Mechanical rectifier
Encyclopedia
A mechanical rectifier is a device for converting alternating current
(AC) to direct current
(DC) by means of mechanically-operated switches. The best-known type is the commutator
, which is an integral part of a DC dynamo
but, before solid-state
devices became available, independent mechanical rectifiers were used for certain applications. Before the invention of semiconductor
s, rectification at high currents involved serious losses.
There were various vacuum/gas devices, such as the mercury arc rectifiers, thyratron
s, ignitron
s, and vacuum diodes. Solid-state technology was in its infancy, represented by copper oxide
and selenium rectifier
s. All of these gave excessive forward voltage drop at high currents. One answer was mechanically opening and closing contacts, if this could be done quickly and cleanly enough.
inverter
. An electromagnet
, powered by DC through contacts it operated (like a buzzer) (or fed with AC), caused a spring to vibrate and the spring operated change-over contacts which converted the AC to DC. This arrangement was only suitable for low-power applications, e.g. auto radio
s and was also found in some motorcycle electrical systems, where it was combined with a voltage regulator
.
. It was suitable for high-power applications, e.g. electrolysis
cells and electrostatic precipitator
s.
(BTH) Rugby, Warwickshire
, England
, in the early 1950s. It is a three-phase
mechanical rectifier working at 220 volt
s and 15,000 ampere
s, and its application was the powering of huge banks of electrolysis cells
.
The central shaft was rotated by synchronous motor
, driving an eccentric
with a throw of about 2mm. (0.077 inch) Push-rods from this operated the contacts. The timing was critical, and was adjusted by rotating the position of the eccentric on its shaft, and by sliding wedges between the eccentric and push-rods.
Crucial to this system were the commutating reactors, inductor
s that ensured the contacts closed when the voltage across them was small, and opened when the current was small. Without these, contact wear would have been intolerably heavy. These were series inductors that operated for most of the cycle with saturated cores. When the current decreased below that for saturation, their inductances reduced the current considerably. Contact switching was timed to occur while their cores were un-saturated.
In the USA, similar rectifiers were made by the I-T-E circuit breaker company.
This machinery was undoubtedly successful; its efficiency was determined to be 97.25%. Contact life was never fully determined but considerably exceeded 2000 hours. However, the rapid development of the silicon diode made it ultimately redundant.
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
(AC) to direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
(DC) by means of mechanically-operated switches. The best-known type is the commutator
Commutator (electric)
A commutator is a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverses the current direction between the rotor and the external circuit. In a motor, it applies power to the best location on the rotor, and in a generator, picks off power...
, which is an integral part of a DC dynamo
Dynamo
- Engineering :* Dynamo, a magnetic device originally used as an electric generator* Dynamo theory, a theory relating to magnetic fields of celestial bodies* Solar dynamo, the physical process that generates the Sun's magnetic field- Software :...
but, before solid-state
Solid state (electronics)
Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...
devices became available, independent mechanical rectifiers were used for certain applications. Before the invention of semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s, rectification at high currents involved serious losses.
There were various vacuum/gas devices, such as the mercury arc rectifiers, thyratron
Thyratron
A thyratron is a type of gas filled tube used as a high energy electrical switch and controlled rectifier. Triode, tetrode and pentode variations of the thyratron have been manufactured in the past, though most are of the triode design...
s, ignitron
Ignitron
An ignitron is a type of controlled rectifier dating from the 1930s. Invented by Joseph Slepian while employed by Westinghouse, Westinghouse was the original manufacturer and owned trademark rights to the name "Ignitron"....
s, and vacuum diodes. Solid-state technology was in its infancy, represented by copper oxide
Metal rectifier
A metal rectifier is an early type of semiconductor rectifier in which the semiconductor is copper oxide or selenium. They were used in power applications to convert alternating current to direct current in devices such as radios and battery chargers...
and selenium rectifier
Selenium rectifier
A selenium rectifier is a type of metal rectifier, invented in 1933. They were used to replace vacuum tube rectifiers in power supplies for electronic equipment, and in high current battery charger applications....
s. All of these gave excessive forward voltage drop at high currents. One answer was mechanically opening and closing contacts, if this could be done quickly and cleanly enough.
Vibrator type
This was the reverse of a vibratorVibrator (electronic)
In early electronics vibrators were used in inverter circuits to provide an alternating current electric power supply from a direct current source....
inverter
Inverter (electrical)
An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
. An electromagnet
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by the flow of electric current. The magnetic field disappears when the current is turned off...
, powered by DC through contacts it operated (like a buzzer) (or fed with AC), caused a spring to vibrate and the spring operated change-over contacts which converted the AC to DC. This arrangement was only suitable for low-power applications, e.g. auto radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
s and was also found in some motorcycle electrical systems, where it was combined with a voltage regulator
Voltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...
.
Motor-driven type
This operated on the same principle as the vibrator type but the change-over contacts were operated by a synchronous motorSynchronous motor
A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the power supply frequency and resulting rotating magnetic field which drives it....
. It was suitable for high-power applications, e.g. electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
cells and electrostatic precipitator
Electrostatic precipitator
An electrostatic precipitator , or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas using the force of an induced electrostatic charge...
s.
BTH rectifier
The machine shown in the reference was designed by Read and Gimson et al., at British Thomson-HoustonBritish Thomson-Houston
British Thomson-Houston was a British engineering and heavy industrial company, based at Rugby, Warwickshire, England. They were known primarily for their electrical systems and steam turbines. They were merged with the similar Metropolitan-Vickers company in 1928, but the two maintained their own...
(BTH) Rugby, Warwickshire
Rugby, Warwickshire
Rugby is a market town in Warwickshire, England, located on the River Avon. The town has a population of 61,988 making it the second largest town in the county...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
, in the early 1950s. It is a three-phase
Three-phase electric power
Three-phase electric power is a common method of alternating-current electric power generation, transmission, and distribution. It is a type of polyphase system and is the most common method used by grids worldwide to transfer power. It is also used to power large motors and other heavy loads...
mechanical rectifier working at 220 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
s and 15,000 ampere
Ampere
The ampere , often shortened to amp, is the SI unit of electric current and is one of the seven SI base units. It is named after André-Marie Ampère , French mathematician and physicist, considered the father of electrodynamics...
s, and its application was the powering of huge banks of electrolysis cells
Electrolytic cell
An electrolytic cell decomposes chemical compounds by means of electrical energy, in a process called electrolysis; the Greek word lysis means to break up. The result is that the chemical energy is increased...
.
The central shaft was rotated by synchronous motor
Synchronous motor
A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the power supply frequency and resulting rotating magnetic field which drives it....
, driving an eccentric
Eccentric (mechanism)
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle ....
with a throw of about 2mm. (0.077 inch) Push-rods from this operated the contacts. The timing was critical, and was adjusted by rotating the position of the eccentric on its shaft, and by sliding wedges between the eccentric and push-rods.
Crucial to this system were the commutating reactors, inductor
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
s that ensured the contacts closed when the voltage across them was small, and opened when the current was small. Without these, contact wear would have been intolerably heavy. These were series inductors that operated for most of the cycle with saturated cores. When the current decreased below that for saturation, their inductances reduced the current considerably. Contact switching was timed to occur while their cores were un-saturated.
In the USA, similar rectifiers were made by the I-T-E circuit breaker company.
This machinery was undoubtedly successful; its efficiency was determined to be 97.25%. Contact life was never fully determined but considerably exceeded 2000 hours. However, the rapid development of the silicon diode made it ultimately redundant.