Charging infrastructure plays a key role in the uptake of electric vehicles. With electric vehicle charging, one hears about AC charging and DC charging. But what is the difference between these two? What is fast charging?
In this article, we will talk about the basics of electric vehicle charging, AC charging vs. DC charging, and find answers to these questions.
The Basics of Battery Capacity
Every electric vehicle works with a battery. In order to use your vehicle, you need to charge the batteries first. But before you jump into charging, you need to understand battery specifications. These days, we are using lithium-ion batteries which have higher energy density.
Energy density is basically the amount of energy stored in a particular space, system or volume. Lithium-ion batteries have an energy density of 250 Wh/kg. Wh (Watt-hour) is the unit of energy. So the battery’s capacity is measured in watt-hours, which is Voltage x Ampere-hour.
If you have seen the EV batteries’ specifications, you will see the unit kWh since the battery packs in the EVs are huge. For example, the Hyundai Kona has a battery pack of 39.2 kWh. For the EV to charge fully, we need to fill in the same amount of energy into the battery pack.
And that’s where the chargers come in. The specifications of the chargers come in kW, which is a unit of power. The charger powers the battery according to its power handling capacity.
In the electricity grid, the electric power is alternating current or AC by nature. However, the electric power of a battery is direct current or DC by nature. Hence, to charge an electric car from the AC grid, the power has to be converted from AC to DC.
If the EV’s battery capacity is 39.2 kWh, and we charge it in the house with a 3.3 kW charger, then it will take more than 12 hours to fully charge the battery. If you use a bigger 10 kW charger, then it will only take roughly 4 hours to charge. If you use a 100 kW DC fast charger to charge these batteries, then ideally it may take roughly 30 minutes to finish charging.
Thus, fast charging is a convenient option for drivers who are in a rush and want to save time. As we increase battery capacity, the power requirements also increase to charge these huge batteries.
Does AC to DC Conversion Depend On The Device?
Yes. In the case of day-to-day portable electronic devices (e.g. mobile phones), a converter is usually placed inside the plug.
In terms of electric vehicles, the converter is found within the vehicle itself.
When it comes to DC chargers and fast-charging EVs, the converter is found inside the charger and it handles the conversion. Thus, DC chargers are generally bigger and more costly. Power should always be converted from AC to DC while charging an EV and the difference between AC and DC charging is more technical – whether power is converted inside or outside the vehicle.
How To Convert Power From AC To DC
When it comes to charging electric devices such as electric vehicles and mobile phones, the power must be converted from AC to DC using a converter.
How To Convert Power From AC to DC with EVs
The power derived from the grid is AC power. Thus, when charging an electric vehicle, power must be converted from AC to DC.
When it comes to DC chargers (for fast EV charging) the converter is located within the charger itself. The converter does the conversion under these circumstances. Thus, DC chargers are generally bigger and more costly.
The Basics of EV Charging
An electric vehicle charging system has three main parts. The first part is the AC to DC power turning converter. As mentioned earlier, this converts the power from AC to DC. The second part is the charging cable with the connector that is used to feed power from an external power supply to the electric car via the vehicle inlet.
Finally, a charge controller on the external power supply side and the battery management system on the vehicle side are responsible for the communication protection and control of the charging process.
They control the charging current and stop the charging, complete draining, short circuit, or overvoltage of the battery. It also ensures that the temperature and balancing between the cells are optimal for long battery life.
EV Charging Levels and Power Current
The easiest way to understand the different ways to charge your EV and the time it will take is to break charging down into three levels.
Level 1 is AC charging wherein the electric vehicle is plugged into the home 240-volt AC socket. While this type of charging may seem easy – there are several socket types everywhere and it is the slowest.
The typical 10-amp socket provides at least 2.0kW charging power, and how long it takes to fully charge your battery from empty will depend on its size, although it would generally be slow and may take a couple of days.
One rule is to divide your battery’s capacity into two to determine the approximate time this charging method takes. For instance, an 80kW battery takes at least 36-40 hours to fully charge.
A more powerful socket like 15-am, 3.6kW should take half the time, although one must keep in mind that the majority of charging involves topping up, instead of recharging a fully drained battery, so it is not likely that will wait 48 hours to fully charge.
