Electronic Systems Module 14
Acknowledgements General Motors, the IAGMASEP Association Board of Directors, and Raytheon Professional Services, GM's training partner for GM's Service Technical College wish to thank all of the people who contributed to the GM ASEP/BSEP curriculum development project 2002-3. This project would not have been possible without the tireless efforts of many people. We acknowledge: The IAGMASEP Association members for agreeing to tackle this large project to create the curriculum for the GM ASEP/BSEP schools. The IAGMASEP Curriculum team for leading the members to a single vision and implementation. Direct contributors within Raytheon Professional Services for their support of translating a good idea into reality. Specifically, we thank: Chris Mason and Vince Williams, for their leadership, guidance, and support. Media and Graphics department under Mary McClain and in particular, Cheryl Squicciarini, Diana Pajewski, Lesley McCowey, Jeremy Pawelek, & Nancy DeSantis. For his help on the Electrical curriculum volume, Subject Matter Expert, Ken Beish, Jr., for his wealth of knowledge. Finally, we wish to recognize the individual instructors and staffs of the GM ASEP/BSEP Colleges for their contribution for reformatting existing General Motors training material, adding critical technical content and the sharing of their expertise in the GM product. Separate committees worked on each of the eight curriculum areas. For the work on this volume, we thank the members of the Electrical committee: Jack Davis, Community College of Baltimore County - Catonsville Jim Halderman, Sinclair Community College Megan Kuehm, Community College of Allegheny County Frank Longbottom, Camden County College Jeff Rehkopf, Florida Community College at Jacksonville Randy Peters, Des Moines Area Community College David Rodriguez, College of Southern Idaho Ed Schauffler, Longview Community College Vince Williams, Raytheon
Contents Module 14 Acknowledgements... 2 Introduction... 4 Objectives... 4 The Charging Circuit... 5 The Generator...6 Delcotron Generators...8 Operation of the Delcotron Generator...10 Automotive Application of Magnetic Induction...12 System Voltage...13 Generator Components...15 Rotor... 15 Stator... 17 Diodes and Diode Bridges...19 Voltage Phases...23 Three Phases of Electrical Current...24 Voltage Regulator...25 System Voltage Control...26 Voltage Settings...27 Voltage Regulator Connections...28 Circuitry and Appearance of Voltage Regulators...28 Generator Construction...29 Slip Ring End Frame...30 Drive End Frame...30 Service...30 Exercise 14-1...32 Experiment 14-1...34 Generator Testing Using the J41450-B Tester...34 Generator Load Testing...36 Voltage Drop Test... 36
Introduction After completing this unit, the technician will demonstrate an understanding of Delcotron CS generators. The technician will also demonstrate the skills required to troubleshoot and replace generators. Objectives Understand the theory of charging system operation Understand the construction and components of a typical charging system Understand the application requirements of charging systems Demonstrate successful troubleshooting skills on Delcotron CS charging systems 14-4
The Charging Circuit The charging system consists of the: Battery Generator Voltage regulator The generator supplies electrical power for charging the battery and for operating electrical accessories. The power generated by a generator is alternating current (AC), but the automobile's circuitry requires direct current (DC). Therefore, the generator uses a diode-rectifier to convert the AG to DC. This type of generator is often called an alternator. However, the SAE-approved term is generator. The voltage regulator sets an upper limit on the amount of voltage sent from the generator to the battery and accessories, thus it protects the battery and accessories from being damaged by too much electrical power. The battery, of course, receives the electrical energy from the generator and stores that power for when it is needed to restart the engine or supply power to accessories when the generator can't. 14-5
The Generator The generator is a key component in an automotive charging circuit. While the battery is an electrochemical device, the generator is an electromechanical device, attached to the automotive engine by means of a belt, that converts mechanical power from the engine into electrical energy. Therefore, in an automotive application, the generator: Recharges the battery when needed Supplies electrical power for vehicle operation In order to supply sufficient power to recharge the battery and power the vehicle, the generator must rotate at sufficient speed. Figure 14-1 shows a typical battery, generator, and electrical load configuration. In this illustration, the generator is not operating and the battery is providing all the load current. If this situation were to continue for an extended period of time, the battery would become discharged. Figure 14-1, Battery Supplying Load Current Figure 14-2 shows both the battery and the generator supplying load current. This primarily occurs when the generator is not operating at sufficient speed for the electrical demand. This requires the battery to make up the difference. If this condition were to continue for an extended period, the battery would become discharged. Figure 14-2, Generator and Battery Supplying Load Current 14-6
