# Charge battery using heat?

## Main Question or Discussion Point

Hi, I don't know so much about electronics but...

I know when you have a junction of two metals that is heated you can get a small voltage. Like wrapping a piece of wire around a nail and holding a flame over it produces a very small but measurable voltage. This is a thermocouple as far as I know.

Now I've heard different metals can produce larger voltages. I was wondering if it might be possible then to make something that could use heat to charge a small battery. It would only have to be enough to light a single LED for 4-5 hours.

So, you could put the junction in some charcoal that is burning all day (like charcoal ovens in 3rd world countries), and then come nighttime have a battery that has enough charge to make a light for you.

I don't really know how a battery charger works, I'm just wondering if something like this is possible. Thanks.

## Answers and Replies

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russ_watters
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NascentOxygen
Staff Emeritus
Science Advisor
So, you could put the junction in some charcoal that is burning all day (like charcoal ovens in 3rd world countries), and then come nighttime have a battery that has enough charge to make a light for you.
No matter what metals you try, one junction doesn't produce anywhere near enough voltage from realistic temperatures to charge a battery. You need lots of junctions.

I have read of these devised around a large kerosene-burning lamp for Soviet peasants in isolated regions to listen to a small radio. Mostly this would be while indoors at night, with the lamp providing meagre room lighting and heating, cooking or water heating, together with the daily propaganda broadcast.

russ,
Yes I've been playing with a cheap thermoelectric generator like the one in that wiki pic. Its not really a steady voltage, and pretty small. But if my goal was just to charge a small button type battery for a single LED, could I do it with some kind of voltage multiplier and regulator?

Nascent,
That sounds great, I'll see if I can find anything more about that.