But you can already get.....
the Biolite camp stove, which runs off of twigs and stuff. And believe me, there is no shortage of wood in Sweden. I'll be taking one with me when I move there (finally) this year.
Sick of running out of charge while on long walks, a Swedish tinkerer has crafted a thermoelectric phone charger to revive his smartphone and GPS by burning butane. Vulture South notes that the setup, posted on Instructables here, is wildly inefficient, but it's a use-in-emergency approach. As David Johansson, the creator of …
for emergency it could help, but if let's say you're hiking or climbing , the -relative - weight issue would be an handicap. And if used in a relatively windy location, a correct box/cover is indispensable, just Imagine you on an emergency situation in the Alps, even in a snowy storm, and try to use such.. need refining and details. But always a good initiative to develop more.
A nice /expensive/ backwards toy, but not much useful power.
The Biolite is very expensive toy, to fund donation of the larger version for 3rd World households, and has a small cooking area for a camping stove; it has been tested to take ages to get hot enough to give some trivial excess power output after driving the air-intake/cooling fan up to speed, and you are not going to want to nurse it for hours to hopefully charge a portable device! You can buy several beefy Li-ion battery packs for the same price; enough to keep mobile devices running for several days!
I looked at various themo-electric power sources before, and they don't look worth the significant cost, and are still quite inefficient, so provide poor power conversion e.g. even an in-development C.H.&P. central heating design I saw could only generate a mere 500W of electricity, from many Kilo Watts of gas combustion heat, at quite a premium total price!
It would seem more efficient to make a portable fuel cell, or gas turbine generator.
I was lucky enough to meet one of the Biolite stove developers at Design West / Embedded Systems Conference two weeks ago.
He happened to be the "booth babe" nearest the stove, a few UV purifiers and other interesting gear. I asked a question, and was pleasantly surprised at a knowledgeable reply. That led to a 30 minute conversation about the capabilities and design.
The stove has a microcontroller to manage the power, optimizing the peak power extraction from the thermal generator , and setting the priority of running the fan, recharging the single A123 cell, and charging a USB device.
Power extraction from the thermal generator is much like a solar cell. Draw too little current and you give up some of the output potential. Draw too much current and the voltage sags more than the extra current gains.
The key to a stove like this is running the fan. The fan cools one side of the thermal generator, then flows around the outside of the combustion chamber to keep it cool, then feeds the flame with now-quite-hot air.
Because it uses forced air, small stuff like twigs burn intensely and completely, whereas a open twig fire will flare up and die down, always burning inefficiently. The drawback is that this is a tiny stove, so you can never move up to bigger stuff. Unless you carry wood pellets with you, you need to constantly feed it more twigs. (That's probably it's biggest problem: it's too heavy to be a backpacking stove, and too attention-seeking to be a casual camping stove.)
The thermal generator does have very low efficiency, in part to keep it reasonably light. But efficiency isn't a huge problem, especially if you treat it as a stove first. There is plenty of source heat and the 'waste' heat still goes into cooking. Now if you are treating it as an electric power source... uhggh. It will use just as much fuel (and attention) as when cooking, and its priority is running the fan and recharging the internal battery before outputting external power.
If you have to carry butane with you to make this huge thing work then you may as well just carry more batteries which are far more energy dense.
If you power it with found materials then this is potentially useful, but a hand crank charger might be faster and more effective.
Nothing at all new in this though... In the Seebeck effect has been used for years to provide power from heat.
In the 1950s, the Russians made a Seebeck effect collar which was fitted to kero lamps to provide power for radios.
In the 1970s, I remember some encyclopedia giving instructions on how to build a Seebeck device to power a single transistor radio.
You could try following the link. Obviously the guy is aware of the prior existence of devices that use the Seebeck effect, since he just bought one off the shelf. As for carrying butane, that is just for testing. As he says himself: "[...] if you use gps tracking the phone is empty in half a day. If you are away for one week, that means 14 recharges and a lot of batteries. If you can power the phone by using only wood, then you only need to bring my 400 grams and a lighter."
"In the 1970s, I remember some encyclopedia giving instructions on how to build a Seebeck device to power a single transistor radio."
World Book encyclopedia - I had a copy. They used themocouple wire and a candle flame, and a very low power AM receiver design. A modern BiTe module would do a lot better.
I have a stack of 5 92.5W elements from eBay. Plug one into the 12v rail from a PC PSU and you'll cook eggs on one side and freeze your fingers to the other, assuming the ceramic doesn't crack first. Some overclockers have been using them to pump even more heat out of the CPU and into the heatsink.
Wildly inefficient as generators, but if it's something less like a butane torch and more like a campfire, then maybe useful.
its not a pain staking task finding a charger for an iphone though
http://www.pcpro.co.uk/news/380692/reactor-for-iphone-5-builds-hand-charger-into-case
http://www.amazon.co.uk/Emergency-Mobile-Phone-Iphone-Charger/dp/B001MA2YO2
and if your just going to freeride XC across scotland and desert etc on your £4000 mountain bike, its not hard to put a dyno hub on the front wheel, and use a old domestic charger for the wire adaptor to the hub
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Personal preference is a factor, but if you're a regular hiker and willing to lug all that you would be better served by a handheld dedicated GPS. Such a widget lasts 18 hours on two AA batts, and is waterproof and rugged for outdoor use, two areas the phone falls flat (pun intended).
Philosophically, how many hoops does one jump through for the "ease and convenience" of using the phone instead of a dedicated widget? Is it worth it to risk your expensive phone in the rain?
Or use a Nokia. Their Nokia Maps^W^W Ovi Maps^W^W Here There Everywhere^W^W^W Pants Maps^W^W... Oh, whatever they call it this week, their maps application stores everything locally meaning that it's still useful even after you leave home. I have never understood the fetish for expensively downloading high resolution satellite maps just so you can figure out which exit to take from the highway.
While I am not sure that a mobile phone is the best choice of technology, we are all a sort of cyborg. We are all rebuilding ourselves with the tools we carry, and have been since the first flint was knapped. Clarke and Kubrick had it right with that jump-cut from a thigh-bone used as a club to an orbiting satellite.
We cannot sense magnetic fields, so we carry a compass. All this is just another step on a long road. I've aligned a paper map using a compass, so that I can match the landscape to the map. Now we have lightweight tablets which have the built-in magnetic sensors and can display the map. I regret that some people may never realise what their tools are doing, but I remember the first time I did this with a map, and connected in my head two places, on different roads, that had seemed completely unrelated yet were about a quarter-mile apart.
Is it right that we come to depend on these machines? I prefer to know the old-style tricks they emulate, because batteries do fail. For this guy--does he work from a garden shed or is Sweden too far north--he's had the fun of solving the problem. And that might be enough reason.