Charging protocol using the CP contact

  • As long as no electric car is plugged in, DC + 12 V are simply applied between CP and PE. If an electric car is plugged in, a diode and a 2.7 kΩ resistor between CP and PE in the type 2 socket of the vehicle pull the + 12 V down to + 9 V. The charging station uses this to recognize that a vehicle is connected.

    Now it activates the 1 kHz PWM signal and uses it to signal the car with what maximum charging current it is allowed to charge. Due to the diode and the resistor, the signal from the charging station now fluctuates between + 9 V and - 12 V. After the electric car knows from the charging station what kind of current it has available, it checks the coding of the cable using the PP contact . If this is successful and the electric car is ready for the charging process, it informs the charging station about this by connecting a further resistor with 1.3 kΩ.

    Only now does the charging station apply the charging voltage to the plug, you can hear the contactor with a * clack * in the charging station. Shortly afterwards you hear two contactors in the electric vehicle * clack clack *, now the charging process begins.

    The PWM signal is maintained during the entire charging process. Should the available power change, the signal will also change. The car must then follow the signal, or better said it must never draw more current than the charging station allows it to. Of course, less is always allowed. Things like load management and PV-led charging work via this PWM signal.

    When the charging process is finished, the electric car deactivates the 1.3 kΩ resistor again. As a result, the PWM signal goes back up to + 9 V and the charging station takes the voltage from the plug again. The contactors (vehicle and charging station) now *clack* in reverse order to the previous start of charging.

    The CP pin is deliberately shorter than all other pins. The reason for this is that it is the first pin that is disconnected if the connection between the plug and socket is disconnected during the charging process. If this is the case, the continuous PWM signal is missing and the charging process is interrupted immediately. This ensures that the plug is never live (apart from the harmless control voltage) when it is not plugged in.


    The used PWM signal is between + 12 V and - 12 V. A few charging stations and wallboxes only use a PWM signal between + 12V and 0 V to save money. This means that some vehicles do not charge at them, as this does not comply with the norm. For example, the smart ED4 with 22 kW does not charge at such charging stations.

Based on the PWM signal, the vehicle knows its maximum current. In addition, the CCS charging process is controlled via the same pins, which is why the CCS charging process can also be initiated via CP. This results in this overview:

PWM signalAC currentnote
0 % - 3 %0 ACharging not allowed
3 % - 7 %0 AAt 5%, the vehicle is informed that a CCS charge and / or Plug & Charge will be used. The corresponding communication is then set up and started via PowerLine.
7 % - 8 %0 ACharging not allowed
8 % - 10 %6 ACharging allowed
10 % - 85 %PWM • 0,6 = max. currentCharging allowed
85 % - 96 %

(PWM - 64) • 2,5 = max. currentCharging allowed
96 % - 97 %80 ACharging allowed
97 % - 100 %0 ACharging not allowed

The signal between 7% - 8% is often used to signal the car to take a break in charging. For example, with PV-guided charging or with load management when there is currently no power available.

CP-Signal PWM - Ampere EN


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