If you are looking at potentially switching to an electric vehicle (EV), charging speed will be at the forefront of your mind. The time it takes to charge an EV can significantly impact your daily routine as an EV owner. DC fast charging is the quickest way to charge an electric vehicle, and it plays an essential part in public EV charging infrastructure. DC fast charging stations are ideal for EV drivers traveling long distances and needing to quickly charge their cars along their journey and for those visiting places for a short time but wanting to keep their car battery topped up.
WHAT IS DC FAST CHARGING?
The power in an electric vehicle battery is stored as direct current (DC); at the same time, the electric grid provides power as alternating current (AC). Inside an EV is an on-board charger that converts AC power into DC power before distributing the power to charge the vehicle’s battery. DC fast charging bypasses this on-board charger and charges the battery directly, dramatically reducing the time it takes to charge an EV. This is made possible as the power conversion from AC to DC occurs in the DC charging station before being output to the vehicle. DC fast charging can provide a much faster EV charging experience than AC-type charging.
DC fast charging is known as DCFC (Direct Current Fast Charging), level 3 charging, and is often referred to as rapid or ultra-fast charging.
Before we delve into the details of DC fast charging, it is essential to understand the different speed levels of EV charging and where DC fast charging fits in.
WHAT ARE THE DIFFERENT LEVELS OF EV CHARGING?
Level 1 EV Charging
Level 1 is the slowest type of electric vehicle charging equipment currently. A level 1 EV charger plugs directly into a standard 120 volt AC outlet. The average power output is 1 kW to 1.8 kW, adding approximately 3 to 7 miles of range to your electric vehicle per hour. Needless to say, Level 1 type chargers are extremely slow and not very practical if you intend on using your electric car regularly. In parts of the world outside North America and Canada where standard household voltages are higher, 230 volt in Europe, for instance, Level 1 charging is unavailable.
Level 2 EV Charging
Level 2 is the next speed up from level 1 charging. A level 2 electric car charger uses a 208 volt to 240 volt connection in North America/Canada and a 230 volt (single-phase) or 400 volts (three-phase) connection in Europe. The power output of a Level 2 charger is between 3 kW and 22 kW depending on where you are located in the world; this would result in 10 to 75 miles of range for an hour worth of charge. Level 2 charging stations are the most popular type of EVSE (Electric Vehicle Supply Equipment), and they can be found at homes, workplaces, and many other public locations.
Both Level 1 and Level 2 EV chargers deliver AC power to the electric vehicle.
Level 3 EV Charging – DC Fast Charging
Level 3 DC fast charging is the quickest and most powerful type of EV charging available. A level 3 charging station is designed to deliver more power at faster speeds than Level 2 type chargers with outputs of 15 kW to over 350 kW, enabling you to charge a standard electric car in 15 to 60 minutes. DC fast charging utilizes commercial-grade three-phase connections and delivers DC power directly to the electric vehicle’s battery, utterly different from how Level 1 or Level 2 EV charging works. Let’s look at the differences in a bit more detail.
WHAT IS THE DIFFERENCE BETWEEN AC AND DC FAST CHARGING?
There are two ways to charge an electric vehicle via AC (alternating current) via a Level 1 or Level 2 type charger or DC (direct current) via a Level 3 DC fast charger. AC charging is often referred to as slow, and DC is fast charging. The power that comes from the electric grid is always AC. However, the energy needed to propel your EV has to be stored in its battery, and batteries can only hold power as DC. With that in mind, the main difference between AC charging and DC fast charging is the location where the AC power is converted to DC. In AC charging, the AC power is converted in the vehicle by its on-board charger, which is time-consuming; however, with DC fast charging, the conversion takes place in the charging station before the power is delivered to the vehicle, and as a result, it can bypass the limitations of the electric vehicles’ on-board charger and deliver more power. This is what makes level 3 DC charging faster than AC charging.
POWER VS VOLTAGE AND CURRENT
With a constant charge power (kW), the DC charge current is dependent on the DC charge voltage, which is different by vehicle, battery, and state of charge (constant current (CC) start to constant voltage (CV) finish), etc.
