Electric motor - Revision history

Red marquis: /* Slip ring */

2010-04-20T12:57:52Z

Slip ring

← Older revision		Revision as of 12:57, 20 April 2010
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	== Slip ring ==		== Slip ring ==
	The slip ring is a component of the wound rotor motor as an induction machine (best evidenced by the construction of the common automotive alternator), where the rotor comprises a set of coils that are electrically terminated in [[slip ~~ring]]s~~. These are metal rings rigidly mounted on the rotor, and combined with brushes (as used with commutators), provide continuous unswitched connection to the rotor windings.		The slip ring is a component of the wound rotor motor as an induction machine (best evidenced by the construction of the common automotive alternator), where the rotor comprises a set of coils that are electrically terminated in slip rings. These are metal rings rigidly mounted on the rotor, and combined with brushes (as used with commutators), provide continuous unswitched connection to the rotor windings.

	In the case of the wound-rotor induction motor, external impedances can be connected to the brushes. The stator is excited similarly to the standard squirrel cage motor. By changing the impedance connected to the rotor circuit, the speed/current and speed/torque curves can be altered.		In the case of the wound-rotor induction motor, external impedances can be connected to the brushes. The stator is excited similarly to the standard squirrel cage motor. By changing the impedance connected to the rotor circuit, the speed/current and speed/torque curves can be altered.

Red marquis: /* Stepper motors */

2010-04-20T12:57:30Z

Stepper motors

← Older revision		Revision as of 12:57, 20 April 2010
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	== Stepper motors ==		== Stepper motors ==

	Closely related in design to three-phase AC synchronous motors are [[stepper ~~motor]]s~~, where an internal rotor containing permanent magnets or a magnetically-soft rotor with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a rotary [[solenoid]]. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the stepper motor may not rotate continuously; instead, it "steps" — starts and then quickly stops again — from one position to the next as field windings are energized and de-energized in sequence. Depending on the sequence, the rotor may turn forwards or backwards, and it may change direction, stop, speed up or slow down arbitrarily at any time.		Closely related in design to three-phase AC synchronous motors are stepper motors, where an internal rotor containing permanent magnets or a magnetically-soft rotor with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a rotary solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the stepper motor may not rotate continuously; instead, it "steps" — starts and then quickly stops again — from one position to the next as field windings are energized and de-energized in sequence. Depending on the sequence, the rotor may turn forwards or backwards, and it may change direction, stop, speed up or slow down arbitrarily at any time.

	Simple stepper motor drivers entirely energize or entirely de-energize the field windings, leading the rotor to "[[cog]]" to a limited number of positions; more sophisticated drivers can proportionally control the power to the field windings, allowing the rotors to position between the cog points and thereby rotate extremely smoothly. This mode of operation is often called ~~[[stepper motor#Microstepping\|~~microstepping]]. Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when part of a digital ~~[[servomechanism\|~~servo-controlled]] system.		Simple stepper motor drivers entirely energize or entirely de-energize the field windings, leading the rotor to "cog" to a limited number of positions; more sophisticated drivers can proportionally control the power to the field windings, allowing the rotors to position between the cog points and thereby rotate extremely smoothly. This mode of operation is often called microstepping. Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when part of a digital servo-controlled system.

