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Why is DC charging faster than AC?

07 March 2021

There are two ways to charge your electric vehicle; AC and DC.

While the acronym is possibly more famous as an Aussie band, in the electric vehicle sector, AC means Alternating Current and DC, Direct Current.

When presenting information about EV charging to our clients, we often talk about AC being a slow charge, and DC being fast charging. So, what’s the difference and why does AC charging take longer than DC charging for electric vehicles? 

Alternating current is most common

Power provided from the grid comes in the form of alternating current (AC ), so all houses and electric vehicle charging stations receive AC power. In fact, it's likely that all the electricity you’ve encountered is, or was, derived from AC power. 

Electric vehicles however, use direct current (DC) to recharge the traction battery. Put another way, electric vehicles cannot run on AC power directly and instead need to convert this power to DC; this can be done internally or externally.  

AC power EV charging - Internal conversion

To charge an EV at home, you might use a wall socket or wall-mounted charger like the solar-aware Zappi. The power supplied by these methods starts out as AC but is converted into DC power by the EVs on-board charger.

This newly converted power then gets routed into your vehicle’s battery, ready to be used. This method is relatively slow.

DC Power Charging- External conversion 

If your car is able to utilize DC fast charging, you have the option to charge at a DC fast charging station, where the power is already converted, ready for you to 'feed' into the traction battery. 

Fast chargers receive large amounts of AC power and are designed solely for converting AC to DC, making them more efficient than your vehicle charging off of AC power. For this reason, DC chargers cost more to use, but they make up for it with their incredible charging speeds. 

So, why is AC slower than DC charging? 

Charging your EV at home typically uses Level 1 or Level 2 AC single phase power, depending on whether you have a dedicated charger or are simply charging from a wall socket. These methods have a limited power supply when compared to a DC faster-charging station. 

AC charging can only use the amount of power your system will allow, whereas a single DC charger typically needs more power than your entire house at any one time, which is why they are being rolled out on freeway stops and petrol stations; the places people stop for a short time on a long journey.

Essentially, DC chargers have access to more power and are constantly converting large amounts of AC power to DC in order to 'refuel' your electric vehicle. AC charging involves lower sources of power that require additional time for the conversion from AC to DC by your EVs on-board charger.

Would you like to know more about electric vehicles and how you can decarbonise your fleet? EVUp specialises in the complete management of Australian-made EV charging hardware and software, with a data-driven approach to rollout. Please contact us for more.

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