Introduction:
The batteries of electric vehicles or plug-in hybrids can be charged with external charging facilities. The car can be connected with a charging cable to a public charging station, public charge point, or a personal wallbox (on the exterior wall or in the garage) to charge the battery through the power grid. There is often also a mobile charger available for charging via an outlet, though it is recommended to use this charger only in emergencies.
The following image shows the charging of an electric car. On the side of the vehicle, there is a flap that resembles a fuel cap of a traditional combustion engine car. Behind the flap is the socket where the charging plug can be inserted.
The sticker in the flap indicates which color the LED next to the plug will light up to indicate a certain status.
Charging Connectors and Connections:
The charging connectors and connections are standardized in Europe. For AC charging (alternating current), we use the Mennekes (type 2), and for DC charging (direct current), the CCS2 plug.
The following image shows a combined Mennekes Type 2 with CSS2 charging plugs. With this plug, it is possible to (rapidly) charge using direct current.
In the image below, you can see the plugs used in other parts of the world. A distinction is made between AC and DC, where the DC variant often extends the AC connector.
Electronic Vehicle Supply Equipment (EVSE):
Public charging facilities are always equipped with an interface with EVSE (Electronic Vehicle Supply Equipment). This ensures security and communication. The EVSE performs the following functions, among others:
- Checking connections: after confirming that all plugs are connected and locked, the charging mode starts;
- Self-diagnosis: if errors are detected, the power supply is interrupted;
- Leakage current detection: any form of leakage current interrupts the power supply;
- Current regulation: communicates with the onboard charger in the car via a PWM signal to limit current intensity.
Charging Options:
When charging with alternating current (AC), electricity from the power grid is converted into direct current (DC) in the car. The disadvantage of AC charging is that there is a considerable chance of induction effects and losses due to conductor resistance. Additionally, within the car, the conversion from AC to DC must occur before the energy reaches the battery, thereby limiting the charging current.
Charging with direct current (DC) allows for “super” fast charging. There is no AC/DC conversion in the onboard charger, but outside the vehicle, allowing the battery to be charged with higher power and fill up faster. This is ideal for a quick charge during a coffee break along the highway for continued travel.
The ways and speeds by which a vehicle can be charged can be divided into four different modes. Mode 1, 2, 3, and 4 indicate how the vehicle is connected to the charging source.
- Mode 1: charging occurs directly through the household power supply. In the vehicle, the voltage is converted from AC (alternating current) to DC (direct current). The charging system offers protection as there is no current limitation or feedback from the vehicle to the socket. This charging method is rarely used due to the risks of danger and defects and is therefore banned in many countries.
- Mode 2: like in mode 1, the wall socket of a home connection is used and limits the charging current to 16 A with a power of 3.68 kW. However, to prevent overloading, the power is generally limited by the charging cables to 2.3 kW (approximately 10 A). With mode 2, the charging station is a mobile charger that can be taken along. In the vehicle, the onboard charger converts AC into DC.
- Mode 3: charging uses a fixed charging station or wallbox connected to a building’s power network, just like in mode 2. The mode 3 charger is suitable for AC charging and powers from 3.68 to 22 kW. Again, the AC is converted to DC in the vehicle’s power electronics.
- Mode 4: whereas modes 1 to 3 use alternating current that must be converted to direct current in the vehicle, in mode 4 charging, the conversion from alternating current to direct current takes place in the charging station itself. The direct current is delivered directly to the battery pack, known as DC charging or fast charging. A DC charging station for mode 4 charging requires an input voltage of at least 480 volts and delivers power starting from 43 kW.
Charging Times:
The charging times of hybrid and electric vehicles can be determined by dividing the battery capacity by the delivered power of the charger.
The available charging power is not only determined by the type of charger and charging cable but also by the maximum charging power for which the vehicle’s power electronics are suitable. New luxury cars are equipped with increasingly larger batteries with more capacity for longer ranges, but as the charging power increases, the charging time can even decrease. For example, we compare a VW e-Golf (32 kWh) to a Mercedes EQS SUV 500 (108.4 kWh). Not all vehicles can charge to 100% with DC. DC charging stops at 80%. The last 20% are charged at lower power via AC to protect the HV battery.
VW e-Golf (32 kWh)
AC charging:
With a Type 2 charging plug, the battery pack can be charged via AC. The maximum charging power of the onboard charger is 3.7 kW. When the battery pack is charged from 20% through a charging station (mode 3), it takes approximately 7 hours. Explanation: 80% (charging) of 32 kWh = 25.6 kWh. We calculate the charging time by dividing the necessary power by the delivered power: (25.6 / 3.68) = 6.96 hours (6 hours and 58 minutes).
When charging via the socket (mode 2), the power is limited to 2.3 kW, resulting in a charging time of 11.13 hours (11 hours and 8 minutes).
DC charging:
When fast charging with direct current at 44 kW, the battery is fully charged after 0.58 hours (35 minutes).
Mercedes EQS SUV 500 4MATIC (108.4 kWh)
AC charging:
With a Type 2 charging plug, the battery pack can be charged via AC. The maximum charging power of the onboard charger is 11 kW. Assuming we start charging from 20%, the delivered power of the charging facility amounts to 86.72 kW.