CONE-BEARING 8D3984 - Caterpillar

System Operation Description:The alternator is an electronic component that is belt driven. The alternator is used to charge the storage battery during engine operation. The alternator converts a combination of mechanical energy and magnetic energy to alternating current and voltage. Alternating current and voltage is created by rotating a direct current electromagnetic field on the inside of the three-phase stator. The alternating current and voltage are generated by the stator. The current and voltage are changed to direct current by the three-phase full wave rectifier. The rectifier uses six silicon rectifier diodes. The alternator also has a diode assembly which rectifies field current. The field current is necessary for alternator output.Note: Use the diagnostic flow chart as a reference, while you are troubleshooting the alternator charging system.
Illustration 1 g00706351
Diagnostic flow chartNote: Severely discharged batteries can cause low system voltage. Severely discharged batteries can occur even while the engine is running above idle, and the alternator is working properly. Proper low engine idle is also important. The alternator is self-excited. Self-excited alternators must exceed a turn-on speed before charging will begin. Alternator output can be low at idle.Test Step 1. CHECK THE SYSTEM VOLTAGE.
Before you start the machine, connect a voltmeter between the "B+" terminal and the "B-" terminal of the alternator. Turn OFF all electrical loads.
Turn the key to the ON position but do not start the engine. Read the voltage on the voltmeter. Make a note of the voltage that was measured.Expected Result:This voltage should be approximately system voltage. Results:
YES - The voltage is approximately system voltage. Proceed to test step 2.
NO - The voltage is less than system voltage. Proceed to test step 4.Test Step 2. CHECK THE OPERATION OF THE ALTERNATOR.Note: For the proper output voltage, refer to Specification, "Alternator".
The voltmeter remains connected between the "B+" terminal and the case of the alternator.
Start the machine. Set the throttle to at least 75 percent. Read the voltage on the voltmeter. Make a note of the voltage that was measured.Expected Result:The voltage measurement is greater than the voltage that was recorded in the previous test step "Check The System Voltage".Results:
VOLTAGE HIGHER - The voltage measurement is greater than the voltage that was observed in the previous test step "Check The System Voltage". The voltage is also less than the maximum voltage that is listed in the specifications for the alternator. The alternator is partially charging the battery. Proceed to test step 3.
VOLTAGE TOO HIGH - The voltage measurement is greater than the voltage that was observed in the previous test step "Check The System Voltage". The voltage is also greater than the maximum voltage that is listed in the specifications for the alternator. The alternator is over charging. Proceed to test step 5.
VOLTAGE LOWER - The voltage is not higher than the voltage that was observed in the previous test step. Proceed to test step 4.Test Step 3. TEST THE ALTERNATOR OUTPUT.Note: For the proper output current, refer to Specification, "Alternator".
Ensure that the batteries are NOT fully charged.Note: