Friday, June 28, 2013

DC Motors: Explained!


DC Motors: Explained!

(information courtesy: http://electrical-machinery.blogspot.in)
DC Motor / Direct current motor, as the name implies, uses a direct current is not direct / direct-unidirectional. DC motors used on the specific use where required ignition high torque or acceleration of the equipment for the range of speeds wide. Figure 3 shows a DC motor which has three main components :

  • Pole field. Put simply illustrated that the interaction of two magnetic poles will cause the rotation of a DC motor. DC motor has a polar field stationary and the moving dynamo bearing on the space between the polar magnetic field. Simple DC motor has two field poles: a north pole and south pole. Line magnetic energy increases across the openings between the poles from north to south. For engines larger or more complex consists of one or more electromagnets. Electromagnet to receive electricity from outside resources as a provider structure field.
  • Dinamo. If the inflow into the dynamo, then the flow will be an electromagnet. A cylindrical dynamo, connected to the countershaft to drive load. For the case of small DC motors, dynamos in rotating magnetic fields formed by the poles, to the north and south magnetic poles changed its location. If this happens, the current is turned to change the poles of north and south of the dynamo.
  • Commutator. This component is mainly found in DC motors. Usefulness is to reverse the direction of electric current in a dynamo. Commutator is also helpful in transmission flows between the dynamo and resources.

The main advantages are as controller of DC motor speed, which is not affect the quality of power supply. These motors can be controlled by regulating:
  • Dynamo voltage - increasing the voltage will increase the speed of dynamo.
  • Flow field - reducing the field current will increase the speed.
DC motors are available in many sizes, but its use is generally restricted for multiple use of low-speed, low power consumption to moderate such as machine tools and rolling mills, because often there are problems with changing direction mechanical electrical current in a larger size. Also, the motor is limited to only use in areas that are clean and not dangerous because the risk of sparks at the brush. DC motors are also relatively inexpensive compared to AC motors.

Separately Excited DC Motor
If the field current is supplied from a separate source of DC motors it is called a separate power source / separately excited.

Self Excited / shunt motor
In a shunt motor, the field winding (shunt field) are connected in parallel with dynamo coil (A) as shown in figure below. Therefore the total current in line represents the total flow and flow field dynamo.


Following the shunt motor speed :
  • Constant speed in practice did not depend on the load up to a certain torque after its speed is reduced and therefore suitable for commercial uses with low initial costs, such as machine tools.
  • The speed can be controlled by placing prisoners in a series arrangement by dynamo (reduced speed) or by putting detainees in the field current (Velocity increases).







DC Motor power itself: series motor 

In a series motor, the field winding (shunt field) is connected in series with the coil dynamo (A) as shown in figure. Therefore, the flow field with dynamo currents. Following on the series motor speed :
  • The speed is limited to 5000 RPM
  • Must avoided running series motor with no load will cause the motor accelerate uncontrollably.
Series motors are suitable for use in the initial ignition requires torque high, such as crane and hoist lifter .



















DC Motor Compounds / Combined

DC compound motor is a combination of series and shunt motors. In the compound motor, field winding (shunt field) are connected in parallel and in series with coil dynamo as shown in figure . Thus, the compound has a torque motor good start ignition and a stable speed. The higher percentage merger (ie the percentage of field windings are connected in series), the more higher the initial ignition torque that can be handled by this motor.

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