Figure 14-3 shows the generator is operating at sufficient speed to provide load current at the same time that it recharges the battery. The generator recharges the battery by creating voltage high enough to send current through the battery in the opposite direction as during discharge, as shown in the illustrations by the highlighted arrows near the battery. This reverses the chemical reactions in the battery and restores it to a charged condition. Figure 14-3, Generator Supplying Load Current and Charging Battery Note: At idle, vehicle loads may exceed the low speed output capabilities of the generator, but the battery can supply this shortfall from its reserve capacities for short periods. 14-7
Delcotron Generators CS generators perform to high standards and are lightweight, offering high voltage output per pound. They feature a built-in, solid-state regulator that's available with a range of internal circuitry. The internal circuitry is designed to match the design of specific vehicle electrical systems, including mounting configuration, voltage output level, and regulator configuration. Therefore, while many of the generators in this series are similar in appearance, they are usually not interchangeable. Installing the wrong generator can cause the generator or other electrical components to malfunction. Name Designations Models in the CS series are designated by an alphanumeric code such as CS-121, CS-130, CS-130D, and CS-144, as shown in Figure 14-4. Note: CS stands for. The numbers represent the diameter of the stator frame. The diameter is measured in millimeters and indicates the overall size group for the unit. Each size group is offered with various ampere output levels. The letter, D, on the end of some model designations indicates dual internal fans. These are the most recent CS designs and provide reduced noise levels and a different configuration of components for cooling the generator. 14-8
THROUGH-BOLT Figure 14-4, Delcotron Generators 14-9
Operation of the Delcotron Generator Delcotron generators apply the principles of magnetic induction to automotive electrical systems to supply proper output and regulate voltage during all driving conditions. Principles of Magnetic Induction Voltage is induced when a magnetic field moves across a conductor. Figure 14-5 shows a simple example of this. A bar magnet, with its magnetic field, rotates inside a conductive loop of wire. The rotating magnet is called a rotor, and the stationary conductor is called a stator. First Half of Rotation The bottom half of Figure 14-5 shows what happens as the bar magnet rotates one half turn. The poles change position: N moves directly under the top conductor S moves directly over the bottom conductor The induced voltage then causes current to flow in the opposite direction. The end of the conductor marked: A changes to negative (-) polarity B changes to positive (+) polarity Second Half of Rotation As the bar magnet completes the second half of the rotation, the N pole and the S pole change back to their original position: A becomes positive (+) again B becomes negative (-) again Consequently, current flows in one direction and then in the other, creating alternating current. This alternating current is developed internally in the generator and is the basis for the term, alternator, that is sometimes applied to a generator using this principle. However, the SAE-approved term is generator. 14-10
Figure 14-5, Magnetic Induction 14-11
Automotive Application of Magnetic Induction A bar magnet rotating inside a single loop of wire is not practical for automotive applications because it produces very little voltage and current. However, performance can be improved when both the loop of wire (the stator) and the magnetic bar (the rotor) are placed inside an iron frame, as shown in Figure 14-6. The iron frame not only provides an environment into which the loop of wire can be assembled and contained, but it also acts as an effective conducting path for the magnetic lines of force. The left side of Figure 14-6 shows that, without the iron frame, magnetism leaving the N pole of the rotating bar magnet must travel through air to get to the S pole. Because air has a high reluctance to magnetism, only a few lines of force generated at the N pole will make it to the S pole. On the other hand, since iron easily conducts magnetism, the iron frame greatly increases the number of lines of force between the N pole and the S pole, as shown in the right side of Figure 14-6. This means that more lines of force will be cutting across the conductor between the rotor and the stator. Figure 14-6, Electromagnetic Assembly 14-12
