# Chap41

8 Oct 2009
1 sur 131

### Chap41

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• 9. Figure 41–1 A typical generator (alternator) on a Chevrolet V-8 engine. Figure 41–2 The end frame toward the drive belt is called the drive-end housing and the rear section is called the slip-ring-end housing. Continued
• 10. Many technicians are asked how much power certain accessories require. A 100-ampere generator requires about 2 horsepower from the engine. One horsepower is equal to 746 watts. Watts are calculated by multiplying amperes times volts: Generator Horsepower and Engine Operation - Part 1 Power in watts 100A x 14.5V = 1450 1hp = 746 W 1450 watts is about 2 horsepower and the generator uses about 2 hp to generate 100 A. Allowing about 20% for mechanical and electrical losses adds another 0.4 horsepower. When someone asks how much power it takes to produce 100 amperes from a generator, the answer is 2.4 hp.
• 11. Generator Horsepower and Engine Operation - Part 2 Many generators delay output to prevent the engine from stumbling when a heavy electrical load is applied. The voltage regulator or vehicle computer is capable of gradually increasing the generator output over a period of up to several minutes. Power in watts 100A x 14.5V = 1450 1hp = 746 W Though it does not sound like much, a sudden demand for 2 horsepower from an idling engine can cause the engine to run rough or stall. The difference in part numbers of various generators is often an indication of the time interval over which the load is applied. Therefore, the use of the wrong replacement generator could cause the engine to stall!
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• 13. Figure 41–3 An OAP on a generator on a Chevrolet Corvette.
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• 15. Figure 41–4 An overrunning alternator dampener (OAD) disassembled, showing all of its internal parts.
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• 17. No. An alternator needs to be equipped with the proper shaft to allow the installation of an OAP or OAD. This also means a conventional pulley cannot be used to replace a defective overrunning alternator pulley or dampener. Can I Install an OAP or OAD to My Alternator?
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• 19. Figure 41–5 A cutaway of a General Motors CS-130D generator showing the rotor and cooling fans that are used to force air through the unit to remove the heat created when it is charging the battery and supplying electrical power for the vehicle. Continued
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• 21. Figure 41–6 Rotor assembly of a typical alternator (AC generator). Current through the slip rings causes the “fingers” of the rotor to become alternating north and south magnetic poles. As the rotor revolves, these magnetic lines of force induce a current in the stator windings. The current necessary for the field (rotor) windings is conducted through carbon brushes to the slip rings. Maximum-rated generator output in amperes is largely dependent on the number and gauge of the windings of the rotor. Substituting rotors from one generator into another can greatly affect maximum output either positive or negative.
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• 24. Figure 41–7 A cutaway view of a typical AC generator (alternator) Continued
• 25. Figure 41–8 An exploded view of a typical generator (alternator) showing all of its internal parts.
• 26. Whenever checking for the root cause of a generator failure, one of the first things that a technician should do is to sniff (smell) the generator! If the generator smells like a dead rat (rancid), the stator windings have been overheated by trying to charge a discharged or defective battery. If the battery voltage is continuously low, the voltage regulator will continue supplying full field current to the generator. The voltage regulator is designed to cycle on and off to maintain a narrow charging system voltage range. If battery voltage is continually below the cutoff point of the voltage regulator, the generator is continually producing current in the stator windings. This constant charging can often overheat the stator and burn the insulating varnish covering the stator windings. If the generator fails the sniff test, the tech should replace the stator and other generator components found to be defective and replace or recharge and test the battery. The Sniff Test
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• 34. Figure 41–14 As the magnetic field, created in the rotor, cuts across the windings of the stator, a current is induced. Notice that the current path includes passing through one positive () diode on the way to the battery and one negative () diode as a complete circuit is completed through the rectifier and stator.
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• 38. Figure 41–16 A stator assembly with six, rather than the normal three, windings. Here is an example of a stator that has six rather than three windings, which greatly increases the amperage output of the generator (alternator). Continued
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• 44. Figure 41–18 A typical electronic voltage regulator showing the connections and the circuits involved. NOTE : Voltmeter test results may vary according to temperature. Charging voltage tested at 32°F (0°C) will be higher than for the same vehicle tested at 80°F (27°C) because of the temperature - compensation factors built into voltage regulators.
