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Re: Homemade Thermopile
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Re: Homemade Thermopile Solar Flare 12-03-2007
Posted by Solar Flare on December 3, 2007, 8:29 pm
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 Soldering nullifies the difference in metals. It's the contact of
differing metals that makes the voltage.

>-> 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?
>
> You'll get only a few millivolts, so to get reasonable power, you'll
> have to arrange to produce plenty of current - amps, or tens of
> amps.
> And that means that your thermopile is going to have to have an
> *extremely* low electrical resistance, less than a thousandth of an
> ohm. That means that the conductors will have to be short and thick,
> and the connections at the junctions will have to be far better than
> is
> easily done. Since you're using aluminum as one of the metals,
> you're
> going to have to do something to get rid of the oxide film that
> usually
> coats it. Making good connections with aluminum is notoriously
> difficult.
>
> Maybe you should use iron and copper, and solder all the
> connections.
>
> You've set yourself a challenge!
>
> dow



Posted by Anthony Matonak on December 3, 2007, 10:22 pm
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 Solar Flare wrote:
> Soldering nullifies the difference in metals. It's the contact of
> differing metals that makes the voltage.

I think you're confusing a battery with a thermocouple.

It's the different metals themselves, each having one end
hot and the other cold, that makes the electricity. The
connection is not where the power is generated.

http://en.wikipedia.org/wiki/Thermocouple
: In 1821, the German–Estonian physicist Thomas Johann Seebeck
: discovered that when any conductor (such as a metal) is subjected
: to a thermal gradient, it will generate a voltage.

Then again, don't let facts get in the way of a good troll.

Anthony

Posted by Solar Flare on December 3, 2007, 11:33 pm
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Interesting. I always thought it was the dissimilar metals that
produced the voltage differential.

Don't miss an oportunity to insult somebody if you can disguise it
inside a helpful post.

> Solar Flare wrote:
>> Soldering nullifies the difference in metals. It's the contact of
>> differing metals that makes the voltage.
>
> I think you're confusing a battery with a thermocouple.
>
> It's the different metals themselves, each having one end
> hot and the other cold, that makes the electricity. The
> connection is not where the power is generated.
>
> http://en.wikipedia.org/wiki/Thermocouple
> : In 1821, the German–Estonian physicist Thomas Johann Seebeck
> : discovered that when any conductor (such as a metal) is subjected
> : to a thermal gradient, it will generate a voltage.
>
> Then again, don't let facts get in the way of a good troll.
>
> Anthony



Posted by daestrom on December 6, 2007, 7:37 pm
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> Interesting. I always thought it was the dissimilar metals that produced
> the voltage differential.
>

Well it is the dissimilar metals, but also the temperature difference. For
example, take copper-constantine thermocouple. If you separate them and
then put copper-iron, iron-Al, Al-zinc and finally zinc-constantine and put
all four junctions in the 'hot' temperature, the mV you get will be the same
as copper-constantine originally.

In temperature instruments, we use copper-constantine a lot and have to run
the copper-constantine wire pair all the way back to a termination cabinet.
We land the wires on an ordinary terminal strip and use simple copper from
there to the A/D units. The only thing 'special' about the termination
cabinet is that the temperature of the cabinet is controlled and also input
to the computer instruments.

The thermocouple voltage is really only a measure of the *difference* in
temperature between the 'hot' and 'cold' junctions. So by measuring the mV,
converting to degrees, then adding the internal temperature of the
termination cabinet, we can get pretty accurate temperature measurements.

But if some one screws up and splices the line with plain copper-copper
pair, they inadvertantly create a third junction. And since we don't know
the temperature of that third junction, we can't get as accurate a reading.
If the 'splice' is near room temperature (near the same as the termination
cabinet temp), then the readings 'look' okay but will drift up/down as the
temperature of the third junction (unauthorized 'splice') varies.

In a pinch you can just take a length of copper-constantine cable, strip the
ends on one end and hand twist them together and voila, you have a
thermocouple. It's just as accurate as the fancy store-bought ones (I know,
I've checked them in a cal-lab). The only downside is that when you mount
it on something, the bare wire end touching metal can cause ground-loops and
that can screw with your A/D or milliVoltmeter.

daestrom


Posted by Solar Flare on December 6, 2007, 11:10 pm
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Let's see if I understand this correctly.

Metals develop a voltage drop across themselves due to temperature
differential along the metal. The trick is to bring the induced
current or potential back to a cold place, where the measurement is
taken, with a metal that has a lower voltage coefficient so there is
some left to measure.

>
>> Interesting. I always thought it was the dissimilar metals that
>> produced the voltage differential.
>>
>
> Well it is the dissimilar metals, but also the temperature
> difference. For example, take copper-constantine thermocouple. If
> you separate them and then put copper-iron, iron-Al, Al-zinc and
> finally zinc-constantine and put all four junctions in the 'hot'
> temperature, the mV you get will be the same as copper-constantine
> originally.
>
> In temperature instruments, we use copper-constantine a lot and have
> to run the copper-constantine wire pair all the way back to a
> termination cabinet. We land the wires on an ordinary terminal strip
> and use simple copper from there to the A/D units. The only thing
> 'special' about the termination cabinet is that the temperature of
> the cabinet is controlled and also input to the computer
> instruments.
>
> The thermocouple voltage is really only a measure of the
> *difference* in temperature between the 'hot' and 'cold' junctions.
> So by measuring the mV, converting to degrees, then adding the
> internal temperature of the termination cabinet, we can get pretty
> accurate temperature measurements.
>
> But if some one screws up and splices the line with plain
> copper-copper pair, they inadvertantly create a third junction. And
> since we don't know the temperature of that third junction, we can't
> get as accurate a reading. If the 'splice' is near room temperature
> (near the same as the termination cabinet temp), then the readings
> 'look' okay but will drift up/down as the temperature of the third
> junction (unauthorized 'splice') varies.
>
> In a pinch you can just take a length of copper-constantine cable,
> strip the ends on one end and hand twist them together and voila,
> you have a thermocouple. It's just as accurate as the fancy
> store-bought ones (I know, I've checked them in a cal-lab). The
> only downside is that when you mount it on something, the bare wire
> end touching metal can cause ground-loops and that can screw with
> your A/D or milliVoltmeter.
>
> daestrom
>



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