7-70V 30A PWM DC Motor Speed Controller, can be directly connected to the motor and adjust the potentiometer to adjust the motor's speed. Instructions for Use and Precautions:Make sure that the positive and negative connections between the power supply and the governor are correct before turning on the power. Reverse connection may burn the circuit board. Do not touch the heat sink with the wiring, or it may burn the circuit board.(Motor) There is no need to distinguish between positive and negative. If the direction of rotation is wrong, please change the two wires of the motor. Note that this is not a power supply module, it must be connected to the motor to adjust the speed. Without the motor, the output of the multimeter not change. It is suitable for DC brushed motors and cannot be connected to 220V household electricity. Used for Children's Toy CarIf the product is used in the modification of children's car, the output end of the speed controller can be connected with a Forward and Reverse Switch to realize the function of forward and reverse control. If there is a forward and reverse circuit regulator on the children's car, please be sure to connect the speed controller in front of the forward and reverse circuit regulator (In other words: between the power supply and the forward and reverse circuit regulator) of the children's car.Otherwise, the speed controller may be damaged. Specifications: Condition: Material:aluminum colour:black+green Package Contents: 1 x DC Motor Speed Controller Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.