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• 50. Figure 41–19 Typical General Motors SI-style AC generator. Full Caption next slide.
• 51. Figure 41–19 Typical General Motors SI-style AC generator with an integral voltage regulator. Voltage present at terminal 2 is used to reverse bias the zener diode (D2) that controls TR2. The hot brush is fed by the ignition current (terminal I) plus current from the diode trio. See the entire schematic on Page 442 of your textbook.
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• 59. Figure 41–21 General Motors CS generator. Notice the use of zener diodes in the rectifier to help control any high-voltage surges that could affect delicate computer circuits. If a high-voltage surge does occur, the zener diode(s) will be reversed biased and the potentially harmful voltage will be safely conducted to ground. Voltage must be preset at the L terminal to allow the generator to start producing current. Continued
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• 63. Figure 41–23 The digital multimeter should be set to read DC volts, with the red lead connected to the positive (+) battery terminal and the black meter lead connected to the negative (-) battery terminal. Figure 41–24 A scan tool can be used to diagnose charging system problems.
• 64. Lower-than-normal generator output could be the result of a loose or slipping drive belt. A common trick used to determine if the noise is belt related is to use grit type hand cleaner or scouring powder. With the engine off, sprinkle some powder onto the pulley side of the belt. Start the engine. The excess powder will fly into the air, so get away from under the hood when the engine starts. If the belts are now quieter, you know that it was the glazed belt that made the noise. Often, the grit from the hand cleaner will remove the glaze from the belt and the noise will not return. However, if the belt is worn or loose, the noise will return and the belt should be replaced. A fast alternative method to see if the noise is from the belt is to spray water from a squirt bottle at the belt with the engine running. If the noise stops, the belt is the cause of the noise. The water quickly evaporates, and therefore, unlike the gritty hand cleaner, water simply finds the problem—it does not provide a short-term fix. The Hand Cleaner Trick
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• 68. Battery voltage measurements can be read through the lighter socket. Construct a test tool using a lighter plug at one end of a length of two-conductor wire and the other end connected to a double banana plug. The double banana plug will fit most meters in the common (COM) terminal and the volt terminal of the meter. The Lighter Plug Trick Figure 41–26 Charging system voltage can be easily checked at the lighter plug by connecting a lighter plug to the voltmeter through a double banana plug.
• 69. Use a Test Light to Check for a Defective Fusible Link Most AC generators (alternators) use a fusible link between the output terminal located on the slip-ring-end frame and the positive (+) terminal of the battery. If this link is defective (blown), then the charging system will not operate. Many AC generators have been replaced repeatedly because of a blown fusible link, not discovered until later. A quick and easy test of the fusible link is to touch a test light to the output terminal. Figure 41–27 Before replacing a generator (alternator), the wise tech checks that battery voltage is present at the output and battery voltage sense terminals. With the other end of the test light attached to a good ground, the fusible link is OK if the light lights. This confirms the circuit between the AC generator and the battery has continuity.
