Flashlight powered by warmth of hand

Anyone heard of such a thing? /ubbthreads/images/graemlins/au.gif

I don't think that's physically practical. You'd be generating power from the temperature difference between your hand and the surrounding air. If that difference is small, there's not much energy available (very low Carnot efficiency, and not much power to begin with). If the difference is large, it means the air is very cold and you don't want to use the flashlight without gloves on! Maybe with big thermocouples you could get enough power out to run a small LED in chilly weather, but it would be quite uncomfortable (like sticking your hand into cold water). You're better off using a mechanical generator, either a squeeze/crank type, or a shake-up-and-down type. See www.shakelight.com for a shake-up-and-down LED light that's sort of borderline practical, and is fun to play with.

Thanks Paulr, Someone else told me about this idea, I thought it would be unworkable. You confirmed that!

But you could build a little table top steam generator powered by a candle to charge your batteries. I think a little stem generator could be vastly more efficient than a thermocouple anyway, and much more fun to operate /ubbthreads/images/graemlins/grin.gif course you couldn't hold it in your hand while operating.

More fun to build a sterling engine into the flashlight. They dont generate much torque though so it would also have to be a single LED running from it. You could certainly make one that would generate enough for an LED from the heat of a cup of coffee,

Thermocouples need a VERY large temperature differential to generate useful current. and in something like a flashlight body you'd need either great big heat fins or a fan or a nice cool breeze, otherwise the temperature would equalize quickly and stop generating anything at all very quickly.

More practical would be using some sort of peizoelectric generators in your shoes to charge a small battery or capacitor to run a LED, if you want "free" energy of some sort.

I've heard another idea for powering tiny LEDs at tiny currents - something akin to the RF-powered crystal radio with a coil to snag RF and some way to store that energy to be expended when required.

I don't know if either approach would generate/capture enough energy to actually work well.

If it was possible with such a small delta T difference, it would have been widely adopted in streetlighting and saltwaterdetillationplants-in-the desert.

Isnt this also a mechanical and not an electrical principle?
(Like reusing heat in industrial plant processes and solarpanel preheated water to for sunboilers )

Edit: BTW There are clocks that are powered by the differences in atmospheric pressure.

Sterling engines use temp differences to run, so it is theoretically possible to use it to power a generater. But handheld, not likely.

http://en.wikipedia.org/wiki/Stirling_engine

idleprocess said:

More practical would be using some sort of peizoelectric generators in your shoes to charge a small battery or capacitor to run a LED, if you want "free" energy of some sort.

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Some guy way back thought of putting piezoelectric disks under his shoes to charge power LEDs for the safety of joggers or runners at night...apparently that idea was abandoned because I can't find any information about it anymore

You could generate electrical energy to power LEDs with the mechanical forces of a ThighMaster. Simple, reliable, and I'd pay good money to see cops trying to use them!
:laughing:

Illum said:

Some guy way back thought of putting piezoelectric disks under his shoes to charge power LEDs for the safety of joggers or runners at night...apparently that idea was abandoned because I can't find any information about it anymore

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What about all the little kids you see with the battery powered light-up shoe heels and soles? And why didn't they put THAT idea on runners I wonder?

Mr Bigglow said:

What about all the little kids you see with the battery powered light-up shoe heels and soles? And why didn't they put THAT idea on runners I wonder?

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Apparently CR2016s were cheaper than piezoelectric discs:thinking: