The Ultimate Guide to Dc Fast Charging
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.
If you're considering switching to an electric vehicle (EV), charging speed is a key factor. Charging time can greatly affect your daily routine as an EV owner. DC fast charging is the fastest way to charge an EV and is crucial for public charging infrastructure. These stations are ideal for long-distance travelers needing a quick charge and for those making short stops who want to keep their 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 works because the AC-to-DC power conversion happens within the DC charging station before reaching the vehicle, enabling significantly faster charging than AC charging.
DC fast charging, also called DCFC (Direct Current Fast Charging) or Level 3 charging, is often referred to as rapid or ultra-fast charging.
Different Levels of EV Charging
Level 1 EV Charging
Level 1 is the slowest type of EV charging. It connects to a standard 120V AC outlet in North America, delivering 1 kW to 1.8 kW of power and adding about 3 to 7 miles of range per hour. Due to its slow speed, Level 1 charging is impractical for regular EV use. In regions with higher household voltages, such as Europe (230V), Level 1 charging is not available.
Level 2 EV Charging
Level 2 is faster than Level 1, using a 208V–240V connection in North America/Canada and a 230V (single-phase) or 400V (three-phase) connection in Europe. Power output ranges from 3 kW to 22 kW, providing 10 to 75 miles of range per hour. Level 2 chargers are the most common type of EVSE (Electric Vehicle Supply Equipment) and are widely available at homes, workplaces, and public locations.
Both Level 1 and Level 2 chargers supply AC power to the vehicle.
Level 3 EV Charging – DC Fast Charging
Level 3 DC fast charging is the fastest and most powerful EV charging option. It delivers significantly more power than Level 2 chargers, with outputs ranging from 15 kW to over 350 kW, allowing a standard EV to charge in 15 to 60 minutes. Unlike Level 1 and Level 2 chargers, which supply AC power, DC fast charging uses commercial-grade three-phase connections to deliver DC power directly to the vehicle's battery. Let's explore these differences further.
Difference Between AC and DC Fast Charging
EVs can be charged in two ways: AC charging (Level 1 or Level 2) and DC fast charging (Level 3). AC charging is slower, while DC charging is much faster.
The electric grid supplies AC power, but EV batteries store energy as DC power. The key difference lies in where AC is converted to DC:
- With AC charging, the conversion happens inside the vehicle using its onboard charger, which takes longer.
- With DC fast charging, the conversion occurs in the charging station before reaching the vehicle, bypassing the onboard charger's limitations and allowing faster charging.
This is why Level 3 DC charging is significantly quicker than AC charging.
Power vs. Voltage and Current
With a constant charging power (kW), the DC charge current depends on the DC charge voltage, which varies based on the vehicle, battery, and state of charge (from constant current (CC) at the start to constant voltage (CV) at the end).
DC fast chargers provide constant power, with voltage typically ranging from 200V to 1000V. The vehicle's battery management system (BMS) ensures charging stays within safe limits and communicates the required power to the charging station.
How DC Fast Charging Works
When using a DC fast charging station, the EV continuously communicates with the charger to regulate power intake. Charging speed depends on several factors, with the key ones being the charging station's power output, the EV's charge acceptance rate, and the DC fast charging curve.
Rate of Charge of a DC Charging Station
EV charging stations are rated by their maximum power output in kilowatts (kW), known as the charging rate. DC fast chargers typically range from 15 kW to 350 kW, with megawatt charging stations in development that can deliver up to 1000 kW. While higher kW chargers generally provide faster charging, the EV's acceptance rate determines the actual charging speed.
EV Charge Acceptance Rate
The charge acceptance rate is the maximum power (kW) an EV can receive. The battery management system (BMS) communicates this limit to the charging station when connected. Older EVs have lower acceptance rates, but newer models are designed to handle higher power inputs for faster charging.
Types of DC Fast Charging
There are four main types of DC fast charging connectors used worldwide: Combined Charging System (CCS), CHAdeMO, GB/T, and Tesla Superchargers. The connector type required depends on the make and model of the EV.
- CCS (Combined Charging System) – Available in two versions: CCS1 (used in North America) and CCS2 (used in Europe).
- CHAdeMO – Primarily used for Japanese-brand vehicles, though many manufacturers are shifting to CCS for new models in North America and Europe.
- GB/T – The standard connector for the Chinese market.
- Tesla Superchargers – Compatible with all Tesla vehicles worldwide, except in the EU, where CCS2 is now used.
Is DC Fast Charging Bad for an EV Battery?
Not really. While it's commonly believed that faster charging leads to quicker battery degradation, studies, including one by the Idaho National Laboratory, show that even with exclusive DC fast charging, the difference in battery capacity decline compared to Level 2 AC charging is minimal.
Every EV battery has an advanced Battery Management System (BMS) that regulates the charge acceptance rate, monitors battery temperature, and adjusts charging speed if necessary to prevent damage. While DC fast charging may have some impact on battery life, it is minimal and does not cause significant harm.
Summary
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.
