Abstract: The converter device comprises a magnetic rotor (2) rotatively mounted integral with primary shaft (1) of the device and a heat exchanger (5) having electrically conducting walls through the helically-shaped inner cavity (6) of which a fluid is caused to flow and within the walls of which rotating induction produced by a rotor generates eddy currents. A tachometer generator (8) measures the shaft rotational speed and controls, as a function of the said speed, the angular position of an electric motor (9), which drives the exchanger (5) along a linear translation path in a direction parallel to the rotor axis. Due to such a closed-loop control, the resistant torque is governed by a predetermined relation. The device can be used to convert to heat rotational kinetic energy from a wind turbine.