Years ago I had a Canon GL-1 camcorder, and it came with this massive battery that allowed for 3 or 4 hours of continuous operation. It was one of those generic aftermarket batteries so after a few months the casing started to split apart and would no longer stay attached camera. So for the past 3 years I have been carrying this around with me:

It’s a 6 cell Li-ion battery pack that outputs 7.2V (6600mAh!) 2S3P configuration. The cells are unbranded 18650 cells, however what makes this pack special is a small protection PCB and self-reseting fuse that prevents the battery from turning into a flaming ball of lithium. Li-ion cells are very sensitive to overcharging and overdrawing. Hobbyists have gotten 3rd-degree burns and set their houses on fire from improper use of Li-ion batteries.

So now that I’ve got this dangerous awesome battery pack I need some application for it. I’ve thought about hacking up an old cordless drill and swapping the NiCd cells for these, or adding them to a small battery powered toy just for fun. However I am leaning towards a more practical use. I want to use them as the power source for an insane bike light.

I occasionally mountain bike during the day, but I’ve been wanting to go out on night rides. You need some serious lighting equipment to keep you from running face first into a tree at 20mph. Most guys run HID setups which run $250-500. My DIY light won’t be as bright, but should still blind most oncoming traffic. I am planning on making this a helmet mounted light with the battery back stored in my camel bak. The head lamp must be as light as possible because a heavy light can really strain your neck after you’ve been wearing it for several hours. Here’s the plan:

• Seoul Semiconductor P7 LED ~700-900 lumens
• Machined aluminum housing, optimized for heat transfer and weight
• Buck converter to drop voltage down from battery
• Completely sealed system, should handle rain easily

That’s it for now. The next step is to pick out a driver and start creating drawings for the housing.