Bike light

I'm writing an article for a magazine, and I thought this might interest you, too. Right now I'm just assembling material, this isn't the article.

If you're gutsy enough to be riding a bike in the rain, you may also ride at night. And that involves safety. The biggest cause of bike accidents at night is not being seen. I think the solution to that is lights.

There are a couple of kinds of lights, the smaller type which enables others to see you, and the more powerful type that allows you to see.

This is about the more powerful type, as there is no real need to improve upon LEDs for just being seen.

The problem with the more powerful lights is the power. Batteries are either expensive or heavy or both. Here's what I've done to get 40W of headlight power with a great Ni-Mh battery system relatively inexpensively.

First, I purchased this headlight in a cheaper version. There is also a 1 light version which would work.

When I got it the battery wasn't good. I shipped it back, and they credited me with a bunch of the price. In the meantime I decided to build my own battery.

After a lot of searching I found these, an absolute steal. Break open the pack and there are 6 cells the diameter of a C cell wired in series to provide the 7.2V. Break off one and you have a 5 cell pack providing 6V at 3AH. That's mildly fantastic for the price, even including shipping. I think surplus 4/3 C cells are available at surplus electronics stores in bulk, but their quality is suspicious. I bought some locally, and nothing I've assembled has worked well.

I purchased 6 of these units broke them up into 5 cell 6V batteries. I have since taped two of these battery packs together into one unit wired in series, to get a single battery providing 12V. I have three of these, and can put 1, 2 or all of them together, depending upon how long I'm going to be out.

The reason I put them together in units of 10 cells is fairly simple. I went to 12V bulbs instead of 6V. I did that because of an experiment. I wondered if the original bulbs would tolerate 7.2V instead of 6V. If it would, I could leave the pack together.

It would, for about 45 seconds. Then, poof!

I ran searches for days looking for cheaper 6V bulbs than available from the bike outlets. They want about $18 for them, which seemed excessive.

I found I could purchase 12V lights on the net for about $8 in a variety of beams. I purchased a couple of narrow beam and broad beam 12V bulbs. I have since found the same bulbs at Home Depot, in a variety of beam patterns, for $4. Oh, well.

The 12V bulbs work just fine in the housing.

Now, the batteries supply 12V X 3A = 36W for each 10 cell pack. That means that optimally I could get about 1 hour 45 minutes for one bulb, or 50 minutes for both. Two packs will get me about 1 Hour 45 minutes for both, and all three will get about 2 and ½ hours. In reality they run longer than that, but at a lower light output. Still a lot of light, though.

At 12 mph that's quite a ways. If I chose to use “just” 20W, one light, I could go for a nominal 5 hours. I have no plans to ride 60 miles at night. I realize the batteries aren't quite that efficient, but they are good.

Re weight. Each 10 cell pack weighs a hair over a pound. And they are small enough I keep them in my handlebar bag, don't have mess with much wiring.

My next project is going to be to wire up a 12V red LED as a taillight. I use two taillights, as I don't want one to burn out. I'll just throw a pack back there for it, too. Should last forever, and these LED running lights are pretty good sized.

As far as charging these batteries, I got a 6V/12V 1A charger from a local store. It was $20, and I'm sure Radio Shack has the same thing. Much faster than the little transformers. So fast, really, that I put it on a timer so as to not forget and wildly overcharge the things.

I won't say that this will solve all lighting problems, but it's pretty good. At a minimum it seems to give drivers something at which to aim.