This is the basic method of communication between the wallbox and the electric vehicle, as defined by international standards. The wallbox uses a signal called pulse-width modulation, or “PWM,” to tell the vehicle the maximum current at which it can charge. The signal can be thought of as rapid voltage switching, where the width—that is, the duration of each pulse—corresponds exactly to the permitted value in amperes. This communication takes place at a voltage level between 0 and 12 volts. The electric vehicle responds to the signal from the wallbox by varying the voltage on the same wire, thereby providing feedback to the station about its status—for example, that it is connected and ready to receive energy.
