Direct current

[1] The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.

Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more.

Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes.

Direct current was produced in 1800 by Italian physicist Alessandro Volta's battery, his Voltaic pile.

French physicist André-Marie Ampère conjectured that current travelled in one direction from positive to negative.

[6] When French instrument maker Hippolyte Pixii built the first dynamo electric generator in 1832, he found that as the magnet used passed the loops of wire each half turn, it caused the flow of electricity to reverse, generating an alternating current.

Under this definition, DC voltages can vary in time, as seen in the raw output of a rectifier or the fluctuating voice signal on a telephone line.

This implies that the system of equations that represent a DC circuit do not involve integrals or derivatives with respect to time.

However, in most DC applications, polarity does matter, and connecting the circuit backwards will result in the load not working properly.

Domestic DC installations usually have different types of sockets, connectors, switches, and fixtures from those suitable for alternating current.

To save weight and wire, often the metal frame of the vehicle is connected to one pole of the battery and used as the return conductor in a circuit.

The "low voltage" DC system typically operates at 12V, and serves the same purpose as in an internal combustion engine vehicle.

[10] The "high voltage" system operates at 300-400V (depending on the vehicle), and provides the power for the traction motors.

The negative polarity is achieved by grounding the positive terminal of power supply system and the battery bank.

Other devices may be powered from the telecommunications DC system using a DC-DC converter to provide any convenient voltage.

Direct current (DC) (red line). The vertical axis shows current or voltage and the horizontal 't' axis measures time and shows the zero value.
Brush Electric Company's central power plant with dynamos generating direct current to power arc lamps for public lighting in New York. Beginning operation in December 1880 at 133 West Twenty-Fifth Street, the high voltages it operated at allowed it to power a 2-mile (3.2 km) long circuit. [ 4 ]
Types of direct current
This symbol which can be represented with Unicode character U+ 2393 (⎓) is found on many electronic devices that either require or produce direct current.