THERMOELECTRIC GENERATOR

• US 3,818,304 A
• Filed: 08/12/1971
• Issued: 06/18/1974
• Est. Priority Date: 05/23/1969
• Status: Expired due to Term

• Current Assignee: David L. Prudy, Steve A. Kokenik, Thomas P. Hursen
• Original Assignee: David L. Prudy, Steve A. Kokenik, Thomas P. Hursen
• Inventors: Hursen, Thomas P., Kokenik, Steve A., Prudy, David L.
• Primary Examiner(s): Beha, Jr., William H.
• Application Number:
  US05/171,383
• Time in Patent Office: 1,041 Days
• Field of Search: 310/3,4 128/419P,421 321/2,8 331/113.1 136/202
• US Class Current: 310/306
• CPC Class Codes: A61N 1/378 Electrical supply
• CPC Class Codes: G21H 1/103 Cells provided with thermo-electric generators
• CPC Class Codes: H02M 3/3384 of the parallel type

Abstract

A heat-to-electricity converter is disclosed which includes a radioactive heat source and a thermoelectric element of relatively short overall length capable of delivering a low voltage of the order of a few tenths of a volt. Such a thermoelectric element operates at a higher efficiency than longer higher-voltage elements; for example, elements producing 6 volts. In the generation of required power, thermoelectric element drives a solid-state converter which is controlled by input current rather than input voltage and operates efficiently for a high signal-plus-noise to signal ratio of current. The solid-state converter has the voltage gain necessary to deliver the required voltage at the low input of the thermoelectric element.

Claims

1. An electrical generator including a heat source and a heat sink, a thermoelectric element formed of a plurality of short thermocouples having a hot junction and a cold junction, said hot junction being connected in heat-deriving relationship with said source, and said sink being connected in heat-deriving relationship with said cold junction, the output of said element being a few tenths of a volt, a solid-state electrical converter having an input responsive to the magnitude of input current as distinct from voltage and said input also having a maximum lowvoltage drop of about .001 volts for the input voltage impressed thereon and thus being operative for a low voltage input of about a few tenths of a volt, said converter also having an output and means for connecting said output to a load, means connecting said element to said input so that the current output of said element is impressed in said input, and the dimensions of said short couples being set in consideration of the fact that the ratio of the power output of said element is substantially independent of its length and being such as to maximize the signal-to-signalplus-noise ratio of its current output whereby the operation is at low voltage output of said element and said low voltage input of said converter.

2. The generator of claim 1 wherein the converter operates at an input of between about 0.3 volts and about 0.6 volts derived from the thermoelectric element.

3. The generator of claim 1 including an electrical converter having transistor means, said transistor means, having emitter means, collector means, and base means, the output of the thermoelectric element being connected in direct-current transmission relationship with said collector and emitter means, the drop between the collector means and the emitter means of said transistor means being about 0.001 volts.

4. An electrical generator including a heat source and a heat sink, a heat shield interposed between said source and sink, a thermoelectric element, formed of a plurality of short thermocouples, said element being in the form of a thermoelectric strip having a hot junction, in heat-interchange relationship with said source, and a cold junction, in heat-interchange relationship with said sink, said thermoelectric strip extending through said shield between said heat source and said heat sink, the only heat-conduction path through said strip from said hot junction to said cold junction being longitudinal of, as distinct from, transverse to, said strip, a solid-state electrical converter having an input responsive to the magnitude of input current, as distinct from, voltage and said input also having a maximum low-voltage drop for the input voltage impressed thereon and thus being operative for a low-voltage input, said converter also having an output and means for connecting said output to a load, means connecting said element to said input so that the current output of said element is impressed in said input, the number of thermocouples of said element being such that the input voltage impressed on said input is high compared to said drop, and the dimensions of said short couples being set, in consideration of the fact that the ratio of the power output of said element is substantially independent of its length, and being such as to maximize the signal-to-signal-plus-noise ratio of its current output, whereby the operation is at low voltage output of said element and said low-voltage input of said converter.

5. The generator of claim 4 wherein the heat-radiation shield is interposed between the heat source and the heat sink to suppress substantially heat transmission by radiation from said heat source to said heat sink and wherein the thermoelectric element, while being short, is of such length that the hot junction is on the source side of said shield and the cold junction on the heat-sink side of said shield.

6. The generator of claim 4 wherein the positioning of the strip in the container is such that any hypothetical radial line from the source to the wall intersects the strip only once.

7. The generator of claim 4 wherein the source is generally cylindrical having a base and the thermoelectric strip is annular with the hot junction at one end of the annulus and the cold junction at the other end of the annulus, said hot junction end being in heat-exchange relationship with said base, the shield concentrating the heat energy of said source on said base.

8. The generator of claim 4 wherein the source is generally cylindrical having a base and the thermoelectric strip is in the form of a generally rectangular plate with the hot junction at one end and the cold junction at the opposite end, said hot junction end being in heat-exchange relationship with said base, the shield concentrating the heat energy of said source on said base.

9. An electrical generator including a heat source and a heat sink, a heat shield of tantalum interposed between said heat source and said heat sink, the said shield enclosing said source and having therein a cavity which winds around said source between said source and said sink, a thermoelectric element extending through said cavity from said source to said sink, said thermoelectric element being formed of a plurality of short thermocouples having a hot junction in heat-receiving relationship with said source and a cold junction in heat-transfer relationship with said sink, a solid-state electrical converter having an input responsive to the magnitude of input current, as distinct from, voltage and said input also having a maximum low-voltage drop for the input voltage impressed thereon and thus being operative for a low-voltage input, said converter also having an output and means for connecting said output to a load, means connecting said element to said input so that the current output of said element is impressed in said input, the number of thermocouples of said element being such that the input voltage impressed in said input is high compared to said drop, and the dimensions of said short couples being set, in consideration of the fact that the ratio of the power output of said element is substantially independent of its length, and being such as to maximize the signal-to-signal-plus-noise ratio of its current output whereby the operation is at the low-voltage output of said element and said low-voltage input of said converter.

10. The generator of claim 9 wherein the cavity is of generally helical form.

11. The generator of claim 9 wherein the source is a radioactive source emitting gamma rays and the tantalum heat shield also serves as a gamma ray shield.