Electrical Systems. Introduction

Transcription

1 Electrical Systems Figure 1. Major Components of the Car s Electrical System Introduction Electricity is used in nearly all systems of the automobile (Figure 1). It is much easier to understand what electricity can do and how to make it do it, than to understand what it is. Electricity is the movement of an energy that is released when electrons move from one atom to another. Getting the electrons to move is the job of the power source. The source of electrical power is the battery or the alternator which supplies electrical power. Wiring connects the power source to and from a device which does some work. Actually it is the flow of electrons (current flow) through the wires and the device (load) that does the work. All electrical circuits can be described by three values: voltage, current, and resistance. NAPA FastTrack Counter Sales Training Electrical Systems Page 1

2 Electrical Terms Voltage is electrical pressure. It is the force that pushes electricity through a circuit. Voltage is often compared to the pressure that pushes water through a hose or pipe. Voltage is measured in volts. The more electrical pressure there is, the higher the voltage. Nearly all electrical systems in a car operate on 12 volts DC (Direct Current). Current is the movement or flow of electricity and is measured in amperes (amps). Current flow is compared to water flowing in a hose. If pressure is always present on one end of the hose, water will continue to flow. Current will flow through an electrical circuit as long as there is voltage applied to one end of the circuit and a ground at the other end. As with water flowing through a hose, current flows from a high pressure to a lower pressure. Resistance is something that restricts current flow. Resistance is measured in ohms. In electrical circuits, resistance is present in all electrical devices, such as lights, motors, and horns. The effect of resistance on an electrical circuit can also be compared to water. If the water pressure stays the same, the flow from the hose will only change if a restriction is added or taken away. If there is a very small amount of resistance, flow will be great. If there is a lot of resistance, the flow will be very low. Power Source In a car, there are two possible sources for electrical energy: the battery or the alternator. A battery (Figure 2) produces electricity through a chemical reaction. The battery has two electrical terminals, one marked positive and the other marked negative, which are connected to the circuit. A circuit is a complete path through which current flows. If a circuit is connected between the battery s two terminals, current will flow through the circuit. The amount of current depends on the resistance in that circuit. As current continues to flow, the battery is being discharged. For this reason, cars are equipped with a charging system that recharges the battery as the engine runs. A battery is simply a storage container for electricity. The battery changes electricity into chemical energy and stores it. When electricity is needed, the battery changes the chemical energy back into electricity. The battery is made of a case which houses positive and negative plates. The positive plates are connected to the positive battery terminal and the negative plates to the negative terminal. The plates are covered by a sulfuric acid solution, called the electrolyte. Electrolyte easily gains or loses electrons. When the battery is being charged, the electrolyte allows the electrons to collect on the negative plates of the battery. When the battery is discharging, the electrons are pulled from the negative plates and moved to the positive plates. When there is an equal number of electrons on the positive plate as there are on the negative plate, the battery is dead. When the chemical properties of the plates or the electrolyte are reduced, the battery will not accept a recharge. In this case, the battery must be replaced. However, if the chemical NAPA FastTrack Counter Sales Training Electrical Systems Page 2

3 properties of the battery are still good, a dead battery can be brought back to life by recharging it. Batteries are replaced quite often, especially in cold weather. They go dead because of some internal problem, an electrical problem somewhere in the car, or because of owner abuse or neglect. Whenever a customer wants a new battery, suggest that the cause of the bad battery be found. Doing this will prevent damage to the new battery and will make the customer happy. Figure 2. The Basic Features and Parts of a NAPA Battery Automotive batteries need care when they are in a car and when they are sitting on a shelf waiting to be bought. Battery stock must be regularly checked and rotated on a first-in, first-out basis. Rely on the factory shipping date code. Always use the oldest battery first to insure good stock rotation. Battery stocks must also be maintained in a fully charged condition. The following are some other tips on maintaining and handling battery stocks: Keep all sparks and flames away from a battery. Batteries create explosive gases. The electrolyte in a battery contains sulfuric acid which can cause blindness or severe burns. If electrolyte happens to get in your eyes, immediately flush your eyes with water and get medical help immediately. NAPA FastTrack Counter Sales Training Electrical Systems Page 3

