EV charging: the difference between AC and DC

Last Updated on April 14, 2023

Electric vehicles (EVs) represent a significant shift toward sustainable transportation, and understanding how they charge is essential. Two main types of electrical currents are involved in EV charging: AC (alternating current) and DC (direct current).

Most home EV chargers and public stations use AC, while DC is primarily reserved for fast charging. The primary difference between AC and DC charging lies in where the conversion from AC to DC happens—either inside the vehicle or at the charging station itself.

Here’s something to keep in mind: the electricity that flows from your wall socket is always AC, whereas the energy stored in EV batteries is always DC. This distinction is crucial because it determines how charging works and affects the overall experience.

• AC power comes from the grid and must be converted before it can charge an EV battery.
• DC power, on the other hand, can be delivered directly to the battery without needing internal conversion.

Let’s dive deeper into these concepts and explore how AC and DC charging differ—and why it matters.

The EV Charging Ecosystem

As electric mobility grows in popularity, the infrastructure supporting it—EV charging stations—has expanded rapidly. These stations come in various forms, from basic level 1 chargers to high-powered DC fast chargers. One major factor differentiating these chargers is the type of current they use.

Think of it this way: just like traditional cars rely on gas stations, EVs depend on charging stations to replenish their batteries. But not all charging stations are created equal. Some are designed for convenience, while others prioritize speed. Understanding AC and DC charging helps you make informed decisions when planning your EV journey.

Understanding AC vs. DC Charging

Before diving into specifics, there are two critical points to remember:

• Grid-supplied electricity is always AC.
• Batteries store energy in DC format.

AC and DC are fundamentally different types of electrical current. They move in opposite directions, operate at varying speeds, and serve distinct purposes. Even the iconic rock band AC/DC has no connection to these concepts—they’re simply named after their famous album cover.

What Is AC Charging?

AC is an electrical current that periodically changes direction, meaning it alternates. It’s commonly produced by renewable sources like wind or hydropower, making it ideal for long-distance transmission. That’s why nearly all global electricity grids rely on AC power.

When you plug your EV into a standard AC charger, the current is converted to DC inside the vehicle. While this method is convenient for everyday use, it tends to take longer compared to DC charging. AC chargers are often found in residential settings or low-stress environments where time isn’t a critical factor.

What Is DC Charging?

Unlike AC, DC moves in a single direction and is ideal for storing energy in batteries. Solar panels, for instance, generate DC power. DC is also widely used in consumer electronics, LED lighting, and portable devices. Since batteries store DC energy, most modern chargers convert AC from the grid into DC for optimal battery performance.

In essence, we receive AC power from the grid, but it gets converted to DC to charge our EV batteries effectively. High-speed DC chargers can deliver up to 400 kW of power, enabling some EVs to reach an 80% charge in under 20 minutes. This makes DC charging particularly valuable during long-distance trips or when time is of the essence.

Key Differences Between AC and DC Charging

One of the most significant distinctions between AC and DC charging lies in the location of the AC-to-DC conversion process. Whether you use an AC or DC charger, the EV’s battery ultimately stores energy in DC format.

At a DC charging station, the conversion happens externally, allowing the charger to supply high-power DC directly to the battery. Thanks to the larger size and advanced technology of DC chargers, they can deliver immense amounts of power quickly. For reference, some DC stations offer up to 400 kW, which translates to rapid charging in mere minutes.

Contrary to popular belief, DC charging does not harm your battery. In fact, it’s perfectly safe and efficient. To dispel any myths, you can read more about this here.

Charging Curves Explained

Another key difference between AC and DC charging relates to how their power output varies throughout a charging session. This phenomenon is known as the EV charging curve.

AC Charging Curve

With AC charging, the power flow remains relatively constant, resembling a flat line. This stability arises because AC chargers use smaller onboard converters, which handle lower power outputs over extended periods.

DC Charging Curve

DC charging bypasses the vehicle’s onboard converter, enabling much higher power delivery. However, its output follows a decreasing curve due to the battery’s initial ability to accept large amounts of power, followed by a gradual reduction as it approaches full capacity.

To illustrate, imagine a glass representing the EV’s battery, a water bottle symbolizing the DC charger, and the liquid inside the bottle as the power. Initially, you can pour water quickly into the glass, but you must slow down near the top to prevent spillage. The same principle applies to DC fast and ultra-fast charging.

Of course, several factors influence charging speed, such as battery chemistry, temperature, and state of charge. If you’re curious about the specific variables affecting EV charging times, check out our in-depth article on the subject.

AC vs. DC Charging: Which Should You Use?

By now, it’s clear that AC and DC charging cater to different needs. While DC charging offers unparalleled speed, it also comes with higher costs and logistical challenges. Due to its reliance on bulky and expensive equipment, installing a DC charger at home isn’t feasible for most people.

As a result, DC charging stations typically charge more than their AC counterparts. However, even the slowest AC chargers can fully charge a mid-sized EV overnight, making them suitable for daily commutes. Where DC truly excels is during long-distance travel, where a fast charger can bring your EV back to life in under an hour.

Ready to Learn More About EV Charging?

Understanding the type of current used by a charging station is just the beginning. There’s much more to explore, including where to locate EV chargers, how to use them effectively, and payment options. Whether you’re new to EV ownership or looking to deepen your knowledge, our comprehensive guide covers everything you need to know about EV charging.