Abstract: The supply, regulation and control of a direct current electrical machine such as a motor or generator having a number of winding sections is controlled by energization of the winding sections by staggered pulses which combine to produce a reasonably constant total winding current, the control being by means of first and second pairs of transistor switches controlled by respective control elements, such as magnetic pick-ups or photoelectric detectors, responsive to the rotation of the machine. Alternatively the machine can be operated with intermittent excitation for low speed traction or starting by supplying appropriately shaped control signals to the control elements connected to the transistor switches.