1. Electromagnetic Principles

2. Definition Electromagnetic is made up of two words. 1.Electro, which has something to do with electricity and 2.magnetic, which has something do with magnetism.

3. Definition So, electromagnetic principles deal with the relationship between electricity and magnetism, as well as the relationship between magnetism and electricity.

4. There are two electromagnetic principles that we are going to review.

5. The first principle that we want to review states that electrons will flow in a conductor when the conductor MOVES or PASSES through a magnetic field. Principle # 1

6. If it were not for this principle, we would not have ‘electricity’ today. Let’s take a closer look at this principle.

7. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 Magnet Conductor SOUTH NORTH Magnet Passing a conductor between two magnets and the magnetic field causes electrons to flow in the wire. This produces electrical current in the wire. Generating Current

8. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 8 0º90º180º270º360º Positive Negative One cycle Magnet SOUTH NORTH Magnet Conductor Alternating Current

9. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 9 Effective voltage Alternating current starts at 0, reaches a peak, then returns to 0 Peak voltage at 90° (electrical degrees) Effective voltage is.707 times peak voltage

10. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 10 0º90º 180º Effective Voltage Peak Voltage 170 v 120 v 0 v Effective voltage =.707 x Peak voltage.707 x 170 = 120 v Note: Meters measure effective voltage Effective Voltage

11. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 11 0º90º 180º Effective Voltage Peak Voltage 340 v 240 v 0 v Effective voltage =.707 x Peak voltage.707 x 340 = 240 v Note: Meters measure effective voltage Effective Voltage

12. The ‘effective voltage’ is also known as the RMS (Root Mean Square) value or the DC (Direct Current) equivalent.

13. Many years ago, there was only Direct Current. AC was not invented yet. But when it was, what do you think the reference current would be?

14. If you said DC, you would be correct. So, 120v AC will do the same ‘work’ that 120 DC will do.

15. In other words, if you plug a 100w incandescent light bulb into 120v AC, it will glow just as bright as if you plugged it into 120v DC, thus the DC equivalent.

16. For another example, if you wired a 240v AC electric hot water tank to 240v DC, it will heat the water just as quickly. Thus, the DC equivalent.

17. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 17 Generating Alternating Current (AC) Passing a conductor through a magnetic field A generator uses many conductors and a large magnetic field to produce electrical current

18. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 18 Expressing AC with a Sine Wave A sine wave shows how alternating current flows in one direction, then reverses to flow in the opposite direction. A sine wave is a mathematical derivation of the trigonometric function – sine. You do not need to know trig. in order to understand AC though.

19. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 19 0º90º180º270º360º Positive Negative One cycle Magnet SOUTH NORTH Magnet Conductor Sine Wave of Alternating Current

20. © 2005 Refrigeration Training Services - E1#2 AC and DC Current v1.2 20 Cycles and Frequency Cycle: – One complete electrical alternation Frequency – Number of cycles in a second Measurement of frequency: – Hertz (Hz) – Cycles U.S. frequency is 60 hertz, or 60 cycles

21. The second principle that we want to review states that a magnetic field will be produced when electrons flow in a conductor. Principle # 2

22. If it were not for this principle, we would not have motors, relays, contactors, solenoids, timers, etc. Let’s take a closer look at this principle.

23. For the first example, let’s take a look at how electricity produces a magnetic field and is used on a device known as a ‘solenoid valve.’

24. © 2005 Refrigeration Training Services - E1#4 Symbols and Wiring Diagrams v1.2 24 Solenoid Valve Magnetic coil energized Plunger pulled up Fluid flows Fluid stops Power off Plunger drops Plunger Seat

25. For the second example, let’s take a look at how electricity produces a magnetic field and is used on a device known as a ‘contactor.’

26. © 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2 26 Side View L1L2 T1T2 LINE LOAD CONTROL CIRCUIT

27. © 2005 Refrigeration Training Services - E2#3 Contactors and Motor Starters v1.2 27 L1 L2 T1T2 LINE LOAD Power to Contactor Power to Load CONTROL CIRCUIT Contacts pulled in Magnetic Coil energized Side View

28. For the third example, let’s take a look at how electricity produces a magnetic field and is used on a device known as a ‘motor.’

29. © 2005 Refrigeration Training Services - E2#1 Fan Motors v1.2 29 Two-pole stator motor N NS _ + S N S Stator (Stationary) When stator is energized the rotor will make a half turn with each half of current cycle Rotor (Rotates) Polarity reverses (N to S) on stator Stator repels & attracts rotor into motion

30. © 2005 Refrigeration Training Services - E2#1 Fan Motors v1.2 30 Second half of cycle NS + _ N S The alternating current now changes direction N S Polarity reverses (N to S) on stator Stator continues motion by repelling and attracting

31. In conclusion, if it were not for electromagnetic principles, we would be living in the dark ages.