4 A fully charged 12-volt battery provides 12.6 volts. To maintain this voltage level, the battery may need periodic charging. Batteries must be stored in a cool, dry place out of direct sunlight. Always leave the vent caps in place except when inspecting the electrolyte level. If you are charging a battery, make sure the immediate area is well ventilated. Spiral Construction of Orbital/Optima Battery The Optima battery from NAPA (Figure 3) is a major breakthrough in battery technology. These batteries are very different from other batteries. It looks a bit like a six-pack. The battery plates are spiral-wound to create six tightly-packed cylindrical cells. This increases the active surface area of each cell for more power, and makes the cells much more resistant to vibration damage than conventional batteries. The cells also contain a gel type electrolyte that is absorbed in glass mat separators. These separators absorb the electrolyte acid much like a paper towel absorbs water. Electrolyte contained in these glass mat separators will never leak, even if the battery is cracked or mounted upside down! The Optima battery has more starting power, recharges faster, and maintains a charge much longer than any conventional battery. They also contain a dual terminal design so they can be used with top mounting or side mounting cables, and even come equipped with a fold-away handle for easier installation. Although slightly more expensive than top-of-the-line conventional batteries, they are ideal for vehicles that have high power electrical accessories (amplifiers, DVD s, hydraulic pumps, etc.) or for vehicles that spend a lot of time in storage. Figure 3. Orbital Battery NAPA FastTrack Counter Sales Training Electrical Systems Page 4

5 Electromagnetic Induction Another way to produce electricity is through a process called electromagnetic induction. Voltage can be induced in a wire if it is passed quickly through the field of a magnet. If the wire is connected to a circuit, current will flow. This process is used to charge the battery. The alternator (Figure 4) has a rotating magnet (rotor) whose field passes through several coils of wire (stator). Voltage is induced in these coils of wire. The electricity induced in the coils is alternating current (AC). AC flows in one direction, then changes to the other direction. AC is the same current found in homes and buildings. Figure 4. An Exploded View of an Alternator Most of the car s electrical system uses direct current (DC). Direct current always flows in one direction. Since AC is produced in the alternator, the AC must be changed to DC in order to be used by the car s electrical system. Also, only DC can be stored by a battery. An alternator is equipped with a set of diodes, called a rectifier. The rectifier changes AC to DC as the voltage leaves the alternator. Electrical Circuits A circuit is the path electricity follows from the power source to the load and back to the power source. Materials that allow electricity to easily flow through them are called conductors. Copper wire is the most commonly used conductor in a car. NAPA FastTrack Counter Sales Training Electrical Systems Page 5

6 The conductors must not contact other conductors. If they did, there would not be a fixed path for current. To contain the current in a conductor, conductors are covered with a material called an insulator. Commonly used insulation materials are rubber, nylon, plastic, and glass. An electrical circuit must have four things: a power source, conductors, a load, and a return path (commonly called the circuit s ground) to the battery. Wire size is referred to as gauge. Heavy gauge (00 to 8 gauge) wires have a large diameter. Higher gauge (10 and higher) wires have smaller diameters. Whenever wires are used in high-amperage circuits, heavier gauge wiring is used. Because the starter circuit requires very high amperage, the wires used in the circuit are large. The heaviest gauge wires are the battery cables. The negative cable is connected from the battery directly to the engine. The positive cable connects the battery to the starter relay, solenoid, and/or starter motor, and also feeds the rest of the electrical system. Starting System Engines need a way to start them turning. This allows the combustion process to begin so the engine can run on its own. The system that does this is the starting system. The starting system changes electricity, from the battery, into a mechanical motion. This motion rotates the engine and allows it to start. The starting system includes: the battery, cables and wires, a starter safety switch, a starter relay and/or solenoid, and a starter motor (Figure 5). Starter safety switches are installed between the ignition switch and the starter relay or solenoid. These switches prevent the engine from starting while the transmission is in gear. NAPA FastTrack Counter Sales Training Electrical Systems Page 6

7 Figure 5. The Major Components of a Starting System If the car has an automatic transmission, the starter safety switch is called a neutral safety switch. This type of switch only allows the engine to start when the transmission is in neutral or park. Many manual transmission cars have a clutch switch. The clutch pedal must be depressed before current flows to the starter motor. The starter system has two circuits. The control circuit which contains the ignition switch, high gauge (small) wiring, starter safety switch, and solenoid or starter relay. The starter motor circuit is made up of the starter relay and/or solenoid, heavy gauge (large) wiring, the battery, and the starter motor. Most often the starter parts that are replaced belong to the starter motor circuit. The reason is simply that this system operates with very high amperage. The starter relay, which is sometimes called a starter solenoid (Figure 6), is an electromagnetic switch. It supplies full battery power to the starter motor, when the ignition switch is in the start position. The relay allows the high amperage circuit to be controlled by a low-amperage circuit. (The starter control circuit controls the starter motor circuit.) The car s ignition switch is designed to handle only low amperage. Therefore the ignition switch directly controls the starter control circuit, and indirectly controls the starter motor circuit. The ignition switch also provides power to many other electrical circuits. The position of the switch determines which circuits have power. The typical ignition switch positions are accessory, off, run, and start. NAPA FastTrack Counter Sales Training Electrical Systems Page 7

