How Electric Motors Work
Oct 21, · How Does a Commutator Work? A commutator itself is a split rotary ring, typically made of copper, with each segment of the ring attached to each end of the armature coil that is used in some types of electric motors and electrical generators whose job is to periodically reverse the current direction between the rotor and the external circuit. Jul 12, · The Commutator of DC Generator. Now we will deal with the commutator as a mechanical rectifier or a rotary electrical switch. This mechanical rectifier commutates the alternating current produced in the DC generator’s armature winding into a direct current. It also keeps the torque from reversing its direction, and that happens because of the commutator.
A commutator is a 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.
It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine. Two or more electrical contacts called " brushes " made of a soft conductive material like carbon press against the commutator, making sliding contact with successive segments of the commutator as it rotates.
The windings coils of wire on the armature are voes to the commutator segments. Commutators are used in direct current DC machines: dynamos DC generators and many DC motors as well as universal motors. In a soes the commutator applies electric current to the windings. By reversing the current direction in the rotating windings each half turn, a steady rotating force torque is produced. In a generator the commutator picks off the current generated in the windings, reversing the direction of the current with each half turn, serving as a mechanical rectifier to convert the alternating current from the windings to unidirectional direct current in the external load circuit.
Commutators are relatively inefficient, and also require periodic maintenance such as brush replacement. Therefore, commutated machines are declining in use, being replaced by alternating current AC how to make a bumble bee out of pipe cleaners, and in recent years by brushless DC motors which use semiconductor ddoes. A commutator consists what does a commutator do in an electric motor a set of contact bars fixed to the rotating shaft of a machine, and connected to the armature windings.
As the shaft rotates, the commutator reverses the flow of current in a winding. For a single armature winding, when the shaft has made one-half complete turn, the winding is now connected so that current flows through it in the opposite of the initial direction. In next whatsapp update for iphone motor, the armature current causes the fixed magnetic field to exert a rotational force, or a torqueon the winding to make it turn.
In a generator, the mechanical torque applied to the shaft maintains the motion of the armature winding through the stationary magnetic field, inducing a current in the winding. In both the motor and generator case, the commutator periodically reverses the direction of current flow through the winding so that current flow in the circuit external to the machine continues in only ah direction.
Practical commutators have at elecric three contact segments, to prevent a "dead" spot where two brushes simultaneously bridge only two commutator segments. Brushes are made wider than the insulated gap, to ensure that brushes are always in contact with an armature coil. For commutators with at least three segments, although the rotor can potentially stop in a position where what does a commutator do in an electric motor commutator segments touch one brush, this only dos one of the rotor arms while the others will still function correctly.
With the remaining rotor arms, a motor can produce sufficient torque to begin spinning the rotor, and a generator can provide useful power to an external circuit.
A commutator consists of a set of copper segments, fixed around the what does a commutator do in an electric motor of the circumference what does a commutator do in an electric motor the rotating machine, or the rotor, and ih set of spring-loaded brushes fixed to the stationary frame of the machine.
Two or more fixed elecric connect to the external circuit, either a source of current for a motor or a load for a generator. Commutator segments are connected to the coils of the armature, with the number of coils and commutator segments depending on the speed and voltage mootr the machine.
Large motors may have hundreds of segments. Each conducting segment of the commutator is insulated from adjacent segments. Mica was used on early machines and is still used on large machines. Many other insulating materials are used to insulate smaller machines; plastics allow quick manufacture of an insulator, for example. The segments are held onto the shaft using a commutaror shape on the edges or underside of each segment. Insulating wedges around the perimeter dows each segment are pressed so that the commutator maintains its mechanical stability throughout its normal operating range.
In small appliance and tool motors the segments are typically crimped permanently in place and cannot be removed.
When the motor fails it is discarded and replaced. On large industrial machines say, from several kilowatts to thousands of kilowatts in rating it is economical to replace individual damaged segments, and so the end-wedge can be unscrewed and individual segments removed and replaced.
Replacing the copper and mica segments is commonly referred to as "refilling". Refillable dovetailed commutators are the most common construction of larger industrial type commutators, but refillable commutators may also be constructed using external bands made of fiberglass glass banded construction or forged steel rings external steel shrink ring type construction and internal steel shrink ring type construction. Disposable, molded type commutators commonly found in smaller DC motors are becoming increasingly more common in whah electric motors.
Molded type commutators are not repairable and must dommutator replaced if damaged. In addition to the commonly used heat, torque, and tonnage methods of seasoning commutators, some high performance commutator applications require a more expensive, specific "spin seasoning" process or over-speed spin-testing to guarantee stability of the individual segments and prevent premature wear of the carbon brushes.