	Stepper motors can be rotated to a specific angle in discrete steps with ease, and hence stepper motors are used for read/write head positioning in computer [[floppy diskette]] drives. They were used for the same purpose in pre-gigabyte era computer disk drives, where the precision and speed they offered was adequate for the correct positioning of the read/write head of a hard disk drive. As drive density increased, the precision and speed limitations of stepper motors made them obsolete for hard drives—the precision limitation made them unusable, and the speed limitation made them uncompetitive—thus newer hard disk drives use [[voice coil]]-based head actuator systems. (The term "voice coil" in this connection is historic; it refers to the structure in a typical (cone type) loudspeaker. This structure was used for a while to position the heads. Modern drives have a pivoted coil mount; the coil swings back and forth, something like a blade of a rotating fan. Nevertheless, like a voice coil, modern actuator coil conductors (the magnet wire) move perpendicular to the magnetic lines of force.)		Stepper motors can be rotated to a specific angle in discrete steps with ease, and hence stepper motors are used for read/write head positioning in computer floppy diskette drives. They were used for the same purpose in pre-gigabyte era computer disk drives, where the precision and speed they offered was adequate for the correct positioning of the read/write head of a hard disk drive. As drive density increased, the precision and speed limitations of stepper motors made them obsolete for hard drives—the precision limitation made them unusable, and the speed limitation made them uncompetitive—thus newer hard disk drives use voice coil-based head actuator systems. (The term "voice coil" in this connection is historic; it refers to the structure in a typical (cone type) loudspeaker. This structure was used for a while to position the heads. Modern drives have a pivoted coil mount; the coil swings back and forth, something like a blade of a rotating fan. Nevertheless, like a voice coil, modern actuator coil conductors (the magnet wire) move perpendicular to the magnetic lines of force.)

	Stepper motors were and still are often used in computer printers, optical scanners, and digital photocopiers to move the optical scanning element, the print head carriage (of dot matrix and inkjet printers), and the platen. Likewise, many computer plotters (which since the early 1990s have been replaced with large-format inkjet and laser printers) used rotary stepper motors for pen and platen movement; the typical alternatives here were either linear stepper motors or servomotors with complex closed-loop control systems.		Stepper motors were and still are often used in computer printers, optical scanners, and digital photocopiers to move the optical scanning element, the print head carriage (of dot matrix and inkjet printers), and the platen. Likewise, many computer plotters (which since the early 1990s have been replaced with large-format inkjet and laser printers) used rotary stepper motors for pen and platen movement; the typical alternatives here were either linear stepper motors or servomotors with complex closed-loop control systems.

Red marquis: /* Torque motors */

2010-04-20T12:56:52Z

Torque motors

← Older revision		Revision as of 12:56, 20 April 2010
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	== Torque motors ==		== Torque motors ==
	A [[torque]] motor (also known as a limited torque motor) is a specialized form of [[induction motor]] which is capable of operating indefinitely while ~~[[Stall (engine)\|~~stalled]], that is, with the ~~[[Rotor (electric)\|~~rotor]] blocked from turning, without incurring damage. In this mode of operation, the motor will apply a steady torque to the load (hence the name).		A torque motor (also known as a limited torque motor) is a specialized form of induction motor which is capable of operating indefinitely while stalled, that is, with the rotor blocked from turning, without incurring damage. In this mode of operation, the motor will apply a steady torque to the load (hence the name).

	A common application of a torque motor would be the supply- and take-up [[reel]] motors in a [[tape drive]]. In this application, driven from a low voltage, the characteristics of these motors allow a relatively-constant light tension to be applied to the tape whether or not the ~~[[Capstan (tape recorder)\|~~capstan]] is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as ~~[[gear]]s~~ or ~~[[clutch]]es~~. In the computer gaming world, torque motors are used in ~~[[Haptic technology\|~~force feedback]] steering wheels.		A common application of a torque motor would be the supply- and take-up reel motors in a tape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively-constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches. In the computer gaming world, torque motors are used in force feedback steering wheels.

	Another common application is the control of the [[throttle]] of an [[internal combustion engine]] in conjunction with an ~~[[electronics\|~~electronic~~]] [[~~governor ~~(device)\|governor]]~~. In this usage, the motor works against a ~~[[spring (device)\|~~return spring]] to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the [[ignition system]] or from a [[magnetic pickup~~]] <ref>http://www.daytronic.com/products/trans/t-magpickup.htm</ref>~~		Another common application is the control of the throttle of an internal combustion engine in conjunction with an electronic governor. In this usage, the motor works against a return spring to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the ignition system or from a magnetic pickup and, depending on the speed, makes small adjustments to the amount of current applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.
	and, depending on the speed, makes small adjustments to the amount of ~~[[ampere\|~~current]] applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.

