AC charging is the method of charging an electric vehicle with alternating current from the grid, where the onboard charger inside the vehicle converts that current into the direct current that the battery stores. In EV charging for electric vehicles, AC charging is the everyday method used at home, at work and at many public parking spaces, typically delivering between about 2 and 22 kW.
Because the conversion happens in the car, the charging station itself is comparatively simple and inexpensive. The trade-off is power: the size of the onboard charger limits charging speed, which makes AC charging ideal for long parking periods and unsuitable for quick stops on long journeys.
How AC charging works
In AC charging, the station acts mainly as a smart, protected power outlet, while the vehicle does the power conversion. The station, often called EVSE for electric vehicle supply equipment, checks the connection, communicates the available current and switches the supply on and off.
- The driver plugs in, and the station and vehicle detect each other through the control pilot signal defined in IEC 61851.
- The station advertises the maximum current it can supply by varying the pulse width of the pilot signal.
- The vehicle requests power, and the station closes its contactors after safety checks such as protective earth and residual current detection.
- The onboard charger rectifies the alternating current, regulates voltage and current, and charges the battery under control of the battery management system.
- The vehicle reduces current as the battery approaches full charge or when the station signals a lower limit.
The actual charging power is the lowest of three limits: the station’s rating, the capacity of the electrical installation and the vehicle’s onboard charger. A 22 kW station connected to a car with an 11 kW onboard charger delivers only 11 kW.
AC charging power levels and charging times
AC charging power depends on voltage, current and the number of phases. Europe commonly uses three-phase supply at 400 volts, while North American homes typically use single-phase 240-volt circuits, which explains why typical power levels differ between regions.
| Configuration | Approximate power | Range added per hour | Typical location |
|---|---|---|---|
| Household socket, 230 V, 8 to 10 A | About 1.8 to 2.3 kW | About 10 to 15 km | Occasional or emergency charging |
| Single-phase, 230 V, 32 A | About 7.4 kW | About 35 to 50 km | Homes with single-phase supply |
| Three-phase, 400 V, 16 A | About 11 kW | About 55 to 75 km | European homes and workplaces |
| Three-phase, 400 V, 32 A | About 22 kW | About 110 to 150 km | Public and fleet parking |
| North American Level 2, 240 V, 32 to 48 A | About 7.7 to 11.5 kW | About 40 to 75 km | Homes and workplaces |
Range added per hour depends on the vehicle’s consumption, so the values above assume typical passenger car efficiency. Charging also loses a share of energy as heat, commonly around 5 to 15 percent, with higher relative losses at very low currents.
AC charging compared with DC fast charging
The fundamental difference between AC and DC charging is where the conversion from alternating to direct current happens. In DC fast charging, large converters inside the station feed the battery directly, bypassing the onboard charger and allowing far higher power.
| Aspect | AC charging | DC fast charging |
|---|---|---|
| Conversion location | Onboard charger in the vehicle | Power modules in the station |
| Typical power | About 2 to 22 kW | About 50 to 350 kW |
| Typical session length | Several hours | About 15 to 45 minutes |
| Station cost | Low | High, plus grid connection costs |
| Connectors in Europe | Type 2 | CCS2 |
| Battery stress | Minimal | Higher at high power and temperature |
| Best use | Overnight, workplace, long parking | Road trips and quick top-ups |
AC charging does not follow the steep charging curve typical of DC fast charging, because its power is low enough for the battery to accept it almost until full. For most drivers with access to a home or wallbox, AC charging covers the large majority of their energy needs.
Planning an AC charging installation
A good AC installation matches the vehicle’s onboard charger, the building’s electrical capacity and the parking pattern. Oversizing the station brings little benefit if the car cannot accept more power or the house connection cannot supply it.
| Situation | Recommended setup | Reason |
|---|---|---|
| Home, overnight parking, three-phase supply | 11 kW wallbox | Matches most onboard chargers |
| Home with limited supply capacity | 7.4 kW or less with load management | Avoids overloading the main fuse |
| Workplace with many cars | Several 11 or 22 kW points with dynamic load balancing | Shares limited capacity fairly |
| Rental or occasional use | Portable charger on a suitable socket | No fixed installation needed |
A dedicated circuit with appropriate residual current protection is essential; many installations require a type B residual current device or a station with built-in DC fault detection. Load management and smart charging can shift charging to off-peak hours or periods of local solar production.
Common mistakes and limitations
Most AC charging disappointments come from mismatched expectations about power. Drivers often assume the station rating determines speed, while the vehicle’s onboard charger frequently sets the real limit.
- Single-phase onboard chargers charge at only 3.7 or 7.4 kW even on a three-phase 22 kW station.
- Regular household sockets are not designed for many hours of continuous high load; prolonged use can overheat worn sockets.
- Cold batteries may accept less power until the vehicle warms them, which extends winter charging times.
- Undersized cables or extension leads cause voltage drop, heating and fire risk and should not be used.
AC charging is also the usual starting point for future bidirectional charging, although vehicle-to-home and vehicle-to-grid functions require compatible vehicles, stations and grid rules.
Put simply
AC charging is the slow, everyday way to charge an electric car, usually at home or at work. The electricity from the wall is converted inside the car into the form the battery can store.
It works like charging a phone overnight. It is not the fastest option, but because the car is parked for hours anyway, it is convenient, inexpensive and gentle on the battery.
In practice
A salesperson drives an electric company car about 120 km per day and parks it at home every evening for at least ten hours. The car’s onboard charger accepts 11 kW on three phases, and the house has a three-phase connection.
An electrician installs an 11 kW wallbox on a dedicated circuit with suitable residual current protection and configures it to start charging after 10 p.m., when the electricity tariff is lower. Each night the car replaces roughly 20 kWh in about two hours.
Over a year, the driver uses public fast chargers only on a handful of long trips. Almost all energy comes from home AC charging, at lower cost and with minimal battery stress.