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Whilst most Australians are aware of the terms AC and DC (probably because of the band), many don't actually know what they stand for, and what they mean in Australia's electrical realm. Both alternating current (AC), and direct current (DC) are integral to how Australians use electricity for generation, transportation, and consumption, and whilst it sounds like an in-depth topic for electricians, it's actually a lot easier to understand than you might think.
Electricity powers almost everything we do, including the device you're reading this article on. Being a large part of our lives, electricity is an important aspect, but did you know not all electricity is the same?
Electricity can come in 2 forms, Direct Current (DC), and Alternating Current (AC), which determines the flow direction of the current. What's the difference?
Alternating Current (AC) refers to the dynamic direction where both positive and negatives are switched at intervals where electrons keep switching directions that change the flow of the electrical current - usually seen in home appliances.
Direct Current (DC) is when the current is consistently flowing in the one direction, which is the form of power that is mainly seen in battery storage, solar energy, and devices like phones and laptops.
An electrical current is the flow of electric charge, commonly transferred by electrons passing through a conductor like a wire. This is measured in amperes (A) or 'amps'.
AC current or alternating current is when the flow reverses direction every second. In Australia, AC current runs at 240V, 50Hz, which means it's switching 50 times a second.
Being the more scalable solution, Nikola Tesla, and George Westinghouse innovated the AC current used for the primary method for electricity distribution as it can be stepped up to higher voltages and lowered again for general household consumption.
AC is now the universal standard for grid electricity.
Being the older one of the two, DC current or direct current flows in a single consistent direction and doesn't switch.
Thomas Edison pushed the boundaries of DC current in the late 19th century, as DC was easy to understand, however it had issues with scalability and transporting over long distances.
To transport over long distances, thick, high-capacity cabling was required to accommodate the high current which was expensive and unrealistic, especially over long distances.
To better understand what AC and DC are used for, let's use some AC vs. DC examples.
In Australia, AC current is the standard for home appliances and electricity distribution, and is what the NEM's infrastructure is built on. The power distributed from the grid is AC, which the voltage can be altered using transformers.
DC current is what powers our batteries and electronic circuits, and is what powers solar energy and electrical transportation.
What Runs on AC?
The energy grid
Home appliances & Outlets
Industrial Equipment
Long-Distance Transmission
What Runs on DC?
Phones & Laptops
Solar & Off-grid systems
AA & Home Batteries
Electric Vehicles
Another AC and DC example could be how we charge our phones.. Back in the good old days, we used to get charging bricks included in the box
which are mini inverters that convert the outlet's AC current to the phone's DC current, which gets hot over time due to conversion
losses.
Alternating Current is the Australian standard for flexible electricity grid production and distribution and optimal efficiency.
Because AC current has variable voltage capabilities, it can be transformed to higher voltages to minimise losses over long distances, with the ability to step back down to residential and commercial usage of 240V using transformers.
A transformer is an AC-exclusive unit that increases and decreases the voltage based on the requirement. If a power station produces power, it is distributed and then arrives to your local transformer to be reduced for everyday household appliances.
DC can also be powered over long distances with voltages over 500,000 V or more, but AC is more commonly used.
So if a home outlet is AC, and a phone battery is DC, how is it converted?
Back in the good old days, we used to get charging bricks included in the box. These are mini inverters that convert the outlet's AC current to the phone's DC current, which gets hot over time due to inefficiencies.
The main difference between Alternating current and Direct current is how the current flows. AC is constantly switching from positive
to negative, whilst DC remains steady in one direction. Below are some example diagrams on how direct and alternating current works.
Let's use solar and battery systems as an example of AC and DC in real life scenarios.
When the sun shines on solar panels, a DC current is generated in its cells, which makes its way to the solar inverter. The inverter is responsible for converting that DC current into AC current for household consumption.
If your solar system has a battery included, it can either be AC or DC-coupled which determines how many times the current is converted from AC to DC and visa-versa.
In an AC-coupled system, a battery converts its own energy with its built-in inverter, and a DC-coupled battery relies on the solar inverter for better efficiency.
As the EV boom continues, we are seeing a lot of interest in EV Chargers for home charging solutions.
The difference between AC vs. DC electric vehicle charging comes down to how the power is delivered to the EV. DC is much faster as it doesn't need inversion, however, AC is more available for home solutions.
A common charger we install is the Tesla Wall Connector Gen 3 charger which is 11.5kW, AC, single-phase charger. This level 2 charger allows the vehicle to be charged much quicker than a standard wall plug, and the Tesla Model 3 for example, has an 11kW onboard inverter which converts your home AC power into your battery’s DC power.
Whilst most home chargers are AC, public superchargers are DC which allows for rapid charging as it eliminates the need to convert the power from AC to DC, which is limited by the inverter, instead it relies on the battery's capability of charging which greatly reduces charging times.
Single and three phase specifically applies to alternating current and not direct current.
In a three-phase system, there are 3 phases of AC current that is predominantly used in industrial and commercial settings where the delivery of high-power levels is required. It’s not incorrect to call DC ‘single-phase’ as it is technically one voltage waveform, but that can remain a discussion topic for another day.
Overall, both Alternating and Direct currents serve their purpose and continue to be the 'battle of the currents' throughout Australia. They aren't in competition, but serve specific purposes and compliment each other in the systems we use.
As we see more innovative energy technology come out over the next decade, it will be interesting where we head with our power generation,
distribution, and consumption whether it be through AC or DC or continue to be through both for years to come.
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