History and Development of Dynamos
– Faraday disk was the first electric generator
– Operating principle of electromagnetic generators discovered by Michael Faraday
– Faraday built the first electromagnetic generator called the Faraday disk
– Faraday disk design was inefficient due to counterflows of current
– Wire windings were introduced to produce higher voltages
– Hippolyte Pixii built the first commutated dynamo
– Pixii used a permanent magnet rotated by a crank
– Spinning magnet induced currents in opposite directions
– Pixii invented the commutator to convert AC to DC
– Antonio Pacinotti improved dynamo design with a multi-pole toroidal coil
– Ányos Jedlik experimented with electromagnetic self-rotors
– Jedlik formulated the concept of the dynamo before Siemens and Wheatstone
– Jedlik’s dynamo used two electromagnets to induce the magnetic field
– Discovery of dynamo self-excitation replaced permanent magnet designs
– Sir Charles Wheatstone, Werner von Siemens, and Samuel Alfred Varley independently invented the modern dynamo
– Dynamo-electric machine used self-powering electromagnetic field coils
– Electromagnets increased power output and enabled high power generation
– Siemens used dynamos to power electric arc furnaces in the 1870s
– Zénobe Gramme improved Pacinotti’s design and generated commercial quantities of power
Design and Components of Dynamos
– A dynamo converts mechanical rotation into direct electric current using rotating coils of wire and magnetic fields
– The stator provides a constant magnetic field, while the armature consists of rotating windings
– Faraday’s law of induction creates an electromotive force, generating an electric current in the wire
– Small machines may use permanent magnets, while larger machines use electromagnets known as field coils
– Dynamo machines consist of a stationary structure (stator) and rotating windings (armature)
– The commutator is necessary to produce direct current in a dynamo
– When a loop of wire rotates in a magnetic field, it generates an alternating current
– The commutator reverses the connection of the windings to the external circuit, producing a pulsing direct current
Excitation and Self-Excitation of Dynamos
– Early dynamos used permanent magnets to create the magnetic field (magneto-electric machines)
– Stronger magnetic fields were achieved by using electromagnets (field coils) on the stator (dynamo-electric machines)
– The field coils were initially separately excited by a smaller dynamo or magneto
– Self-excited dynamos were discovered to bootstrap themselves using current generated by the dynamo itself
– Self-excited dynamos have a combination of series and parallel field windings supplied power by the rotor through the commutator
Uses of Dynamos
– Dynamos were widely used in power stations to generate electricity for industrial and domestic purposes
– They were used in motor vehicles to generate electricity for battery charging
– Dynamos still have some uses in low power applications, particularly where low voltage DC is required
– Hand cranked dynamos are used in clockwork radios, hand powered flashlights, and other human-powered equipment to recharge batteries
– The generator used for bicycle lighting may be called a dynamo, but these are almost always AC devices and would be called alternators
Limitations and Decline of Dynamos
– Low voltage, high current machines like dynamos have inefficiency due to the resistance of the commutator contacts
– The sliding friction between brushes and commutator consumes power, especially in low power dynamos
– Brushes and copper commutator segments wear down over time, requiring regular replacement and occasional resurfacing
– The resistance of the sliding contact between brush and commutator causes a voltage drop called the brush drop, leading to power losses
– Commutated machines cannot be used in low particulate or sealed applications or in equipment that requires long periods without maintenance
– Dynamos, usually driven by steam engines, were widely used in power stations
– Large industrial dynamos with series and parallel windings can be difficult to use together in a power plant
– Dynamos have been replaced by alternators in power stations and motor vehicles
– Alternators are more efficient and easier to use compared to dynamos
– Dynamos still have some uses in low power applications where low voltage DC is required
– Alternators with semiconductor rectifiers can be inefficient in these applications Source: https://en.wikipedia.org/wiki/Dynamo
A dynamo is an electrical generator that creates direct current using a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter.
Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using rectifiers (such as vacuum tubes or more recently via solid state technology) is effective and usually economical.
