What metals/semiconductors(?) used in a thermo-electric generators?
Also are TEGs AC or DC?
Best answer:
Answer by Anita
PN junctions
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Anita
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Most thermoelectric generators make use of the Seebeck effect to produce an emf (voltage difference) between a heated junction of dissimilar electrically conductive materials and a cooled junction of the same dissimilar materials. In other words, the thermoelectric generator is a thermocouple or TC.
If a few hundred TCs are wired in series in a radial zig-zag fashion, so the heated junctions are in the center while the cooled junctions are fanned out around the outer circumference, a small amount of electrical power can be produced. Such a device is called a thermopile.
The chimney of a kerosene lamp can be used to direct heat to the centrally located junctions. The outer cold junctions can be attached to a finned heat-sink for radiative and conductive dissipation of the heat flowing up the wires from the center. The larger the temperature difference between the hot inner junctions and the cold outer junctions, the more power will be produced.
The former Soviet Union made a few experimental kerosene lamp thermopiles early in the last century, intending to power radios located in remote or rural areas where electric power was not yet available. This wasn’t very practical at the time because transistor radios were not widely available. Electron tube radios are huge electrical power hogs, because of the requirement to electrically heat their tube filaments hot enough for thermionic electron emission.
A typical pair of dissimilar metals that can be used to create TC junctions is copper and German silver, the latter being an alloy, used in the jewelry business, made of copper, zinc, and nickel but containing absolutely no silver. Copper and Constantan or iron and Constantan are also common TC materials. A chapter in the now out of print book by Alfred P. Morgan, “The Boy Electrician,” described a copper-German silver thermopile with 40 to 50 junctions that produced about six volts at one quarter ampere when the inside junctions were heated “good and hot” with a small alcohol lamp.
It is also possible to create a thermoelectric generator by operating a Peltier effect heat-pump device in reverse. Most Peltier devices consist of a few dozen to perhaps a hundred or so small, square, pieces of N-doped and P-doped bismuth telluride arranged in a single layer, side by side. The individual pieces are electrically connected in series with copper conductors while being effectively connected in parallel thermally. There is no PN diode junction formed by this arrangement, rather instead there are multiple thermocouple junctions formed, similar to the thermopile described above.
Although Peltier coolers have had some success as point-of-load coolers, for computer microprocessors for example, they are not very efficient. When operated backwards as thermoelectric generators they are even less efficient. Nevertheless, the military is extremely interested in this means of producing electrical power, having become dangerously addicted to disposable as well as rechargeable batteries to fund the new electronic gee-haws now necessary to field a combat soldier.
TEGs are DC, but you can add an inverter if you need AC.
A good source for more information is: http://www.peltier-info.com