Charging methods

A distinction is made between four charging modes where the term ‘mode’ refers to the charging technology (power, communication and safety).

Mode 1 is unlimited charging via a standard 230V AC outlet. The maximum charging current is 10A depending on the region. Such a charging method works without a current limiter and is therefore hardly ever used for larger vehicles for safety reasons. This charging method is more suitable for e-bikes.

No test equipment is needed for this charging mode as this is basically just a cable connected to a standard wall socket.

Mode 2 is a safer way of charging via a standard 230V AC socket. It uses a charging cable with a built-in current limiter. The electronics in the charging cable communicate with the car to start or switch off the charging process. The charging current here, as in Mode 1, is also 10A or an output of 2.3kW. Fully charging a 100kW battery as in the Tesla X then takes several days. Practically, therefore, this method is only suitable for hybrid vehicles equipped with batteries smaller than 20kW.

No test equipment is needed for this charging mode as this is basically just a cable connected to a standard wall socket.

Mode 3 is metered charging where there is communication between the charge point and the vehicle about the appropriate power. A separate circuit is provided to which the AC charge point is connected. This allows larger capacities of up to 7.4kW single-phase, 22kW (32Ax3) three-phase and even 43kW (63Ax3) three-phase. This charging method is the only one standardised and must comply with the IEC61851 standard. To charge the battery, in Mode 1 to 3, alternating current is converted to direct current by the inverter present in the vehicle.

Mode 4 is charging with direct current, also known as fast charging. The conversion from alternating current to direct current takes place at the charge point itself. So no inverters are used in the electric vehicle. Control of charging and monitoring of safety limits is also provided by the charge point. Since the limits of the inverter in the car do not have to be taken into account, much higher power outputs can be used. This mode is used for fast charging with powers from 50kW to >1MW. Consider, for example, the recently launched Tesla V3 DC supercharger, a charging station with 4 charge points of 250kW and a total power of 1MW.

Automated charging

In addition to connecting manually to charge the battery, there are also ways of automated charging, or Automated Connect Device (ACD).

Charging with pantograph. This charging method delivers high conductive energy transfer from the charging infrastructure in a very short time. This charging method is mainly used for charging large electric vehicles such as buses but also other applications such as E – trucks and port and airport vehicles. Currently, two variants of these ACD systems are already widely used in buses, namely the top down pantograph (built into the charging structure) and the roof top pantograph (built on the roof). These systems come in both AC and DC versions and can generate power up to +600kW. There are now already developments up to 900kW and 1200kW loaders. Communication to position the vehicle and contact the charging point is wireless or via PLC.

Pantograph charging is mainly used for brief, very quick recharging of buses, for example at the terminus of a journey or at interchanges. In this way, city buses can be recharged in minutes for the next trip. In this method, the pantograph is built into the charging infrastructure. The roof top method is the most commonly used ACD charging variant. The pantograph is located on the roof of the bus and makes mechanical contact with the overhead charging infrastructure for charging.

Wireless Induction Charging. This form of charging involves charging without the intervention of cables. Energy is transferred via a magnetic field. This field is created between two magnetic coils. One of these coils is located in the car and the other in the charging platform. Energy is transferred via a magnetic field between the two coils. With induction charging, charging takes place using alternating current, which will be converted to direct current in the vehicle. Efficiency is another issue being worked on. Power losses with induction charging can be as high as 25%. This method of charging is still under development and is currently only used for the smaller capacities. No standards have yet been provided.

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