What’s the difference between AC and DC charging?

Unlike internal combustion engines, which use refined unleaded gasoline or diesel as their fuel source, there is one type of fuel for a battery-powered car – electricity.

But, just as there are different pumps at the petrol station for petrol and diesel, there are two distinct ways to replenish a battery with electrons – through AC or DC charging options.

AC is an acronym for alternating current and is the common method of delivering power to households as it is safer and can travel longer distances via power lines as electrons are generated in a wave like form.

All Australian household power points provide an AC power source with a standard rating of 240 volts.

DC is an acronym for direct current, and, as the name suggests, is generated in a constant flow.

While it can deliver higher voltage power, it cannot be transported via power lines as effectively.

Most batteries, solar cells and alternators provide a DC power current and most electronic devices require DC power, meaning there is usually a built-in AC-to-DC converter within the plug, cord or the machine to operate properly.

Electric cars are no different. Their lithium-ion battery packs deliver a DC current to drive the electric motors but they can be replenished using either power source, each providing unique benefits.

When using an AC power source, such as a household power point, to recharge an electric car, owners obviously have the convenience of being able to fill up almost anywhere – at home, the office, even from the corner store in the most remote outback town.

But AC power is only delivered at 2.4kW and, owing to its alternating current, is like refuelling a petrol car through a coffee filter. The convenience is offset by its slow speed and low output.

Higher voltage charging installations and some public fast chargers still use AC power, but speed up the wave form (or reduce the level of filtration) and increase the power delivery to between 7kW for household wallboxes and 22kW for fast chargers.

These significantly reduce the time it takes to refill an electric car’s battery.

In any case, when charging an electric car using an AC power source it requires an on-board charger – either in the plug or the vehicle itself – to convert the power from AC to DC in order for it to be stored in the battery cells.

Using a DC charger, on the other hand, is the optimum way to top up an electric car.

For starters, it bypasses the need for an on-board charger to convert the current and generally provides a higher voltage flow of electricity.

The downside is that DC current cannot be utilised in household environments and is therefore exclusively available from public charging stations fitted with rapid or ultra-rapid chargers providing 50kW or more of power.

The benefit is that these charging stations can replenish a battery (usually to no more than 80 per cent capacity to prevent them from overheating and to protect their longevity) in less than one hour.