Level 2 is AC fast-charing like those exemplified by wall-box chargers installed at people’s homes. These provide 7.2kW with a 240-volt AC single-phase power, which significantly reduces the charging time.
It would take a 13.8kW battery only two hours to charge fully from empty, while an 80kW battery will fully charge in 10 hours.
Wall-box chargers are generally viewed as a great choice for PHEVs or Plug-in Hybrid Electric Vehicles that have an internal-combustion engine and electric motor since their smaller batteries take a while to charge.
While it’s crucial to remember that many EV batteries – such as those of PHEVs that have smaller batteries, only charge at 7.6kW maximum capacity, there’s the option to install a 22kW charger with a 415-volt three-phase power electrical source.
Level 2 AC fast charging is generally available in public charging stations. There are several apps that can help you find charging stations and provide detailed information about them, which can be used to determine those that provide 7.2kW or 22kW charging.
Level 3 is DC rapid charging, available through 480-volt DC rapid public chargers that offer charging power at 50kW.
These charger types are crucial for drivers travelling at long distances and looking for short charging times, even though charging can be sped up with particular ultra-rapid chargers that deliver 350kW power.
If you possess a PHEV, remember that they don’t work with ultra-rapid chargers or DC fast chargers – only AC charging works with them.
In terms of charging time, DC fast-chargers match the kW chargers deliver to km for every 10 mins of charging, which means 10 mins at 50kW provides 50 km of range, while 10 mins at 175kW provide 175km of range, etc.
Again, your friend here is a smartphone app that will enable you to locate the right charger type for your vehicle as long as you know the maximum charging capacity of your vehicle.
3 Levels of Charging
There are three commonly referred to as levels of EV charging. The levels (1, 2 and 3) mostly correspond to the speed with which the charger can fill an EV battery:
Level 1 (AC)
Level 1 is basically the power we use every day: The AC power outlets inside our house and workplace can power your electric vehicle. Level 1 power is accessible and inexpensive but the low-voltage AC power is slow and most EV owners who drive on a regular basis don’t consider it the best way to charge.
Level 2 (AC)
Level 2 is the most common EV charging method. This method still depends on AC but utilizes a transformer to increase the speed and voltage to charge an EV. Level 2 is a fantastic option for homes, businesses, and multi-unit dwellings since the speed of these chargers are suitable for active EV owners.
Level 3 (DC)
Also called “fast charging” or “rapid charging”, Level 3 charging is among the fastest EV charging methods. Although it is more expensive to construct, the stable DC power of Level 3 charging can fully charge an EV battery in just 30 minutes. These chargers are perfect for charging stations along highways and major routes.
Two Types of Chargers
There are two types of chargers – on-board chargers and off-board chargers. In easier terms, we categorize them as AC chargers and DC chargers. The onboard chargers are present in the vehicle itself where you can gain AC supply from the grid and charge the batteries directly.
Still, you cannot just insert two wires of line and neutral coming from the grid and connected to the vehicle. Further, you need a device named EVSE or Electric Vehicle Supply Equipment. Some people call it a wall-mount charger. It comes with the vehicle itself or can be bought separately. The EVSE is connected between the vehicle and the grid.
Hence, to charge electric vehicles, AC power from the office of the grid is fed to the car via the vehicle inlet using the charging cable and connector. The onboard charger, which is an AC-to-DC power converter, converts the AC power to DC power suitable for charging the battery.
What we have seen till now is referred to as AC charging. The size and weight of the onboard charger are dependent on the maximum charging power. Typically, onboard chargers have maximum power in the range of 1.9 to 22 kilowatts.
If the charging power has to be further increased then the charger will become bigger and heavier. However, due to the size and weight restrictions inside the vehicle, the onboard charger is limited in size and weight as well.
An off-board charger is present outside the vehicle. It actually converts AC into DC on its own and supplies DC power to the vehicle through its inlet. This time the power is directly forwarded to the battery pack. DC chargers are more powerful than AC chargers. Greater power means more size and cost.
Therefore, the solution to increasing the charging power is to move to the AC/DC converter outside the vehicle and place it in an off-board charger. This is referred to as DC charging. With no size and weight restrictions, that off-board charger can have a maximum charging power in order to 50 to 230 kilowatts.
In the case of DC charging, the off-board charger has an AC to DC power converter. And DC power is directly fed to the car through a DC vehicle inlet. We hence have both AC and DC charging electric cars, depending on whether the onboard or offboard charger is used.