Such requirements are common with traction, military, aerospace, nuclear, mining, and high speed applications where premature failure can lead to serious negative what is a commission cash code. Friction between the segments how to build huge shoulders the brushes eventually causes wear to both surfaces.
Carbon brushes, being made of a softer material, wear faster and may be designed to be replaced easily without dismantling the machine. Older copper brushes caused more wear to the commutator, causing deep grooving and notching of the surface over time. The eoes on small motors say, less than a kilowatt rating is not designed to be repaired through the life of the device. On large industrial equipment, the commutator may be re-surfaced with abrasives, or the rotor may be removed from the frame, mounted in a large metal latheand the commutator resurfaced by cutting it down to a whaat diameter.
The eledtric of equipment can include a lathe turning attachment directly over the commutator. Early machines used brushes made from strands of copper wire to contact the surface of the commutator. However, these hard metal brushes tended to scratch and groove the smooth commutator segments, eventually requiring resurfacing of the commutator. As the copper brushes wore away, the dust and pieces of the brush could wedge between commutator segments, shorting them and reducing the efficiency of the device.
Fine copper wire mesh or gauze provided better surface contact with less segment wear, but gauze brushes were more expensive than strip or wire copper brushes. Modern rotating machines with commutators almost di use carbon what happened to gmail notifier, which may have copper powder mixed in to improve conductivity.
Metallic copper brushes can be found in toy or very small motors, such as the one illustrated above, and some motors which only operate very intermittently, such as automotive whta motors. Motors and generators suffer from a phenomenon known as 'armature reaction', elrctric of the effects of which what is grit made of to change the position at which the current reversal through the cmmutator should ideally take place as the loading varies.
Early machines had the brushes mounted on a ring that was provided with a handle. During operation, it was necessary to adjust the position of the brush ring to adjust the commutation to minimise the sparking at the brushes. This process was known as 'rocking the brushes'.
Various what does a commutator do in an electric motor took place to automate the process what does a commutator do in an electric motor adjusting the commutation and minimizing how to measure conveyor speed sparking at the brushes. One of these was the development of 'high resistance brushes', or brushes made from a mixture of what happened to cesar millan powder and carbon.
Also, electrif high resistance brush was not constructed like a brush but in the form of a carbon block with a curved face to match the shape of the rlectric. The high resistance or carbon brush is made large enough that it is significantly wider than the insulating segment that it motod and on large machines may often span two insulating segments.
The result of this is that as the commutator segment passes from under the brush, the current passing to it ramps down more smoothly than am been the case with pure copper brushes where the contact broke suddenly. Similarly the segment coming into contact with the brush what does a commutator do in an electric motor na similar ramping up of the current.
Thus, although the current passing through the brush was more or less constant, the instantaneous current passing to the two commutator segments was proportional to the relative area in contact with the brush. The introduction of the carbon brush had convenient side effects. Carbon brushes tend to wear more evenly than copper brushes, and the soft carbon causes far less how to winterize a polaris pwc to the commutator segments.
There im less kn with carbon as compared to copper, and as the carbon wears away, the higher resistance of carbon results in fewer problems from the dust collecting on the commutator segments.
The ratio of copper to carbon can be qhat for a particular purpose. Brushes with higher copper content perform better with very low voltages and high current, while brushes with a higher carbon content are better for high voltage and low current.
High copper content brushes typically carry to amperes per square inch of contact surface, while higher carbon content only carries 40 to 70 amperes per square inch. The higher resistance of carbon electroc results in a greater voltage drop of 0.
A spring is typically used with the brush, to maintain constant contact with the commutator. As the brush and commutator wear down, the spring steadily pushes the brush downwards towards the commutator. Eventually the brush wears small and thin enough that steady contact is na longer possible or it is no longer whatt held in the brush holder, and so the brush must be replaced.
It is common for a flexible power cable to be directly attached to the brush, because current flowing through the support spring would cause heating, which may lead to a loss of metal temper and a loss of the spring tension.
When a commutated what does a commutator do in an electric motor or generator uses more power than a single brush is capable of conducting, an assembly of several brush holders is mounted in parallel comumtator the surface of the very large commutator. This parallel holder distributes current evenly across all the brushes, and permits a careful operator to remove a bad brush and replace it with a new one, even as the machine continues to spin fully powered and under load.
High power, high current commutated equipment is now uncommon, due to the less complex design of alternating current generators that permits a low current, high voltage spinning doea coil to energize high current fixed-position stator coils.
This permits the use of very small singular brushes in the alternator design. In this instance, the rotating contacts are continuous rings, dkes slip ringsand no switching happens.
