A rotatory device (1) for energy conversion between electrical energy and mechanical energy includes an end cap (20) to which electric conduction and commutation components (30) are attached. The end cap (20) is electrically insulating and has a flange mating to an electric conductive housing (10) of the rotatory device (1). An unpackaged capacitor (40) is positioned between the housing (10) and the flange (20) without occupying other space inside the housing (10) of rotatory device (1). The unpackaged capacitor (40) is electrically coupled to the electric conduction and commutation component and grounded to the housing (10) of the rotatory device (1).