1. Introduction To Electricity  To understand electricity properly we must start by finding out what it really is. This means we must use our imagination and think of very small partials that we cannot see just using our eye's.  The molecule is the smallest part of matter (the stuff that the universe is made up from) that can be recognised as matter, however, if we look inside a molecule, we can see it is made up of atoms.  The atom consists of a central nucleus, which it self is made up of protons and neutrons. The neutrons has an equal positive and negative charge and is therefore neutral. The protons are positively charged, this means the nucleus contains a positive charge. Around the nucleus orbit electrons, likes planets around the sun. The electrons are negatively charged and are held in orbit around the nucleus by the attraction of the positively charged protons.  The atoms of some materials have electrons which are easily detached from their atom, these electrons move on to the next atom, in doing so they move electrons from this atom to another (like polarities repel) and so on through the material. These are called ‘free electrons’ and their movement forms the basics of electricity, this movement is referred to as current flow.

2. Introduction To Electricity  Electron flow – we need to apply some of electrical pressure to make the electrons move through the conductor, this may be in the form of a battery or generator.  The unit of electrical pressure (electromotive force) is called ‘Voltage’. In order for electrons to flow their must be a pressure source e.g. a battery and a complete circuit i.e. the conductors (wires).  The number/rate of electrons flowing in the circuit is referred to as the ‘current flow’ and this will depend upon the electrical pressure applied and any resistance opposing or trying to stop the electrons moving.  The measurement of the number/rate of electrons/current flowing is referred to as the Ampere.  Any opposing force which tries to stop the movement of the electrons is referred to as ‘Resistance’  The unit of electrical resistance is referred to as the ‘ Ohm ’  When voltage causes current to flow, it has the ability to do useful work. The unit in which we measure this work (power) is called the ‘Watt’

3. Basic Electrical Circuits  All materials are conductors, some are better than others. Silver, copper and aluminium are among the best. Liquids which will allow current flow are called electrolytes.  Insulators are generally non-metallic and include rubber, porcelain, glass, plastic,cotton,silk,wax,paper and some liquids.  Some materials can act as an insulator or a conductor depending upon its condition. They are referred to as semi conductors and are used to make transistors and diodes.  The amount of resistance offered by a conductor depends upon the following.  Length – the greater the length the greater the resistance.  Cross sectional area (how thick it is) – the larger the area the smaller the resistance.  The material – the resistance of a material depends upon what it is made from.  Temperature – most metals increase their resistance as their temperature increases.

4. Current And Voltage Current is measured in amperes (A), often shortened to ‘amps’. By applying a force, these outer ‘free’ electrons can be made to move. This force, the Electro-Motive Force (EMF), is also known as potential difference or voltage and is measured in volts (V). All matter is made up of atoms that consist of a nucleus around which orbits negatively charged electrons. In electrical conductors, the outer electrons can easily escape from their orbits and move to other atoms. This flow of electrons is called the electrical current, which is a measurement of the rate of flow of charge past a fixed point. Next >

5. Nature of Resistance When a current flows through a conductor, the moving electrons collide with the atoms within the material. This restricts the movement of the electrons, which in turn limits the flow of current. Limiting the flow of current in a circuit is an important part of all electrical circuits. The effect of restricting the current in this way, is called Resistance. A resistor is a component that is used to specifically limit the flow of current in a circuit. Next >

6. Nature of Resistance The effect that resistance has on the flow of current can be compared with the flow of water through a pipe. A high resistance is like a pipe with a narrow diameter. The pipe restricts the flow of water, only allowing a small amount through at a time. A low resistance is like a pipe with a very large diameter. There will be very little opposition to the water flowing through it. Next >

7. Ohm’s Law Mathematically, this can be written as: The unit of resistance is the ohm, symbol , named after the scientist who first discovered the relationship between voltage, current and resistance. Ohm’s law states that the ratio of voltage to current is a constant, provided that all physical conditions do not change. This constant is called resistance. If two of the three variables are known, the equation for Ohm’s Law can be rearranged to find the unknown third variable. The equation can be written in a triangular pattern. If any variable is covered, the formula that is left can be used to calculate the covered variable. Next >

9. Direction of Current - Polarity We now know that electrons are negatively charged and are repelled by the negative EMF terminal and attracted to the positive terminal. This is called Electron Current Flow. Early scientists assumed that current flowed from the positive EMF terminal to the negative terminal. This is known as Conventional Current Flow, as it was the convention originally used for the flow of current. When current only flows in one direction, it is known as Direct Current (DC), irrespective of convention used. Next >

