that doesn't include the blue neon, battery, or charger. Most expensive of those is probably the charger, but with a basic model charger and battery I'd still have some money to play with. My battery is probably heavier and cheaper, but the Yuba was never a weight weenie.

There's also the pleasure in making my own system, which I can alter as I please. Definitely worth the trouble taken.


Keith said...

Nice! And nice writeup too - thanks!

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