While Tesla cars use the same vehicle inlet for both AC and DC charging, all other manufacturers have separate inlets for AC and DC charging as shown in the picture. AC and DC charging is characterized by the connector type and the charging power levels that can be reached.
AC Connector Types
For AC chargers, there are two types of supplies:
This input goes directly to the EVSE and at the output of the charger, these supply charging cables are extended, but there’s a contactor or relay in between to ensure isolation and safety between output and input.
There’s one more wire coming from the connector named “pilot signal” which ensures communication between the charger and EVSE. This signal gives information that the vehicle is connected, the vehicle is ready for charging, and charging is taking place.
One more important function of the pilot signal is to provide the current capacity of the input supply to the vehicle. The EVSE sends a signal to the vehicle about the status of the charging with the pilot signal. And once the vehicle is sufficiently charged, the EVSE stops charging for safety.
One more important feature of the EVSE is that no supply will take unless the EV is connected. The EVSE becomes live and supply takes place only if the charger is connected. So don’t get confused, or believe in the myths that you will get electrocuted while charging.
However, there is a limitation for AC charging in that you cannot go beyond power limits due to the limitation of on-board charges. These chargers cannot handle higher powers due to the size constraints inside the vehicle.
That’s why we go to off-board chargers. On the off-board chargers, which are DC type, a regular output of continuous current charging and continuous voltage charging would need a lot of the batteries power.
But for that, the vehicle should be compatible with DC fast charging. Of all the vehicles present in the market, mostly four-wheelers or commercial vehicles and buses support DC charging because of their very large battery pack. It would take a very long time for these vehicles to undergo AC charging.
On the two-wheeler side, we have smaller batteries. So AC charging is sufficient to charge these batteries.
In the case of DC chargers, the charger communicates with the Battery Management System. This system commands the charger and provides information regarding the present State of Health (SOH) of the battery and its State of Charge or SOC.
The State of Charge can be displayed on the screen embedded in the charger. We get information about how much of it is charged.
Pros and Cons of Available Electric Vehicle Charging Infrastructure
AC charging, like Level 2 charging, remains quite popular. Thus, you can’t always drive into an area of DC charging, even if you want to, since the nearest location may still be far away. While AC charging remains excellent and safe, it requires more charging hours because it’s slow compared to DC charging.
Using DC fast charging also presents some disadvantages. Thermal issues are among the concerns. Prolonged charging using DC fast chargers can heat up electric vehicle batteries, and it can gradually degrade the battery over time. While its effects in the long term as still debatable, it opens the proposal for heat control technology.
Also, it is costly to install, and this is a disadvantage. When it comes to DC charging stations, higher voltages are required. They require a 480-volt level of electricity to work for the majority of the time and this voltage requirement costs relatively more than its AC counterpart.
So, for the installation companies and EV drivers, there are cost implications. Conversion to DC takes place within the vehicle. Conversion is also done outside the vehicle within a charging station. The charging curve looks like a flat line and it charges at a constant rate.
If the charging rate reduces with time, the charging curve becomes a degrading curve. This means that the initial fast rate at where the battery gets power will reduce as it gets close to the total capacity.
Charging speeds generally go from 22kW-43kW per km/h to 50-100kW per km/h. AC stations are also quite common. The new DC charging stations can be found in Europe although they’re not as common as AC charge points.
AC chargers operate with a limited onboard charging converter. DC chargers operate with a bigger converter outside the electric vehicle for fast bidirectional charging.
Advantages of AC Over DC
AC charging using a plug is among the most common EV charging method. Because the vehicle is built in the vehicle, power is converted from AC to DC within the car before sending it to the battery. The charging speed depends on the charging point’s output power and the convertor’s ability to covert power.
- AC charging is generally effective in parking areas where the vehicle can be parked for a while.
- An AC charger’s manufacture, installation and use are less costly than that of DC.
- AC units are compact and simple. They don’t need much maintenance and repairs during operation.
- Because the present magnitude isn’t constant, a conductor can be used to reduce it with less energy loss.
- It’s easy to convert AC power to DC using rectifiers.
- Several voltages can be acquired using a transformer.
- Line losses aren’t much compared to DC transmission while AC is made available at higher voltages for long-distance travel.
