1. DC MOTOR

2. Magnetism Opposites Attract / Likes Repel

3. Magnetic Fields Direction of Field: North  South

4. A Simple Electromagnet A Nail with a Coil of Wire Q – How do we set up a magnet? A – The battery feeds current through the coil of wire. Current in the coil of wire produces a magnetic field (as long as the battery is connected).

5. Right Hand Rule # 1 Electric Currents  Magnetism!

6. Right Hand Rule # 2 Electric Currents  Magnetism!

7. Electromagnetism

8. Right Hand Rule # 3 The Right Hand Rule is used to determine the direction of the force when the direction of the current and the direction of the magnetic field are known.

9. Force Current Magnetic Field Right Hand Rule # 4 Electric Currents & Magnetism  Force

10. Lab 3P. 10Autumn Quarter Force in a Conductor

11. Lab 3P. 11Autumn Quarter Force in a Conductor

12. Simple DC Motor

13. Motor Basics Motors convert electric energy to mechanical motion. Either an AC or DC electrical energy source serves as the input to the motor. Motors are powered by electricity, but rely on principles of magnetism to produce mechanical motion. The result is mechanical motion of the output shaft, that is a rotation about or a translation along the shaft, provided the load carried by the shaft does not exceed the maximum load the motor is designed to carry.

14. Choosing a Motor There are numerous ways to design a motor, thus there are many different types of motors. The type of motor chosen for an application depends on the characteristics needed in that application. These include: ◦ How fast you want the object to move, ◦ The weight, size of the object to be moved, ◦ The cost and size of the motor, ◦ The accuracy of position or speed control needed.

15. Motor Parameters The level of performance a motor can provide is described by its parameters. These include: Rated Speed ◦ Speed measured in shaft revolutions per minute (RPM), a way to specify how fast the motor turns. Torque ◦ Rotational force produced around a given point, due to a force applied at a radius from that point Torque-Speed performance of a motor

16. Types of Motors The different types of motors possess different operating characteristics. ◦ Heavy Industrial applications: AC motors ◦ Mobile robotics & hobby robots: dc motor, dc servo motor, and stepper motors Brief overview of the operation characteristics of: ◦ AC motors ◦ DC motors ◦ DC servo motors ◦ Stepper motors

17. DC Electric Motors Electric Motors or Motors convert electrical energy to mechanical motion Motors are powered by a source of electricity – either AC or DC. DC Electric Motors use Direct Current (DC) sources of electricity: ◦ Batteries ◦ DC Power supply

18. Principle of How Motors Work: Electrical current flowing in a loop of wire will produce a magnetic field across the loop. When this loop is surrounded by the field of another magnet, the loop will turn, producing a force (called torque) that results in mechanical motion.

19. Brushed DC Motor Components

20. 20 DC Machine Construction DC motor stator with poles visible.

21. Lab 3P. 21Autumn Quarter Diagram of a Simple DC Motor

22. How Does an Electric Motor Work?

23. 23 DC Motor Operation In a dc motor, the stator poles are supplied by dc excitation current, which produces a dc magnetic field. The rotor is supplied by dc current through the brushes, commutator and coils. The interaction of the magnetic field and rotor current generates a force that drives the motor

24. DC Motor Operation The magnetic field lines enter into the rotor from the north pole (N) and exit toward the south pole (S). The poles generate a magnetic field that is perpendicular to the current carrying conductors. The interaction between the field and the current produces a Lorentz force, The force is perpendicular to both the magnetic field and conductor ( a) Rotor current flow from segment 1 to 2 (slot a to b) (b) Rotor current flow from segment 2 to 1 (slot b to a)

25. DC Motor Operation The generated force turns the rotor until the coil reaches the neutral point between the poles. At this point, the magnetic field becomes practically zero together with the force. However, inertia drives the motor beyond the neutral zone where the direction of the magnetic field reverses. ( a) Rotor current flow from segment 1 to 2 (slot a to b) (b) Rotor current flow from segment 2 to 1 (slot b to a)

26. To avoid the reversal of the force direction, the commutator changes the current direction, which maintains the counterclockwise rotation.

