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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. But what's the difference?
What is Alternating Current (AC)? 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.
What is Direct Current (DC)? 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 230V, 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 is, let's use some real-life examples on what both AC and DC are used for and their differences.
In Australia, AC current (AC) is the standard for home appliances and grid 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 stepped up or down using transformers.
Things like the grid, home appliances, outlets, industrial, equipment, and long-distance energy transmission all run on AC power.
DC current (DC) is what powers our batteries and electronic circuits, and is what powers solar energy and electrical transportation like electric vehicles (more on this later). Elements like phones, laptops, solar & battery systems, AA batteries, and EVs run on DC power.
A real-life example on AC vs. DC, could be the way we charge our phones. Back in the day, we used to get a charging brick included in the box which when plugged in, would invert the outlet's AC power to the phone's DC power. The heat occurs due to the efficiency losses that heat over longer charging periods.
Alternating Current is the Australian standard for both the grid and homes throughout Australia.
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 230V using transformers.
What is a transformer? A transformer is an AC-exclusive unit, typically seen on electricity line poles, 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.
The main difference between Alternating current and Direct current is how the electrical 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.
Using solar and battery systems as an example for AC and DC, the sun shines and generates DC power which is sent to the inverter to be converted to AC for general household usage and grid export.
Depending on if a battery is AC or DC-coupled, the battery may be responsible for its own power conversion or may rely on the hybrid inverter to convert the stored power.
AC and DC is an important part of solar and battery systems as each component generates and runs on different systems which requires inversion.
Let's use electric vehicle charging as an example as NSW's EV boom continues. The difference between AC vs. DC electric vehicle charging comes down to how the power is delivered to the EV.
Because the EV battery runs on DC, the energy that is being delivered will need to be or converted to DC power. When DC chargers are used, it alleviates the need to invert the energy before it enters the battery, enabling higher charging rates.
For AC chargers like the popular Tesla Wall Connector Gen 3, it can only deliver a certain amount of power as the charger delivers AC power to the EV which needs to be converted to the EVs required DC power using an onboard inverter.
Onboard EV inverters vary in speeds like how the Tesla Model 3 has an 11kW onboard inverter for AC charging. DC charging doesn't need conversion and can be charged as much faster rates like superchargers that can deliver up to 420kW of power.
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.
Explore Australia's first CEC-approved bidirectional and vehicle-to-grid capable electric vehicle, the V2Grid Numbat, a 6.2kW V2G/H charger now ready.
Explore how battery nominal & useable energy capacity is different to power output, and learn about state of charge, depth of discharge, and cycles.
Explore the differences between AC and DC electric vehicle charging in Australia and how it affects the way you charge your EV, and the pros & cons.
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