GFS Power

AC Versus DC: Power Supply Basics Explained

June 16th, 2016 by Raymond Gibb

Electricity is used in every aspect of our lives, from our homes to our industrial plants. But many people are unaware that there are actually two types of electricity in use – AC and DC – and they are used to power different kinds of electrical equipment. Here’s an introduction to the basic elements of electricity.

What are the differences?

AC stands for alternating current. Electricity is produced at a generator by rotating magnets inside coiled copper wires. As the magnets rotate, electricity is generated inside the wires and flows out. But the electricity generated is constantly reversing its direction, or alternating, emerging from one side of the generator coil then the other. That’s because the turning of the magnets means their north and south poles are flipped over with each half rotation and the electricity follows their polarisation. The power that reaches our homes is AC current and it’s what we use to power our fans, fridges and heaters. However, there are some appliances that need a different type of current.

Uses of DC power

DC, or direct current, is electricity that flows only in one direction. This is the type that batteries produce. It’s used in electronics, so your computer, hi-fi amplifier and TV all use a DC power supply circuit. It’s used because semi-conductor based circuits (e.g. computer circuits and amplifiers) need a unidirectional flow to work. DC is not as good at travelling over long distances as AC, which is why power comes from the power plant as AC and is converted to DC when needed. The adapter of your laptop, for example, is a DC converter. In fact, the term ‘converter’ is a general one for what is more properly called a ‘rectifier’.

Rectifying the AC current

A rectifier removes the ‘reversed’ part of the AC current cycle described above so that the electricity always flows in one direction. Stand alone rectifiers for powering IT, telecommunications and other commercial and industrial applications can take 240 volts of AC power and convert it to 24 volts of DC power for example (DC equipment needs a lower voltage too).

A rectifier’s main component is a diode (or diodes) which only allows current to flow through in one direction. Diodes are now tiny, but their work used to be done by a vacuum tube or valve, as seen on old television sets and radios. That’s why those old sets were so big and today’s smartphones and televisions are so small and slender.



Rectifiers versus inverters

The opposite of a rectifier is an inverter, which turns DC current into AC. There are a number of types, including wall mount inverters. An inverter is used in solar panel systems, where electricity is stored in batteries that produce DC output. Inverters are therefore useful for people who work remotely or off the grid. Because there are no spinning magnets inside them generating the electricity as in an AC generator, the current flow from batteries is constant in one direction. But as we know, DC can’t power fans, fridges, etc, so this current is converted to AC with an inverter.

We take electricity for granted, but in fact it takes many forms and can be manipulated to have a varying array of characteristics if you have the right equipment.

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