AC vs DC charging

Context

Recharging an electric vehicle (EV) may be trickier than refuelling a conventional internal combustion engine vehicle (ICEV). Unlike the latter, the EV driver cannot walk into any charging station and hope to drive away with a fully charged vehicle in minutes. The charging process is a function of vehicle-charger compatibility and time available to charge, among other factors. Broadly, EV chargers are categorised into alternating-current (AC) chargers and direct-current (DC) chargers. Alternatively, they may be classified as slow and fast chargers. 

Charging an EV is like charging any electrical device. Power flows in from the grid into the charger, which is then plugged into the device. Similarly, with EVs, power flows from the grid to the EV charger, which is then plugged into the vehicle. Power flowing in from the grid is always AC, whereas electrical devices – be it EVs, mobile phones, or laptops – drink DC only. Therefore, before a device can be charged, the AC from the grid must be converted into DC form. In the case of household appliances, this conversion happens inside the plug of the charger. Once converted, the wire of the charger supplies DC to the device to consume. However, there are two possible ways of converting AC from the grid to DC in EVs. Chargers are categorised according to where this conversion takes place.

AC chargers

What? 

In the case of AC charging, conversion of the electrical current to DC happens inside the EV. All EVs come with onboard chargers capable of converting the current before supplying it to the car’s battery. AC chargers are more common in the EV ecosystem as they are comparatively less expensive to produce, install, and operate¹.

Further, they may be sub-categorised into:

• Type 1: slow AC charging, which are simply home sockets used for AC trickle charging 
• Type 2: fast AC charging, which are faster wall-box chargers explicitly installed for EVs 

Who?

While these may be used to charge two-, three-, and four-wheelers, the larger the battery, the more time it takes to charge. These are suitable for overnight home charging, charging in parking spaces, and to charge vehicles for daily use. 

DC chargers

What? 

On the other hand, DC chargers enable the conversion of current from AC to DC outside the vehicle. This transformation takes place inside the charger itself. DC is then directly fed into the EV, surpassing the need for onboard conversion. These chargers require a lot more power from the grid – nearly 125 A – and are much more expensive to produce, install, and operate². Reduced time for charging is the result of a larger converter present inside the charger in charging stations, as compared to the onboard charger of the car. As a result, a higher output of power is provided to the EV battery in lesser time³. 

Who? 

DC fast chargers are suitable mainly for four wheelers with large batteries that require instant charging, and may be found on highways or other locations where an EV might require a quick charge-up in minutes. They are suitable for vehicles travelling long distances or for commercial fleets⁴. 

Charging speeds are not just a function of AC or DC chargers but also of the output power of the charge point. Countries differ in the kind of chargers they mandate, as these depend on specific EV-use cases. In India, chargers are categorized as slow and fast chargers as per the Ministry of Power’s 2019 guidelines on “Charging Infrastructure for Electric Vehicles (EV): Revised Guidelines & Standards – Reg⁵’. This distinction is as follows: 

Figure 1: Charger plugs in India⁶

Source: CEEW-CEF electric mobility dashboard

Who should care? 

• Potential EV buyers
• Charge-point operators
• Researchers and policymakers
• Residences and workspaces with mandated EV charging