At the 2000 Mont 24Hr Mountain Bike Race , a 2nd light was compulsory. It didn't have to be anything more than a maglite , or even a $5 K-mart jobbie, but dammit, how am I supposed to blind other competitors with one of those things?
The solution lay in something I'd had lying around for years - an old mining lamp, which I'd used as a caving lamp. These things had a 4.5V lead acid battery that you wore on your belt, and a really schmick light with a halogen mainbeam and a conventional low beam that clipped to a dedicated bracket on your helmet. The battery had long since snuffed it, and 4.5 is a silly number of Volts. No, the One True Path was 6V, since I could get appropriate (sort of) bulbs...
A quick visit to Jaycar provided the neccessary supplies - a 6V 4Ah battery, a 7.2V halogen globe, and a 6V conventional globe, along with a couple of connectors that weren't compatible with my 12V systems, since I didn't really want to accidentally put 12V through a bulb rated for 1/2 that. A little chopping, a little soldering, a little filing of the reflector assembly so the backup bulb would fit, and voila! The light was working.
Of course, a working light is useless without a way of attaching it, so a little more ingenuity was required. Some scraps of sheet metal that were in the garage were bent and riveted to make a bracket, and a couple of sleeping bag compression straps attached it to my helmet... Weeee, let's go for a night ride!
The 24Hr was the acid test (beta testing? That's for wimps!) for this setup, and overall it worked well. The bracket was originally mounted too low at the front of the helmet, meaning the beam shone quite close to me. This is about where you'd want it for caving, since it helps to see what you're walking on, but for cycling you want to see where you're going. A stop at the halfway mark, where the officials had set up a light, allowed me to remedy this. The only other problem was a dodgy connector - 5 minutes work with a Gerber multitool fixed this one, and I've subsequently reinforced the cable at this point to stop it stressing the connection.
This light is amazingly bright, with a very narrow focus. It's kind of hard to ride with it on its own, but in conjunction with the bar mounted V4.0 hippy lights , this is great light!
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