Abstract: Insulation between a rotor shaft and slip rings for electrical connection to a rotary winding is provided by a layer coating the shaft that is sintered in place from fluidized bed material, providing a thin layer that is sufficiently tough for slip rings to be mounted on top so that the layer provides the insulation from the shaft. The slip rings may be quite thin, thus keeping the active surface of the slip ring to a very small diameter. Brass and bronze slip rings may be press-fitted onto the shaft while maintaining the insulation of the layer, but carbon slip rings, which are desirable for long life are best secured by means of an adhesive. The slip ring assembly is particularly useful for three-phase alternators of motor vehicles.