EV Chargers Explained: kW Ratings and Charging Speed

Good ev charger installation is about matching your charger to your car and your home setup. This article covers EV Chargers Explained: kW Ratings and What They Mean for Charging Speed, giving clear guidance so homeowners can make informed choices.

One of the first questions many new electric vehicle owners ask is how long it will take to charge their car. The answer depends largely on the kW rating of the charger and the capacity of the car’s battery. Understanding what kW ratings mean, and how they relate to charging speed, helps drivers make better decisions about home installations, workplace charging, and public charging options. It also ensures expectations are realistic and avoids confusion when comparing different types of chargers.

What does kW mean in EV charging?

The term kW stands for kilowatt, which is a measure of power. In simple terms, it describes how much energy a charger can deliver to the vehicle every hour. For example, a 7kW charger supplies seven kilowatt-hours of energy to the battery each hour. A kilowatt-hour (kWh) is the unit you see on your electricity bill and represents the amount of energy consumed. This means that if your car has a 60kWh battery, charging it with a 7kW charger from empty to full would take a little under nine hours.

The most common EV charger ratings in the UK

In the UK, home chargers are most commonly available in 3.6kW and 7kW versions. A 3.6kW charger adds around 15 miles of range per hour, while a 7kW charger can deliver roughly 30 miles per hour. Faster chargers rated at 11kW or 22kW are possible but require a three-phase electricity supply, which is uncommon in domestic properties. These higher-rated chargers are more often found in workplaces, commercial premises, or public charging stations. At the top end of the scale, rapid chargers of 50kW or more are used on motorways and in public charging hubs, providing much faster charging but at significantly higher installation and running costs.

How battery size affects charging time

While the charger’s kW rating determines how quickly energy can be supplied, the car’s battery size dictates how much energy is needed. A small plug-in hybrid might have a battery of just 10kWh, meaning it can be fully charged in under two hours on a 7kW charger. By contrast, a large electric SUV with a 100kWh battery could take over 14 hours to charge fully on the same unit. In practice, drivers rarely charge from empty to full, and most daily charging involves topping up the battery, which reduces the time required.

The role of the vehicle’s onboard charger

Another important factor is the car’s onboard charger, which converts the alternating current (AC) from the mains into direct current (DC) stored in the battery. This component sets a maximum charging speed that the vehicle can accept. For example, even if you install a 22kW charger, if your car’s onboard charger is limited to 7kW, you will not benefit from faster charging. Always check your vehicle’s specifications before deciding which home charger to install, as there is little point in paying for extra capacity you cannot use.

AC versus DC charging

Most home and workplace chargers use AC, with ratings between 3.6kW and 22kW. DC rapid chargers, typically found at motorway services, bypass the car’s onboard charger and feed power directly into the battery. This allows much higher charging rates, from 50kW up to 350kW in the latest ultra-rapid stations. While this means drivers can add hundreds of miles of range in under an hour, the equipment is expensive and requires substantial grid connections. For everyday home use, AC charging at 7kW remains the most practical solution for most UK households.

How charging speed translates into miles of range

To put charging speeds into practical terms, consider how much driving range you gain per hour of charging. A typical EV achieves around four miles per kWh. Using this figure, a 3.6kW charger adds roughly 15 miles of range per hour, a 7kW charger adds about 30 miles, and an 11kW charger adds around 45 miles. At a 50kW rapid charger, you could gain 150 to 200 miles in just an hour. These figures vary depending on the efficiency of the car, but they provide a useful rule of thumb when planning charging.

The impact of electricity supply at home

The speed of home charging is not only limited by the charger and the car but also by the household electricity supply. Most UK homes have a single-phase supply, which caps charging at 7kW. A three-phase supply allows for faster 11kW or 22kW charging, but this is rare and expensive to install in domestic properties. For most households, a 7kW charger provides a good balance between speed, cost, and practicality, allowing a typical EV to be fully charged overnight.

Smart charging and managing demand

Smart chargers help make the most of charging speeds by scheduling sessions during off-peak times or when electricity is cheapest. While a 7kW charger always delivers the same power, using it at the right times can significantly reduce running costs. Some smart systems also integrate with solar panels, using surplus renewable energy to charge the vehicle. Others include load balancing, which ensures the EV does not overload the household system when other high-demand appliances are in use.

Why faster is not always better

While rapid charging is impressive, it is not always the best option for battery health or household budgets. Charging too quickly on a regular basis can increase battery wear over time, although modern management systems minimise this risk. More importantly, installing a faster charger than your home or car can support leads to unnecessary costs. For most drivers, the convenience of plugging in overnight with a 7kW charger is more than sufficient, and rapid charging can be reserved for longer journeys.

Planning for the future

When choosing a charger, it is worth considering not just your current vehicle but also future needs. As EV technology evolves, cars are being built with larger batteries and higher charging capabilities. Installing a charger with smart features now ensures your home is prepared for the next generation of vehicles. While three-phase supplies remain rare, keeping capacity in mind when upgrading your consumer unit or fuse board can save time and expense if faster home charging becomes more practical in the future.

Conclusion

kW ratings are central to understanding EV charging speeds. A higher kW rating means more energy delivered per hour, but the actual charging time depends on battery size, vehicle limits, and your home’s electricity supply. For most UK households, a 7kW charger provides the ideal balance of speed and practicality, allowing overnight charging for even large batteries. By understanding how kW ratings work, drivers can make informed decisions about home installations, manage expectations, and plan effectively for the future of electric motoring.

You may also find Grants and Government Schemes for EV Charger Installation and Home EV Charger Installation: What You Need to Know Before You Start useful when planning your setup. More help is available in ev charger guidance.