DIFFERENCES BETWEEN ALTERNATING AND DIRECT CURRENT? - SCIENCE - 2025

The difference between alternating and direct current is fundamentally in the way electrons move in the wires that carry it. In alternating current it is an oscillatory movement, while in direct current the electrons flow in only one direction: from the negative to the positive pole.

But there are more differences, ranging from generation to efficiency in use, safety and transportation. Each has its advantages and disadvantages, so the use of one or the other depends on the application.

	Alternating current	Direct current
Direction of current	Bidirectional (Oscillating)	Unidirectional (Uniform)
Source	Alternators	Batteries, batteries, dynamos
Sources of electromotive force (emf)	Oscillating or rotating conductors or conductors in the presence of magnetic field.	Electrochemical reactions inside cells and batteries. Switched or rectified AC generators with diodes
Operating frequency	In domestic and industrial outlets 50Hz or 60HZ	0 Hz
Operating voltage	110 V or 220 V	1.5V; 9V; 12V or 24V
Long distance transmission voltage	Up to 380,000 Volts	It cannot be transported long distances because it has many losses
Amps circulating in a 1 Hp motor	Single phase 110V 60Hz: 16 amps	At 12 volts DC: 100 amps
Maximum current per Joule of consumption	110V: 0.01 A / J 220V: 0.005 A / J	12V: 0.08 A / J 9V: 0.1 A / J
Passive elements in circuits	Impedances: -Resistive -Capacitive -Inductive	-Resistance
Advantage	Few losses when being transported.	It is safe because it is low voltage. Storable in batteries and batteries.
Disadvantages	Not very safe due to the high operating voltage.	It cannot be transported long distances because it has many losses
Applications	Domestic and industrial: washing machines, refrigerators, manufacturing plants.	Portable electronic equipment: smartphones, laptops, radios, flashlights, watches.

Alternating current

It is not possible to talk about alternating current without mentioning Nikola Tesla (1846-1943), the engineer of Serbo-Croatian origin who invented and promoted it. He was the one who generated the most patents for its applications, transportation and uses.

All these patents were assigned to the American company Westinghouse Electric Co by its creator, in order to obtain the necessary financing for its experiments and projects.

The first tests in alternating current were made by one of the main pioneers of electricity: Michael Faraday (1791-1867), who discovered electromagnetic induction and built the first alternating current generator.

The transmission of alternating current is much more efficient. Source: Pixabay.

One of its first practical uses in 1855 was electrotherapy with alternating current to activate muscle contraction. For this type of treatment, alternating current was much superior to direct current.

Later in 1876, the Russian engineer Pavel Yáblochkov invented a lighting system based on electric arc lamps and alternating current generators. By 1883 the Austro-Hungarian company Ganz Works had already installed around fifty alternating current lighting systems.

Tesla's inventions

Among the main contributions of Nicola Tesla for the development and use of alternating current are the invention of the electric motor that works with alternating current, without the need to be converted to direct current.

Nikola Tesla also invented the three-phase current, to make the most of the energy in the production and the infrastructure in the transport of electricity. Today this system is still used.

Transformer

The other great contribution in the development of alternating current was the invention of the transformer. This device allows the voltage to be raised for long-distance transportation and the voltage to be lowered for safer use in homes and industry.

Definitely, this invention made alternating current a better alternative as an electrical power distribution method than the direct current method.

The forerunner of the modern transformer was an iron-core device called a "secondary generator," exhibited in London in 1882 and later in Turin, where it was used for electrical lighting.

The first closed iron core transformer, as we know it today, was presented by two Hungarian engineers from the Ganz company in Budapest. The patents were purchased by Westinghouse Electric Co.

Transformer fundamental characteristic

The fundamental characteristic of the transformer is that the quotient between the output voltage in the secondary V _S and the input voltage in the primary V _P is equal to the quotient between the number of turns of the secondary winding V ₂ divided by the number of turns of the primary winding No. ₁:

V _S / V _P = N ₂ / N ₁

By simply choosing the appropriate turns ratio between primary and secondary of the transformer, the correct output voltage can be achieved accurately and without appreciable loss of power.

