What is the Difference Between Alternating and Direct Currents?

If you’re reading this post, there’s a good chance you’re probably doing so on a device that’s powered using either direct or alternating currents. While these two types of currents both share the same basic function of moving energy from point A to point B, they do so in very different ways. For quite some time, the widespread use of either one of these currents was debated very heavily. Each side believed that one was superior to the other for various reasons, and history determined that both of them have a rightful place.

Alternating Current

What is the Difference Between Alternating and Direct Currents?In an alternating current, the charge being sent between points periodically reverses direction. During a short amount of time, an alternating current will rise and fall above and below the line of absolute zero with periods of positive and negative energy transfer. Compared to DC, AC allows for more consistent transfer of energy over longer distances without any significant energy loss. It can also be generated and set at various voltage levels, allowing high amount of energy to be transformed to lower amounts of energy more suitable for home appliances and lighting.

Lights running on alternating currents tend to flicker at a rate that is beyond most people’s ability to perceive. Roughly 60 times per second, the amount of energy sent to an AC outlet hits zero.

Nikola Tesla favored the use of alternating currents due to their ability to maintain a charge over long distances.

Direct Current

Direct currents are more constant. Instead of delivering a fluctuating amount of positive and negative energy, with occasional drop in current, DC is constantly flowing in one direction. Direct currents are commonly used in battery-powered devices today. While mostly every home is now powered with AC, DC is considered the best mechanism for powering low-voltage, portable electronics. Solar applications are also powered through direct currents as they are presently incapable of producing alternating currents. DC is also predominantly used in most automotive applications. A car’s alternator produces an alternating current, but this is quickly transformed into a direct current through use of a rectifier. Most electronic systems require a DC current to operate. Power supplies are put in place to convert AC to DC in these cases.

Thomas Edison created the first electronic power transmission using direct currents.

5 comments On What is the Difference Between Alternating and Direct Currents?

  • A great overview of the principles. A bit off topic, but for some considerable time I’ve been worried about safety aspects in the home. I just don’t know about the USA, but here in the UK the average home may have dozens of low-voltage DC adaptors. Few bear any clear message about which device they’re intended for, and even where there’s a manufacturer’s logo, it may not help if you have more than one device of that make and they use different voltages.

    Even the low-voltage plug and socket system is a mess – no attempt whatever to standardise connectors (usually coaxial) with voltages. It wouldn’t need a complete redesign – just varying plastic shrouds and matching sockets.

    I’m a bit hyper about this right now as it’s just days since an elderly neighbour had to ring the fire brigade after a low-voltage adaptor burst into flames (it was the wrong one for the device she was trying to power). The firemen said it wasn’t an uncommon situation.

    I’m sure it wouldn’t be beyond manufacturers to arrange (or for governments to statutorily insist) that all low voltage adapters CLEARLY bear information onthe devices they’re intended for. Plus it should be physically impossible to connect adaptors to devices using another voltage – not a complete answer I know, but something at least.

    And it could all so easily be made academic anyway. Why – given the number of low-voltage devices around our homes and the drawers-full of adaptors we keep – are adaptors even necessary any longer? I see no reason why every mains socket in my home shoudn’t also include a built-in low-voltage supply. I’m told that voltages vary too much, but surely that’s a detail for the manufacturers to address.

    Failing that, my desktop PC equipment at least – given all the usual stuff plus a couple of external HDDs, router, etc – now itself uses no less than NINE adaptors. Some of them taking up more room than the kit they power! Surely one suitably-designed low-voltage source is all I should need? If there is anything like that on the market her in the UK, I’ve yet to find it.

    • You’ve missed one important element in your excellent summary. That is the role of International Standardization. Note the international in this respect (as opposed to regional or national) since that is what allows trade to take place across frontiers, from one individual country to another.

      Everyone needs standards that provide a common “language” in terms of electrotechnical measurements and specifications to which everyone can refer. They ensure that manufacturers can trade what they produce; traders can import or export; importers or exporters can cross frontiers in full respect of governmental regulations; regulators or governments have some sort of measure on which to base their legislation and testers can carry out conformity assessments to ensure that legislation is adhered to so that the user remains safe.

      Those measures are the International Standards on which the manufacturers within their various Technical Committees have agreed. They have come to consensus of opinion about what it is that makes a particular specification safe, efficient, functional and interoperable.

      In short, within an international organization such as the IEC that is responsible for global standards in electricity and electronics and so on, you have representatives from industry throughout the world, often from competitive companies, who come together and define a multitude of devices and systems.

      One of these is the universal adaptor.

  • Note that some of the world operates at 50 Hz instead of 60 Hz AC.

  • the big difference between AC-DC is {skin effect}

  • Edison created the first electronic or should it say electric power transmission?

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