Abstract: Method and apparatus for controlling DC traction motors on opposite sides of a vehicle, particularly a mining machine, by means of an SCR converter. The motors are accelerated while controlling the firing angles of the SCR's such that the current and voltage supplied to the motors increase along ramps until desired normal operating values of voltage and current are reached with the voltage across the series-connected motors being of a substantially greater value than the value it would be if the motors were connected in parallel. In contrast to prior art systems, the traction motors are maintained in a series-connected configuration during normal, essentially steady-state operation; while the voltage across the motors is maintained at said substantially higher value. When one of two drive wheels connected to the traction motors is slipping, the motors are connected in parallel to increase torque with a corresponding decrease and increase in voltage and current, respectively.