Transformer schematic. Source: Wikimedia Commons. KundaliniZero

The first commercial electrical distribution system that used transformers was inaugurated in the state of Massachusetts, United States, in 1886.

But Europe was keeping pace with electrical development, as in the same year a transmission line based on the newly invented transformer was installed in Cerchi, Italy, which transmitted alternating current over a distance of 30 km at an effective voltage of 2000 volts..

The transformer was not only a revolution in the field of electric power transmission. Also in the field of the automotive industry, when it was used by the Ford Motor Company in the ignition coil system of the Ford Model T spark plugs.

Direct current

Direct current was produced in 1800 through the invention of the voltaic pile, so named because its inventor was the Italian physicist Alessandro Volta, who lived between 1745 and 1827.

Although the origin of the current was not well understood, the French physicist André Marie Ampere (1775-1836), identified two polarities in voltaic cells and conjectured that the electric current flowed from the positive to the negative pole.

Today this convention is still used, although it is known that the carriers of electrical charge are the electrons that go just the opposite, from the negative terminal to the positive terminal.

Figure 4. Direct current is conveniently and conveniently stored in batteries. (pixabay)

The French inventor Hippolyte Pixii (1808–1835) built a generator consisting of a loop or loop of wire that rotated around a magnet, noting that every half turn the current flow was reversed.

At the suggestion of Ampere, the inventor added a commutator and thus the first dynamo or direct current generator was created.

Regarding electrical lighting systems, between 1870 and 1880 electric arc lamps were used that required high voltage, either direct or direct current.

As is known, high voltage is very unsafe to be used in homes. In this sense, the American inventor Thomas Alva Edison (1847-1931) made the use of electricity for lighting purposes safer and more commercial. Edison perfected the incandescent light bulb in 1880 and made it profitable.

The War of the Currents: AC vs DC

Just as Nikola Tesla was the promoter of alternating current, Thomas Alva Edison was the promoter of direct current because he considered it safer.

Even in order to discourage the use of alternating current for commercial purposes, Edison invented the alternating current electric chair, so that the public would understand its danger to human life.

Initially, Nikola Tesla worked at the Edison Electric power company and made various contributions to improve direct current generators.

Figure 5. From right to left Henry Ford, Thomas Edison, United States President Warren G. Harding, and Harvey S. Firestone, 1921, via Wikimedia Commons.

But since Tesla was convinced of the advantages of alternating current from the point of view of its transportation and distribution, it did not take long for the differences with Edison to bring these two strong personalities into conflict. Thus began the war of the currents: AC vs. DC.

The advantages of alternating current transmission and the first interurban alternating current distribution systems in 1891 caused Edison, who stubbornly continued to advocate for direct current, to lose the presidency and direction of the company that he had founded, which passed to be called General Electric company.

Nor did Nikola Tesla win this war, because eventually George Westinghouse and the shareholders of his company became millionaires. Tesla, who became obsessed with the idea of ​​transmitting electrical power over long distances without wires, ended up poor and forgotten.

High voltage direct current

The idea of ​​using direct current for long-distance electrical power distribution has not been entirely discarded, since such systems were developed in the 1950s.

Today the longest submarine cable in the world for the transport of electrical energy, the NorNed cable, which links Norway with the Netherlands, uses direct current of 450 thousand volts.

Figure 6. Route of the NorNed submarine cable between the Netherlands and Norway, which carries direct current through the North Sea. Source: Wikimedia Commons.Michiel1972

The use of alternating current for submarine cables is not suitable as seawater is an excellent conductor of electricity and an alternating current submarine cable induces eddy currents in salt water. This would cause great losses of the electrical energy that wants to be transmitted.

High voltage direct current is also used today to power electric trains by means of rails.

References

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