10. Battery Switch Lamp Basic DC Circuit A basic DC circuit is shown to the right. It contains a battery, a switch, a lamp and wiring to connect the items together. When the switch is closed, DC voltage from the battery appears across the lamp and current flows around the circuit - the lamp comes on, and stays on, until the switch is opened. In this assignment, you will learn about the terminology used to describe the operation of a basic DC circuit. Next >

11. Circuit Interpretation If a second identical lamp is connected in series, the potential difference across each lamp will be approximately 6V. The voltage developed across the lamp is known as the potential difference. In this case it is 12V. The current flowing in the circuit is represented by an arrow. The arrow is pointing away from the positive battery terminal, representing conventional current flow. Next > A battery can be connected to a lamp to make a basic DC circuit. The total voltage across both lamps is approximately equal to the EMF of the battery.

12. Battery Symbol This is the circuit symbol for a 12V battery. Each pair of long and short lines represents a cell. Next > The top long line represents the positive battery terminal. The 12V battery symbol may also be drawn like this: The bottom short line represents the negative battery terminal. + - 6 cells 12V

13. Basic Electrical Circuits  Series Circuits – when resistors e.g. bulbs, motors etc are connected so there is only one path for the current to flow through each resistor, they are connected in series.  The valve of the current flow is same in all parts of the circuit.  The voltage in the circuit varies depending upon the valve of the individual resistors, however, these different valves must add up to the supply voltage.  The total resistance of the circuit equals the sum of all the individual resistances added together.

14. Basic Electrical Circuits  Parallel Circuits – when resistors are connected so they provide more than one path for the current to flow through, they are connected in parallel.  The voltage applied to each resistor is the same.  The current flowing through the circuit varies and depends upon the valve of the individual resistor in that part of the circuit. The valve of the current flow in each branch of the circuit must add up to the total current flow.  The total resistance of the circuit is the sum of the reciprocal (one divided by the resistance), of the individual resistors

15. The Battery – Converts Chemical Energy Into Electrical Energy. Electrical systems require electrical power to operate A large amount of battery power is required to start an engine. Battery provides electrical power when engine is stationary. Alternator provides electrical power when the engine is running. Electrical energy is converted Into mechanical energy. Starter motor Alternator Battery Mechanical energy is converted into electrical energy.

16. Batteries - Cell Construction Plates Separators Plate Groups Plates contain grids that hold the active material and provide an electrical path. Insulate the plates from each other, but allow electrolyte to flow freely. Alternate positive and negative plates are grouped together, and connected by straps. Separators Lead straps / connectorsPositive plates Negative plates Grid Next >

17. Batteries - Cells An element contains plate groups connected in parallel and separators, and is commonly known as a cell. Each cell produces about 2V, so 6 cells are required for a 12V battery. Cell (x6) Lead straps Battery terminals Cells are connected in series by lead straps. Straps across end cells are part of the terminals. Next >

18. Batteries - Active Materials Positive plate active material is lead peroxide, and the negative plate active material is porous lead. Electrolyte is made from sulphuric acid and distilled water. Battery plates contain the active materials that react with the electrolyte. Positive plate Negative plate Electrolyte Separator Load Fundamental battery cell Container Next >

19. Batteries - Chemical Action Electrolyte sulphate combines with lead on plates to form lead sulphate. Charging Current flow reverses chemical action. Electrolyte hydrogen combines with positive plate oxygen to form water. Sulphate is forced back into electrolyte and combines with hydrogen, while oxygen returns to the positive plate to form lead peroxide. Discharging Electrolyte chemically reacts with lead plates. Process continues while voltage is applied, until all lead sulphate is converted. Next > A lead Acid car battery can only be recharged by using DC ( direct current) charge by forcing the current flow back through the battery

20. Batteries – Case And Terminals Case is made of polypropylene (plastic) or a hard rubber compound. Ribs at bottom of each cell collect excess material from plates. Dividers help separate cells.

