engineer-in-wonderland

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An engineer in wonderland – Foxes and charging bloody Li ion batteries

arctic-fox.jpg I once saw an artic fox in Norway. The beautiful fluffy white creature trotted up and sat down only a few metres away, not at all fussed by a couple of cyclists sitting eating sandwiches. Only I didn’t get a photo because my camera had run out of film. So when I bought a digital camera, I bought one that took easily available AA cells so that I could not run out of film or batteries. And that worked well for a long time, until I wanted a camera with more than a 3x zoom.

So now I have another digital camera: a Ricoh R7 which is pretty damn good – although if you can take the extra size and weight, we found on holiday that the Panasonic TX3 always gets the shot whereas the Ricoh occasionally gets confused. Anyway, the compromise I had to make is that good compact cameras no longer allow AA cell operation. So on the R7/TX3 holiday – in Cuba, very nice – I took a mains charger and all was well. But I like to backpack in mountains, so what I really want is a little gadget that I can stuff an AA cell into to charge my camera’s Li ion cell. Sadly, unlike phones, few cameras include a charger circuit. Otherwise I could get one of those little 1AA to 5V inverter phone chargers and do it that way. Actually, I have bought one of those – from Boots the chemist – and am looking for a way to convert it to generate, say, 4.1V to allow me to push something into my Li ion cell. Do read my safety note (below) at this point. Before I embark on this modification, or a scratch build, does any kind soul know where I can buy the right thing from? A scratch build should be pretty easy if time can be found. Boost converters tend to have a diode on the output, so are unlikely to flatten the battery they are supposed to be charging. And by deliberately setting the charge current and voltage a bit low, things will stay safe. An anti-frustration luxury would be a couple of LEDs – one to show the AA is flat (0.9V), and another to indicate the transition between constant current and constant voltage charge – showing the battery has a usable amount of charge in. Any ideas? ‘Alice’ A SAFETY NOTE Please don’t go making Li ion chargers if you don’t know what you are doing. The cells are full of: a, flammable liquid b, energy And ‘b‘ is inclined to spontaneously ignite ‘a‘ if you over-charge them beyond a limit that it remarkably close to the normal charging level. Take a look at www.youtube.com/watch?v=WeWq6rWzChw They also spontaneously ignite if they get too hot. The US Consumer Product Safety Commission has put together a particularly useful public advice sheet on safe Li ion use (Picture – Squish_E, under Creative Commons Attribution Licence)

Tags: cyclists, diode, holiday in cuba, ion batteries, Ricoh R7

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2 Comments

  1. 'Alice'
    April 10, 2008 10:48

    I have seen the Freeloader but, as far as I can work out, it produces 5V and so is only suitable for things with built-in chargers.
    It is a neat device through, with its own internal Li ion cell.
    I have given my problem a bit more thought and the easiest answer is probably a tiny 5V-powered Li ion charger that would plug into my AA to 5V converter, or things like the Freeloader.
    Although if I can reverse-engineer the converter, changing it to 4.0 or 4.1V should not be too tricky.

  2. Simon Pain
    April 08, 2008 14:44

    I don’t know the technical details and whether it would work for you but the first thing that springs to my mind for power while backpacking is a Freeloader. http://www.solartechnology.co.uk/products/solar_chargers/freeloader.asp

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