DC fast chargers have constant power, and DC Voltage usually ranges from 200 volts to 1000 volts. The electric vehicle battery management system (BMS) will ensure it is being charged within the tolerances of the battery at any given state and communicates the demand to the EV charging station.
HOW DOES DC FAST CHARGING WORK?
When charging an electric vehicle with a DC fast charging station, the EV is constantly communicating to control how much power is drawn. Several variables determine the speed at which your EV is charged; however, the main variables we will focus on are the rate of charge of the charging station, the acceptance rate of the electric vehicle, and the DC fast charging curve.
Rate of Charge of a DC Charging Station
All EV charging stations are measured as their maximum output power in kilowatts (kW), known as the rate of charge or charging rate. DC fast charging stations range from 15 kW to 350 kW; even megawatt charging stations are megawatt charging stations currently in development that can output 1000 kW of power. Generally speaking, the higher the kW, the faster the charge; however, choosing a higher kW DC fast charger over a lower kW one does not necessarily mean that the electric vehicle can be charged quicker. This is where the acceptance rate of the electric vehicle influences the charger’s rate of charge.
EV Charge Acceptance Rate
An EV charge acceptance rate is the maximum amount of power in kW that an electric vehicle can input. The vehicle’s battery management system communicates this to the charging station when a DC fast charger cable is connected to the car. Some early electric vehicles have very low charge acceptance rates; however, more and more EVs on the market have higher charge acceptance rates to improve charging speed.
For example, let’s take a car with an EV charge acceptance rate of 50 kW. That would mean that the rate of charge would be approximately the same regardless of whether it was being charged at a 50 kW, 100 kW DC fast charging station, or even a 350 kW. Let’s look at another example, but the other way around, the Porsche Taycan has a charge acceptance rate of 270 kW, meaning it can take a peak charge of 270 kW. It would not reach its peak if you were to charge it at a 150 kW fast charging station. It would only be able to take in 150 kW as that is the maximum rate of charge of the charging station.
DC Fast Charging Curve
The DC fast charging curve is another influential variable in determining an EVs charging speed. Every EV model has its unique charging curve, which determines how much power it can take over time as it charges. In the below chart, you can see a typical DC fast charging curve. The chart’s vertical axis shows the power output being drawn by the EV and the horizontal axis illustrates the EV battery SOC (State of Charge) over time. Typically, an EV will charge at its maximum rate for only a part of the charging cycle. Once the electric vehicle has communicated with the DC fast charging station, it will quickly reach top charging speed; then, from that point, it will slowly start to draw less power as the battery becomes more charged; you can see a steep drop-off occurs when an EV battery is charged to 80% of its capacity. Most EV manufacturers and many studies recommend charging 80% of the vehicle’s battery capacity to help prolong battery life and allow other EV drivers to use the charging station as the charge speed from 80% to 100% is vastly decreased.
WHAT TYPES OF DC FAST CHARGING ARE THERE?
There are currently four types of DC fast charging connectors used worldwide: Combined Charging System (CCS), CHAdeMO, GB/T, and Tesla Superchargers. Depending on what make and model your electric vehicle is will determine which DC connector you can use to charge it. With CCS, there are two types CCS1 which is used in North America, and CCS2, which is used in Europe. CHAdeMO is primarily for Japanese brand vehicles. However, these manufacturers are moving over to the CCS connector for newly released models in North America and Europe. GB/T is the standard connector for the Chinese market, and Tesla’s Supercharger works with all Tesla vehicles worldwide except in the EU.
HOW FAST IS DC FAST CHARGING?
With different types of electric vehicles with varying battery capacities, various level 3 DC fast charging stations with numerous power outputs, and several factors that can influence charging speed, it isn’t easy to give a precise answer to how fast DC charging is. However, we can provide an estimate of how many miles of range a DC fast charger can deliver to an electric vehicle within 60 minutes based on the power output of the charger and the kWh per 100 miles (kWh/100 mi) of the average EV, which is 34.6.
HOW MANY KW IS A DC FAST CHARGER?
