Comparison of AC and DC Chargers
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When we talk about charging an electric vehicle (EV), there are two different types of current that can be used: alternating current (AC) and direct current (DC). Both types of current can charge the battery of an electric vehicle, but they work differently and are used in different scenarios.
In contrast, direct current means that the current continues to flow in one direction and does not change direction repeatedly, as alternating current does. Direct current is commonly used in batteries and other devices that require a stable power supply because of its ability to provide a consistent power output. When you use a battery to power a device, whether it's a phone, a laptop or an electric car, you're actually using direct current.
However, when you need to charge your electric car quickly, DC charging stations come in handy. Dc charging stations are specifically designed for high-speed charging and are able to charge a large amount of energy into an electric vehicle's battery in a shorter period of time. These charging stations are usually located at highway rest areas or major transportation hubs in cities to allow drivers to quickly restore battery power during long trips.
When you use an AC charging station, the conversion of current is done inside the vehicle. Electric cars have an onboard charger built in, which is responsible for converting alternating current from the grid into direct current for storage in the battery. However, the power of such on-board chargers is usually low, so the speed of AC charging is relatively slow.
Instead, when you use a DC charging station, the conversion from AC to DC is done inside the charging station. Since the charging station can be equipped with a more powerful converter, it is able to transfer large amounts of power to the battery at a faster speed. This is why DC charging is often referred to as "fast charging". Some DC charging stations can even provide up to 400 kilowatts of power, capable of fully charging an electric vehicle's battery in minutes.
First, DC charging stations are complex, expensive and require high-voltage connections to the grid, which means they are often installed in public places rather than homes. Due to the high construction cost of DC charging stations, operators often set high charging fees. In addition, although DC charging is faster, it is primarily designed for long-distance travel, where quick power recovery is important.
On the other hand, AC charging station equipment is relatively simple, low cost and suitable for home installation. Even the slowest AC charger can fully charge a mid-size electric car overnight. Therefore, for daily commutes and short trips, AC charging is more economical.
Basic Concepts of Alternating Current and Direct Current
There are two forms of electricity: alternating current (AC) and direct current (DC). Alternating current is a current that changes direction periodically, meaning that it changes the direction of the flow repeatedly in one cycle. One of the advantages of AC is that it can be efficiently transmitted over long distances over power lines, and as such, it is the standard form of electricity used by most power grids worldwide. When you plug in any appliance in your home, what you receive is alternating current from the grid.In contrast, direct current means that the current continues to flow in one direction and does not change direction repeatedly, as alternating current does. Direct current is commonly used in batteries and other devices that require a stable power supply because of its ability to provide a consistent power output. When you use a battery to power a device, whether it's a phone, a laptop or an electric car, you're actually using direct current.
Electric Vehicle Charging Current Type
For electric vehicle charging, home chargers and most public charging stations use alternating current. This is because the AC infrastructure is already mature and suitable for long, slow charging. Usually, when you charge an electric car at home or work, you use an AC charger. This charging method, while slower, is enough to provide enough range for electric vehicles for a few hours at night or during the day.However, when you need to charge your electric car quickly, DC charging stations come in handy. Dc charging stations are specifically designed for high-speed charging and are able to charge a large amount of energy into an electric vehicle's battery in a shorter period of time. These charging stations are usually located at highway rest areas or major transportation hubs in cities to allow drivers to quickly restore battery power during long trips.
AC & DC
When discussing electric vehicle charging, the main difference between AC and DC charging is where the conversion from AC to DC occurs. The electricity transmitted by the grid is always AC, while the electric vehicle battery stores direct current. Therefore, whether an AC charging station is used or a DC charging station, the current that eventually enters the battery must be direct current.When you use an AC charging station, the conversion of current is done inside the vehicle. Electric cars have an onboard charger built in, which is responsible for converting alternating current from the grid into direct current for storage in the battery. However, the power of such on-board chargers is usually low, so the speed of AC charging is relatively slow.
Instead, when you use a DC charging station, the conversion from AC to DC is done inside the charging station. Since the charging station can be equipped with a more powerful converter, it is able to transfer large amounts of power to the battery at a faster speed. This is why DC charging is often referred to as "fast charging". Some DC charging stations can even provide up to 400 kilowatts of power, capable of fully charging an electric vehicle's battery in minutes.
AC and DC Charging Differences
The charging curve refers to how the speed at which the battery receives electricity changes during the charging process of an electric vehicle. Ac charging and DC charging have significant differences in terms of charge curve.AC Charging Curve
For AC charging, the output of the current is usually smooth, which means that the electricity received by the electric vehicle remains constant throughout the charging process. This smooth power output is due to the power limitations of the on-board converter, resulting in it only being able to charge continuously at a lower speed. This charging method is suitable for long periods of charging, such as at night or while working.DC Charging Curve
The power output of DC charging shows a decline curve. This is because at the beginning of charging, the battery can accept a lot of power, but as the charging progresses, when the battery is close to full, the speed of accepting power gradually slows down. Imagine filling a glass of water with a large bottle, at first you can quickly pour in the water, but when the glass is nearly full, you need to slow down to avoid overflowing. The same applies to DC charging: in the first 80% of charging time, the battery of an electric car is able to charge at a very high speed, but the charging speed is significantly reduced when it is close to full charge.the Applications of AC Charging and DC Charging
Now you may be thinking, if DC charging is faster, why not use it every time? While DC charging is indeed faster, it is not suitable for all scenarios.First, DC charging stations are complex, expensive and require high-voltage connections to the grid, which means they are often installed in public places rather than homes. Due to the high construction cost of DC charging stations, operators often set high charging fees. In addition, although DC charging is faster, it is primarily designed for long-distance travel, where quick power recovery is important.
On the other hand, AC charging station equipment is relatively simple, low cost and suitable for home installation. Even the slowest AC charger can fully charge a mid-size electric car overnight. Therefore, for daily commutes and short trips, AC charging is more economical.
Sum up
Ac and DC charging each have advantages and disadvantages, and are suitable for different scenarios. Understanding the difference between these two charging methods and how they work can help you better manage the charging needs of your electric vehicle. Whether charging slowly at home or quickly on the road, choosing the right charging method will add convenience and efficiency to your EV experience.