21. The Purpose of the Charging System The charging system can only function when an engine is running. Charges the battery. Supplies electrical power to all electrical systems. The charging system: The Alternator: Uses mechanical energy to produce electricity. Alternator Drive Belt: Drives the alternator from the crankshaft. Battery Warning Lamp: Dashboard mounted lamp to display charging system operation

22. Alternator Components  Brushes – made from soft carbon, the brushes allow a small electric current to pass through the slip rings to the field windings.  Slip rings – copper rings which together with the brushes, allow electric current to pass though the rotating rotor.  Rotor and winding – the cast iron rotor contains the windings and is an electro magnet, creating a magnetic field.  Pulley – this transfers the drive to the alternator rotor shaft, it is usually driven by a vee or poly vee belt via the engine.  Stator – this has electricity (AC) induced into its windings by the rotating magnet field of the rotor. It normally contains three windings.  Rectifier (Diodes) – the (AC) output of the alternator must be converted to (DC) for use in the vehicles electrical systems and for battery charging. This is carried out by Diodes (one way electrical valves).  Regulator – controls the electrical output of the alternator.  Battery warning light – part of the rotor electrical circuit to show if the alternator is working.  Cooling fan – cools the alternator

23. The rotor: A rotating field winding that creates a magnetic field The Alternator (Internal View) The diagram shows the components found in a typical alternator. They are: Brush box and regulator Cooling fans Drive pulley Rotor End cover Rectifier assembly Stator Slip ring end housing Retainer nut Casing retainer bolts The stator: A stationary winding which the rotor’s magnetic field cuts across inducing a electrical current in it. Rectifier assembly: A diode rectifier bridge.This changes AC current to DC current. Brush box and voltage regulator: Controls the alternator output. Cooling fans: Provide air circulation. 23 of 20

24. Field winding Slip rings Brushes Main shaft Iron, claw-shaped, finger pole pieces Alternator Components - The Rotor 24 of 20 A typical rotor consists of an iron core, a field winding, two slip rings, and two claw-shaped finger pole pieces. The field winding is wound over an iron core, which is part of the shaft. The claw-type finger poles surround the field winding. Each end of the field winding is attached to a slip ring, which picks up voltage via a brush. The rotor assembly is supported at each end by bearings.

25. Stator windings Curved flux lines Rotor Magnetic Field When voltage is applied to the field winding, it creates a magnetic field that induces voltage into the stator windings. The closeness of the poles, which concentrates the flux lines. They bow outward, into the windings of the stator. 25 of 20 Magnetic field strength is due to: The magnetic field saturates the iron finger poles, one pole becomes a north pole and the other a south pole. The spinning rotor creates alternating north south magnetic fields. The amount of field current flowing.

26. Stator 3 outputs Enamel copper wire windings Soft iron lamination Alternator Components - The Stator The stator is constructed with three sets of windings. They are positioned around a frame of soft iron laminations. The interlaced windings are cut by the magnetic flux of the rotor as it turns. The output leads of the stator connect to a diode rectifier bridge, in either a wye or delta formation. This produces AC voltages in the stator winding that are 120° apart. Output voltage depends upon rotor speed and magnetic field strength. 26 of 20

27. Magnetic field Winding Rotor Single Phase Voltage Induction 27 of 20 Maximum voltage is induced when the winding is cut by maximum flux. The top diagram shows a magnet and a single winding. As magnetic field direction changes, the polarity of the induced voltage is reversed. As the magnet rotates, it induces a voltage in the winding. This occurs when the magnet is at 90° to the winding. The bottom diagram shows the corresponding relationship between the rotor and a single stator winding. + - 0

28. Remember that the stator has three sets of windings. They are physically spaced to provide three sinewave voltages that are 120° apart. 28 of 20 The voltages are added together to produce a stable three phase output, which is converted to DC. Three Phase Voltage Induction As the magnet rotates, it induces voltages in all three windings. The windings are connected to a rectifier circuit, using either a Star or Delta configuration. StarDelta 0180360 + 0 -

29. Output Diode AC voltage Battery emf + - Output AC voltage D1 D4 D2 D3 Battery emf + - Diodes are check valves. They allow current to flow in only one direction. 29 of 20 Rectification If four diodes are used, current can flow during both positive and negative parts of the AC voltage, producing a totally positive output, with no missing cycles. A diode conducts when a forward voltage is applied to the anode. In the circuit shown, this is when the positive part of the AC voltage appears at the anode. AnodeCathode +-

30. ‘B’ terminal Negative diodes Stator terminals Positive diodes The Rectifier Bridge converts 3 phase voltage into DC voltage. 30 of 20 Alternator Components - The Rectifier Bridge Six or eight diodes are used in the conversion process. Half of the diodes are use on the positive side of the bridge and half are used on the negative side. The diodes are mounted on a heat sink.

