How Does a Controller Work for an Electric Car?by Isaiah David
As in gas cars, the pedal in an electric car controls the amount of power the motor puts out. In electric cars, the pedal is attached to a potentiometer, a type of resistor. Resistors have that name because they resist the flow of electricity. The more resistance, the less current that flows through the resistor. A potentiometer differs from normal resistors in that its resistance changes as it is pressed down.
Controlling the Controller
The pedal controls the motor controller. A small current flows through the pedal to a circuit that monitors it. By measuring the amount of electricity that flows through the pedal, the circuit can tell how far down the pedal is pushed and how much power the controller needs to provide.
The Simple Route
The batteries of the car put out a set amount of power, but the motor must be able to put out more power when the pedal is down and less power when it is up. The easiest way to do this is with another potentiometer to control the amount of current from the battery to the motor. Unfortunately, resistors waste some electricity by turning it into heat, and such a large resistor would waste a tremendous amount of power. Controllers use an entirely different system that is much more efficient.
Controlling the Motor
The controller controls the power to the motor by a transistor, a type of high-speed electronic switch. The transistor does not send a constant current to the motor. Instead, the transistor sends tens of thousands of pulses of electricity every second. If the transistor wants to lower the current by a certain amount, it omits pulses regularly. For example, if the transistor wanted to lower the current by one-fifth, it would turn off for one of every five pulses. This lowers the average current, making the motor run at lower power when lower power is needed.