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Help! I need electricity from Heat.

R

Raymond

Jan 1, 1970
0
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples and, I understand
that many thermocouples, are called a thermopyile (pile?), but, my
problem is that I can't find anything that generates anything more in
output than milliamps, like, 20. (I'm not stuck on thermocouple
technology either.)

Can anyone help? I'd be VERY appreciative. p.s. (don't say
steam...thnx)

Feel free to e-mail me at [email protected]
 
S

Spehro Pefhany

Jan 1, 1970
0
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples and, I understand
that many thermocouples, are called a thermopyile (pile?), but, my
problem is that I can't find anything that generates anything more in
output than milliamps, like, 20. (I'm not stuck on thermocouple
technology either.)

You could use a Peltier device in reverse (a ready made device with
hundreds of thermocouple junctions), but don't expect more than a few
percent efficiency. If you need than 20mA but at a very low voltage,
for some reason, that may not be a factor.
Can anyone help? I'd be VERY appreciative. p.s. (don't say
steam...thnx)

How about a Sterling engine?
Feel free to e-mail me at [email protected]

Best regards,
Spehro Pefhany
 
J

John Popelish

Jan 1, 1970
0
Raymond said:
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples and, I understand
that many thermocouples, are called a thermopyile (pile?), but, my
problem is that I can't find anything that generates anything more in
output than milliamps, like, 20. (I'm not stuck on thermocouple
technology either.)

Can anyone help? I'd be VERY appreciative. p.s. (don't say
steam...thnx)

Feel free to e-mail me at [email protected]

The trick to generating electricity from heat involves heat flow from
a high temperature to a low temperature.

Thermocouples generate only a couple millivolts each, but (can) have
very low impedance. So putting many in series the impedance to build
up the voltage you can still get useful current through them. The
concept is to series two different metals (copper and iron work pretty
well and are cheap and available) while alternating the temperature of
the junctions between a hot reservoir and a cold one. This is a
thermopile. For instance you might run a copper wire to a hot place.
Connect to an iron wire which runs to a cold place. There, connect it
to another copper wire that runs back to the hot place (insulated from
the other wires, of course), etc. You can use actual thermocouple
metal wires, but they are expensive, because of their guaranteed
purity. For simple power generation, this is little use. The
junctions can be any connection that is low resistance and suitable
for the temperatures involved (welded, soldered, brazed, silver
soldered, clamped, etc.)
Search google for a table of seebeck constants. The larger the
difference, the more voltage each couple produces per degree.
Antimony bismuth is good, but expensive fragile and high resistance,
compared to copper iron.

If you want to purchase something that is easier to clamp between a
hot and cold surface you can use a peltier stack. It works something
like a thermopile, but with semiconductors instead of metals.
These are sold on ebay for pretty reasonable prices, sometimes with a
heat sink attached to one side.
Search peltier.
 
T

Tim Auton

Jan 1, 1970
0
Spehro Pefhany said:
You could use a Peltier device in reverse (a ready made device with
hundreds of thermocouple junctions)

I think "thermoelectric generator" is the posh term.
, but don't expect more than a few
percent efficiency. If you need than 20mA but at a very low voltage,
for some reason, that may not be a factor.

With such a poor temperature differential nothing is going to be
efficient.
How about a Sterling engine?

Are they used "in the wild"? I've never seen one except as a
curiosity.


Tim
 
S

Spehro Pefhany

Jan 1, 1970
0
Are they used "in the wild"? I've never seen one except as a
curiosity.

The ones I've *seen* are mostly whittled out of scrap metal by old
farts^H^H^H^H^H "Model Engineers" with lots of time on their hands.

But yes, they seem to be used in some applications:

http://www.stirlinginfo.com/

Best regards,
Spehro Pefhany
 
D

Dave VanHorn

Jan 1, 1970
0
Raymond said:
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant.

A bunch of thermoelectric coolers, in series, with a large heatsink, or
(ideally) running water, works beautifully.. I have such a beast, uses eight
peltier panels, outputs 15V at about 300mA in addition to running it's
internal fan. You don't want to get the peltiers too hot though. Check the
specs.
 
