Homemade Thermopile

[Dunc]

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?

 

[Spehro Pefhany]

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.

You need more than a temperature differential-- you have to be able to
force heat to flow through the thermopile, at an acceptable cost per
unit of heat flow.

My questions are as follows:

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

Even with exotic materials, efficiencies in the 3-8% range are
typical.

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

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


Best regards,
Spehro Pefhany

 

[Ken S. Tucker]

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?

I've been thinking about quietly buying up old smoke
detectors for the Americium content, to build a
basement reactor. A 50 gallon drum glowing at 300F
saves heating bills.
Seriously, a "so-called" thermopile needs an energy
source. Anything useful needs Watts, a few hundred
at least.
Ken

 

[Tim Williams]

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.

Useless. Efficiency is what, parts per million with common materials?
It's not even worth counting percent anymore.

Probably, a printed form would be best. Or given optimal materials (IIRC,
NASA's RTGs use Si-Ge), lithography might be more appropriate. You want to
integrate as many junctions as possible into a very small space. What you
gain in thermal characteristics (in terms of heat loss) you lose in
electrical resistivity, so you might as well minimize the material between
junctions.

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

Probably, like, silicon and germanium. Oops...

Do the cross-sectional area, distance between or shapes of the
junctions effect the output?

Ya- junctions act like perfect voltage sources, so you're just talking
resistor stuff here. The figure of merit of any two materials depends on
the junction potential and their combined bulk resistivity. What length
and thickness you want between junctions is up to you, but you might as
well make it small. That means you need a steep thermal gradient, which
means lots of power input, but also lots of current you can draw (depending
on just how many junctions you've stacked). So you see, it makes up for
itself.

Tim

 

[Larry Snyder]

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?

Hi. I'm building this:
http://www.pacificsites.com/~snyder/Motor/high_efficiency_power_conversion.htm
It could easily run a generator. If you have maching capabilities, let's
work together.
Larry

 

[John Larkin]

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?

An iron-copper thermocouple can be made from hardware-store stuff. It
will give about 50 microvolts per degree C temp differential, and you
can put multiple junctions in series to get more voltage. Of course,
the resistance goes up as the heat source:sink distance goes up, and
as you add thermocouples in series. Done just right, expect thermal
efficiency on the ballpark of 0.5%. It's unlikely that you can harvest
even a couple of milliwatts from the sorts of sources you mention. A
10 degree C temp differential is about 500 uV per couple, so you'd
need ballpark 3,000 thermocouples in series to light an LED.

Older water heaters and furnaces use a thermocouple, in the pilot
flame, to hold in the gas solenoid valve. I guess they use multiple
junctions, too. 50 millivolts is typical here.


The iron will rust, too.

John

 

[Larry Snyder]

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?

If you don't want to work together, check out:
http://www.pacificsites.com/~snyder/GoodIdea.html
Larry

 

[Guy Macon]

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.

 

[John Larkin]

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

Microvolts, actually.

John

 

[Barry Lennox]

snip

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?

There were some made during WW2 for the SOE and resistance groups,
These put out a low voltage and a half-decent current to charge
batteries.

I have a reference to one that used 350 thermocouples
(chromium-constantan) in a brazier heated by a good-sized charcoal
fire. My guess is the efficiency was awful, but it beat having no
power.

 

[John Popelish]

There were some made during WW2 for the SOE and resistance groups,
These put out a low voltage and a half-decent current to charge
batteries.

I have a reference to one that used 350 thermocouples
(chromium-constantan) in a brazier heated by a good-sized charcoal
fire. My guess is the efficiency was awful, but it beat having no
power.

I wonder how their efficiency and voltage output compare to
a modern Peltier cooler operated as a generator.

 

[Martin Griffith]

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?

Didn't Voyager use thermopiles and plutonium? They still seem to be
working


martin

 

[Spehro Pefhany]

Microvolts, actually.

John

What's three orders of magnitude between friends?


Best regards,
Spehro Pefhany

 

[John Larkin]

What's three orders of magnitude between friends?

Yeah, I shouldn't be so didactic, academic, advisory, donnish,
edifying, enlightening, exhortative, expository, homiletic, hortative,
instructive, moral, moralizing, pedagogic, pedantic, preachy,
preceptive, schoolmasterish, sermonic, sermonizing, teacherish,
teacherly, teachy, dainty, eclectic, exacting, fastidious, finical,
finicky, fussy, nice, overparticular, particular, persnickety, picky,
picky-picky, select, selective, or precise.

Sorry.

John

 

[Paul Hovnanian P.E.]

Why not attack the problem by starting with the available heat source
and then finding the technologies that best suit the delta T and heat
flow. Also, consider what your system requirements (electrical load,
weight and size cinstraints, reliability) are.

