T8 Alternator Overcharging - Test
- Many Caterpillar machines are equipped with a connector for the 6V-2150 Starting/Charging Analyzer. See Systems Operation, SENR2947, "Starting and Charging Systems". Use of this analyzer replaces the testing that is listed below. If the analyzer finds a problem, correct the problem and retest the system. Go to Troubleshooting, "Initial Troubleshooting Procedure".
- Run the engine at 75 percent. Turn ON all electrical accessories for all test steps below. Allow the engine to run for at least 3 minutes before you continue to 4. The following table will assist in making calculations during the test.
Show/hide table
Table 1 Test Step     Voltage Reading     Voltage should be below this for 12 volt system     Voltage should be below this for 24 volt system     4         5         4 minus 5         1.0 volt     2.0 volts     6                 7         6 minus 7         0.5 volt     1.0 volt    
- Measure the voltage between the "B+" terminal and ground.
- Measure the voltage across the battery. Put the red lead on the + battery terminal, and put the black lead on the negative battery terminal. Step 5 should be completed as quickly as possible after Step 4.
Expected Result: On 12 volt systems, the voltage is within one volt of the voltage that was recorded in Step 4. On 24 volt systems, the voltage is within 2 volts.
Results:
- YES - If the voltage in Step 4 is not more than 1 volt for 12 volt systems (2 volts for 24 volt systems) higher than the voltage in Step 5, this step is complete and the related wiring is correct at this time. There is an internal malfunction in the alternator. Refer to Testing and Adjusting, "Component - Test".
- NO - If the voltage in Step 4 is more than 1 volt for 12 volt systems (2 volts for 24 volt systems) higher than the voltage in Step 5, there is high circuit resistance: corrosion, loose connections and damaged wiring. Go to Step 7.
- YES - If the voltage in Step 4 is not more than 1 volt for 12 volt systems (2 volts for 24 volt systems) higher than the voltage in Step 5, this step is complete and the related wiring is correct at this time. There is an internal malfunction in the alternator. Refer to Testing and Adjusting, "Component - Test".
- Check the voltage between the machine's frame and the "B+" terminal. Record the voltage.
- Check the voltage between the machine frame and the + battery post. Step 7 should be completed as quickly as possible after Step 6.
Expected Result: The voltage difference between Step 6 and Step 7 does not exceed 1 volt on 24 volt systems or 0.5 volts on 12 volt systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. There is an internal malfunction in the alternator. Refer to Testing and Adjusting, "Component - Test".
- NO - The voltage difference exceeds the tolerance. There is high resistance in the charging circuit: loose cables, corroded cables, damaged cables, faulty circuit breaker and faulty main relay. Correct the problem. Go to Troubleshooting, "Initial Troubleshooting Procedure" and retest the system.
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. There is an internal malfunction in the alternator. Refer to Testing and Adjusting, "Component - Test".
Caterpillar Information System:
30SI Series and 34SI Series Alternator T7 Identifying Source of Current Draw - Test
30SI Series and 34SI Series Alternator T6 Residual Magnetism Restoration
30SI Series and 34SI Series Alternator T5 Alternator Current - Test
30SI Series and 34SI Series Alternator T4 Alternator Drive System - Check
30SI Series and 34SI Series Alternator T3 Charging System - Test
3406E and 3456 Generator Set Engines Fuel Quality - Test
30SI Series and 34SI Series Alternator T2 Electrical System Current - Test
30SI Series and 34SI Series Alternator T1 Alternator Output - Test
3508B Engine for 854G Wheel Dozers and 992G Wheel Loaders MID 036 - CID 0277 - FMI 08 Timing Calibration signal abnormal
3126B Engine for Caterpillar Built Machines Engine Will Not Crank
3054B Industrial Engine Gear Group (Front) - Install
3054B Industrial Engine Gear Group (Front) - Remove
C-12, C-15 and C-16 Engines for Caterpillar Built Machines Alternator - Charging Problem
3306B Generator Set Generator Set Installation
Electronic Modular Control Panel II+ (EMCP II+) for EUI Engines CID 168 FMI 4 Electrical System Voltage Below Normal - Test
C-9 Engine for TK711, TK721, TK722, TK732, TK741, TK751, and TK752 Track Feller Bunchers Coolant in Engine Oil
Air Conditioning and Heating R134a for All Caterpillar Machines Refrigerant Condenser
3126B Marine Engine Coolant Level Sensor - If Equipped
3126B Marine Engine Engine Oil Pressure Sensor
3406E and 3456 Generator Set Engines Turbocharger - Inspect
Customer Communication Module (CCM) for Diesel Engines Parameter Identifiers for EMCP II
C27 and C32 Engines for Caterpillar Built Machines Aftercooler - Test
3406E and 3456 Generator Set Engines Engine Valve Lash - Inspect/Adjust
3126B Marine Engine Overspeed