I

Ian Stirling

Jan 1, 1970
0
Spehro Pefhany said:
You could use a Peltier device in reverse (a ready made device with
hundreds of thermocouple junctions), but don't expect more than a few
percent efficiency. If you need than 20mA but at a very low voltage,
for some reason, that may not be a factor.

With a common 20W 12V peltier, I measured the power produced when
it had its maximum temperature difference of 60C across it and a cold
temp of around 0C.
The power out was around 1% of the 7% maximum thermodynamic efficiancy.
IIRC around 2mw.
 
B

Boris Mohar

Jan 1, 1970
0
F

Fred Bloggs

Jan 1, 1970
0
Raymond said:
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples and, I understand
that many thermocouples, are called a thermopyile (pile?), but, my
problem is that I can't find anything that generates anything more in
output than milliamps, like, 20. (I'm not stuck on thermocouple
technology either.)

Can anyone help? I'd be VERY appreciative. p.s. (don't say
steam...thnx)

Feel free to e-mail me at [email protected]

You want something like this:
http://www.sitechina.com/thermoelectric/Pspec.html
 
R

Robert Lacoste

Jan 1, 1970
0
I think you are targeting the most difficult power level for this kind of
application : If your need was tens of mW then a peltier-based or thermopile
will be adequate. If your need was some kW then a thermal pump and a
vapor-based turbine/generator will be adequate. But for a couple of W I
don't know any solution...

Good luck,
Robert
 
J

James Meyer

Jan 1, 1970
0
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples and, I understand
that many thermocouples, are called a thermopyile (pile?), but, my
problem is that I can't find anything that generates anything more in
output than milliamps, like, 20. (I'm not stuck on thermocouple
technology either.)

Can anyone help? I'd be VERY appreciative. p.s. (don't say
steam...thnx)

Feel free to e-mail me at [email protected]

Most thermocouples are made with thin wire and that is what limits the
current available. I have seen thermocouples made with 2 inch wide, 1/4 inch
thick, plates of iron and copper that can generate tens of amps. They were made
for physics classroom demonstrations.

Jim
 
S

Spehro Pefhany

Jan 1, 1970
0
Most thermocouples are made with thin wire and that is what limits the
current available. I have seen thermocouples made with 2 inch wide, 1/4 inch
thick, plates of iron and copper that can generate tens of amps. They were made
for physics classroom demonstrations.

Obviously it takes a lot of power to maintain that temperature
differential with massive chunks of metal. T/Cs designed for
measurement purposes are not normally supposed to affect the
temperature itself very much, so minimizing the heat flow is
desirable.

In ye olden days of yore when mechanical meter movements were driven
directly by T/Cs the source resistance was of some importance (though
it tended to be dominated by the compensation leadwire), but with
electronics other factors are now generally limiting.

Best regards,
Spehro Pefhany
 
B

Barry Lennox

Jan 1, 1970
0
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples and, I understand
that many thermocouples, are called a thermopyile (pile?), but, my
problem is that I can't find anything that generates anything more in
output than milliamps, like, 20. (I'm not stuck on thermocouple
technology either.)


There was something used during WW2 or perhaps later, for special
forces to power a radio. I gather it was a large array of TCs, powered
from a gas stove, I have a photo of it in use somewhere together with
a little detail. I'll try to find it, and will post again if I do.

Barry Lennox
 
B

Barry Lennox

Jan 1, 1970
0
Hey People, I hope one of you can help.

I need a way to generate current (low voltage) from a fairly constant
heat source. Probably need about 3 watts. The heat will be around 200
degrees F., maybe hotter, but always fairly constant. I've been told
about, and have done some reading, on thermocouples

Ha, found it. It was used during WW2 to recharge batteries for the
resistance. (Fighting kind, not Ohms!)

It consisted of 350 chromium-constantan TCs in a fireproof brazier.
With a decent wood or charcoal fire it would charge a 6 volt battery
at up to 1 amp.


Barry Lennox
 
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