	== Slip ring ==		== Slip ring ==

Red marquis: /* AC motors */

2010-04-20T12:55:39Z

AC motors

← Older revision		Revision as of 12:55, 20 April 2010
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	== AC motors ==		== AC motors ==

	In 1882, [[Nikola Tesla]] discovered the ~~[[alternator\|~~rotating magnetic field]], and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, [[Galileo Ferraris]] independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.		In 1882, Nikola Tesla discovered the rotating magnetic field, and pioneered the use of a rotary field of force to operate machines. He exploited the principle to design a unique two-phase induction motor in 1883. In 1885, Galileo Ferraris independently researched the concept. In 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in Turin.

	Tesla had suggested that the ~~[[Commutator (electric)\|commutator]]s~~ from a machine could be removed and the device could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin to building a [[perpetual motion machine~~]].<ref>"''[http://www.pbs~~.~~org/tesla/ll/ll_early.html Tesla's Early Years]''". [[PBS]].</ref>~~ Tesla would later attain ~~{{US patent\|0416194}}~~, ''Electric Motor'' (December 1889), which resembles the motor seen in many of Tesla's photos. This classic alternating current electro-magnetic motor was an [[induction motor]].		Tesla had suggested that the commutators from a machine could be removed and the device could operate on a rotary field of force. Professor Poeschel, his teacher, stated that would be akin to building a perpetual motion machine. Tesla would later attain U.S. Patent 0,416,194, Electric Motor (December 1889), which resembles the motor seen in many of Tesla's photos. This classic alternating current electro-magnetic motor was an induction motor.

	[[Michail Osipovich Dolivo-Dobrovolsky]] later invented a three-phase "cage-rotor" in 1890. This type of motor is now used for the vast majority of commercial applications.		Michail Osipovich Dolivo-Dobrovolsky later invented a three-phase "cage-rotor" in 1890. This type of motor is now used for the vast majority of commercial applications.

	===Components===		===Components===

Red marquis: /* Universal motors */

2010-04-20T12:54:56Z

Universal motors

← Older revision		Revision as of 12:54, 20 April 2010
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	== Universal motors ==		== Universal motors ==
	A series-wound motor is referred to as a ~~'''~~universal motor~~'''~~ when it has been designed to operate on either AC or DC power. The ability to operate on AC is because the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) in synchronism, and hence the resulting mechanical force will occur in a constant direction.		A series-wound motor is referred to as a universal motor when it has been designed to operate on either AC or DC power. The ability to operate on AC is because the current in both the field and the armature (and hence the resultant magnetic fields) will alternate (reverse polarity) in synchronism, and hence the resulting mechanical force will occur in a constant direction.

	Operating at normal ~~[[utility frequency\|~~power line frequencies]], universal motors are very rarely larger than one kilowatt (about 1.3 [[horsepower]]). Universal motors also form the basis of the traditional railway [[traction motor]] in ~~[[Railway electrification system#Low-frequency alternating current\|~~electric railways]]. In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies, with 25 and 16.7 hertz (Hz) operation being common. Because they are universal motors, locomotives using this design were also commonly capable of operating from a [[third rail]] powered by ~~[[Direct current\|~~DC]].		Operating at normal power line frequencies, universal motors are very rarely larger than one kilowatt (about 1.3 horsepower). Universal motors also form the basis of the traditional railway traction motor in electric railways. In this application, to keep their electrical efficiency high, they were operated from very low frequency AC supplies, with 25 and 16.7 hertz (Hz) operation being common. Because they are universal motors, locomotives using this design were also commonly capable of operating from a third rail powered by DC.

