CHARGING SYSTEM TESTING AND SERVICE. The charging system can be tested as part of a routine vehicle inspection or to determine the reason for a no-charge or reduced-charging circuit performance. CHARGING SYSTEM TESTING AND SERVICE Charging Voltage Test. Step 1 Select DC volts.
Step 1 Select DC volts.
Step 2 Connect the red meter lead to the positive (+) terminal of the battery and the black meter lead to the negative (-) terminal of the battery.
Step 3 Start the engine and increase the engine speed to about 2000 RPM (fast idle) and record the charging voltage.
FIGURE 21-1 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 21-2 A scan tool such as this Chrysler DRB III can be used to check the generator output voltage.
FIGURE 21-3 If the rear bearing is magnetized, the voltage regulator, generator brushes, and rotor are functioning.
1. The voltage regulator is working.
2. The generator brushes are working.
3. The rotor in the generator is producing a magnetic field.
1. The voltage regulator is not working.
2. The generator brushes are worn or stuck, and they are not making good electrical contact with the rotor slip rings.
3. The generator rotor could be defective.
FIGURE 21-4 A GM generator with an internal voltage regulator can be identified by the horizontal plug-in connector.
FIGURE 21-5 Connections required to full-field a GM generator with an external voltage regulator.
FIGURE 21-6 Connections required to full-field a Ford generator with an external voltage regulator.
FIGURE 21-7 Jumper wire connections required to full-field a Ford (or Leece-Neville) generator with an internal electronic voltage regulator.
FIGURE 21-8 Wiring diagram of a Ford integral generator or regulator (IAR) assembly.
FIGURE 21-9 Connections required to full-field a Chrysler generator with a mechanical voltage regulator.
FIGURE 21-10 Connections required to full-field a Chrysler generator with an electronic voltage regulator.
FIGURE 21-11 Charging system voltage can be easily checked at the lighter plug by connecting a lighter plug to the voltmeter through a double
FIGURE 21-12 Before replacing a generator (alternator), the wise technician checks that battery voltage is present at the output and battery voltage sense terminals.
FIGURE 21-13 This accessory drive belt should be replaced because it has 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 in. length.
1. Belt tension gauge
2. Marks on a tensioner
3. Torque wrench reading
Step 1 Set the digital meter to read AC volts.
Step 2 Start the engine and operate it at 2000 RPM (fast idle).
Step 3 Connect the voltmeter leads to the positive and negative battery terminals.
Step 4 Turn on the headlights to provide an electrical load on the generator.
FIGURE 21-14 AC ripple at the output terminal of the generator is more accurate than testing at the battery due to the resistance of the wiring between the generator and the battery. The reading shown on the meter is only 78 mV (0.078V),far below what the reading would be if a diode were defective. (Courtesy of Fluke Corporation)
FIGURE 21-15 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.
Step 1 Start the engine and turn on the lights to create an electrical load on the generator.
Step 2 Using a clamp-on meter, place the clamp around either all of the positive (+) battery cables or all of the negative (-) battery cables.
Step 3 Read the meter display and determine the needed service.
Step 1 Start the engine and run it at a fast idle (about 2000 engine RPM).
Step 2 Turn on the headlights to ensure an electrical load on the charging system.
Step 3 Using any voltmeter, connect the positive test lead
(usually red) to the output terminal of the generator. Attach the negative test lead (usually black) to the positive post of the battery.
1. If there is less than a 0.4 volt reading, then all wiring and connections are satisfactory.
2. If the voltmeter reads higher than 0.4 volt, there is excessive resistance (voltage drop) between the generator
output terminal and the positive terminal of the battery.
3. If the voltmeter reads battery voltage (or close to battery voltage), there is an open circuit between the battery and the generator output terminal.
FIGURE 21-16 Voltmeter hookup to test the voltage drop of the charging circuit.
FIGURE 21-17 Typical GM SI generator. Note the location and wire color used for terminals 1 and 2.
Step 1 With the ignition on (engine off), a test light should be bright if touched to the “BAT” terminal and terminal 2.
Step 2 With the engine running, touching any of the three terminals should produce a bright test light. The BAT terminal and terminal 2 should both cause a bright light because both are battery voltage sources. Terminal 1 should also light the test light brightly because when the generator is producing a current, the internal voltage rises and applies an opposing voltage on the dash light bulb, which causes current to stop flowing through the bulb and the charge light to go out.
FIGURE 21-18 Typical GM CS generator wiring plug identification. Note that terminal F is sometimes terminal I on some generators.
FIGURE 21-19 Typical hookup of a starting and charging tester.
Step 1 Connect the starting and charging test leads according to the manufacturer’s instructions.
Step 2 Turn the ignition switch on (engine off) and observe the ammeter. This is the ignition circuit current, and it should be about 2 to 8 amperes.
Step 3 Start the engine and operate it at 2000 RPM (fast idle). Turn the load increase control slowly to obtain the highest reading on the ammeter scale. Note the ampere reading.
