Re: Homemade Thermopile




Dunc wrote:

There are two major problems with thermopiles as tool to generate
electricity. Very low efficiency and high initial cost. It appears
that the only way to attack efficiency is to utilize more exotic (read
expensive) materials.

What I was wondering is could a "homemade" thermopile be constructed
using very cheap or recycled materials (nails, aluminum cans, aluminum
foil, metal scrap, etc.). If you consider sweat equity to be free you
might be able to produce a viable installation.

If possible, it would be best to utilize a natural occurring
temperature differential such as air to ground, air to water, or dry
bulb to wet bulb. I recognize that these are relatively small delta
T's, but they are completely free and universally available.

My questions are as follows:

Which, if any, commonly available materials would be best for such a
device?

What design parameters should be considered?
For example:
Do the cross-sectional area, distance between or shapes of the
junctions effect the output?

The design parameter you should be considering are those that are
available in the third world; that is the only place where the
labor is cheap enough to do waht you are thinking of doing.

You need to pick an environment, such as in the sun on one side,
in a river on the other side.

You will have to make a list of available materials and then
determine the Seebeck voltage for each pairing. Start with
materials that have large differences between Seebeck
coefficients. Here are the Seebeck coefficients of some
common materials in millivolts per degrees C at at 0 degrees C:

Aluminum 3.5
Iron 19.0
Lead 4.0
Carbon 3.0
Nickel -15.0
Copper 6.5

Source:
http://www.efunda.com/DesignStandards/sensors/thermocouples/thmcple_theory.cfm

This is just a starting point. You need to find the figures for
your target operating temperature, and balance cost against available
voltage. I suggest doing your own experiments.


--
Guy Macon
<http://www.guymacon.com/>

.

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