27. DC Motor Operation Before reaching the neutral zone, the current enters in segment 1 and exits from segment 2, Therefore, current enters the coil end at slot a and exits from slot b during this stage. After passing the neutral zone, the current enters segment 2 and exits from segment 1, ( a) Rotor current flow from segment 1 to 2 (slot a to b) (b) Rotor current flow from segment 2 to 1 (slot b to a)

28. This reverses the current direction through the rotor coil, when the coil passes the neutral zone. The result of this current reversal is the maintenance of the rotation.

29. Lab 3P. 29Autumn Quarter Electric Motor

30. How the Commutator Works As the rotor turns, the commutator terminals also turn and continuously reverse polarity of the current it gets from the stationary brushes attached to the battery.

31. Controlling Motor Direction To change the direction of rotation: – Simply switch the polarity of the battery leads going to the motor (that is, switch the + and – battery leads) +-+- -+-+ Direction of Rotation

32. DC Motor The brush

33. DC Motor

34. Practical DC Motors Every DC motor has six basic parts – axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. For a small motor the magnets is made from permanent magnet

35. DC Motors – Components Field pole North pole and south pole Receive electricity to form magnetic field Armature Cylinder between the poles Electromagnet when current goes through Linked to drive shaft to drive the load Commutator Overturns current direction in armature

36. 2 pole motor Animate

37. 2 pole motor Animate

38. 2 pole motor Animate

39. 2 pole motor Animate

40. 2 pole motor Animate

41. 2 pole motor Animate

42. 2 pole motor Animate

43. 2 pole motor Animate

44. 2 pole motor Animate continue

45. 3 pole DC motors + − The coil for each poles are connected serially. The commutator consist of 3 sector, consequently one coil will be fully energized and the others will be partially energized. 1 3 2

46. 3 pole DC motors animate next The commutator and the coil is arranged in such a way that the polarity of each pole is as shown

47. 3 pole DC motors animate next The commutator and the coil is arranged in such a way that the polarity of each pole is as shown

48. animate next The commutator and the coil is arranged in such a way that the polarity of each pole is as shown 3 pole DC motors

49. animate next 3 pole DC motors The commutator and the coil is arranged in such a way that the polarity of each pole is as shown

50. DC motors As the rotor is rotating, back emf (E a ) will be produced, the faster the rotor turn the higher E a and the smaller I a. The starting current of motors will be much higher then the rating current. motor V EaEa IaIa

51. DC motors For big motors the magnet is made from coil and core. The current flowing in the coil is called I f and the current flowing in the armature is called I a. The armature winding and the field winding are connected to a common power supply Field winding Armature winding

52. The armature winding and the field winding are often connected in series, parallel, or compound. The torque characteristic will be different for each connection. The figure shows a parallel connection

53. SERIES DC MOTOR Field and armature winding are series connected, this type of motor is called series DC motor

54. Shunt DC motors Field and armature winding are parallel connected, this type of motor is called shunt DC motor

55. Compound DC MOTOR Compound DC motor is DC motor having 2 field winding the first one is connected parallel to the armature winding and the other is connected series

56. DC MOTOR Torque: T = KΦIa – K is a constant – Φ magnetic flux – I a is armature current Magnetic flux is constant if it is from permanent magnet It is depend on the I f if it is produced by current

57. Starting a DC Motor If we apply full voltage to a stationary motor, the starting current in the armature will be very high (20- 30 times the nominal load current) and we run the risk of: – Burning out the armature – Damaging the commutator and brushes, due to heavy sparking – Overloading the supply – Breaking the shaft due to mechanical shock – Damaging the driven equipment due to the sudden torque surge

58. All DC motors must therefore be provided with a means to limit the starting current to reasonable values

59. Stopping a DC Motor There are three ways to brake a DC motor: Mechanical (friction) braking Dynamic braking Plugging

60. Merits High starting torque Speed control over a wide range,both above and below normal speed Accurate seedless speed control Quick starting and stopping

61. Demerits High initial cost Increased operating and maintenance costs because of commutator and brush gear

62. Applications Lathes, Drills, Boring Mills, Shapers, Spinning and Weaving Machines. Elevators, air compressors, vacuum cleaners, hair drier Sewing machines, Presses