EV charging speeds explained: From AC and DC to the effects of weather

Sally Bailey, head of EV Chargers at Vestel Mobility UK, looks at the factors that affect EV charging speeds and offers advice on how to speed up your charging.

Electric vehicles (EVs) have quickly become a common sight on our roads, offering not only a greener alternative to traditional petrol or diesel vehicles but also a smoother, quieter driving experience. However, for many people considering an EV, questions about how quickly these vehicles charge, potentially from blisteringly fast to frustratingly slow, can be a key factor in EV liveability.

At its simplest, charging an EV is akin to charging your smartphone, albeit on a much larger scale. You plug your electric car into a power source, and electricity flows into the vehicle’s battery, replenishing the stored energy that powers the car. But unlike your phone, an EV’s charging speed can vary significantly depending on several factors, including charger type, battery size, and environmental conditions.

AC v DC

Charging speed depends mainly on the type of charger you use. There are two main types: Alternating Current (AC) and Direct Current (DC) chargers.

AC chargers are typically what you’ll find at home or at small public charging points as you might find in hotel car parks and are powered by a standard 230V AC mains electricity supply. They provide power to your vehicle more slowly, from a ‘trickle charge’ of 2.5-3kW per hour from a portable cable plugged into a standard three-pin mains socket up to a ‘fast charge’ 7kW per hour from a dedicated home EV home charger. If you are lucky enough to have three-phase electricity supply, that can be up to 22kW – easily capable of charging large EV battery from almost empty to full in five hours of cheap overnight electricity.

With an AC charger, your EV does the hard work of converting the AC power to DC to feed the battery, so it is limited by the electronics in the car. All new EVs will handle 7-11kW AC, and premium cars often handle 22kW AC from a suitable charger as well. This is perfect for overnight charging at home or during longer stays at public parking spaces. Think of this as gently filling a water tank with a regular garden hose; it’s slower but effective over time.

DC chargers, often found at motorway services and dedicated EV charging stations, supply energy directly to the battery at a much higher speed the power bypasses the AC/DC converter in the car. This is akin to filling that water tank with a fire hose; far quicker and more convenient when you’re on the move or in a hurry.

Rapid and ultra-rapid DC charging stations can charge an EV from low (10-20%) to around 80% in as little as 20 minutes.

What affects EV charging speed?

EVs do not charge at the same rate across their entire battery range, as electronics in the vehicle control the maximum charge rate. Typically, this is as fast as the charger will supply power from 20% up to about 80% of the EV’s battery capacity. Below 20% and above 80% charging is deliberately slowed down. This is designed to protect the battery from overheating and prolong its life. Charging a battery generates heat, and higher heat can degrade battery performance over time. By slowing down the charging rate, particularly as battery gets fuller, EV manufacturers help ensure that batteries stay healthier for longer, maintaining range and efficiency over the vehicle’s lifetime.

Temperature also significantly affects charging speed. Batteries prefer mild conditions that are neither too hot nor too cold. In colder climates, the chemical reactions within the battery slow down, meaning that charging your EV in winter can take a little longer. Similarly, in extremely hot conditions, the battery management system will again slow charging to prevent overheating. Modern EVs often feature sophisticated temperature management systems, which help mitigate these extremes. Thankfully, temperature extremes well below freezing or above 35 degrees are relatively rare in the UK, so it’s not a major concern.

Load balancing the power in the local area could be another factor that can influence how quickly your EV charges. When multiple EVs are connected to chargers at the same location, such as shopping centres or workplace car parks, the available electrical power supply from the grid can be shared among all charging vehicles. The system automatically distributes the energy in the most efficient way, ensuring everyone gets their fair share of power.

While this may reduce individual charging speeds, particularly in busy areas with numerous vehicles charging simultaneously or with a busy power-hungry shopping centre nearby, it helps maintain overall network stability and ensures everyone gets charged. If you get the opportunity to use public chargers at quieter, less crowded times, you will get the fastest charge.

Finally, the condition and age of your EV’s battery can also affect charging speeds, albeit to a lesser degree than the type of charger, temperature or load balancing. Just like the smartphone analogy, EV batteries degrade slowly over many years and thousands of charging cycles. As they age, they may not accept a charge as quickly as they did when brand new. Regular maintenance and good charging practices, such as avoiding frequent charging to 100% or letting the battery run completely flat, can help keep your battery in optimal condition. Using these techniques, EV batteries only lose around 1% of their maximum capacity per year.

How to choose the right charger and charging speed

Advances in technology are continually improving charging speeds, battery health, and the convenience of infrastructure. Public charging stations are increasingly common, with many supermarkets, shopping centres, and even residential streets now providing easy-to-access fast and rapid charging options. Nip in for an hour’s shopping while charging the car can easily keep your EV topped up for its next journey.

If you can charge your car overnight at home, there is less need for a fast charging speed, particularly since energy companies typically offer five- to six-hour overnight windows of cheap electricity for charging. Additionally, charging at home overnight can be incredibly convenient, with an always-topped-up car on the drive and no need to factor in fuel/charging stops on most journeys.

In conclusion, EV charging speed is not complicated but it is all about charging in the right place at the right time. By understanding the difference between AC and DC charging, recognising the influence of temperature and load balancing, and adopting good charging habits, you can ensure that your EV ownership experience is smooth, convenient, enjoyable, and environmentally friendly.

Of course, the benefits of driving electric, from reduced emissions and lower running costs to a more pleasant and refined driving experience, far outweigh minor considerations around charging speeds – which are improving all the time. As infrastructure continues to expand and technology evolves, there’s never been a better or easier time to make the switch to electric driving.