chap41 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 41, the reader should be able to: • • • • Describe how a generator works Discuss the various generator test procedures Explain how to disassemble a generator and test its component parts Discuss how to check the wiring from the generator to the battery Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: AC voltage • brushes charging voltage delta-connected stator • delta winding • diodes • diode check • diode trio • drive-end (DE) housing • duty cycle Electrical power management (EPM) fusible link generator output test Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: overrunning alternator dampener (OAD) • overrunning alternator pulley (OAP) poles rectifier bridge • rotors sine wave • slip ring end (SRE) • stators • stator tap temperature compensation • thermistor wye-connected stator Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 All vehicles operate electrical components by taking current from the battery It is the purpose and function of the charging system to keep the battery fully charged The Society of Automotive Engineers (SAE) term for the unit that generates electricity is the generator The term alternator is also commonly used, especially in service manuals before 1993 when the SAE term was adopted by most vehicle manufacturers Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PRINCIPLES OF GENERATOR OPERATION All electrical generators use the principle of electromagnetic induction to convert mechanical energy into electrical energy Electromagnetic induction involves the generation of an electrical current in a conductor when the conductor is moved through a magnetic field The amount of current generated can be increased by the following factors: Increasing the speed of the conductor through the magnetic field Increasing the number of conductors passing through the magnetic field Increasing the strength of the magnetic field Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ALTERNATING CURRENT GENERATORS (ALTERNATORS) An AC generator generates an alternating current when the current changes polarity during the generator’s rotation A battery cannot “store” alternating current; therefore, this alternating current is changed to direct current (DC) by diodes inside the generator Diodes are one-way electrical check valves that permit current to flow in only one direction Most manufacturers call an AC generator an alternator Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 GENERATOR CONSTRUCTION A generator is constructed of a two-piece cast-aluminum housing Aluminum is used because of its lightweight, nonmagnetic properties and heat transfer properties needed to help keep the generator cool A front ball bearing is pressed into the front housing (called the drive-end [DE] housing) to provide the support and friction reduction necessary for the belt-driven rotor assembly The rear housing, or the slip ring end (SRE), usually contains a roller-bearing support for the rotor and mounting for the brushes, diodes, and internal voltage regulator (if the generator is so equipped) See Figures 41–1 and 41–2 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Generator Horsepower and Engine Operation - Part Many technicians are asked how much power certain accessories require A 100-ampere generator requires about horsepower from the engine One horsepower is equal to 746 watts Watts are calculated by multiplying amperes times volts: Power in watts 100A x 14.5V = 1450 1hp = 746 W 1450 watts is about horsepower and the generator uses about 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 Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Cold Weather Charge Lamp Problem A customer brought his vehicle (Ford) to an independent service facility complaining that occasionally, whenever the temperatures dropped below 10°F (-12°C), his charge indicator lamp stayed on until he had driven for several minutes The customer left the vehicle overnight and the technician observed that, indeed, the charge lamp was on after starting the vehicle the next morning The tech immediately got out of the vehicle, opened the hood, and checked to see if the rear bearing was magnetized—it was not After a few minutes of operation, the charge lamp went out and the rear generator bearing was magnetized The technician then knew that the problem was sticking generator brushes The brushes had worn to less than one-half length, and the springs were not strong enough, when cold, to exert sufficient pressure on the rotor slip rings to conduct the current for the field (rotor) After the technician replaced the brushes and cleaned and checked all other generator components, the problem did not recur Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Weak But Good Generator An 80-ampere generator was tested at 2000 engine RPM and found to be producing only 69 amperes The recommended spec for a generator is the output should be within 10% of the rated output Ten percent of 80 amps is amps; therefore, the minimum recommended output is 72 amp (80 - = 72) Because 69 amps is less than 72 amps, the generator should be serviced (repaired or replaced) However, because the test result was so close to specs, it was decided a charging system requirement test should be performed This determines the electrical load of that may be required on a continuous basis The procedure: Turn on everything electrical, except horn or other shortterm accessories Add amps to the reading and the result is the minimum current required of the generator The electrical demand test indicated that only 49 amps was needed Add amps (49 + = 54) and you see that a 54-amp generator is all that is needed Because the original generator is capable of 69 amps, it is more than adequate for the vehicle Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The Two-Minute Generator Repair A Chevrolet pickup truck was brought to a dealer for routine service The owner stated the battery required a jump-start after a weekend of sitting The tech tested the battery and charging system voltage using a small hand-held digital multimeter The battery voltage was 12.4 volts (about 75% charged), but the charging voltage was also 12.4 volts at 2000 RPM Because normal charging voltage should be 13.5 to 15.0 volts, it was obvious that the charging system was not operating correctly The tech checked the dash and found the “charge” light was not on, even though the rear bearing was not magnetized, indicating the voltage regulator was not working Before removing the generator for service, the tech checked the wiring connection on the generator When the two-lead regulator connector was removed, the connector was discovered to be rusty After the contacts were cleaned, the charging system was restored to normal operation The tech had learned that simple things should always be checked first before tearing into a big (or expensive) repair Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Help! A technician wanted help in determining what the generator output should be on a Toyota truck If the generator is protected by a fuse, check the fuse rating In this case, the fuse was listed as being 80 amperes The 80% rule states that the maximum current in a circuit should not exceed 80% of the fuse rating Eighty percent of 80 amps is 65 amps The generator output was measured to be 62 amps, well within the normal range of within 10% of specifications (10% of 64 is 6.4 amps) Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Generator (Alternator) Overhaul Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Generator Overhaul (cont.) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Generator Overhaul (cont.) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Generator Overhaul (cont.) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Generator Overhaul (cont.) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 PHOTO SEQUENCE Generator Overhaul Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman (cont.) ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY Charging system testing requires the battery be at least 75% charged to be assured of accurate test results The charge indicator light should be on with the ignition switch on but should go out whenever the engine is running Normal charging voltage (at 2000 engine RPM) is 13.5 to 15.0 volts If the system is not charging properly, the rear bearing of the generator should be checked for magnetism If it is magnetized, voltage regulator, brushes, and generator rotor are functioning correctly If the rear bearing is not magnetized, the voltage regulator, generator brushes, or rotor is not functioning Bypass the voltage regulator by supplying battery voltage to the field If the rear bearing is now magnetized and the charging system output is normal; the voltage regulator is at fault Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) To check for excessive resistance in the wiring between generator and battery, a voltage-drop test should be performed Generators not produce their maximum-rated output unless required by circuit demands Therefore, to test for maximum generator output, the battery must be loaded to force the generator to produce its maximum output Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Each generator should be marked across its case before disassembly to ensure proper clock position during reassembly After disassembly, all generator internal components should be tested using a continuity light or an ohmmeter The following components should be tested: a b c d e f Stator Rotor Diodes Diode trio (if the generator is so equipped) Bearings Brushes (should be more than 1/2 inch in length) Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) Electronic voltage regulators can be tested either off the vehicle using a special tester or on the vehicle using the fullfield bypass procedure Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458