Step 4 Total the amperes from steps 2 and 3. Results should be within 10% (or 15 amperes) of the rated output. Rated output may be stamped on the generator.
FIGURE 21-20 The output rating on the General Motors generator (alternator) is stamped into the case.
FIGURE 21-21 The output on this generator is printed on a label.
1. Start the engine and operate to about 2000 RPM (fast idle).
2. Turn the heat selector to air conditioning (if the vehicle is so equipped).
3. Turn the blower motor to high speed.
4. Turn the headlights on bright.
5. Turn on the radio.
6. Turn on the windshield wipers.
7. Turn on any other accessories that may be used continuously (do not operate the horn, power door locks, or other units that are not used for more than a few seconds).
FIGURE 21-22 When connecting an inductive ammeter probe, be certain that the pickup is over all wires. The probe will work equally well over either all positive or all negative cables because all current leaving a battery must return.
FIGURE 21-23 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.
Step 1 Before disconnecting the negative battery cable, use a test light or a voltmeter and check for battery voltage at the output terminal of the generator. A complete circuit must exist between the generator and the battery. If there is no voltage at the generator output terminal, check for a blown fusible link or other electrical circuit fault.
Step 2 Disconnect the negative (0) terminal from the battery.
Step 3 Remove the accessory drive belt that drives the generator.
Step 4 Remove the fasteners and brackets, as necessary, and remove the generator from the vehicle.
FIGURE 21-24 Always mark the case of the generator before disassembly to be assured of correct reassembly.
FIGURE 21-25 Explanation of clock positions. Because the four through bolts are equally spaced, it is possible for a generator to be installed in one of four different clock positions. The connector position is determined by viewing the generator from the diode end with the threaded adjusting lug in the up or 12 o’clock position. Select the 3 o’clock, 6 o’clock, 9 o’clock, or 12 o’clock position to match the unit being replaced.
FIGURE 21-26 Testing a generator rotor using an ohmmeter.
FIGURE 21-27 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.
FIGURE 21-28 An open in a delta-wound stator cannot be detected using an ohmmeter.
FIGURE 21-29 Typical diode trio. If one leg of a diode trio is open, the generator may produce close to normal output, but the charge indicator
light on the dash will be on dimly. The plus signs indicate the anodes, and the minus sign indicates the cathode terminal of the diodes.
FIGURE 21-30 A GM rectifier bridge that has been disassembled to show the individual diodes.
FIGURE 21-31 Diodes being soldered to the stator on a Ford generator.
FIGURE 21-32 Testing a GM SI internal voltage regulator using a voltage regulator tester. This tester can be used to test most internal and external electronic voltage regulators by using the appropriate adapter harness and test leads.
FIGURE 21-33 A brush holder assembly shown assembled in the generator. The brush retainer is actually a straightened-out paper clip.
FIGURE 21-34 (a) A generator for a GEO Prism looks like a typical General Motors CS-130 except for this adapter that converted the Toyota wiring harness to the GM generator. (b) After removing the adapter, the original generator
connection is visible.
Step 1 Verify that the replacement generator is the correct unit for the vehicle.
Step 2 Install the generator wiring on the generator and install the generator.
Step 3 Check the condition of the drive belt and replace, if necessary. Install the drive belt over the drive pulley.
Step 4 Properly tension the drive belt.
Step 5 Tighten all fasteners to factory specifications.
Step 6 Double-check that all fasteners are correctly tightened and remove all tools from the engine compartment area.
Step 7 Start the engine and verify proper charging circuit operation.
2. If the charging system is not charging properly, the rear bearing of the generator should be checked for magnetism. If the rear bearing is magnetized, the 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.
3. To check for excessive resistance in the wiring between the generator and the battery, a voltage drop test should be performed.
4. Generators do 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.
5. 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:
d. Diode trio (if the generator is so equipped)
f. Brushes (should be more than 1/2 in. long)
6. Electronic voltage regulators can be tested either off the vehicle using a special tester or on the vehicle using the full-field bypass procedure.
1. To check the charging voltage, connect a digital multimeter (DMM) to the positive (+) and the negative (-) terminals of the battery and select _____.
2. To check for ripple voltage from the generator, select _____.
3. The maximum allowable AC current in amperes that is being sent to the battery from the generator is _____.
4. Why should the lights be turned on when checking for ripple voltage or AC current from the generator?
5. An acceptable charging circuit voltage on a 13 volt system is _____.
6. Technician A says that by full-fielding the generator, you are bypassing the voltage regulator. Technician B says that voltage regulators control the generator output by controlling the field current through the rotor. Which technician is correct?
8. When testing a generator rotor, if an ohmmeter shows zero ohms with one meter lead attached to the slip rings and the other meter lead touching the rotor shaft, the rotor is _____.
9. A generator diode is being tested using a digital multimeter set to the diode check position. A good diode will read _____ if the leads are connected one way across the diode and _____ if the leads are reversed.
10. A generator (alternator) could test as producing lower-than normal output, yet be okay, if _____.