Dynamo

"Dynamo Electric Machine" (end view, partly section, )
The Faraday disk was the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disk (D). When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact m (connected to B') through the external circuit, and back through B to the center of the disk through the axle
Hippolyte Pixii's dynamo. The commutator is located on the shaft below the spinning magnet
Pacinotti dynamo, 1860
The Woolrich Electrical Generator in Thinktank, Birmingham
Small Gramme dynamo, around 1878
Low voltage dynamo for electroplating from the turn of the century. The resistance of the commutator contacts causes inefficiency in low voltage, high current machines like this, requiring a huge elaborate commutator. This machine generated 7 volts at 310 amps.

Electrical generator that creates direct current using a commutator.

- Dynamo

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Direct current

One-directional flow of electric charge.

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 mi long circuit.
Types of direct current
This symbol which can be represented with Unicode character (⎓) is found on many electronic devices that either require or produce direct current.

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.

Commutator (electric)

Rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit.

Commutator in a universal motor from a vacuum cleaner. Parts: (A) commutator, (B) brush, (C) rotor (armature) windings, (D) stator (field) windings, (E) brush guides, (F) electrical connections.
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Cross-section of a commutator that can be disassembled for repair.
A tiny 5-segment commutator less than 2 mm in diameter, on a direct-current motor in a toy radio control ZipZaps car.
Various types of copper and carbon brushes.
Compound carbon brush holder, with individual clamps and tension adjustments for each block of carbon.
Different types of brushes have different brush contact angles
Commutator and brush assembly of a traction motor; the copper bars can be seen with lighter insulation strips between the bars. Each dark grey carbon brush has a short flexible copper jumper lead attached. Parts of the motor field winding, in red, can be seen to the right of the commutator.
Commutating plane definitions.
Centered position of the commutating plane if there were no field distortion effects.
Actual position of the commutating plane to compensate for field distortion.
Brush advance for Self-Induction.
Low voltage dynamo from late 1800s for electroplating. The resistance of the commutator contacts causes inefficiency in low voltage, high current machines like this, requiring a huge elaborate commutator. This machine generated 7 volts at 310 amps.

Commutators are used in direct current (DC) machines: dynamos (DC generators) and many DC motors as well as universal motors.

Alternator

Electrical generator that converts mechanical energy to electrical energy in the form of alternating current.

Alternators made in 1909 by Ganz Works in the power generating hall of a Russian hydroelectric station (photograph by Prokudin-Gorsky, 1911).
In what is considered the first industrial use of alternating current in 1891, workmen pose with a Westinghouse alternator at the Ames Hydroelectric Generating Plant. This machine was used as a generator producing 3,000-volt, 133-hertz, single-phase AC, and an identical machine 3 miles away was used as an AC motor.
Diagram of a simple alternator with a rotating magnetic core (rotor) and stationary wire (stator) also showing the current induced in the stator by the rotating magnetic field of the rotor.
Alternator mounted on an automobile engine with a serpentine belt pulley (belt not present.)

Until the 1960s, automobiles used DC dynamo generators with commutators.

Electric current

Stream of charged particles, such as electrons or ions, moving through an electrical conductor or space.

A simple electric circuit, where current is represented by the letter i. The relationship between the voltage (V), resistance (R), and current (I) is V=IR; this is known as Ohm's law.
The electrons, the charge carriers in an electrical circuit, flow in the opposite direction of the conventional electric current.
The symbol for a battery in a circuit diagram.
Magnetic field is produced by an electric current in a solenoid.
Alternating electric current flows through the solenoid, producing a changing magnetic field. This field causes an electric current to flow in the wire loop by electromagnetic induction.
A proton conductor in a static electric field.

Direct current is produced by sources such as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type.

Electric generator

Device that converts motive power into electric power for use in an external circuit.

