Abstract: A system and method is disclosed for drilling a borehole using a silicon controlled rectifier (SCR) system. The SCR system includes analog rack mounted hardware cards for control of an engine AC generator and a DC load. The engine AC generator of the SCR system generates alternating current (AC) that is then converted to direct current (DC) by a silicon controlled rectifier transformer connected to the output of the engine AC generator. The DC power from the silicon controlled rectifier transformer drives one or more DC motors that are coupled to a load by a mechanical linkage. An AC generator controller controls the engine AC generator and includes an engine control module that controls operating speed of the engine AC generator and air-fuel mixture at engine start. A DC load controller coupled to the silicon controlled rectifier transformer and DC motors performs automatic load share control between the DC motors.