System Voltage Generator voltage increases in three ways: the first two are considered from a design point of view, and the third is used as a method for controlling the generator's voltage while operating on the vehicle. 1. Increase the number of turns, or windings, in the stator. 2. Increase the speed of rotor rotation. 3. Increase the strength of the rotor's magnetic field. Increasing the Number of Stator Windings The first method is to increase the number of windings in the stator. The greater the number of windings the magnetic lines of force cut through, the greater the amperage induced in the windings. Increasing the Rotor Rotation Speed The second method is to increase the rate of rotor rotation. This causes the magnetic lines of force to be cut more frequently. In turn, this causes more voltage to be increased into the stator windings. Rotor speed increases when the automotive engine rpm also increases. A belt connected to the engine's crankshaft drives the generator rotor inside the stator windings. Increasing the Rotor Magnetic Field Strength In contrast to the first and second approach, controlling the rotor's magnetic strength is the most practical tool for controlling the generator's voltage output. This is due to the fact that the strength of the magnetic field will impact the voltage induced. The stronger the field, the greater the induced voltage. The weaker the field, the lower the induced voltage. Replace the rotor's bar magnet with an electromagnet to accomplish the third method. As an electromagnet, the amount of current flowing through the coil of wire, or field, wound around the rotor determines the rotor's magnetic strength. Zero current produces zero voltage. Moderate current produces moderate voltage. Maximum current produces maximum voltage output, or maximum available field strength. 14-13
Maximum field strength can often produce more induced voltage than the electrical system needs at any given moment. A voltage regulator provides a practical method for turning the field current on and off to limit the voltage to an acceptable amount. In Delcotron CS generators, the voltage regulator is built in. A single component contains power generation and regulation. For this reason, a Delcotron CS generator is referred to as a charging system (CS). The generator uses rectifiers to change the AC power into the DC power that the vehicle electrical system requires. Maximum field strength can often produce more induced voltage than the electrical system needs at any given moment. A voltage regulator provides a practical method for turning the field current on and off to limit the voltage to an acceptable amount. In Delcotron CS generators, the voltage regulator is built in. A single component contains power generation and regulation. For this reason, a Delcotron CS generator is referred to as a charging system (CS). The generator uses rectifiers to change the AC power into the DC power that the vehicle electrical system requires. 14-14
Generator Components CS generators have four primary components: Rotor Stator Diodes in a diode bridge Voltage regulator Rotor The rotor is the rotating part of a generator. It consists of: Two pole pieces with interlacing fingers A rotor core of field windings A rotor shaft and core Two copper slip rings Carbon brushes Figure 14-7 shows the two iron pieces with interlacing fingers that serve as N poles and S poles. The fingers are mounted over the field winding, cores and shaft. The core, field winding, and pole pieces are assembled on the rotor shaft. Figure 14-7, Rotor 14-15
Rotor Core Figure 14-8 shows the rotor core and the field windings forming a strong electromagnet. When current flows through the field winding, the fingers of the pole pieces mounted on each side of the core alternate polarity between north and south. Figure 14-8, Rotor Core Rotor Circuit Figure 14-9 shows the wires from the ends of the field winding, which run along the rotor shaft and terminate at copper slip rings on the end of the shaft. These slip rings are insulated from the shaft, and each of the wires connects to only one of the rings. Carbon brushes ride on the slip rings and provide the path for current to the field winding. Figure 14-9, Rotor Circuit 14-16
Stator The stator is the stationary part of the generator. It consists of: Stator frame Stator windings The stator in a CS generator consists of many turns of three wire windings assembled into an iron frame. Figure 14-10 shows that each winding has several separate coils. These are placed in the iron frame so that the magnetic field polarity is the same on each of the coils of a winding at the same time. Because the windings are connected in series, the voltage induced in all of the windings is added together to produce the desired output. Figure 14-10, Complete Stator Assembly 14-17
Stator Windings The rotor spins freely inside the stator frame. As it does, the fingers on the rotor's pole pieces are positioned so that the magnetic fields between alternating N poles and S poles move across the conductors in the stator. Since alternating poles are passing next to the stator coils, the voltage induced in each phase in the stator is the AC voltage. CS generators use either a delta connection or a Y connection in the stator. The delta name comes from the triangular, or delta, shape of the stator's three phases that will be created, as shown in the schematic in the left side of Figure 14-11. A Y connection works in the same basic way as a delta connection. It's schematic is shown in the right side of Figure 14-11. Figure 14-11, Stator Windings 14-18