31. Three Phase Rectification Two diodes are connected to each stator lead for full wave rectification. The conversion process creates 3 positive voltages, which are added together to form a DC voltage, with ripple. Stator output 31 of 20 Rectifier output

32. Rotor Field Excitation The rotor requires voltage to produce a magnetic field. This is provided by the battery, until the engine is running. Engine stopped, ignition switch set to on, the battery is connected to the rotor, via the charge warning lamp. The lamp is illuminated and current flows through the rotor field winding. Engine running, alternator speed increases, voltage output also increases. When alternator voltage rises above battery voltage, the lamp goes out, indicating that charging is taking place, current is flowing through the rotor. Self excitation circuit

33. 33 of 20 Alternator Components - Voltage Regulator The voltage supply to the field winding of the rotor must be regulated to maintain alternator output at a specified voltage level. The voltage regulator senses the alternator's output and changes field winding current to maintain the proper voltage level. When output voltage is too low, the regulator increases field current, (strengthening the magnetic field), resulting in output voltage increase. When output voltage is too high, the regulator decreases field current, (weakening the magnetic field), resulting in output voltage decrease.

34. Starting System The layout below shows how the components in the starting system are connected. The purpose of the starting system is to rotate the crankshaft quickly enough to start the engine. Next > The engine The battery The starter solenoid The starter motor The starting system includes: Battery Solenoid Starter motor Flywheel of engine

35. Terminology Solenoid – A winding which is magnetised when electricity is supplied. Engaging mechanism – (Pre – engage), the magnetism attracts the plunger, which levers the pinion into mesh with the ring gear on the engine flywheel. When the solenoid is switched off, a spring moves the pinion out of mesh with the flywheel. Main contacts – when the pinion is fully in mesh, these strong copper contacts close to make a good electrical connection from the battery to the main starter terminal and the brushes. Brushes – the copper carbon mix brushes pass the electricity to the commutator. Commutator - the many segments of the copper commutator pass electricity through the correct winding in the armature. Armature – the armature windings become magnetic and cause the motor to turn because the magnetism of the armature is repelled by the main field magnetism. Fields – the main magnetic field is created by permanent magnets on most motors, but some do use heavy duty windings to create a powerful electro magnet. Pinion – this is a small gear with a ratio of about 10-1 compared to the ring gear, this increases the torque when the pinion is engaged with the flywheel. A one way clutch behind the pinion prevents the engine driving the starter motor.

36. Pre – Engage Starter Motor (the pinion is moved into mesh with the flywheel before the pinion rotates)

37. Inertia Drive Starter Motor

39. Simple Relay Components Windings Soft iron core 1 3 Moving contact (Armature) Fixed contact 2 4 Return spring Relay switches high currents, but are controlled (turned off and on) by small current flow. Windings wrapped around iron core to form electromagnet. Construction Contains fixed and moving contacts. Spring ‘returns’ moving contact to ‘home’ position. Next >

40. The Basic Bulb Filament Support 1 Support 2 Centre contact Cap Glass Bulb uses electrical current to produce light. Filament held in position by supports. One support connects to centre contact. One support connects to cap. Air removed to reduce heat loss, oxidation and vaporization. Next >

41. Bulb Types Small bayonet cap, single contact type. Small bayonet cap, twin contact type. Used in side, rear, license plate, fog and indicator lights. Used in combined brake and rear lamps. Xenon HID bulbs, used in headlights. Produce more light than halogen bulbs and use less power. Next >

42. Bulb Types Quartz halogen type. Shields allow bulb to produce required beam patterns. Quartz used instead of glass, due to strength and high temperature properties. Used in headlights, spot, driving and fog lights. Interior is pressurized to reduce burning away of filaments. Halogen bulb Main filament Dip filament End shield Shield Voltage terminals Metal flange with lugs Lugs on metal flange ensure bulb is fitted correctly. Quartz Next >

43. Basic Headlight Beam Patterns Parabolic reflector Filament at focal point Parallel beam Bulb Shape of reflector determines beam pattern. Parallel beam produced by positioning filament at focal point. Ideal design for spot lights. Next >

44. Basic Headlight Beam Patterns Filament above focal point Dip beam Parabolic reflector Bulb Dip beam produced by positioning filament above focal point. Side beam produced by positioning filament to one side of reflector. Next >

45. The Lens A lens optically distributes the beam pattern and protects the reflector and the bulb. Generally, modern lenses are made from plastic. Prisms on the inner surface bend light to achieve the required beam pattern. Next >