AC vs DC Charging: A UK Home Charging Guide

What happens during AC charging?

A home AC chargepoint supplies alternating current to the vehicle. The car's onboard charger converts it to direct current for charging the battery. The wall unit controls the supply and communicates with the vehicle; it does not turn a 7kW domestic connection into a public rapid charger.

The conversion is rectification, not the action normally described as an inverter converting DC to AC. That terminology matters when reading specifications: look for the car's maximum AC charging power, supported phases and current, rather than its peak DC charging number.

The slowest compatible part sets the limit

The available supply, installation setting, chargepoint, cable and onboard charger all affect the result. A higher number printed on the wallbox cannot override a lower vehicle limit. Equally, a capable vehicle cannot obtain three-phase charging power from a single-phase connection.

For example, a car limited to 3.6kW AC will not charge at 7kW simply because it is plugged into a 7kW unit. A vehicle accepting 11kW AC needs a compatible supply and installation to reach that figure. Ask the installer what power will actually be available at your property.

References: Energy Saving Trust: charging electric vehicles

How DC rapid charging differs

With DC charging, power conversion takes place in equipment outside the car and the DC charging path bypasses the onboard AC charger. The vehicle still controls what its battery can accept. Battery temperature, state of charge and the charging station's available output influence the session.

A quoted peak is not the average across an entire charge. Power commonly changes during a session, so dividing battery capacity by a headline rapid-charger rating can give an unrealistic time. Compare manufacturer charging-time conditions and the starting and finishing battery percentages.

Compare a top-up using consistent assumptions

For a simple AC example, adding 21kWh to a battery at an assumed 90% overall efficiency requires 23.3kWh from the supply. At constant input power, that is about 6.5 hours at 3.6kW or 3.3 hours at 7kW. The example excludes interruptions and does not represent a measured vehicle test.

Do not reuse that constant-power estimate as a guaranteed DC charging time. The power curve and any thermal preparation can change the result. For a journey, use a realistic arrival battery level and the amount needed to reach the next dependable stop, rather than assuming every stop must reach 100%.

Does a home need DC equipment?

Residential or specialist DC equipment exists, but its suitability cannot be decided from a generic price multiplier or a claim that every product requires the same supply. It needs a specific equipment and installation assessment. For ordinary home planning, first determine whether an appropriate AC installation can replace your daily driving energy.

A faster setup is only useful if your car can use it and the saved time matters. Someone parked for ten hours may gain little from an expensive upgrade that reduces a two-hour top-up. Someone returning briefly between shifts has a different requirement. Write down that requirement before comparing products.

Questions to answer before ordering

Record your exact vehicle variant and its AC specification, the parking position, the connection type and your usual time at home. Ask for an installed quote that states the supported power rather than quoting only the charger's maximum specification.

If you are replacing the vehicle soon, check the next model separately. Avoid promises of universal future compatibility. Use the charging-time calculator with the lowest applicable AC limit and realistic battery information; treat its output as a planning estimate to compare with real sessions after installation.