Thermopiles fit a very small set of potential applications.

 

[Clifford Heath]

I wonder how their efficiency and voltage output compare to a modern
Peltier cooler operated as a generator.

A friend of mine ran a primary school team that entered a model boat
contest with a 60W Peltier device that had ice one side, boiling
water or candle heat (I forget) the other, and drove an electric
motor. They won the contest hands-down, ten seconds to cover 10m.
Might not have been efficient, but it generated good power for a
short period.

 

[Jan Panteltje]

A friend of mine ran a primary school team that entered a model boat
contest with a 60W Peltier device that had ice one side, boiling
water or candle heat (I forget) the other, and drove an electric
motor. They won the contest hands-down, ten seconds to cover 10m.
Might not have been efficient, but it generated good power for a
short period.

OK I have a 'Zibro' air dehumifier.
It has a peltier in it, and runs one some separate swicthmode that outputs
13.6V 5A DC.
Been running for days..
I disconnected the DC plug from the switchmode,
measured the open voltage on t connector from the Peltier : 1.2V
measured the short circuit current (amp meter ) .45A

Not bad!!!!!!!!!!
Because it is handwarm on the hot side, and about 1 C or so at the cold side,
not even freezing, just cold enough to create condensation.

Indeed I think that if yo uuse ice and a falme it can run a small electric motor.
Now how's that for quick test

 

[Dunc]

THANKS FOR ALL YOUR IINPUT

To clarify the concept, what I am trying to do is see if there is a
low tech, relatively cheap method of utilizing the UNLIMITED
FREEenergy represented by the low-grade temperature differentials
between natural occurring sources like ambient air and ground water.

I know that thermopiles are not very efficient. But since the energy
is free and I am not looking to manufacture and sell anything (hence
the "homemade") the labor is free, the only cost consideration is the
material costs. If the material costs can be made low enough, a
viable alternative may be achievable even with very low efficiencies.

In the example shown below, alternating layers (of equal thickness)
Iron Foil (folded at one end), Paper (insulation), and Aluminum Foil
are utilized. As many layers as needed could be added. Insulated bolts
would compress the layers to insure the junction contacts. The whole
assembly could be dipped or coated in plastic to seal out air and
moisture.




XXX XXX WWW W = Copper wire
XBX XBX W
XXXXXBXXXXXXXBXXXXXXWX X = Thin plastic coating to
prevent oxidation
XIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIWX I =
Iron foil folded at one end
H XIIPPPPPP PPPPPPPPPPX` P = Paper
J XAAAAAAAAAAAAAAAAAX C A= Aluminum foil
XPPPPP PPPPPPPPPPPIIIX J HJ = Hot Junctions
XIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIX
H XIIPPPPPP PPPPPPPPPPX CJ = Cold Junctions
J XAAAAAAAA AAAAAAAAAX C
XPPPPPPPP PPPPPPPWIIX J
XXXXXBXXXXXXXBXXXXXWXIX B = Compression Bolts
XB X X BX W
XXX XXX WWW

In a given system, the voltage differential is strictly a function of
the number of junctions and the temperature differential. What I want
to know is how to calculate the watts.

If I hold the temperature differential constant:

Is the wattage produce the same or is it dependent on the number of
junctions?
With the same number of junctions, is the wattage the same if I double
the thickness of the layers or make the layers 3 inches by 30 inches
instead of 3 inches by 3 inches?

For those of you that are interested in early thermo-electric devices
http://www.dself.dsl.pipex.com/MUSEUM/POWER/thermoelectric/thermoelectric.htm#mk

 

[Tim Williams]

Didn't Voyager use thermopiles and plutonium? They still seem to be
working

At somewhat lower efficiency (past the halfway point IIRC) by now. Partly
due to the decay of the Pu238 (note it's not the more infamous Pu239 of
weapons fame, nor Pu244 or so of reactor grade fame), which is quite rapid.

The largest RTG NASA has sent up was on Cassini, IIRC. Remember people
were making a big stink about the 80-some odd pounds of plutonium on
launch?

Tim

 

[Spehro Pefhany]

OK I have a 'Zibro' air dehumifier.
It has a peltier in it, and runs one some separate swicthmode that outputs
13.6V 5A DC.
Been running for days..
I disconnected the DC plug from the switchmode,
measured the open voltage on t connector from the Peltier : 1.2V
measured the short circuit current (amp meter ) .45A

Not bad!!!!!!!!!!
Because it is handwarm on the hot side, and about 1 C or so at the cold side,
not even freezing, just cold enough to create condensation.

Indeed I think that if yo uuse ice and a falme it can run a small electric motor.
Now how's that for quick test

I believe you can buy Peltier powered fans that work in stovepipes, so
the ice may not be necessary. ;-)

Best regards,
Spehro Pefhany