	An advantage of the universal motor is that AC supplies may be used on motors which have some characteristics more common in DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the ~~[[Commutator (electric)\|~~commutator]]. As a result, such motors are usually used in AC devices such as food mixers and power tools which are used only intermittently, and often have high starting-torque demands. Continuous speed control of a universal motor running on AC is easily obtained by use of a [[thyristor]] circuit, while (imprecise) stepped speed control can be accomplished using multiple taps on the field coil. Household blenders that advertise many speeds frequently combine a field coil with several taps and a [[diode]] that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC).		An advantage of the universal motor is that AC supplies may be used on motors which have some characteristics more common in DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the commutator. As a result, such motors are usually used in AC devices such as food mixers and power tools which are used only intermittently, and often have high starting-torque demands. Continuous speed control of a universal motor running on AC is easily obtained by use of a thyristor circuit, while (imprecise) stepped speed control can be accomplished using multiple taps on the field coil. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC).

	Universal motors generally run at high speeds, making them useful for appliances such as ~~[[blender (device)\|~~blenders]], [[vacuum ~~cleaner]]s~~, and [[hair ~~dryer]]s~~ where high RPM operation is desirable. They are also commonly used in portable power tools, such as ~~[[electric drill\|~~drills]], ~~[[circular saw\|~~circular]] and ~~[[jigsaw (power tool)\|~~jig saws]], where the motor's characteristics work well. Many vacuum cleaner and ~~[[String trimmer\|~~weed trimmer]] motors exceed 10,000 RPM, while [[Dremel]] and other similar miniature grinders will often exceed 30,000 RPM.		Universal motors generally run at high speeds, making them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high RPM operation is desirable. They are also commonly used in portable power tools, such as drills, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed trimmer motors exceed 10,000 RPM, while Dremel and other similar miniature grinders will often exceed 30,000 RPM.

	Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the unit is operated with no significant load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In some smaller applications, a ~~[[fan (mechanical)\|~~fan blade]] attached to the shaft often acts as an artificial load to limit the motor speed to a safe value, as well as a means to circulate cooling airflow over the armature and field windings.		Motor damage may occur due to overspeeding (running at an RPM in excess of design limits) if the unit is operated with no significant load. On larger motors, sudden loss of load is to be avoided, and the possibility of such an occurrence is incorporated into the motor's protection and control schemes. In some smaller applications, a fan blade attached to the shaft often acts as an artificial load to limit the motor speed to a safe value, as well as a means to circulate cooling airflow over the armature and field windings.

	== AC motors ==		== AC motors ==

Red marquis: /* DC Motors */

2010-04-20T12:54:02Z

DC Motors

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Red marquis at 12:50, 20 April 2010

2010-04-20T12:50:34Z

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Red marquis: /* Comparison of motor types */