Diodes and Diode Bridges The previous subsections on rotor and stator covered alternating current (AC) voltage generated by CS generators. In automotive electrical systems for internal combustion engines, conversion of AC to direct current (DC) is required. A series of diodes in a rectifier system, often called a diode bridge, converts AC to DC voltage. Diodes A diode is a device that allows current to flow in only one direction. It is a two-terminal semiconductor device shown in Figure 14-12: Anode, which is positive Cathode, which is negative When positive voltage is connected to the anode and negative voltage is connected to the cathode, current flows through the diode. If the connections are reversed, current does not flow because of the blocking characteristic of the diode. The diode, therefore, acts like a check valve and allows current to flow in only one direction. Figure 14-12, Diode 14-19
Diode Bridge A diode bridge is an arrangement of diodes. Figure 14-13 shows a bridge of four diodes connected to a loop of wire called A-B. As AC voltage is induced in loop A-B, it is converted to DC by the four diodes in the bridge. The diodes: Convert all the AC to DC Allow current to flow in one direction only through the battery Because all of the AC voltage is converted to DC voltage, this diode bridge is referred to as a full-wave rectifier. The graph at the bottom of Figure 14-13 represents the current flow that results in DC output. Figure 14-13, Diode Bridge 14-20
Typical Diodes A generator uses an arrangement of six diodes, as shown in Figure 14-14, to fully rectify the three windings. During operation, the delta arrangement of the stator generates the highest DC voltage output available in the combined stator phases at any given time. The graph in Figure 14-15 shows the resulting DC output from the three phases. A typical CS diode bridge is shown in Figure 14-16. Note the three connections for the stator windings. Function of a Diode Bridge The function of a diode bridge can be best understood by knowing how AC voltage is generated in the stator's conductors, described next. Figure 14-14, Delta Stator and Six-Diode Bridge 14-21
Figure 14-15, Phase Voltage Figure 14-16, Diode Bridge 14-22
Voltage Phases Voltage is created in each winding, or phase, as the rotor completes one revolution at a constant speed. Figure 14-17 shows one revolution in five rotor positions. The first position and the fifth position are identical and represent the beginning and ending of the revolution. The top portion of Figure 14-17 illustrates a voltage curve. The curve diagram shows the magnitude of the voltage generated in the stator. The voltage curve also represents the generated voltage of electrical pressure that can be measured at the generator outputs. Position One In position one: Zero voltage, neither positive nor negative, is generated. The poles on the rotor are perpendicular to the conductor, with the S pole to the left and the N pole to the right. No current is flowing. Position Two As the rotor turns and approaches position two, the weak magnetic field at the leading edge of the rotor begins to cut across the conductor and voltage begins to increase. In position two, the conductor is being cut by the heaviest concentration of magnetic lines of force. Therefore, Voltage is at its maximum positive value. The rotor poles are directly under the conductor, with S above N. The top loop is positive. The bottom loop is negative. Position Three As the rotor turns from position two to three, the voltage begins to decrease. In position three: Voltage returns to zero, neutral, as in position one. The rotor poles are perpendicular to the conductor, as in position one, but in the opposite directions. No current is flowing. 14-23
Position Four As the rotor turns and approaches position four, the weak magnetic field at the leading edge of the rotor begins to cut across the conductor and voltage begins to increase. In position four: Voltage is at its maximum negative value. The rotor poles are directly under the conductor, as in position two, but N is now above S. The top loop is negative. The bottom loop is positive. Position Five Position five repeats position one, thus the voltage curve in Figure 14-17 represents one complete turn, or cycle, of the rotor. Three Phases of Electrical Current As mentioned earlier, CS generators produce three phases of electrical current at one time. Refer back to Figure 14-15 to see how the voltage graph might look for all three phases operating at the same time. In a CS generator, the coils of the three phases overlap to smooth out the generated voltage. Figure 14-17, Rotor Cycle 14-24
