This power pack has smooth speed control for gentle starts and power increases in speed up to the maximum speed. It also has single-knob operation for setting the voltage in the track and for changing the direction of travel by turning the control knob away from the center position. 120V. Power pack dimensions: 130 mm L x 70 mm W x 50 mm H / 5-1/8" L x 2-3/4" W x 2" H