Abstract: The alternator comprises an induction winding sub-divided into two half-windings (1, 2) each connected to the input terminals of a respective double half-wave rectifier circuit (3, 4). It further includes thyristors (14) each of which connects a terminal (A, B, C) of one half winding (1) to a non-homologous terminal (C',A',B') of the other half-winding (2) such that, when the thyristors (14) are triggered, the electromotive forces generated in the two said half-windings (1, 2) are added in phase with each other. When the speed of rotation of the engine of the motor vehicle is less than a predetermined value, the said thyristors (14) are triggered and hence the two half-windings (1, 2) are connected in series with each other. If the speed of rotation of the engine surpasses this predetermined value, the thyristors (14) are not triggered, and the two half-windings (1, 2) are connected in parallel with each other.