Test Step 14. TEST THE OUTPUT CURRENT OF THE ALTERNATOR BELOW 0.015 AMPERES.
- Disconnect the wire from the “B+” terminal of the alternator. Set the multimeter on the 10 amp scale. Connect the red lead of the multimeter to the wire that was disconnected. Connect the black lead of the multimeter to the “B+” terminal of the alternator. Make a note of the current that was measured.
Expected Result:
The current is less than 0.015 A.
Results:
- YES – The current is under 0.015 A. The alternator is operating correctly. There may be a current draw on the machine. Proceed to test step 15.
- NO – The current is over 0.015 A.Repair: There is an internal problem with the alternator. Replace the alternator or proceed to Systems Operation, “Component Description”. Use the descriptions of the components in order to determine the component that has failed. Proceed to the appropriate component test.
STOP
Test Step 15. IDENTIFY THE SOURCE OF EXCESSIVE CURRENT DRAW.
- Make sure that every electrical component is turned OFF. Make sure that the keyswitch is turned OFF. Make sure that the dome lights are OFF.
- Clamp a 9U-5795 Current Probe or 225-8266 Ammeter Tool Gp around the main ground cable. Clamp the tool with the positive side away from the battery. Reset the probe (zero) before clamping the probe around the wire. Use the current probe if the draw is above approximately 2 A. Use the Ammeter if the draw is below approximately 2 A.
- Remove the fuses or open the circuit breakers one at a time. Check the current after each fuse has been removed or each circuit breaker has been opened. After observing the current, reinstall the fuse or close the circuit breaker. Start with the main circuits first, and proceed to smaller circuits.
- Check if any components on the circuit are ON.
- If everything is OFF, then disconnect electrical components on the circuit one at a time. Monitor the current after each component is disconnected.
- All of the components in the circuit should be disconnected. If the problem still exists, then check the wiring in the circuit. There may be circuit leakage through corrosion or circuit leakage through a short.Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem. However, some large machines with multiple electronic control modules have a higher acceptable limit. For more information, contact a Caterpillar dealer or contact the business unit that produces the machine.
Expected Result:
The source of the excessive current draw was determined.
Results:
- YES – The source of the excessive current draw was determined.Repair: Repair the problem or replace any component that has failed. Exit this procedure and retest the alternator charging system.
STOP
- NO – The source of the excessive current draw was not determined.Repair: Exit this procedure and retest the alternator charging system.
STOP
Test Step 16. TEST FOR AN OVERCHARGING CONDITION FROM THE ALTERNATOR.
- Verify that the nut on the “B+” alternator terminal is tight. Also, verify that the wire has a good connection to the “B+” terminal.
- Many Caterpillar machines are equipped with a connector for the 6V-2150 Starting/Charging Analyzer . Use of this tester replaces the remainder of this test step. To operate the analyzer, refer to Tool Operating Manual, SEHS7768, “Using the 6V-2150”.
- Start the engine and set the throttle to at least 75 percent. Turn ON all electrical accessories for the remainder of this test step. Allow the engine to run for at least 3 minutes before continuing.
- Measure the voltage between the “B+” terminal of the alternator and the case of the alternator. Make a note of the voltage that was measured. Perform the next measurement immediately.
- Measure the voltage across the battery. Put the red lead on the positive terminal of the battery, and put the black lead on the negative terminal of the battery. Make a note of the voltage that was measured.
Expected Result:
The voltage at the battery should be less than the voltage at the alternator. On systems that are 12 V, the difference in voltages should not be more than 1 V. On systems that are 24 V, the difference should not be more than 2 V.
Results:
- YES – The voltage at the battery is less than the voltage at the alternator. Also, the difference in voltages is less than 1 V for 12 V systems and the difference is less than 2 V for 24 V systems. The wiring that is related to the alternator is correct at this time.Repair: There is an internal problem with the alternator. Replace the alternator or proceed to Systems Operation, “Component Description”. Use the descriptions of the components in order to determine the component that has failed. Proceed to the appropriate component test.
STOP
- NO – The voltage at the battery is less than the voltage at the alternator. However, the difference in voltages is greater than 1 V for 12 V systems and the difference is greater than 2 V for 24 V systems. Proceed to test step 17.
Test Step 17. TEST THE POSITIVE SIDE OF THE CHARGING CIRCUIT.
- Measure the voltage between the frame of the machine and the “B+” terminal of the alternator. Make a note of the voltage that was measured. Perform the next measurement immediately.
- Measure the voltage between the frame of the machine and the positive terminal of the battery. Make a note of the voltage that was measured.
Expected Result:
The voltage difference does not exceed 1 V on 24 V systems or 0.5 V on 12 V systems.
Results:
- YES – The voltage difference does not exceed the tolerance. The positive circuit is good.Repair: There is an internal problem with the alternator. Replace the alternator or proceed to Systems Operation, “Component Description”. Use the descriptions of the components in order to determine the component that has failed. Proceed to the appropriate component test.
STOP
- NO – The voltage difference exceeds the tolerance.Repair: There is high resistance in the positive side of the charging circuit that is caused by one of the following conditions:
- An electrical connection has loosened.
- An electrical connection has corroded.
- The main relay has failed.
- A circuit breaker has failed.
Correct the problem. Exit this procedure and retest the alternator charging system.STOP