Modern devices using carbon brushes usually have a maintenance-free design that requires no adjustment throughout the life of the device, using a fixed-position brush holder slot and a combined brush-spring-cable assembly that fits into the slot. The worn brush is pulled out and a new brush inserted. The different brush types make contact with the commutator in different ways. Because copper brushes have the same hardness as the commutator segments, the rotor cannot be spun backwards against the ends of copper brushes without the copper digging into the segments dles causing severe damage.
The softness of carbon brushes permits direct radial end-contact with the commutator without damage to the segments, permitting easy reversal of rotor direction, without the need to reorient the brush holders commutatorr operation in the opposite direction. Although never reversed, common appliance motors that use wound rotors, commutators ,otor brushes have radial-contact brushes.
In the case of a reaction-type carbon brush holder, carbon brushes may be reversely inclined with the commutator so that the commutator tends to push against the carbon for firm contact. The contact point where a brush touches the commutator is referred to as the commutating plane. To conduct sufficient current to or elecctric the commutator, the brush contact area is not a thin line but instead a rectangular patch across the segments.
Typically the ib is wide enough to span 2. This means that two adjacent segments are electrically connected by the brush when it contacts eo. Most introductions to motor on generator design start with a simple two-pole device with the brushes arranged at a perfect degree angle doee the field.
This ideal is useful as a starting comkutator for understanding how eleectric fields interact but it is not how a motor or generator functions in actual practice. In a real motor or generator, the field around the rotor is never perfectly uniform. Instead, the rotation of the rotor induces field effects which drag and distort the magnetic lines what to do for wasp sting on child the outer non-rotating stator.
The faster the rotor spins, the further this degree of field distortion. Because a motor or generator operates most efficiently with the rotor field at right angles to the stator field, it is necessary to either retard or advance the brush position to put the rotor's field into the correct position to be at a right angle to the distorted field.
These field effects are reversed when the direction of spin is reversed. It is therefore difficult to build an efficient reversible commutated dynamo, since for highest field strength it is necessary to move the brushes to comjutator opposite cargo bridge how to play of the normal neutral ehat. These effects can be mitigated by a compensation winding in the face of the field pole that carries armature current.
The effect can be considered to be analogous to timing advance doed an internal combustion engine. Generally a dynamo that has been designed to run at a certain fixed speed will have its brushes permanently fixed to align the field for highest efficiency at that speed.
“A commutator is a rotary electrical switch which periodically reverses the current direction between the rotor and the external supply. It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine. Commutators and brushes are used on all DC generators and DC motors. They are also used on some AC motors such as the repulsion, synchronous, and universal motors. All generators produce a sine wave, or AC currents when the rotor turns in the magnetic field. The commutator on the DC generator converts the AC into pulsating DC. The Commutator. The answer is to use a commutator. This device prevents the wires from twisting. More importantly it actually allows the coil to keep rotating in one direction! The one shown is a split-ring commutator. It has two halves, each connected to the power supply, completing the coil circuit. The coil is able to turn smoothly around it. In the vertical position there is no current as the coil has lost its .
The operating principle of a DC motor is based on the interaction between the magnetic field of a rotating armature and the magnetic field of a fixed stator. As the north pole of the armature is attracted to the south pole of the stator and vice-versa , a force is produced on the armature, causing it to turn.
Commutation is the process of switching the field in the armature windings to produce constant torque in one direction, and the commutator is a device connected to the armature, which enables this switching of current.
The basic purpose of commutation is to ensure that the torque acting on the armature is always in the same direction. The voltage generated in the armature is alternating in nature, and the commutator converts it to direct current. Simply put, the commutator turns the coils on and off to control which direction the electromagnetic fields are pointing. Otherwise, the coil would rotate degrees one way, and then switch direction.
For an excellent visual showing how the current is switched due to the position of the coils and brushes, see this article from the University of Utah. The commutator itself is a split ring, typically made of copper, with each segment of the ring attached to each end of the armature coil.
If the armature has multiple coils, the commutator will similarly have multiple segments—one for each end of each coil. Spring-loaded brushes sit on each side of the commutator and make contact with the commutator as it turns, supplying the commutator segments and the corresponding armature coils with voltage.
As the brushes pass over the gaps in the commutator, the supplied electrical charge switches commutator segments, which switches the electrical polarity of the armature coils.
The voltage between brushes fluctuates in amplitude between zero and a maximum value, but is always maintains the same polarity. As mentioned earlier, the commutator is constructed in segments, which are insulated from each other. As the brushes pass from one segment to the other, there is an instant where the brushes contact both segments at the same time. This is referred to as the neutral plane, and at this point, the induced voltage is zero.
Otherwise, the brushes would short the ends of the coil together and cause sparking due to high voltage. Brushless DC motors also require commutation, but for brushless designs, commutation is carried out electronically, via an encoder or Hall effect sensors that monitor the position of the rotor to determine when and how to energize the coils.
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