The higher the output power (kW) of a DC fast charger, the quicker it can potentially charge an electric vehicle. The kW output power can vary depending on the installation location, the brand, and the model. Current DC fast chargers on the market range from 15 kW to 350 kW. These can be standalone DC chargers that provide the full kW power to one plugged-in vehicle or split chargers that distribute the power to more than one charging cable, simultaneously charging multiple EVs by sharing the kW power output of the charger. At EVESCO, we have both standalone and split DC fast chargers that span from 50 kW upwards.
CAN ALL EVS USE DC FAST CHARGERS?
There are different types of electric vehicles on the market; battery electric vehicles (BEVs), which are all-electric and run entirely on electricity, can generally use DC fast charging stations. Their EV charge acceptance rate will depend on how much output power they can use. Some electric vehicles can accept DC fast-charging up to 300 kW. The Lucid Air Dream edition was recently tested with its peak charge at 297 kW, whereas others have a lower charge acceptance rate. Some early BEVs and hybrid EVs (HEVs) can not use DC fast charging as their battery capacity is too small. When choosing an electric vehicle, it is essential to look at the charge acceptance rate and the battery capacity to see whether you can utilize DC fast charging to its fullest.
IS DC FAST CHARGING BAD FOR AN EV BATTERY?
The simple and quick answer is not really. The accepted notion within the industry is that the faster the charging, the faster the EV battery capacity will decline, which is technically accurate. However, the Idaho National Laboratory study looked into how fast charging affects battery life. It showed that even if the only type of charging used was DC fast charging, the difference in the rate of decline of the EV battery capacity compared to Level 2 AC charging is minimal.
Every electric vehicle battery has an advanced Battery Management System (BMS), which has set parameters specifically configured to prevent damage to the EV battery. The BMS controls the charge acceptance rate and monitors the battery temperature, and if needed, can lower the rate of charge to protect the battery.
While DC fast charging can affect an EVs battery life, it is minimal and doesn’t damage the battery.
HOW MUCH DOES DC FAST CHARGING COST TO USE?
DC fast charging stations are designed for industrial and commercial locations and are not suitable for installation at home due to the required three-phase connection. You can find DC fast charging in many public places, including fuel stations, service stations, commercial car parks, shopping centers, and EV charging hubs. Public DC fast charging stations can vary dramatically in price depending on the location and the time of the day they are being used. For example, in California, EV drivers can expect to pay around 30 cents per kWh for using a Level 2 charger and 40 cents per kWh for using a DC fast charger. In contrast, in another example, we found an EV driver was billed 29 cents per minute for using a DC fast charger in Chicago; a 25-minute charging session cost $7.25, adding only 50 miles of range. Tesla charges an average of 28 cents per kWh for using their superchargers when the cost per kWh is allowed.
HOW CAN YOU FIND A DC FAST CHARGER?
DC fast charging stations are growing in popularity as more and more EV drivers want to charge their cars quickly when out on the road. There are an increasing number of DC fast chargers being installed in public locations, but how do you find them? There are a few ways to find these EV charging stations.
- Google maps – more chargers are being added to google maps every day
- Plugshare – a helpful app for finding EV charging stations; it shows which ones are available and whether they are AC or DCFC
- Open Charge Map – a useful website that shows up to 500 charging stations per search
- DOE – The Department of Energy has a charging station locator for the USA, which shows not only EV charging stations but also Hydrogen, Bio-Diesel, and other alternate fuels
- EV charging networks – If you are a member of an EV charging network, then you can access their DC fast charging locations via their apps
As electric vehicle adoption accelerates, the need for DC fast charging is increasing. DC fast charging is essential for public EV charging infrastructure and will help enable long-distance traveling and give households with no home EV charging somewhere to charge their cars quickly. DCFC will also be critical as we transition larger vehicles to electric, requiring larger batteries and higher charging rates to make them usable in real-world environments.
As of the end of 2021, there were only 21,676 DC fast charging stations in the USA; this number needs to increase dramatically if we are going to reach the ambitious targets set for electric vehicle numbers in the next five years.