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• 72. Generator output can be easily measured using a digital mini clamp-on-type digital multimeter. A typical clamp-on meter is capable of reading as low as 10 mA (0.01 A) to 200 A or more. To set up for the test, clamp the meter around the generator output wire and select DC amperes and the correct scale. Start the engine and turn on all lights and accessories and then observe the meter display. The results should be within 10% of the specified generator rating. An AC/DC current clamp adapter can also be used along with a conventional digital multimeter set on the DC millivolt scale. To check for AC current ripple, switch the meter to read AC amperes and record the reading. A reading of greater than 10 amperes AC indicates defective generator diodes. The Mini Clamp-On DMM Test
• 73. Figure 41–29 A mini clamp-on digital multimeter can be used to measure generator output. This meter was set on the 200-A DC scale. With the engine running and all lights and accessories on, the generator was able to produce almost exactly its specified rating of 105 A. Continued
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• 78. Continued If the reading is over 0.2 volt, connect one end of an auxiliary ground wire to the case of the generator and the other end to a good engine ground. Most voltage-drop specifications range between 0.2 and 0.4 volt. Generally, if the voltage loss (voltage drop) in a circuit exceeds 0.5 volt (1/2 volt), the wiring in that circuit should be repaired or replaced. During automotive testing, it is sometimes difficult to remember the exact specification for each test; therefore, the technician can simply remember “2 to 4” and that any voltage drop over this amount indicates a problem. “ 2 to 4”
• 79. Whenever diagnosing a generator charging problem, try using jumper cables to connect the positive and negative terminals of the generator directly to the positive and negative terminals of the battery. If a definite improvement is noticed, the problem is in the wiring of the vehicle. High resistance, due to corroded connections or loose grounds, can cause low generator output, repeated regulator failures, slow cranking, and discharged batteries. A voltage-drop test of the charging system also can be used to locate excessive resistance (high-voltage drop) in the charging circuit, but using jumper wires (cables) is often faster and easier. Use Jumper Cables as a Diagnostic Tool
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• 84. The battery and generator (alternator) had been replaced by another shop, yet the battery would be totally discharged after three days. A check of the charging system showed that the generator was not charging. The Chevrolet Van Story - Part 1 Before another generator was installed, the tech checked for voltage at both the output terminal of the generator ( B terminal) and the L terminal with the ignition switch in the on (run) position. There was no voltage at the L terminal indicating the problem was in the wiring to the L terminal, because without voltage at this terminal, the CS130 will charge. Checking the schematic in the service information showed that the power to the L terminal came from the gauges fuse and then through the charge warning lamp. See Figure 41–33 following. What could have caused the fuse to blow? Further checking of the circuit showed that the gauges fuse also fed the automatic transmission torque converter clutch circuit. A visual inspection discovered a damaged wire under the van most likely due to road debris. Repairing the wire and installing a new fuse solved the charging system problem.
• 85. The Chevrolet Van Story - Part 2
• 86. Figure 41–33 A schematic showing a typical wiring for a General Motors CS generator, showing that the L terminal is fed from the gauges fuse. If the fuse was blown, the charger light would never light and the generator (alternator) will not charge. The Chevrolet Van Story - Part 3
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• 89. Figure 41–34 This accessory drive belt should be replaced because it has so many cracks. The usual specification for when a serpentine belt requires replacement is when there are three or more cracks in any one rib in any 3-inch length. Figure 41–35 Typical hookup of a starting and charging tester.
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• 91. HINT: Step #2 can be skipped if the ammeter current clamp can be connected around the generator output wire instead of the battery cable(s). Figure 41–36 The best place to install a charging system tester amp probe is around the generator output terminal wire as shown.
• 92. Figure 41–37 The output on this generator is printed on a label.
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• 94. NOTE: If using an inductive-pickup ammeter, ensure the pickup is over all the wires leaving the battery terminal. Failure to include the small body ground wire from the negative terminal to the body or the positive wire (if testing from the positive side) will greatly decrease current flow readings. Figure 41–38 A diagram showing the location of the charging system wiring of a typical vehicle. The best location to use to check for the generator (alternator) output is at the output wire from the B+ (BAT) terminal. Notice that the generator supplies all electrical needs of the vehicle first, then charges the battery if needed.
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• 96. Many technicians are asked to install a higher-output generator to allow the use of emergency equipment or other high-amperage equipment such as a high-wattage sound system. Although many higher-output units can be physically installed, it is important not to forget to upgrade the wiring and the fusible link(s) in the generator circuit. Failure to upgrade the wiring could lead to overheating. The usual failure locations are at junctions or electrical connectors. Bigger is Not Always Better
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• 102. Figure 41–42 If the ohmmeter reads infinity between any two of the three stator windings, the stator is open and, therefore, defective. The ohmmeter should read infinity between any stator lead and the steel laminations. If the reading is less than infinity, the stator is grounded. Stator windings can be tested if shorted because the normal resistance is very low. Continued
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