AC vs DC EV Charging: Comparing Efficiency and Speed


When you charge an EV, the main distinction between AC and DC charging is where the conversion from AC to DC happens. Because an EV’s battery can only store DC energy, regardless of the charging station used.

AC charging transfers current to an EV as a flat line due to the limited capacity of the onboard charger. DC charging forms a degrading charging curve, allowing for a more rapid and efficient energy transfer. 

In the context of EV charging stations:

1️⃣ AC chargers convert AC power from the grid to direct current (DC) power, which is stored in the EV’s battery.

2️⃣ DC charging stations provide DC power directly to the battery, bypassing the EV’s onboard charger and achieving faster charging speeds.

Now let’s delve into the mechanics of EV charging and how it powers electric cars starting with Alternating Current (AC) charging.

AC Charging

AC charging is ideal for charging EVs at home or at work because you can leverage the grid’s alternating current (AC) power. In this section, we will dive into the two primary levels of AC charging: Level 1 and Level 2.

Level 1 Chargers

A Level 1 charger typically comes with your EV and plugs into a standard 120-volt AC outlet. 

With a charging speed of about 2-5 miles of range per hour, Level 1 chargers are ideal for charging at home overnight or when your car is parked for longer periods of time. 

The main advantage of Level 1 charging is its simplicity- it doesn’t require extra charging infrastructure or incur extra costs.

Level 2 Chargers

Level 2 chargers are more powerful than Level 1 and utilize 240-volt AC power to charge your car faster. 

These charging stations can require professional installation either at home (but not always) or at public charging stations. Public Level 2 chargers can provide a charging rate of up to 22 kW, significantly reducing the overall charging time compared to Level 1 chargers.

While AC charging offers lower speeds, it is sufficient for everyday use, home charging, and most public charging networks. It’s cost-effective and does not put as much strain on the grid as DC networks.

Charger TypePower SourceCharging Rate
Level 1120-volt AC2-5 miles/hour
Level 2240-volt AC3-6 kW

DC Charging

Unlike AC charging, which relies on an onboard charger to convert AC power from the grid to DC power for the battery, DC charging, and its inner workings involve this conversion being done externally at the charging station. 

So these stations can have much larger converters which allows for a much faster charging speed. Making it ideal for situations where time is of the essence or on long journeys where extended charging times may be inconvenient.

Fast Charging

The charging speed of a DC charger greatly depends on the charging infrastructure and the electric vehicle’s capabilities.

DCFC stations are typically found at public charging locations, such as highway rest stops and commercial parking lots. These stations can provide an 80% charge in as little as 30 minutes, depending on the vehicle’s battery capacity and the charger’s power output.

Innovations in charging technology have seen speeds increase up to 350 kW rapid charging, which can significantly reduce charging times for compatible vehicles. In some cases, these chargers can replenish up to 80% of a battery’s capacity in as little as 15-20 minutes.

As the charging infrastructure for electric cars continues to grow, more public charging stations will offer DC fast charging options, helping to reduce range anxiety and make EV ownership more accessible and convenient.

It is important to remember that not all electric vehicles are compatible with every DC charging speed or charger type. EV owners should always check their vehicle’s specifications to ensure they select the appropriate charging option for their car, whether at home or on the go.

Pros and Cons of AC and DC Power

AC Charging
AdvantagesThe 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.
DisadvantagesSlower charging rate compared to DC charging, conversion from AC to DC power happens inside the vehicle, which can limit charging speed
DC Charging
AdvantagesMore expensive charging infrastructure, less accessible to some users, prolonged usage can potentially cause thermal issues and degrade the battery over time.
DisadvantagesMore expensive charging infrastructure, less accessible to some users, prolonged usage can potentially cause thermal issues and degrade the battery over time.

Differences Between AC and DC Charging Stations 

Let’s explore the differences between these two types of charging and their suitability for public and residential use.

Charging speed: DC charging is faster than AC charging due to its external conversion process.
Charging curve: AC chargers have a flat charging curve, while DC chargers provide power more efficiently and rapidly.
Charging infrastructure: Public charging stations usually have DC chargers, while residential stations typically use AC chargers.
Onboard charger: The conversion of AC power to DC power is done by the vehicle’s onboard charger when using Level 2 AC charging.

This table shows AC and DC in terms of public and residential charging, which is another way to think of them.

Public Charging InfrastructureResidential Charging
Power ConversionFast DC chargers can deliver up to 350 kW, enabling a full charge in under an hour.Ideal for overnight charging as most vehicles have enough time to fully charge.
SpeedTypically uses Level 2 AC chargers, which charge slower but are ideal for overnight charging.AC to DC power conversion is done using the vehicle’s onboard charger, which can limit the charging speed.
Use CasePerfect for quick recharges while on the goIdeal for overnight charging as most vehicles have enough time to fully charge
Type of ChargersPrimarily consists of DCFC stationsTypically involves Level 2 AC chargers
EfficiencyOffers faster charging speeds due to external power conversionMore suitable for home use due to efficiency, availability, and affordability

Vehicle Compatibility

Not all EVs are created equal. All BEVs can use AC charging, while DCFC is typically limited to certain models that support higher power levels. 

There’s a further distinction to be made in the type of charging ports, such as CCS and CHAdeMO. Always consult your vehicle’s owner manual or contact the manufacturer for detailed compatibility information.

Future Trends

Wireless Charging

This technology could remove the necessity for EVs to connect directly to AC or DC charging stations, offering greater convenience. 

Rather than plugging in, drivers would park over a wireless charging pad for automatic battery charging. Though still in development, wireless charging holds the potential for a more efficient, user-friendly future in EV charging.

Smart Charging Systems

smart charging systems are becoming pivotal in managing increased demand. Utilizing real-time data, these systems optimize charging speed and schedule, lessen grid impact, and ensure access to essential charging resources. 

They efficiently convert AC power from the grid to DC power for the EV battery, cater to both AC and DC power needs, and enable off-peak home charging, which is cost-effective and reduces peak-hour grid demand. 

With a rise in fast charging installations, especially in China, the demand for these systems is set to grow, significantly influencing future EV charging practices and infrastructure interaction.

Key Takeaways

1️⃣ AC charging is ideal for home and workplace charging, with Level 1 and Level 2 chargers providing slower but cost-effective charging options.

2️⃣ DC charging, including fast and ultra-fast charging, offers much quicker charging speeds, making it suitable for public charging stations and long trips.

3️⃣ The main difference between AC and DC charging lies in where the conversion from AC to DC power occurs, with DC chargers providing faster speeds due to external conversion.

Your familiarity with AC and DC will become second nature once you’ve learned to use charging stations.