Even More Hippies on your Head!
While strolling through a local discount store I happened upon a rather cheap head torch . While the quality isn't as good as some   other   brands , as a basis for a DIY torch it's not bad, especially for less than 10 bucks.
Unpacking the box shows a fairly basic torch - there's a fairly cheap and nasty head strap, a battery box with room for 3 AA cells, and a reflector assembly. This torch uses the high-tech "screw the reflector in until the bulb touches the contact" switch found on a variety of cheap and not so cheap torches. In this implementation, the contact is a little dodgy unless the reflector is screwed right in. But hey, what do you expect for the price of a cheap takeway meal?
Across the road from the shop where I got the torch is an electronics chain . For some reason they had 5.5V halogen torch globes, which normally retail for $10-15 if they're available at all, for $2.50. Strangely enough their stock was soon depleted... If you can't find a similar deal, the Krypton globes from 5 D-Cell Maglites aren't too expensive, are reasonably easy to get hold of, and almost as bright. Throwing in a cheap switch and some cable I had lying around at home, I had the basis for a nice lightweight helmet mounted torch, for less than $10 total (excluding battery).
In the components picture you can see my cheap 6V battery, from my previous Head lights . It's a 4Ah SLA jobbie from Jaycar , which cost around $20. SLA chargers can be made out of plugpacks for a few bucks, or they're not particularly pricey to buy. I've also got a few other 6V options - some old 2Ah NiCd video camera batteries I got dirt cheap, and some 5AA NiMH battery packs I made up. NiMH batteries are nice and light, and these days fairly cheap. But they're still more expensive than SLAs. If you're not doing much riding, a 6V "Dolphin" style battery with some appropriate leads will power this nicely for ages.
The first thing to do was rip out the existing 4V bulb so I could put in a more appropriate bulb. As an aside, after building this I threw the original bulb back in to see what happened. It was actually brighter than the halogen. Well, for a little while anyway... Overvolting bulbs makes them very bright, but has rather nasty effects on their life. A 5% overvolt tends to give about 10% more light at the cost of about 30% of globe life. The 50% overvolt had a rather drastic effect on bulb life...
After swapping in the new bulb, it was time to play with the rest of the light. Flipping the back cover open showed a rather basic set of connections - two large chunks of copper to run back the bulb, and two smaller bits to join the batteries in series. The smaller bits weren't required, so out they came.
Next step was to get some cable running in to provide power. I drilled a hole in the side and ran some cable I had at home. Splitting the two strands then knotting them together provides some stress relief for the solder joins. The pictured cable is fairly thin - I've subsequently replaced it with some nice thick 8A automotive cable. The thicker the cable the better for this type of application, within reason of course. Smaller cable has higher resistance, which costs battery power which would be better used driving your lights.
The next step was to rough up the copper contacts so solder would stick nicely. I used a Dremel clone with a grinding attachment, but a bit of sandpaper or a file would do just as well. The shiny patch on the left is the rough bit, catching the flash from the camera.
When I first put this together I didn't worry about a switch, since it was testing. If you're lazy then this works fine - just unplug the battery to turn the light off. However this can be a bit annoying in some situations, like waiting in transition at a night race . But it's only 2 soldered joints to make...
A better design is to put a small switch in, rated at a healthy current so it doesn't melt down on you. This thing is going to sit rather close to a flammable helmet, which is on your head... Jaycar cat SK0975 is a nice one because it's got a low profile. Dremel out a hole for it on top, and solder appropriately:
Flip the battery cover back on, and you're ready to mount the light. On my helmet it sits nicely at the back. A couple of velcro straps holds it on nicely, or you can do as I've done in this picture and zip tie it on. Or if you feel like completing the bodge, use some gaffa tape as well... The best thing about this light is when you crash it into a tree or the ground, you're not going to be out too much cash to replace it, which was the major fear I had with Mk1. So go on, get down to your local $2 shop and see what they've got...
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