A Guide to EV Charging – AC vs DC

When it comes to electric vehicles, there are two separate electrical currents can be used to charge the vehicles called Alternating Current and Direct Current.

AC (Alternating Current) – The Power comes from the grid for example a domestic socket.

DC (Direct Current) – The energy that is stored in batteries is always DC.

These are two different types of electrical currents. Both travel in different directions, flow at different speeds, and have different applications.

AC is an electrical current that periodically changes direction, this means it alternates. It can be generated from renewable sources using rotating generators, such as wind or hydro turbines. This flow charge can also be efficiently transported over long distances, this is why all of the world’s electricity grids use AC, and why it is used to power our homes and offices.

However, DC always moves in a straight line, and can be generated by renewable power technologies such as solar panels. It can be used for energy storage, LED lighting, and batteries store this current too. You might know that every time you charge your laptop or phone, the chargers convert the AC power from the grid into DC power for the battery.

AC and DC charging in Electric Vehicles 

The main difference between AC and DC charging is where the conversion happens. No matter whether an EV uses an AC or DC charging station, the EV’s battery will still only store DC energy. 

When you use a DC charging station, the conversion from AC to DC happens within the charging station, thus allowing the DC power to flow directly from the station and into the battery. As the conversion process happens within a more spacious charging station and not the EV, larger converters can be used to convert AC power from the grid very quickly. Whereas with an AC charger it is converted to DC when charging an electric vehicle, instead of being converted in the charging station it is converted inside the vehicle via the onboard charger.

Another difference is the charging curve, with AC charging the power flowing to an EV represents a flat line. This is due to the relatively small charger that can only receive a limited power spread over longer periods. DC charging on the other hand forms a degrading charging curve. This is due to the EV’s battery initially accepting a quicker flow of power but gradually going less as it reaches full capacity.