Control Pilot Interface

Control Pilot (Mode)

Control Pilot is the main communicating wire between the electric vehicle supply environment(EVSE) and the electric vehicle(EV). The EVSE(charger) generates 1kHz ,+-12 signal and is transmitted to Electric vehicle through this control pilot(CP) interface. The vehicle respond it by placing different load (resistor) on the line which affects its voltage level which is responded back to electric vehicle supply environment(EVSE).

Control Pilot Signal States

State A, State B and State C are the basic functionality state of the CP interface and the remaining state D,E and E occurs only in the rare case. The normal connection process follows the following steps:

  • The EVSE generates +12v signal and place it in CP interface . This transmission signals the vehicle when the plug is connected.
  • When the plug is connected,the vehicle places a 2.74-kΩ load on the pilot line, which drops the voltage from 12v to 9 V.
  • The EVSE moves to state B which indicates that EV is connected and it is ready to charge. The EVSE enables PWM signal which indicates vehicle how much current it can draw. The EVSE also on the relay so that the mains supply reaches the EV terminal for powering the vehicle.
  • The vehicle starts to draw power and places a 822-Ω load on the pilot line,which drops the voltage from 9 V to 6 V,signaling the EVSE that charging has started.
  • Even when the vehicle is fully charged , Most of the vehicle continues to pull a low amount of power in the state C. so we can end the charging process by unplugging the cable from the slot. Once we unplug the cable the voltage switch back to 12V and and enters the state A.

Control Pilot (Current limit)

Charger uses Pluse Width Modulation(PWM) signal to determine the maximum current that a vehicle can draw from the charging station.The duty cycle of the pilot signal determine the amount of current that the vehicle can draw from the EVSE . The vehicle uses this current in the charging circuitry which has direct relation with the charging time. The current rating is primarily determined by the EVSE source and electromechanical components used in EVSE such as conductors, relays, contractors etc.

The relation between duty cycle and current is provided by two different equations depending upon the current range:




DUTY CYCLE = AMPS/2.5 + 64

To demonstrate this relationship further, below table shows some of the common service ratings.

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