2010-04-20T12:45:52Z

Comparison of motor types

← Older revision		Revision as of 12:45, 20 April 2010
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	! Typical Drive		! Typical Drive
	\|-		\|-
	~~\| [[Shaded-pole motor~~\|AC Induction<br />(Shaded Pole)]]		\| AC Induction<br />(Shaded Pole)
	\| Least expensive<br />Long life<br />high power		\| Least expensive<br />Long life<br />high power
	\| Rotation slips from frequency<br />Low starting torque		\| Rotation slips from frequency<br />Low starting torque
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	\| Uni/Poly-phase AC		\| Uni/Poly-phase AC
	\|-		\|-
	~~\| [[AC induction motor~~\|AC Induction<br />(split-phase capacitor)]]		\| AC Induction<br />(split-phase capacitor)
	\| High power<br />high starting torque		\| High power<br />high starting torque
	\| Rotation slips from frequency		\| Rotation slips from frequency
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	\| Uni/Poly-phase AC		\| Uni/Poly-phase AC
	\|-		\|-
	~~\| [[Synchronous motor~~\|AC Synchronous]]		\| AC Synchronous
	\| Rotation in-sync with freq<br />long-life (alternator)		\| Rotation in-sync with freq<br />long-life (alternator)
	\| More expensive		\| More expensive
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	\| Uni/Poly-phase AC		\| Uni/Poly-phase AC
	\|-		\|-
	~~\| [[Stepper motor~~\|Stepper DC]]		\| Stepper DC
	\| Precision positioning<br />High holding torque		\| Precision positioning<br />High holding torque
	\| Requires a controller		\| Requires a controller
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	\| DC		\| DC
	\|-		\|-
	\| [[Brushless DC ~~electric motor\|Brushless DC]]~~		\| Brushless DC
	\| Long lifespan<br />low maintenance<br />High efficiency		\| Long lifespan<br />low maintenance<br />High efficiency
	\| High initial cost<br />Requires a controller		\| High initial cost<br />Requires a controller
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	\| DC		\| DC
	\|-		\|-
	\| [[Brushed DC ~~electric motor\|Brushed DC]]~~		\| Brushed DC
	\| Low initial cost<br />Simple speed control		\| Low initial cost<br />Simple speed control
	\| High maintenance (brushes)<br />Low lifespan		\| High maintenance (brushes)<br />Low lifespan
	\| Treadmill exercisers<br />automotive starters		\| Treadmill exercisers<br />automotive starters
	\| Direct DC or [[PWM]]		\| Direct DC or PWM
	\|-		\|-
	~~\| [[Electric_motor#Printed_Armature_or_Pancake_DC_Motors~~\|Pancake DC]]		\| Pancake DC
	\| Compact design<br />Simple speed control		\| Compact design<br />Simple speed control
	\| Medium cost<br />Medium lifespan		\| Medium cost<br />Medium lifespan
	\| Office Equip<br />Fans/Pumps		\| Office Equip<br />Fans/Pumps
	\| Direct DC or [[PWM]]		\| Direct DC or PWM
	\|}		\|}

	===Servo motor===		===Servo motor===

	~~{{Main\|Servo motor}}~~

	A servomechanism,or servo is an automatic device that uses error-sensing feedback to correct the performance of a mechanism. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback which controls position—the operator does this by observation. By contrast the car's cruise control uses closed loop feedback, which classifies it as a servomechanism.		A servomechanism,or servo is an automatic device that uses error-sensing feedback to correct the performance of a mechanism. The term correctly applies only to systems where the feedback or error-correction signals help control mechanical position or other parameters. For example, an automotive power window control is not a servomechanism, as there is no automatic feedback which controls position—the operator does this by observation. By contrast the car's cruise control uses closed loop feedback, which classifies it as a servomechanism.

	===Synchronous electric motor===		===Synchronous electric motor===
	~~{{Main\|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 alternating current and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip to produce torque. A synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to rotor. The rotor poles connect to each other and move at the same speed hence the name 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 alternating current and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip to produce torque. A synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to rotor. The rotor poles connect to each other and move at the same speed hence the name synchronous motor.

	===Induction motor===		===Induction motor===

	~~{{Main\|Induction motor }}~~

	An induction motor (IM) is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction. Another commonly used name is squirrel cage motor because the rotor bars with short circuit rings resemble a squirrel cage (hamster wheel).		An induction motor (IM) is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction. Another commonly used name is squirrel cage motor because the rotor bars with short circuit rings resemble a squirrel cage (hamster wheel).
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	===Electrostatic motor (capacitor motor)===		===Electrostatic motor (capacitor motor)===
	~~{{Main\|Electrostatic motor }}~~

	An electrostatic motor or capacitor motor is a type of electric motor based on the attraction and repulsion of electric charge. Usually, electrostatic motors are the dual of conventional coil-based motors. They typically require a high voltage power supply, although very small motors employ lower voltages. Conventional electric motors instead employ magnetic attraction and repulsion, and require high current at low voltages. In the 1750s, the first electrostatic motors were developed by Benjamin Franklin and Andrew Gordon. Today the electrostatic motor finds frequent use in micro-mechanical (MEMS) systems where their drive voltages are below 100 volts, and where moving, charged plates are far easier to fabricate than coils and iron cores. Also, the molecular machinery which runs living cells is often based on linear and rotary electrostatic motors.		An electrostatic motor or capacitor motor is a type of electric motor based on the attraction and repulsion of electric charge. Usually, electrostatic motors are the dual of conventional coil-based motors. They typically require a high voltage power supply, although very small motors employ lower voltages. Conventional electric motors instead employ magnetic attraction and repulsion, and require high current at low voltages. In the 1750s, the first electrostatic motors were developed by Benjamin Franklin and Andrew Gordon. Today the electrostatic motor finds frequent use in micro-mechanical (MEMS) systems where their drive voltages are below 100 volts, and where moving, charged plates are far easier to fabricate than coils and iron cores. Also, the molecular machinery which runs living cells is often based on linear and rotary electrostatic motors.

