In the last chapter, the generator was described as a device used to change MECHANICAL ENERGY into electricity. In this chapter, the motor is described as a mechanism that changes the ELECTRICITY back into MECHANICAL ENERGY. Radiomen do not have many contacts with motors, other than by pressing a button to start or stop them. But every man in the radio rates should know and understand the principles of electric motors.
The MOTOR-GENERATOR sets that power the large transmitters use an ELECTRIC MOTOR to drive one or two GENERATORS, depending upon the model of transmitter. The motors take their power from the 110-, 220-, or 440- volt ship's supply, and the GENERATOR delivers several voltages-both a.c. and d.c.-to the transmitter.
Your ship's real source of power is the oil in the tanks.
|Figure 5.-Action of a conductor in a magnetic field.|
|The ACTION of a motor is based upon the old, familiar law-UNLIKE POLES ATTRACT, and LIKE POLES REPEL.To review the laws, look at figure 5. A conductor is hung in a position that will permit it to swing freely either in or out of the horse shoe magnet. Two dry cells are connected to the wire through a double-pole, double-throw switch. The switch is so connected that by throwing the switch from one set of contacts to the other the current through the conductor is reversed.Closing the switch in one direction causes the CONDUCTOR to move INTO the magnet. And throwing the switch in the opposite direction causes the conductor to move OUT.|
|The conductor's movement is caused by the COMBINED ACTION of TWO MAGNETIC FIELDS-the field around the conductor and the field of the horse shoe magnet.|
|Figure 6.-Motor action.|
|In the bottom drawing of figure 6A, The conductor's field and the flux of the field coil combine to CANCEL each other at the BOTTOM and ADD to each other at the TOP. This leaves a GREATER FORCE tending to move the conductor DOWN than up-and the conductor will move DOWN.In figure 6B, The current is flowing in the opposite direction, and the effect of the field is reversed. The two fields CANCEL ON TOP and ADD on the bottom, so the conductor moves UP.|
|The action of a conductor in a magnetic field is known by many different names, but the term "motor action" is as good as any.PARTS OF D.C. MOTORThe essential parts of a d.c. motor are similar to those of a generator. Look at figure 7. The four main parts are-STATOR, ARMATURE, COMMUTATOR, and BRUSHES. A battery attached to the brushes provides the energy to drive the motor.The differences between a d.c. motor and a generator are usually only in the manner of mounting the brushes and connecting the windings. Actually, some d.c. motors may be used as d.c. generators without any change at all.|
|Figure 7.-Parts of an electric motor.|
|segment to the other, and the direction of the current in the loop will be reversed. The black leg will now move UP and the white leg DOWN.|
MAGNETS. MAGNETISM. | Find the equivalents of following word combinations. | Read and translate the text. | Complete the sentences with given words. | Gerund constructions. | Ïåðåâåä³òü íà àíãë³éñüêó ìîâó. | Ïîâòîðåííÿ ãåðóíä³ÿ ³ ãåðóíä³àëüíèõ îáîðîò³â | Unit 4. | Brushes and brush rigging | Answer the questions. |