U.S. NRC image of a modern steam turbine generator (STG).
Early Ganz Generator in Zwevegem, West Flanders, Belgium
The Faraday disk was the first electric generator. The horseshoe-shaped magnet (A) created a magnetic field through the disk (D). When the disk was turned, this induced an electric current radially outward from the center toward the rim. The current flowed out through the sliding spring contact m, through the external circuit, and back into the center of the disk through the axle.
Hippolyte Pixii's dynamo. The commutator is located on the shaft below the spinning magnet.
This large belt-driven high-current dynamo produced 310 amperes at 7 volts. Dynamos are no longer used due to the size and complexity of the commutator needed for high power applications.
Ferranti alternating current generator, c. 1900.
A small early 1900s 75 kVA direct-driven power station AC alternator, with a separate belt-driven exciter generator.
The Athlone Power Station in Cape Town, South Africa
Hydroelectric power station at Gabčíkovo Dam, Slovakia
Hydroelectric power station at Glen Canyon Dam, Page, Arizona
Mobile electric generator
Protesters at Occupy Wall Street using bicycles connected to a motor and one-way diode to charge batteries for their electronics

Dynamos generate pulsing direct current through the use of a commutator.

Werner von Siemens

German electrical engineer, inventor and industrialist.

He claimed invention of the dynamo although others invented it earlier.

Alternating current

Electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction.

Alternating current (green curve). The horizontal axis measures time (it also represents zero voltage/current) ; the vertical, current or voltage.
A schematic representation of long distance electric power transmission. From left to right: G=generator, U=step up transformer, V=voltage at beginning of transmission line, Pt=power entering transmission line, I=current in wires, R=total resistance in wires, Pw=power lost in transmission line, Pe=power reaching the end of the transmission line,  D=step down transformer, C=consumers.
Three-phase high-voltage transmission lines use alternating currents to distribute power over long distances between electric generation plants and consumers. The lines in the picture are located in eastern Utah.
A sine wave, over one cycle (360°). The dashed line represents the root mean square (RMS) value at about 0.707.
The Hungarian "ZBD" Team (Károly Zipernowsky, Ottó Bláthy, Miksa Déri), inventors of the first high efficiency, closed-core shunt connection transformer
The prototype of the ZBD transformer on display at the Széchenyi István Memorial Exhibition, Nagycenk in Hungary
Westinghouse Early AC System 1887
(US patent 373035)

The first alternator to produce alternating current was a dynamo electric generator based on Michael Faraday's principles constructed by the French instrument maker Hippolyte Pixii in 1832.

Homopolar generator

DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field.

Faraday disk, the first homopolar generator
Faraday disc
The remains of the ANU 500 MJ generator
Basic Faraday disc generator
Working principle of a homopolar generator: due to Lorentz force FL negative charges are driven towards center of the rotating disk, so that a voltage shows up between its center and its rim, with the negative pole at the center.

It was the beginning of modern dynamos — that is, electrical generators which operate using a magnetic field.

Rotary converter

Type of electrical machine which acts as a mechanical rectifier, inverter or frequency converter.

1909 500 kW Westinghouse rotary converter
Wiring schematic for a simplified bipolar field Gramme ring single-phase to direct current rotary converter. (In actual use, the converter is drum-wound and uses a multipolar field.)
Wiring schematic for a simplified two-phase to direct current rotary converter, with the second phase connected at right angles to the first.
Wiring schematic for a simplified three-phase to direct current rotary converter, with the phases separated by 120 degrees on the commutator.
Railroad Rotary Converter from Illinois Railway Museum

if the coil is rotated, direct current can be taken from the commutator, and it is called a dynamo.

Stator

Stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors.

Rotor (lower left) and stator (upper right) of an electric motor
Stator of a 3-phase AC-motor
Stator of a brushless DC motor from computer cooler fan.
Stator winding of a generator at a hydroelectric power station.
Stator of a 3-phase induction motor

The first DC generators (known as dynamos) and DC motors put the field coils on the stator, and the power generation or motive reaction coils on the rotor.