The ornamental design for a thermoelectricgenerator for powering an external electrically operated device, as shown and described.
FIG. 1 is a top, front and left side isometric view of a thermoelectric generator for powering an external electrically operated device showing my new design;
FIG. 2 is a front view thereof, the left, right, and rear side views being a mirror image;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a bottom plan view thereof, with the broken lines for the base removed for ease of illustration.
The broken lines shown represent unclaimed subject matter and form no part of the claimed design.