Because it’s alternating current, this kind of power may undergo electricity loss while travelling distances. It’s part of the reason why power girds use transformers. By increasing the voltage to higher levels, power companies can distribute power at long distances and not underdo serious electricity loss.
AC can also lead to a slower power transfer at lower voltages w used on a daily basis. For electric vehicles, this entails that AC charging is slower than DC charring.
Advantages of DC Over AC
DC charger can send power straight to the vehicle’s battery without the need for any onboard charger that converts it. It already has a convertor built inside the charger itself. It is costly because it needs a transformer or power supply which results in higher charging tariffs.
Advantages of DC charging in terms of electric vehicles include:
- DC chargers are faster and bigger compared to AC chargers
- Converts power before it flows into the car, such that power enters the car’s battery directly, bypassing the car’s converter
- Suitable for fast recharge through long-distance travel for vehicles supporting DC charging
- It’s less dangerous to operate with DC than AC with high voltages
The major disadvantage of DC power is the lack of available infrastructure. Since the power grid relies on AC power, infrastructure for DC charging is less prevalent, especially in smaller operations.
But companies have been installing the infrastructure in the last few years and continue to do so that DC charging has become more accessible. As we’ve stated, there is some discussion about how frequently DC charging should be used by EV drivers and most manufacturers don’t recommend daily DC charging.
The majority of chargers use AC power due to the lower costs spent during manufacture, installation and use compared to DC. It’s a safe and viable option for travelling over long distances.
Even though DC is more costly to install, it’s faster in transmitting power than AC charging and is therefore a preferable option for long-distance travel.
AC and DC charging evolves fast and therefore operates better with electric vehicles. DC charging is still ahead in terms of charging speed. It also has a capacity level in terms of current, voltage and power.
You can opt for both AC and DC charging options but if you want more efficiency we recommend that you go for DC charging.
The cost of charging depends on the amount of power you’re using over a time period. The calculations are derived from this. The charger type also plays a major role in the expense.
In terms of AC charging, a type 1 connector is generally used in the U.S. and Japan while Types 2 & 3 are the commonly used connector types in Europe. Tesla has a proprietary connect in the U.S. and Japan, and a Type 3 connector in Europe.
Other parts of the world are often adopting the Type 2 connector as it can work with 300 volts, single-phase connections, and 400 volts three-phase connections.
In terms of DC charging, the Chademo Type 4 connector is used by Japanese car manufacturers globally. While American and European car manufacturers have adopted a combined AC/DC connection called the “combined connector” combo. Interestingly, Tesla uses the same connector. meant for AC charging and DC charging as well.
In the case of China, they have their own DC connection.
How AC and DC Charging Are Used
The conclusion is that the electric vehicle industry has not fully agreed on one specific connector. So depending on the car brand, country, and whether it is AC or DC charging, the connector varies in shape, size and configuration.
With AC/DC charging, the charging power can be split into three levels – Level 1 up to Level 3. Generally, Level 1 refers to a charging power of up to 10 kW, while Level 2 refers to a charging power of up to 50 kW. Both AC and DC charging can provide Level 2 charging power.
Beyond 50 kilowatts, only DC charging using an off-board charger is used to provide charging power as high as 350 kilowatts. Level 3 charging is often called fast charging.
If we assume that an electric vehicle can drive 5 kilometres using 1 kW hours of energy, this charging power can be translated into kilometres of range that can be added per hour or charging.
We can easily see how Level 1 and Level 2 charging is sufficient for commuting needs, while Level 3 charging is useful for quicker high-level charging.
Which Choice Is Best For Your Situation?
Essentially, the better option will depend upon your immediate needs. If you’re looking for a fast recharge to maintain your frequent long-distance trips, then DC charging is the better choice for you. Besides that, AC charging should suffice, especially if you’re not frequently going on long drives.
Note: The charging capacity of the charge point must match the charging capacity of your car.
To wrap up, electric vehicles can be charged by AC or DC charging. The main difference is that in DC charging, the AC and DC power converter is placed outside the vehicle in an offboard charger. And hence, the charging power can be as high as 350 kilowatts.
In the case of AC charging, the onboard charger is used, which is usually restricted to less than 22 kilowatts. Finally, since car manufacturers have not agreed on a single connector, various connectors are used for AC and DC charging globally.