Red marquis: /* Categorization of electric motors */

2010-04-20T12:44:05Z

Categorization of electric motors

← Older revision		Revision as of 12:44, 20 April 2010
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	== Categorization of electric motors ==		== Categorization of electric motors ==
	The classic division of electric motors has been that of [[Alternating Current]] (AC) types vs [[Direct Current]] (DC) types. This is more a ''de facto'' convention, rather than a rigid distinction. For example, many classic DC motors run on AC power, these motors being referred to as ~~[[#Universal motors\|~~universal motors]].		The classic division of electric motors has been that of Alternating Current (AC) types vs Direct Current (DC) types. This is more a de facto convention, rather than a rigid distinction. For example, many classic DC motors run on AC power, these motors being referred to as universal motors.

	Rated output power is also used to categorise motors, those of less than 746 Watts, for example, are often referred to as [[fractional horsepower motors]] (FHP) in reference to the old imperial measurement.		Rated output power is also used to categorise motors, those of less than 746 Watts, for example, are often referred to as fractional horsepower motors (FHP) in reference to the old imperial measurement.

	The ongoing trend toward electronic control further muddles the distinction, as modern drivers have moved the commutator out of the motor shell. For this new breed of motor, driver circuits are relied upon to generate sinusoidal AC drive currents, or some approximation thereof. The two best examples are: the [[brushless DC motor]] and the [[stepping motor]], both being poly-phase AC motors requiring external electronic control, although historically, stepping motors (such as for maritime and naval gyrocompass repeaters) were driven from DC switched by contacts.		The ongoing trend toward electronic control further muddles the distinction, as modern drivers have moved the commutator out of the motor shell. For this new breed of motor, driver circuits are relied upon to generate sinusoidal AC drive currents, or some approximation thereof. The two best examples are: the brushless DC motor and the stepping motor, both being poly-phase AC motors requiring external electronic control, although historically, stepping motors (such as for maritime and naval gyrocompass repeaters) were driven from DC switched by contacts.

	Considering all rotating (or linear) electric motors require synchronism between a moving magnetic field and a moving current sheet for average torque production, there is a clearer distinction between an [[asynchronous motor]] and [[synchronous ~~motor\|synchronous]]~~ types. An asynchronous motor requires slip between the moving magnetic field and a winding set to induce current in the winding set by mutual inductance; the most ubiquitous example being the common AC [[induction motor]] which must slip to generate torque. In the synchronous types, induction (or slip) is not a requisite for magnetic field or current production (e.g. permanent magnet motors, synchronous ~~[[doubly-fed electric machine#Brushless doubly-fed versions\|~~brush-less wound-rotor doubly-fed electric machine]]).		Considering all rotating (or linear) electric motors require synchronism between a moving magnetic field and a moving current sheet for average torque production, there is a clearer distinction between an asynchronous motor and synchronous types. An asynchronous motor requires slip between the moving magnetic field and a winding set to induce current in the winding set by mutual inductance; the most ubiquitous example being the common AC induction motor which must slip to generate torque. In the synchronous types, induction (or slip) is not a requisite for magnetic field or current production (e.g. permanent magnet motors, synchronous brush-less wound-rotor doubly-fed electric machine).

	== Comparison of motor types ==		== Comparison of motor types ==

Red marquis at 12:42, 20 April 2010

2010-04-20T12:42:41Z

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