What is DC charging?
What is DC charging and how does it work?
DC charging is the fastest way to charge electric vehicles. It’s the type of quick charging you do at rapid chargers at charging hubs or motorway service stations.
The number of DC public charging stations around the UK is growing fast. In December 2024, we had 14,471 rapid and ultra-rapid DC EV chargers, across 5,850 locations. That’s up an impressive 43% in the last 12 months. (Zapmap data)
This growing network of DC chargers will play a big part in encouraging more and more people to switch to electric vehicles.
So, let’s look at how fast charging for EVs works, why it’s different to AC charging – and when it’s best to use a DC fast charger for an electric vehicle.
What does DC charging mean?
There are two types of electrical current: AC (alternating current) and DC (direct current).
AC is the type of electricity the national grid supplies to homes and businesses across the country. But pretty much any device with an in-built battery – including smart phones, laptops and electric cars – is charged with DC power.
A DC fast charger, also known as a DC rapid charger, converts the AC current from the grid into DC which can be safely and easily stored in a battery.
What is the difference between AC and DC?
An alternating current and direct current behave in very different ways – both have their advantages and uses.
Alternating current (AC)
AC charge flows in two directions, alternates positive and negative voltages around the neutral causing the current to change direction many times a second. Historically, AC power was easier to transmit and convert from one level to another.
As mentioned, this is useful for transmitting power over long distances across the power grid. The electric current that flows through the power lines is set at a very high voltage to minimise energy loss. The voltage is then reduced before the electricity is sent into homes and businesses, so that it can power lights and domestic appliances safely.
Direct current (DC)
Direct current flows constantly in one direction. That consistency gives the DC charge a stable voltage level, which means it can be safely stored in a device’s battery.
The DC charge can also be easily regulated for a controlled energy release, which helps protect the battery and the device.
AC and DC currents compared
What’s the difference between AC and DC electric vehicle chargers?
AC charging
As the name suggests, an AC charger sends AC power into an electric car. The car’s built-in charger then converts the AC power to DC power, before sending it to the vehicle’s battery.
The conversion limits electric car charging speeds, which is why AC chargers are often called ‘slow chargers’. You’ll find AC chargers in homes, streets and car parks.
EV fast charging was recently standardised by the UK Government as rapid and ultra-rapid DC chargers.
DC charging
A DC fast charger is quicker than its AC counterpart. A DC fast charger does the AC-DC conversion before sending it directly to the EV battery.
EV fast charging was recently standardised by the UK Government as rapid and ultra-rapid DC chargers. They are found at charging hubs and motorway service stations, as well as some workplaces and shopping centres.
A public rapid and ultra-rapid DC fast charger cannot be installed at home due to the high amount of AC power they need from the grid. This is why EV fast charging is available in public places like retail parks and motorway services, as there is a general business need for high levels of electricity.
AC and DC chargers compared
How does DC fast charging work?
EV fast charging is quick and efficient because it delivers a charge straight from the DC charging station to the car battery, bypassing the on-board charger.
The EV fast charger you find at a charging station is far bigger and heavier than any on-board converter in an electric car. They house a powerful convertor that can quickly transform large amounts of AC power from the grid to DC power.
As a result, a DC fast charger can achieve a rapid charging power output of 50kW to 150kW and ultra-rapid charging achieves over 150kW. A rapid charger can deliver 150kW of DC power – and can charge a standard 64kWh EV battery from 20% to 80% in just 18 minutes.
For comparison, a standard home AC charger delivering 7kW of power will take more than 6 hours to charge the vehicle. (Inch Calculator data)
Why are DC chargers so fast?
A DC charging station handles high amounts of power fast
- They can handle the large amount of high-voltage power needed for DC fast charging.
- They contain a high-power convertor, which efficiently converts large amounts of AC power to DC charging power.
- They have advanced cooling mechanisms to deal with the heat generated by high charging power levels generated from an EV fast charger.
DC chargers are efficient
- DC chargers deliver power directly to the car battery, bypassing the speed limitations of a car’s on-board charger.
- A DC fast charger can deliver 150kW of power, and charge a car in just 18 minutes.
- An DC ultra-rapid charger can deliver 350kW of power, and can charge a car in just 8 minutes.
Types of DC charging
An EV fast charger is split into two types, based on their charging speed.
DC rapid chargers
DC rapid chargers (50kW+) are found at some petrol stations, as well as at some retail and commercial business car parks and workplaces.
An ultra-rapid DC charger (150kW+) is found at specialised EV hubs or large motorway service stations.
DC Ultra-rapid chargers
An ultra-rapid DC charger (150kW+) is found at specialised EV hubs or large motorway service stations.
You might also have heard of something called level 3 charging. This refers to all types of DC fast charging.
Types of DC fast charging connectors
DC chargers in the UK generally have two cables attached, each with a different type of plug (connector):
- The CCS (or ‘combined charging standard) plug combines a 7-pin, type 2 AC connector with two larger pins for DC fast charging. It’s common in the UK, US and Europe.
- The CHAdeMO plug has 10 pins: two for DC charging, seven signal pins and one reserve. It’s common in Asia.
Tesla Superchargers have a third type of connector. The early versions (V1 and V2) can only charge Tesla cars; but the later versions (V3 and V4) can be used by any electric car with a CCS port.
Read more about EV charger connectors
How fast is DC charging?
The quickest EV fast charger, known as an ultra-rapid, can charge a car from 20% to 80% in as little as 8 minutes (see table below).
But the speed depends on several factors, including the power output of the charger, the car’s battery capacity and charging rate, and the state of charge.