Voltage Regulator The CS generator provides adequate voltage at low speeds, such as when an engine idles. However, limiting the generator's maximum voltage output is required when operating the automotive engine at high rpms. The voltage regulator built into the CS generator limits this voltage output. Figure 14-18, Voltage Regulator Limit The chart in Figure 14-18 illustrates that generator voltage increases as generator speed increases until it finally reaches the voltage regulator limit. The need to limit voltage is critical to many vehicular electrical components because unlimited voltage output can damage or shorten the service life of the battery, light bulbs, external wiring, electronic modules, and other electrical or electronic components. The voltage regulator functions by sensing conditions such as: Battery voltage Generator temperature To limit voltage output, the voltage regulator in CS generators controls the current flow in the field winding that affects the magnetic field in the rotor. 14-25
System Voltage Control The regulator switches the field voltage on and off at a fixed frequency of about 400 cycles per second. Voltage control is obtained by varying the on-off time of the field current. Thus, at low speeds, the field may be turned on 90% of the time and off 10% of the time. This results in a relatively high average field current, which, when combined with the low generator speed, produces the desired system voltage. As generator speed increases, less field current may be needed to generate the desired system voltage. The duty cycle changes to reduce the average field current. For example, at high engine speeds, the regulator may be on only 10% of the time and off 90% of the time. This duty cycle will change, as operating factors change, to provide just the right amount of field current to generate the required system voltage. Figure 14-19 does not show actual field current, but serves to illustrate how the turned on and turned off time can vary. Most regulators are temperature compensated to provide the optimum voltage needed for battery charging. As the temperature increases, the voltage setting will decrease. Conversely, under cold weather conditions, the regulator will operate at a higher voltage setting to provide the higher voltage required by the battery for charging under these conditions. Figure 14-19, Generator Field Current Time 14-26
Voltage Settings Regulator settings vary and most are temperature compensated, which means the voltage setting is automatically changed to protect the battery from overcharging at high temperatures and to raise the charging voltage for a quicker recharge at low temperatures. Figure 14-20 shows typical voltage variations over the temperature range. Remember that the voltage regulator only limits the maximum voltage output of the generator. It doesn't control minimal voltage output. When demands on the vehicle electrical system are such that even the full output of the generator is not as high as the regulator setting, the regulator leaves on the field current to provide the most output possible. In other words, the regulator controls the maximum voltage the electrical system can produce. However, combining all of the electrical loads in the vehicle can often cause the actual system voltage to be less than the regulator setting. Figure 14-20, Temperature vs. Voltage Regulation 14-27
Voltage Regulator Connections The voltage regulator is connected to the vehicle's electrical harness through the 4-pin connector port on the generator. The control and fault detection signals between the vehicle system and the generator all pass through this connector. In order to operate, CS generators must have at least one wire coming from the vehicle harness to this connector. Depending on the vehicle system, there may be as many as four wires connected to the regulator. Circuitry and Appearance of Voltage Regulators The electronic circuits in the CS generator's regulator are very complex and time-consuming to describe in detail. In fact, regulators that look identical from the outside may be quite different on the inside, and a circuit hooked to a particular regulator terminal on one vehicle may be quite different from the circuit on another vehicle. Because of these differences, voltage regulators in CS generators are not usually interchangeable. There are over 20 different regulators made for CS generators that all look the same, and it is important that the exact regulator specified for a particular vehicle be used to avoid possible problems. When replacing an entire CS generator, use the exact part number specified for the vehicle to assure that the proper regulator is included. 14-28
Generator Construction The CS-121, CS-130, CS-130D, and CS-144 generators each include the major components discussed in the previous sections, including the rotor, stator, rectifier bridge, and regulator. All CS generators are electrically similar, even though the components may look somewhat different. Figure 14-21 represents one electrical schematic of all models in the series. CS-130D generators have the electronic components mounted on the outside of the slip ring end (SRE) frame under a black cover and have no external fans. An internal fan mounted on the rotor shaft near the electronic components CS-121, CS-130, and CS 130D models helps cool the generator. The bearings that hold the rotor shaft in all CS generators contain a lifetime supply of high-quality grease. Long-life brushes maximize generator life. The generator requires no periodic maintenance. Figure 14-21, Typical Electrical Schematic 14-29
