How to Work Motor

How to Work Motor

You can find DC motors in many portable home appliances Automobiles and types of industrial equipment In this site, we will logically understand the operation and construction of commercials DC motors Let, first start with the simplest DC motor possible looks like this. The stator provides a constant magnetic field and the armature, which is the rotating part, is a simple coil armature is connected to a DC power source through a pair of commutator rings when the current flows through the coil, an electromagnetic force is induced on it according to the Lorentz law the coil will start to rotate. notice that as the coil rotates, the commutator rings connected with the power source of opposite polarityAs it result on the left side of the coil the electricity will always flow "away"And on the right side electricity will always flow "towards"This ensures that the torque action is also in the same direction throughout the motionSo the coil will continue rotatingBut, if you observe the torque action on the coil closely wil notice that when the coil is nearly perpendicular to the magnetic fluxthe torque action nears zeroAs a result there will be irregular motion of the rotorif you run such a DC motorHere is the trick to overcome this problem:Add one more loop to the rotor, with a separate comutator pair for itIn this arrangement when the first loop is in the vertical positionthe second loop will be connected to the power source, so the motor force is always present in the systemMoreover , the more such loops, the smoother will be the motor rotationIn a practical motor the armature loops are fitted inside slots with highly permeable steel layersThis will enhance magnetic flux interactionSpring loaded comutator brushes help to mantain contact with the power sourceA permanent magnetic stator pole is used only for very small DC motorsMost often, an electromagnetic is usedThe field coil of the electromagnetic is powered from the the same DC sourceThe field coils can be connected to the rotor windings in two different waysParallel or seriesThe result is two differents kinds of DC motor constructionsa shunt and a series motorsThe series wound motor has good starting torque, but speed drops drastically with the loadThe shunt motor has a low starting torque but it is able to run almost at a constant speedIrrespective of the load acting on the motorUnlike the other electrical machines, DC motors exhibits a unique characteristic:The production of BACK EMFA rotating loop in a magnetic field will produce an EMF according to the principle of the electic magnetic inductionThe case of the rotating armature loops is also the sameAn internal EMF will be induced that opposes to the applied input voltageThe BACK EMF reduces armature current by a large amountBACK EMF is proportional to the speed of the rotorAt the starting of the motor BACK EMF is too low, thus the armature current becomes too highleading to the burnout of the rotorThus a proper starting mecanism that controls the applied input voltage is necessary in large DC motorsOne of the interesting variation of the DC motor is a universal motorwhich is capable to run under both AC and DC power sourcesTo know more about it, please check the next post.
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