2023-07-05

EV Charging: AC vs. DC

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In the early 20th century, Thomas Edison and Nikola Tesla were both involved in developing the types of electricity we use today. Edison advocated for direct current (DC), which initially became the standard power in the United States. In contrast, Tesla introduced alternating current (AC) to overcome some of the challenges posed by DC. The efforts of these two scientists led to significant technological advancements and competition in the power industry, ultimately resulting in the establishment of modern electrical systems.

2 types of electricity: AC and DC

There are two methods of electric current: direct current (DC) and alternating current (AC).

  • DC flows consistently in one direction, similar to the flow of a river. It is commonly generated by batteries, solar cells, and other sources.
  • AC periodically switches between positive and negative sides, causing the direction of electricity to change accordingly. It is obtained from generators and outlets. Power plants generate AC, which is then transmitted to homes.


AC

AC, or alternating current, is generated by power plants, where mechanical energy is converted into electrical energy. AC power has a key advantage – it can be easily transformed from one voltage level to another using transformers. This makes it efficient for transmitting electricity over long distances. This is why AC power is universally used in electricity grids and readily available for our daily needs. When necessary, AC power can be converted to DC power by conver.

DC

Direct Current (DC) is the steady flow of electric charge in one direction, generated by batteries, rectification, generators, or photovoltaic cells. Unlike Alternating Current (AC) which changes direction periodically, DC provides a constant and predictable source of power, making it ideal for electronic devices and batteries.
DC power finds widespread use in electronics, telecommunications, automotive systems, and renewable energy. For instance, when charging electric vehicle batteries, we convert alternating current to direct current for efficient power transfer.

The difference between AC and DC charging for EV

Batteries, including the ones in your EV, can only be recharged using direct current (DC). So, the main distinction between AC charging and DC charging lies in where the conversion from AC to DC takes place — either inside or outside the vehicle.


AC Charging for EV

AC charging is the most common method for recharging electric vehicles. Inside the car, there is a converter called the onboard charger (OBC) that converts AC power from charging stations or wall outlets into DC power. The converted DC power is then directed to the car’s battery. AC charging is widely used, and most chargers rely on AC power.

DC Charging for EV

DC charging represents an exciting breakthrough for electric vehicles. Since power from the electrical grid is always supplied in AC form, the main difference between AC charging and DC charging lies in where the AC power conversion takes place. Unlike AC chargers, DC chargers have the converter directly built into the charger itself. As a result, they can supply power directly to the car’s battery without the need for the onboard charger to perform the conversion. DC chargers are often larger and faster than AC chargers, showcasing significant advancements in electric vehicle technology.

AC and DC EV charging: the pros and cons

Speed

Speed is a key factor that distinguishes AC and DC charging. DC charging delivers power faster than AC charging because it converts the electricity outside the car. However, DC charging speed also varies depending on the battery size, how full it is, the temperature, and how the power changes over time.

Assuming the car has a battery capacity of 60 kWh and an efficiency of 4 miles per kWh, here’s an estimate of how many ranges it can drive after being charged for 30 minutes:
  • 3.5 kW (AC): about 1.75 miles (2.8 km)
  • 7 kW  (AC): about 3.5 miles (5.6 km)
  • 11 kW  (AC): about 5.5 miles (8.8 km)
  • 60 kW (DC): about 30 miles (48 km)
  • 120 kW (DC): about 60 miles (96 km)
  • 240 kW (DC): about 120 miles (193 km)

Please note that these are just estimates and the actual range may vary depending on several factors such as temperature, driving conditions, and battery degradation.

Cost

DC charging is more costly than AC charging for several reasons. DC chargers have a significantly higher initial cost than AC chargers, typically ranging from $5,000 to $50,000, while a commercial AC charger typically costs between $1,000 and $3,000, while a high-power commercial AC charger can cost over $3,000. Another reason is that DC chargers have higher installation and grid connection costs than AC chargers, because they need specific infrastructure and equipment. A third reason is that DC chargers charge more for the service, as much as about $10 per 100km of charge. This is much higher than home charging, which costs around $3 per 100KM on the average electricity plan.

Availability

AC charging is the most common method of EV charging, compatible with most electric vehicles, ideal for home or public charging stations with AC chargers, easily connects to the existing AC power grid. However, DC charging requires a high-voltage connection to the power grid and a dedicated infrastructure. Not all electric vehicles have DC charging ports, and not all places have DC charging stations.

Safety

DC charging may pose higher risks of arc flash or overcharging due to the higher voltage and current involved，while AC charging may cause overheating or electromagnetic interference due to the multiple conversions between AC and DC power. Therefore, both AC and DC charging have safety standards and requirements to ensure the isolation of the vehicle and the charger from the power source.

EV charging levels

EV chargers have three levels (1, 2 and 3) based on charging speed. AC chargers are Level 1 or 2, and DC chargers are Level 3.

  • Level 1 Chargers (AC): Level 1 EV chargers use a standard 120-volt outlet and offer 2-5 miles of range per hour. They are ideal for overnight charging at home or long-term parking.
  • Level 2 Chargers (AC): Level 2 EV chargers require a 240-volt circuit and offer 10-20 miles of range per hour. They are suitable for both home and public charging stations, such as in workplaces or multi-unit dwellings.
  • Level 3 Chargers (DC): Level 3 EV chargers, or DC fast chargers (DCFC), use direct current (DC) and offer 60-80 miles of range in 20-30 minutes. They are located along highways or other places where drivers need a quick battery boost.


Conclusion

AC and DC charging have distinct roles and features. AC charging is generally cheaper and more suitable for home, apartment, and workplace charging. On the other hand, DC charging is known for its fast charging speed, making it ideal for use along highways or when you’re in a hurry.

NECS offers AC chargers ranging from 3.5 to 22kW and fast DC chargers from 30 to 120kW to suit your business needs.