Slip Ring End Frame The stator, rectifier bridge, and regulator are mounted to the half of the generator housing referred to as the slip ring end (SRE) frame, along with the brush holder assembly. The SRE name actually refers to the slip rings on the rotor and indicates that the housing is positioned over the end of the rotor shaft that has the slip rings. The brush holder is positioned so that the two brushes ride on the slip rings to transfer field current to and from windings. The rotor shaft rides in a bearing mounted in the center of the SRE frame. Figure 14-22 shows a typical arrangement of SRE components in CS-130 models. Drive End Frame The other half of the CS generator housing is commonly known as the drive end (DE) frame. This frame is positioned over the end of the rotor shaft that holds the drive pulley, resulting in the name, drive end. A cooling fan is mounted on this end of the rotor shaft, either inside or outside the DE frame. The rotor shaft rides in a bearing mounted in the center of the DE frame. Figure 14-20 also shows a typical arrangement of DE frame components, along with the rotor and pulley. Service Generators do not require periodic lubrication. The rotor shaft is mounted on ball or roller bearings at the drive end and at the slip ring end. Each bearing contains a permanent grease supply. Check the mounting bolts at periodic intervals for tightness. Tighten bolts to specified torque. Do not disassemble the CS-121, CS-130, and CS-130D generators. These units must be serviced as a complete unit. The only model which can currently be serviced by repair is the CS-144. 14-30
Figure 14-22, Cross Section, CS-130 or CS-121 Generator Only 14-31
Exercise 14-1 Read each question carefully and choose the correct answer. 1. Delcotron CS generators use a(n) to convert alternating current to direct current. A. magnetism B. induction process C. diode bridge (rectifier) D. resistor network 2. The letter "D" on some generator model numbers refers to. A. direct current B. di-pole regulator C. dual internal fans D. none of the above 3. Delcotron generators apply the principles of to produce electrical output. A. magnetic induction B. electron flow C. gravity D. hydraulic pressure 4. The voltage regulator controls voltage by changing. A. windings in the stator B. speed of rotor rotation C. strength of rotor's magnetic field D. all of the above 5. The primary components of a CS generator are. A. rotor and stator B. diodes in a diode bridge C. voltage regulator D. all of the above 14-32
6. On CS generators, ride on the slip rings to provide current to the field windings. A. pole pieces B. copper shoes C. carbon brushes D. all of the above 7. The diodes in a CS generator. A. convert AC to DC B. consist of an anode and a cathode C. are attached to the three stator windings D. all of the above 8. The voltage regulator built into CS generators limits. A. voltage output B. voltage input C. AC current D. all of the above 9. The only model of CS generator which can be serviced by repair is. A. CS-121 B. CS-130 C. CS-130D D. CS-144 14-33
Experiment 14-1 Generator Testing Using the J41450-B Tester Connect the tester to the generator by attaching its red alligator clip to the generator battery terminal and the black clip to the grounded generator housing. The green lamp on the tester illuminates indicating the generator has battery power and ground. If the green lamp does not illuminate, there is an open circuit in the generator output and/or ground circuits. Be sure the tester clamps are tight, and then check all fuses, junctions in the circuit, wiring, and terminals. With the alligator clips connected to the generator, unplug the four-way generator connector and install the matching connector from the tester. (The tester is now substituting for the generator turn-on circuit, which may include the IP, PCM, or other components.) 14-34
The red indicator lamp should not be on. This is normal with the ignition on and the engine not running. The red indicator lamp should go out when the engine is started and remain out while the engine is running. If the red indicator lamp is on when the engine is running, an under or over charge condition is indicated and the generator must be either repaired or replaced. 14-35
Generator Load Testing If all tests are OK, connect a carbon pile tester such as a VAT-40 to test the generator under load. Observe the red indicator lamp as you increase engine speed to 2500 RPM. The lamp should remain OFF. Apply a load equal to the generator's rated output. The red indicator lamp should remain off indicating that the generator output is OK. If the red indicator lamp comes on, either repair or replace the generator. Voltage Drop Test Maintain 2500 engine RPM and carbon pile load. Use a digital multimeter to check the voltage drop in the cable between the generator output terminal and the battery positive terminal. Also check the voltage drop between the generator case and the battery negative terminal. A voltage drop in excess of 0.5 volt indicates excessive resistance in the circuit. Locate and repair the cause of the excessive voltage drop. 14-36