EV charging: how the system works

To plan charging, start with how much energy you need to replace and how long the car will be parked. AC charging commonly serves longer stays at home, work or other destinations; DC fast charging replenishes energy during shorter stops. U.S. Alternative Fuels Data Center — Electric vehicle charging stations

How AC and DC charging work

During AC charging, alternating current passes through the charging equipment and cable to the car’s onboard charger, which converts it to direct current. The external equipment, called electric vehicle supply equipment (EVSE), provides the controlled connection and associated protection. In common Type 1 and Type 2 AC systems, control-pilot signalling tells the car the maximum current it may draw; the onboard charger can draw less. IEC 61851-1 — General requirements for conductive EV charging systems Phoenix Contact: vehicle charging controllers Argonne National Laboratory: PEV charging response characterisation (October 2025)

During DC charging, the main power conversion takes place outside the vehicle. A grid-fed station typically converts AC to regulated DC, bypassing the onboard AC charger. In CCS charging, the vehicle and station establish communication, exchange operating limits and complete electrical safety checks before charging begins. During charging, the station adjusts delivery to the vehicle’s requests within the available limits. CharIN: Combined Charging System design guide V7

Wireless charging transfers energy through magnetic coupling rather than a plug. It requires compatible equipment on the vehicle and ground, with alignment, communication and protection designed for that system. SAE J2954 addresses stationary wireless charging for light-duty vehicles. U.S. Alternative Fuels Data Center — Electric vehicle charging stations SAE J2954 — Wireless power transfer for light-duty electric vehicles

Why the same charger gives different results

Power, measured in kW, is the rate of energy transfer. Energy, measured in kWh, is the amount transferred over time. Voltage in volts and current in amperes determine instantaneous DC power:

DC power (kW) = voltage (V) × current (A) ÷ 1,000

For an illustrative connection supplying 700 V at 400 A, the output is 280 kW. At 400 V and the same 400 A, it is 160 kW. A station needs sufficient voltage range, current capability and available power to deliver either result. A high kilowatt rating alone does not tell you what a particular car will receive.

AC charging also depends on the number of phases the car can use. In a nominal 230/400 V system, an 11 kW three-phase wallbox limited to 16 A per phase can supply about 3.7 kW to a car using one phase: 230 V × 16 A ≈ 3.7 kW, assuming a power factor near one. A car rated for 7.4 kW single-phase charging needs about 32 A on one phase, so this 16 A wallbox would limit it to about 3.7 kW. These are electrical input powers, before conversion losses. Schneider Electric: EVlink Home Smart technical data

Available power can fall when a site shares its supply among vehicles or reduces charging to accommodate other building loads. US Department of Energy: smart charge management implementation The chapters on DC fast charging and Smart charging explain how these limits are managed.

As the battery approaches full charge, the car usually reduces charging power, slowing the final part of a fast-charging stop. To compare cars or chargers, use energy added and elapsed time over a stated charge window, with the battery temperature and charging equipment identified. Battery charging, in the battery series, explains why charging slows and why a charger delivers more energy than the battery stores.

Compatibility includes communication and access

A connector that fits is the first requirement. The vehicle and equipment must also support compatible electrical limits and charging signals. EV charging connectors and inlets helps you identify the correct interface and any approved adapter.

Access is a separate check: a station can have a compatible connector yet reject the charging account used to start the session. In a networked system, the Open Charge Point Protocol (OCPP) connects the station to its management system, which can handle authorisation. Open Charge Alliance — Open Charge Point Protocol For charging-card access, automatic authorisation and billing, see Charging protocols and services.

North American Level 1 and Level 2 are AC supply categories, while IEC charging modes describe how the car is connected and controlled. For a useful comparison, identify AC or DC, the connector, the voltage and current capabilities, and the applicable vehicle input limit. U.S. Alternative Fuels Data Center — Electric vehicle charging stations IEC 61851-1 — General requirements for conductive EV charging systems

Find the chapter you need

Equipment and everyday charging

• EV charging connectors and inlets — Which plugs and adapters fit your car, and will the cable reach?
• Home EV charging — Choose enough charging power for your parking time and plan the installation.
• DC fast charging — Understand station limits and plan charging stops around your journey.

Control and services

• Smart charging — Use cheaper hours, solar surplus and shared electrical capacity.
• Charging protocols and services — Find out why a charging card may be refused and how automatic authorisation and billing work.
• Bidirectional EV charging — Establish which functions a system supports: appliance power, grid-connected home supply, outage backup or grid export.

Managed one-way charging adjusts when and how quickly the car draws electricity. Supplying electricity from the battery to external loads requires bidirectional capability. US Department of Energy: managed and bidirectional charging

Battery exchange

• Battery swapping — Check vehicle compatibility, charged-pack availability and subscription terms.

A swap station installs a charged pack and recharges the removed pack separately, separating the exchange from the removed pack’s charging time.