High tech comes to Am Sci & Surp!! It is here in the form of a Peltier junction, a thermo-electric device that translates electric power into heat, and perversely, into cool. Apply current @ 3-12 VDC to the gizmo and it extracts thermal energy from one face, thereby cooling it. The heat is dumped onto the other face, thereby heating it. Please note: you must use a heat sink on the hot side or the junction will fry itself, since it can quickly create a 65° C temperature differential in a no load situation. Stack two, or build a cascade to increase the thermal differential created. Or run it backwards. Apply heat or cold to the relevant face and produce a current. Amazing for science projects and experiments. Practical for coffee warmers, beer coolers and mini-refrigerator or warming oven applications. Comes with instructions. Large is 1-9/16" sq. x 3/16" thick.