Saturday, 23 October 2010

My bike light

I've posted before about a bike light I had made, following an idea I saw on Instructables.com. In short, it is using an old Nokia phone to power a 50-odd LED cheap lamp. It worked quite well, and gave around 4 hours of light on a full charge.

The trouble was that despite having 50-odd cheap LED's, it didn't give off a great deal of light. Oh sure, it was fine for cycling in urban areas, but when cycling in the dark in places where there are no other source of light I had to go along at walking pace. Clearly I needed something better!

Any decent light system has two components to it: the actual lamp, and the battery. Batteries can cost an absolute fortune, especially Lithium Ion batteries (which give the best performance).

Now to be frank, I cannot for the life of me understand people that are willing to spend £700 or more on lights for their bikes! Sure, you can get 1200 lumens light systems in that price range, but it remains stupidly expensive for what you get. More so when you take a good look at the price of components!

My new headlight design started with the lamp. I would've preferred a few CREE LED's as they give brilliant performance without needing your own nuclear power station to keep them going, but the cheapest I could find were somewhat out of my price range. They have since come down in price again, so I'm thinking of building a new light, but more on that another time.

I compromised and settled on a 12v 50w halogen pinspot, with a 30 degree reflection. Lamp selected, I needed a housing and the British Army kindly supplied one in the shape of the spent casing of an illumination flare that I found when walking out on Dartmoor. Just the right diameter for my lamp, and made out of aluminium. I had to cut it shorter, obviously, but that only took a moment.

My lamp uses an MR11 push fitting, so I acquired one and fitted it inside the housing using silicon. Halogen lamps produce quite a bit of heat, and silicon can handle a lot of heat. Plus it's cheap and very easy to work with. Pretty soon the light was assembled and left for the silicon to set.

That left me with the battery. My son had an old RC car that was knackered, so at first I tried using the NiCad battery pack from that. At 14v it was in the right sort of region for the lamp I picked, but sadly the battery pack was at the end of it's life and typically went from fully charged to flat in 20 minutes.

At this point I eyed up my laptop's extended battery. Rated 11,2 V and 6600 mAH it seemed a very good alternative. The trouble was I needed to make an adapter to fit the battery, into which I could plug the light. After a bit of thinking I made one using copper contacts that slot into the battery, held in place by a wad of plastic putty trimmed to shape. The copper contacts are connected to a female Molem connector (from inside a computer) and I fitted a Molem connector to the end of the light's cable.

Now since the battery doesn't supply 12 V I don't quite get 50W of light from this setup, but not a great deal less.What I do get is roughly 4 and 1/2 hours of light bright enough for me to cycle in the darkest places. Well, to be honest, although pretty good, my light has some drawbacks - once I get up to around 25 mph in the dark it isn't quite enough light. This is annoying as it means I have to keep braking on nice downhills, just so I can see where I'm going!

The adapter I made for my laptop's battery is obviously removable, and it also fits my laptop's normal battery (4400 mAH) so between the two batteries I can have enough light to cycle all through the night. Well, in summer I can, anyway.

Of course, when the batteries are run down I just pop them back into my laptop and charge them up again! Some people would say using the batteries in this manner will destroy them. I've been running my lights like this for over a year now and both batteries are still in good shape.

CAUTION: Lithium Ion batteries are dangerous, and can combust or even explode. They should NEVER be allowed to get wet. If you do anything similar, it is through your own choice and at your own risk!

I also built a similar light for my son to use on his bike, and he normally uses one of my batteries. His light looks a great deal better than mine and the housing was made out of white PCV plumbing bit. When I build me next light (CREE LED) I'll probably use white PVC again as it looks far better than the aluminium housing I first used. I've also found a supplier of 12v 4400 mAH Lithium Ion batteries (including charger) for under £20-00, so I'll probably be changing the power source, too.