Describe the purpose of the commutator in a DC motor?
No, Jimmy K is incorrect. If the motor were being spun by another motor, then the commutator would make the current that would be produced in the rotor coils that is AC in nature, come out as DC. As a motor, the commutator connects the various coils that connect to opposite commutator bars to the DC or AC power source, to make the motor spin. To prove the connection, take a DC motor with a commutator, and with the use of an ohm meter, touch one lead to one commutator bar, and while holding that connection, go around to another bar half way around the commutator, so that you are directly opposite of the first bar, and connect the other ohm meter lead there. You should read about 0 ohms. Each coil set will do the same thing. The brushes connect these coils, one at a time, to the power source, and make the motor turn. A "Universal" motor, is a DC or AC motor, since such a motor has a commutator, and will operate with either power source.
Why doesn't an ac motor need a commutator?
an ac motor doesn't need a commutator because unlike the dc current a commutator is not needed to reverse the polarity of the current as it is already alternating, hence why it's called an alternating current. This is also because a dc motor works by changing the polarity of the current through the rotating part of the motor whilst the ac motor does the same thing but through the STATIONARY part of the motor. so there you go, hope that helped.... :) - nickie xx
Will a DC motor without a commutator run if we give it an AC supply?
A DC generator will always need a commutator(and carbon brushes) to convert the alternating current generated in the armature windings of the d.c generator into direct current. In D.C motor, commutator is used to provide unidirectional torque (commutator reverses the current flow at any point).
Can a DC motor run without a commutator?
No. Without commutator it will not rotate and the armature oscillates between north and south poles. No motor action.Reason is….The commutator alternates the current in conductor in armature. If there is no commuter , the current in conductor is fixed an one direction, outward or inward.assume in conductor A current is inward and it is under the N pole. So torque produced is in ACW direction. And when this conductor comes under S pole, current is still inward in this conductor, now the torque is in CW direction. So The torque in not in a single direction.So if no commutator in DC motor then no motor action.
Why the brushes are made of carbon and not of copper for a dc machine?
Though carbon is brittle but it's more durable , besides it's pseudo electric characteristics
What are the uses of brushes in a DC motor?
This is an example of spring-loaded brushes for an electric motor.The following figure shows a simplified DC motor with the split-ring commutator and brushes. In this case the stator consists of a single permanent magnet and the rotor has a single coil.The current is supplied to the the coil through brushes slightly pushed against the commutator.When the electric current passes through the coil in the magnetic field produced by the permanent magnet, the magnetic force produces a torque which turns the DC motor. The commutator reverses the current direction after each half revolution to keep the coil turning.
Why is carbon used in the brushes in a DC generator?
The carbon in a “carbon brush” is actually not pure carbon or graphite (a soft form of carbon) but a combination of carbon and copper. The “carbon brush” is also not actually a brush but a block.The combination of copper and carbon allows the “brush” to be low resistance compared to a pure graphite block and relatively softer than a pure copper mesh or brush.The resistance of the carbon brush allows less current inrush during commutation between adjacent segments in the commutator of DC motors compared to a copper brush.The “carbon brush” is also softer than the commutator (for dc motors) or the slip rings (for ac motors/generators). This way, the brush wears easier and more evenly than the commutator or slip ring. This will result to less maintenance issues since the brushes can be easier to replace than the slip rings or commutator bars.
Even if we are providing DC supply to DC motor then why we use commutator?
A DC motor made entirely of either of North or of South as its field poles but not both, if a motor of such kind was allowed to exist, then it could have quite done away with the commutator ! A simple slip-ring would have sufficed instead !! Unfortunately, magnetic monopoles are prohibited by the laws of Nature !Magnetic field poles exist in pairs (Dipole). Magnetic monopoles are forbidden by the classic laws of nature [Ref. Classic Laws of Electromagnetism].Nothing can violate the basic laws of nature. Any such violation if at all it should be discovered would attract the attention of the scientific community.A DC machine is no exception to any of the basic laws. Hence, a North pole in DC motor field is inherently followed by its Southern counterpart.Now having said that, lets visualize the DC machine. An armature conductor that moves past a N-pole at some time, sooner or later comes under the confines of Southern counterpart. That calls for an immediate automatic directional adjustment of its current in order to preserve the direction of motor torque.Such an adjustment sought to automatically reverse current direction in an armature conductor is called alternation or commutation in the context of DC machine.Otherwise in the absence of such commutation, the total torque that machine develops would would be 0 (Tug of war between clockwise and anticlockwise forms of Torque, mutually nullifying each other).The Alternation of Current (AC) inside the confines of the DC machine is serviced by a commutator - A mechanism as simple as possible to achieve the goal.Thus, essentially, the commutator-brush engagement quite conceals its electro-mechanical conversion to AC internally within the machine.Thus, the outside world sees a “DC” machine powered or powering a DC supply !