DC Charger Type | Power Rating | Estimated Time to Charge |
Rapid Charger | 50kW | 52 minutes |
Rapid Charger | 150kW | 18 minutes |
Ultra-rapid Charger | 350kW | 8 minutes |
*Simplified for example purposes; reference Inch Calculator
Read more about EV charging speeds
Charger power
The amount of power an EV fast charger can deliver is measured in kW. An EV fast charger with a high kW power rating will generally charge a car faster than one with a low kW rating.
The power rating helps you work out what type of DC car charger you’re using:
- Rapid DC charger – 50kW to 150kW
- Ultra-rapid DC charger– Over 150kW
Car battery size and EV charge acceptance rate
An electric car’s battery capacity is measured in kilowatt hours (kWh). Typically, the bigger the capacity, the longer it takes to charge – but you’ll probably get greater mileage from a car with a larger battery.
However, the battery’s cell type, construction and cooling system also affect charging speeds – as does the car’s battery management system (BMS). This means that every car will have its own maximum charge acceptance rate – which can never be exceeded, no matter the power of the DC car charger.
The car manufacturer’s specifications will give you a guide to the charging speeds your EV can achieve.
State of charge and the DC charging curve
The state of charge (SoC) of a battery – that’s how full the car battery is – has a big impact on a DC charge speed.
An EV’s fastest charge speed is achieved when the EV car battery is almost empty (less than 5% charged). The rate of charge of DC fast charger is highest when the SoC is between 5% and 20%, then levels off between 20% and 80%. After that, the DC charger’s speed drops significantly as the battery reaches 100% SoC.
This variation in DC charging speed is represented as a ‘charging curve’ (see diagram below).
The DC charging curve
Advantages and disadvantages of DC and AC charging
The main benefit of using DC fast chargers is time: it’s great when you’re out and about and in a hurry because you can charge your vehicle quickly. The one drawback of this benefit will be the price per kW. On average, it can cost around 80p1 per kWh to use an EV fast charger.
A DC EV charger is more expensive than an AC charger, which is around 57p1 per kWh. A public AC charger will take longer to fully charge your electric vehicle. However, if you are out for a few hours at the supermarket or gym, an AC charger can give a low battery a quick boost, giving you enough miles to get back home and use your home AC charger.
Nothing could be more convenient than plugging your EV in at home and leaving it to charge overnight. You can also take advantage of specialised EV tariffs, like Intelligent Octopus Go by Octopus Energy.
At the time of writing, off-peak unit rates were available from 7p per kWh; with peak rates at around 24p per kWh2. It gets even better if you have solar panels and can charge for free.
Pros and cons of public DC and AC charging
Charger Type | Typical Locations | Time To Charge3 | Cost Per Mile4 | Convenience |
Domestic plug socket (2.3kW) | Home | 18 hours 34 min | Off-peak: 2p Peak: 8p | Uses a standard domestic plug socket |
Slow AC (7kW) | Home or workplace | 6 hours 6min | Off-peak: 2p Peak: 8p | Plug in near your home Charge while you work |
Fast AC (22kW) | On-street (public) | 1 hour 57 min | 12p | Plug in while you shop or work Top up miles |
Rapid DC (150kW) | Supermarkets, Retail parks motorway services | 0 hours 18 min | 17p | Plug in and wait |
Ultra-rapid DC (350kW) | Specialist EV charging hubs Larger motorway services | 0 hours 8 min | 17p | Plug in and wait |
1 Typical public AC and DC charging cost per kWh at the time of writing: Zap Map
2 Typical home energy cost per kWh at time of writing; Which?
3 Estimated time to charge a Hyundai Kona, 64kwH, with a 301 mile range from 20% to 80%; reference Inch Calculator
4 Cost per mile calculated with www.osv.ltd.uk
Where and when to use a DC charger
Charging on a road trip
When you’re on a long journey, the last thing you want to do is hang about waiting for your EV to charge. That’s why motorway service stations are well-equipped with rapid and ultra-rapid DC EV chargers.
Charging in a hurry
Even if you have a home EV charger, you’ll sometimes need a quick power boost. Using an EV fast charger at your local charging station can give you substantial mileage in a relatively short amount of time.
Time-sensitive businesses, like couriers or those managing fleets often install DC fast chargers for the EV charging they need.
Charging at work
More and more employers are offering workplace EV charging as a benefit to employees. Many of these EV charging stations are AC chargers: speed isn’t too important to employees who are at work all day.
Some workplaces offer a combination of AC slow chargers and DC fast chargers to cater for the different charging needs of employees, clients and customers. Time-sensitive businesses, like couriers or those managing fleets often install DC fast chargers for the EV charging they need.
DC fast charging for commercial fleets
Many businesses are starting to electrify their fleet for cost and sustainability reasons. DC car chargers can cope with high turnover and charge multiple EVs in a short time – both of which help maintain high vehicle uptime and operational efficiency.
Why is DC fast charging more expensive?
EV fast charging from a DC rapid charger is usually more expensive than a public AC or charging at home. This is because the equipment, installation and maintenance of a DC car charger requires calls for a significantly higher investment.
The grid connection and electricity usage fees that charge-point operators have to pay are also much higher than those for domestic customers.
How Petalite DC fast charging is different
We’ve developed a new approach to electric charging at Petalite. Our unique sinusoidal direct current (SDC) technology radically simplifies the AC-DC conversion process.
It is a game-changer in DC charging. Compared to leading market alternatives, we have simplified the process and design of rapid and ultra-rapid chargers. This has solved many issues around reliability and scalability experienced by Charge Point Operators (CPOs) and EV drivers.
SDC is redefining the possibilities of DC rapid chargers, by offering transformational availability, reliability and scalability. Read more about our technology