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Electricity What's the difference between AC and DC power?

| Author / Editor: Luke James / Erika Granath

Electricity comes in two forms—alternating current (AC) and direct current (DC). Both are essential to enable the functioning of our electronics, but do you know the difference between the two and what they apply to?

Both AC and DC describe types of current flow in a circuit. In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically.
Both AC and DC describe types of current flow in a circuit. In direct current (DC), the electric charge (current) only flows in one direction. Electric charge in alternating current (AC), on the other hand, changes direction periodically.
(Source: Unsplash)

What is AC power?

Alternating current (AC) power is the standard electricity that comes out of power outlets and is defined as a flow of charge that exhibits a periodic change in direction.

AC's current flow changes between positive and negative because of electrons—electrical currents come from the flow of these electrons, which can move in either a positive (upward) or negative (downward) direction. This is known as the sinusoidal AC wave, and this wave is caused when alternators at power plants create AC power.

Alternators create AC power by spinning a wire loop inside a magnetic field. Waves of alternating current are made when the wire moves into areas of different magnetic polarity—for example, the current changes direction when the wire spins from one of the magnetic field's poles to the other. This wave-like motion means that AC power can travel farther than DC power, a huge advantage when it comes to delivering power to consumers via power outlets.

What is DC power?

Direct current (DC) power, as you may suss from the name, is a linear electrical current—it moves in a straight line.

Direct current can come from multiple sources, including batteries, solar cells, fuel cells, and some modified alternators. DC power can also be "made" from AC power by using a rectifier that converts AC to DC.

DC power is far more consistent in terms of voltage delivery, meaning that most electronics rely on it and use DC power sources such as batteries. Electronic devices can also convert AC power from outlets to DC power by using a rectifier, often built into a device's power supply. A transformer will also be used to raise or lower the voltage to a level appropriate for the device in question.

Not all electrical devices use DC power, though. Many devices, household appliances, especially, such as lamps, washing machines, and refrigerators, all use AC power, which is delivered directly from the power grid via power outlets.

What's the need for two different power types?

Although many of today's electronics and electrical devices prefer DC power because of its smooth flow and even voltage, we could not get by without AC. Both types of power are essential; one is not "better" than the other.

In fact, AC dominates the electricity market; all power outlets bring power into buildings in the form of AC, even where the current may need to be immediately converted into DC power. This is because DC is not capable of traveling the same long distances from power plants to buildings that AC is. It is also a lot easier to generate AC than DC due to the way generators turn, and the system is on the whole cheaper to operate—with AC, power can be hauled through national grids via miles and miles of wire and pylons easily.

DC primarily comes into play, where a device needs to store power in batteries for future use. Smartphones, laptops, portable generators, torches, outdoor CCTV camera systems… you name it, anything battery-powered relies on storing DC power. When batteries are charged from the mains supply, AC is converted to DC by a rectifier and stored in the battery.

This is not the only method of charging used, though. If you have ever charged your phone using a power bank, for example, you are using a DC power supply rather than an AC one. In these situations, DC-DC power supplies may need to change the voltage of the output (in this case, the power bank) for the device's (in this case, the phone) use.

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