8 Figure 6. Typical Starter Relay A solenoid (Figure 7) is an electromagnetic device that changes electrical energy into mechanical movement. It contains a coil of wire that surrounds a bar of small metal. The bar is able to move in and out of the coil. When current flows through the coil, a magnetic field is created. This pulls the steel bar into the coil. The movement of the bar causes the movement of whatever is attached to it. In a starting system, the bar is connected to the starter drive gear. As the bar moves, it pushes the starter drive gear toward the engine s flywheel. When the starter motor rotates, the flywheel turns with the drive gear. NAPA FastTrack Counter Sales Training Electrical Systems Page 8

9 Figure 7. A Starter Solenoid Mounted on a Starter Motor Most often, starting systems have a starter relay or a solenoid. Both are controlled by the ignition switch and complete the circuit between the battery and the starter motor. On engines that only use a starter relay, the starter drive gear engages the flywheel when the starter motor is activated. Solenoids complete the starter motor circuit and push out the starter drive gear. The starter motor is located at the rear of the engine. It is positioned so that its drive gear can mesh with the gear on the engine s flywheel. When the starter motor is activated, the motion of the motor causes the engine to turn over. When the starter motor is not activated, its starter gear is pulled away from the flywheel. This totally disengages the starter motor from the flywheel. If the starter drive gear is damaged, the gear on the flywheel should also be checked for damage. If damaged, the flywheel should be replaced or, on some models, a ring gear can be installed on the flywheel. The solenoid and starter drive gear are replaceable on most starter motors. However, the normal practice is to replace the entire starter motor assembly when there is a problem. NAPA FastTrack Counter Sales Training Electrical Systems Page 9

10 Charging System A car needs a charging system because the battery would totally discharge if it were the only source of electrical power. Whenever the engine is running, the charging system recharges the battery and serves as the power for the car s electrical system. Common system voltage is between 13.8 volts and 14.5 volts. The charging system includes the battery, alternator, voltage regulator, and a charge indicator. Common types of charge indicators are warning lights, ammeters, and voltmeters. A warning light comes on when the alternator is not producing enough voltage. The ammeter shows the amount of charge the battery is receiving in amps. The voltmeter shows the charging voltage. The alternator is driven by the engine with a belt. It produces voltage as the magnet (the rotor) rotates inside many coils of wire (the stator assembly). As the rotor spins inside the stator, AC is induced in the stator. The change from AC to DC is done by the rectifier. The output of the alternator is a steady flow of DC current. The rotor is an electromagnet. Power from the battery is used to create the magnetic field. The strength of the magnetic field affects the output of the alternator. By controlling the electricity that flows through the rotor, the output of the alternator can also be controlled. The rotor is turned by the engine s crankshaft through a drive belt. The tension of this belt is important to the life of the alternator as well as its output. If the belt tension is too loose, the belt will slip on the alternator s pulley and will not rotate the rotor at the correct speed. If the belt tension is too tight, the bearings on which the rotor rotates will wear prematurely. Always remind your customers to replace the alternator belt when replacing the alternator and to tighten it to the correct tension. The best way to check belt tension is with a NAPA belt tension gauge. The voltage regulator controls the current to the rotor. Therefore, the voltage regulator controls the output of the alternator. It is important that alternator output be controlled because too much output could ruin a battery and/or burn up electrical components. The voltage regulator is set so that it provides enough alternator output to charge the battery and power the car s accessories. When this unit fails, either the battery is destroyed or the alternator will have no output. The voltage regulator is either external to the alternator or built into the alternator. They can be replaced as a unit on nearly all alternators. Sometimes because of the work involved with disassembling the alternator, a complete alternator with regulator is installed. The output of an alternator also depends on its design and condition. One of the most difficult parts about finding the correct replacement alternator is finding out what the output of it should be. Your catalog gives you guidance in this task. If an alternator is not capable of meeting the electrical needs of the vehicle, it will soon burn out. Alternators operate under high heat. In fact the harder they work, the more heat they generate. Remember to tell your customers they can save money by replacing their bad alternator with a good remanufactured alternator. NAPA FastTrack Counter Sales Training Electrical Systems Page 10

