AC vs DC Charging: 7 Fundamental Differences

If you own an electric vehicle, sooner or later, you will bump into some information about AC vs DC charging. Perhaps, you are already familiar with these abbreviations but have no clue how they relate to your EV. 

This article will help you understand the difference between DC and AC chargers. After reading it, you will also know what way of charging is faster and which one is better for your car.

Let’s start!

There are two types of electricity transmitters that can be used for charging electric vehicles. They are called Alternating Current (AC) and Direct Current (DC) power. 

The power coming from the electricity grid is always Alternating Current (AC). However, an electric car battery is able to accept only Direct Current (DC). The main difference between AC and DC charging though, is the location where the AC power gets converted. It can be converted outside or inside the car.

The DC chargers are usually bigger since the converter is inside the charging station. This means that it is faster than the AC chargers when it comes to charging the battery.

By contrast, if you use AC charging, the converting process only starts inside of the car. Electric vehicles have a built-in AC-DC converter called an "onboard charger" that converts AC power to DC power. After converting the power, the car’s battery is charged.

Theoretically, you can install a DC charger at home. However, it does not make much sense. 

1. DC chargers are significantly more expensive than AC chargers. 

2. They take up more space and require much more complex spare parts for processes such as active cooling. 

3. A high power connection to the power grid is necessary. 

On top of that, DC charging is not recommended for constant use - we will talk about this later. Given all these facts, you can conclude that an AC charger is a much better choice for a home installation. DC charging points are mostly found along highways.

Only AC chargers can be mobile. And there are two main reasons for it:

• Firstly, the DC charger contains an extremely heavy converter of power. So, carrying it with you on a trip is impossible. Therefore, only stationary models of such chargers exist. 

• Secondly, such a charger requires inputs of 480+ volts. So, even if it was mobile, you are not likely to find a suitable power source in many places. Furthermore, a majority of public EV charging stations provide AC charging, while DC chargers are mainly along highways.

Another important difference between AC and DC charging is the speed. As you already know, the DC charger has a converter inside of it. This means the power coming out of the DC charging station bypasses the car’s onboard charger and goes straight into the battery. This process is time-saving since the converter inside the EV charger is much more efficient than the one inside the car. Therefore, charging with direct current can be ten or more times faster than charging with alternating current.

Another fundamental difference between AC and DC charging is the charging curve shape. In case of AC charging, the power delivered to the EV is simply a flat line. The reason for this is the small size of the onboard charger and, accordingly, its limited power.

Meanwhile, DC charging creates a degrading charging curve, as the EV battery initially accepts a faster flow of energy, but gradually requires less when it reaches maximum capacity.

If you have to decide whether to spend 30 minutes or 5 hours charging your car, your choice is pretty obvious. But it’s not that simple, even if you don’t care about the price difference between the rapid (DC) and regular charging (AC).

The thing is, if a DC charger is used continuously, battery performance and durability may be impaired. And this is not just a scary myth in the e-mobility world, but an actual warning that some e-car manufacturers even include in their manuals.

Most new electric cars support constant current charging at 100 kW or more, but charging at this speed creates excessive heat and amplifies the so-called ripple effect - the AC voltage fluctuates too much on the DC power supply.

The telematics company Geotab conducted a study comparing the impact of AC and DC chargers. After 48 months of analysing the condition of electric car batteries, it found that cars that used rapid charging more than three times a month in seasonal or hot climates had 10% more battery degradation than those that never used DC fast chargers.

One significant distinction between AC and DC charging is the price — AC chargers are much cheaper to use than DC ones. The thing is that DC chargers are more expensive. On top of that, installation costs and grid connection costs for them are higher.

When you charge your car at a DC power point, you can save a lot of time. So it's ideal for situations where you're in a hurry. In such cases, it is reasonable to pay a higher price for increased charging speed. Meanwhile, charging with AC power is cheaper but takes longer. If you can charge your EV close to the office while working, for example, there's no need to overpay for super-fast charging.    

When it comes to price, home charging is the cheapest option. So buying your own charging station is a solution that will definitely suit your wallet.