11 Other Electrical Circuits There are other electrical circuits that are not controlled by the headlight or ignition switches. These circuits are controlled by separate switches. These circuits include instruments and gauges, power windows, power door locks, the radio, emergency flashers, and the horn. Most of these circuits have individual parts that can be replaced. The most common part replaced is the turn signal and/or emergency flasher. Although there are few flasher designs, it is important that the customer receive the correct one for the system. Each gauge circuit has a sensing unit connected to the gauge. The sensing unit sends an electrical signal to the gauge. This signal controls the reading on the gauge so that the driver knows the condition of whatever is being displayed by the gauge, such as fuel level, oil pressure, etc. Gauges are also used to display vehicle speed (speedometer), engine speed (tachometer), and time (clock). The gauges can be either analog (have a moving needle), digital (displaying numbers), or both. Circuit Protection Electrical systems occasionally develop a problem in which too much current flows through the circuit. This excessive current can burn up wires and/or the components in the circuit. The name given to the type of electrical problem that causes an increase in current flow is a short. To protect the electrical circuits from these overloads, some sort of circuit protection device is used. The common circuit protection devices are fuses, fusible links, and circuit breakers. A fuse contains a strip of metal that easily melts when it is hot. This metal strip is held in a glass or plastic container. The fuse assembly is placed into the circuit it is protecting. When excessive current flows through the circuit, the metal strip in the fuse melts and opens the circuit. This stops the flow of current and prevents the circuit from being damaged. Also, when the fuse blows, none of the parts in the circuit will work. The cause of the increase in current must be found and corrected before a new fuse is installed. Fuses are designated by the amount of current they will carry before they melt. For example, a 30-amp fuse will allow 30 amps to flow through the circuit. As soon as the current increases above that amount, the fuse will blow. A fusible link looks like a normally insulated wire. However, fusible links are designed to melt when there is an increase in circuit current. Like a fuse, they must be replaced after the repair to the circuit is made. A circuit breaker, however, does not need to be replaced after a shorted circuit is repaired. It has a switch that opens from the heat created by the excessive current. Once the current is stopped by the breaker, the switch cools and then closes again. Some circuit breakers do not automatically close the circuit they must be manually reset. This type of circuit breaker has a button that is depressed to reset it. NAPA FastTrack Counter Sales Training Electrical Systems Page 11

12 Key Terms AC alternating current. Amps the unit of measurement for current. Circuit breaker a circuit protection device that has a switch that opens from the heat created by the excessive current. Some circuit breakers do not automatically close the circuit they must be manually reset. Conductor a material that allows electricity to easily flow. Current the movement or flow of electricity. Diodes the primary electronic device inside an alternator s rectifier. These are typically compared to one-way valves and work to change AC to DC as the voltage leaves the alternator. DC direct current. Electricity the movement of an energy that is released when electrons move from one atom to another. Electrolyte a sulfuric acid solution that covers the plates in a battery. Electromagnetic induction producing electricity by passing a wire through a magnetic field. Electrons the parts of an atom that rotate around the nucleus. Fuse a circuit protection device that contains a strip of metal that easily melts when heavy current passes through it. Fusible link a circuit protection device that looks like a normally insulated wire. However, fusible links are designed to melt when there is an increase in circuit current. Gauge the standard measure of wire diameter. Insulator a material that does not allow electricity to flow. Load an electrical device that changes electrical energy into a form of work (movement, light, etc). Ohms the unit of measurement for resistance. Rectifier a set of diodes that changes AC to DC as the voltage leaves the alternator. Resistance something that restricts current flow. Rotor the rotating magnetic field in an alternator. Sensing unit connected to a gauge circuit, it sends an electrical signal to the gauge. Short an electrical problem that causes an increase in circuit current. Solenoid an electromagnetic device that changes electrical energy into mechanical movement. Starter relay an electromagnetic switch that supplies full battery power to the starter motor, when the ignition switch is in the start position. Starter safety switches installed between the ignition switch and the starter relay or solenoid to prevent the engine from starting while the transmission is in gear. NAPA FastTrack Counter Sales Training Electrical Systems Page 12

13 Stator the stationary windings in an alternator. Voltage is induced in these windings. Voltage electrical pressure; the force that pushes electricity through a circuit. Voltage regulator controls the output of the alternator by controlling the current to the rotor. NAPA FastTrack Counter Sales Training Electrical Systems Page 13