Electronic Modular Control Panel II (EMCP II) Caterpillar

Often when problems with the charging system are being investigated, the alternator is not the problem. If a low battery condition is present test the batteries first. See Special Instruction, SEHS7633, "Battery Test Procedure" for more information. If the engine cranks slowly, then test the starting system. See Service Magazine, SEPD0020, "Testing The Starter On The Engine" for more information.

Note: 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.

Test Step 1. CHECK THE SYSTEM VOLTAGE.

1. Before you start the generator set, connect a voltmeter between the "B+" terminal and the case of the alternator. Disconnect all loads from the battery. Disconnect the battery voltage to the EMCP II.

2. Turn the disconnect switch 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.

1. The voltmeter remains connected between the "B+" terminal and the case of the alternator.

2. Start the generator set. 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 16.

• 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 table 1.

1. Ensure that the batteries are NOT fully charged.

   Note: A fully charged battery may have open circuit voltage above25 V on 24 V systems.

2. If the batteries are fully charged, then crank the engine for 30 seconds. This action reduces the battery voltage.

3. Connect the 9U-5795 Current Probe to a DMM (digital multimeter) or use a 225-8266 Ammeter Tool Gp . The multimeter must have a peak hold feature. Clamp the probe around the alternator output wire "B+". Before you clamp the probe around the wire, ensure that the probe is "zeroed".

4. Set the digital multimeter to "peak hold" or "max mode" on the "mV" scale.

5. Start the generator set, and immediately set the throttle to at least 75%. The peak current will appear on the voltmeter in "peak hold" or "max" mode.

Expected Result:

The current reading should be at least 90% of the specified peak output.

Results:

• YES - The current is at least 90% of the specified peak output. Proceed to test step 10.

• NO - The current is less than 90% of the specified peak output. Proceed to test step 4.

Test Step 4. CHECK THE DRIVE SYSTEM OF THE ALTERNATOR.

1. Check the condition of the alternator drive belt. Clean the pulley and replace the drive belt if the drive belt is oily. Dry the drive belt if the belt is wet. Replace the drive belt, if the belt is worn.

2. Check the tension of the alternator drive belt. Adjust the drive belt to the correct tension.

3. Check the nut on the alternator pulley. Tighten the nut if the nut is loose.

Expected Result:

The drive system of the alternator is functioning correctly. No corrections to the drive system were necessary.

Results:

• YES - The drive system of the alternator is functioning correctly. No corrections were necessary. Proceed to test step 5.

• NO - The drive system of the alternator was not functioning correctly. Corrections were necessary.

  Repair: Ensure that the problems have been corrected. Exit this procedure and retest the alternator charging system.

  STOP

Test Step 5. TEST THE CHARGING CIRCUIT.

1. Verify that the nut on the "B+" alternator terminal is tight. Also, verify that the wire has a good connection to the "B+" terminal.

2. Start the engine and set the throttle to at least 75 percent. Allow the engine to run for at least 3 minutes before continuing.

3. Measure the voltage between the "B+" alternator terminal and the alternator case ground. Make a note of the measured voltage. Perform the next measurement immediately.

4. Measure the voltage across the battery. Put the red lead on the battery positive terminal, and put the black lead on the battery negative terminal. 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. The difference should not be more than 2 V on 24 V systems.

Results:

• YES - The voltage at the battery is less than the voltage at the alternator. Also, the difference in voltages 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. Repair the alternator or replace the alternator.

  STOP

• NO - The voltage at the battery is less than the voltage at the alternator. However, the difference in voltages is greater than 2 V for 24 V systems. Proceed to test step 6.

Test Step 6. TEST THE POSITIVE SIDE OF THE CHARGING CIRCUIT.

1. Measure the voltage between the frame ground and the "B+" alternator terminal. Make a note of the voltage that was measured. Perform the next measurement immediately.

2. Measure the voltage between the frame ground and the + battery post. Make a note of the voltage that was measured.

Expected Result:

The voltage difference does not exceed 1 V on 24 V systems.

Results:

• YES - The voltage difference does not exceed the tolerance. The positive circuit is good. Proceed to test step 7.

• 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.

  • A circuit breaker has failed.

  Repair the problem or replace any component that has failed. Exit this procedure and retest the alternator charging system.

  STOP

Test Step 7. TEST THE NEGATIVE SIDE OF THE CHARGING CIRCUIT.

1. Check the voltage between the negative battery post and the alternator case ground.

Expected Result:

The voltage does not exceed 1 V on 24 V systems.

Results:

• YES - The voltage difference does not exceed the tolerance. The negative circuit is good. Proceed to test step 8.

• NO - The voltage difference exceeds the tolerance.

  Repair: There is high resistance in the negative side of the charging circuit that is caused by one of the following conditions:

  • An electrical connection has loosened.

  • The alternator ground has loosened.

  • The engine ground has opened.

  Repair the problem or replace any component that has failed. Exit this procedure and retest the alternator charging system.

  STOP

Test Step 8. TEST THE CIRCUIT OF THE "R" TERMINAL.

1. Start the engine and set the throttle to at least 75%.

2. Connect a voltmeter between the "B+" terminal and the alternator case ground.

3. Disconnect the wire from the "R" terminal. Select "YES" if the "R" terminal is not used on the generator set.

Expected Result:

The voltage does not change.

Results:

• YES - The voltage does not change. Proceed to test step 9.

• NO - The voltage rises and the alternator begins charging.

  Repair: The wire to the "R" terminal is shorted. Repair the wiring or replace the wiring. Exit this procedure and retest the alternator charging system.

  STOP

Test Step 9. RESTORE THE RESIDUAL MAGNETISM OF THE ROTOR.

1. Connect one end of a jumper wire to the "B+" terminal of the alternator.

2. Connect the other end of the jumper wire to the "R" terminal of the alternator for 2 seconds.

Expected Result:

The voltage output rises on the "B+" terminal. The residual magnetism of the rotor has been restored.

Results:

• YES - The voltage output rises. The residual magnetism of the rotor has been restored. The alternator is now charging.

  Repair: Exit this procedure and retest the alternator charging system.

  STOP

• NO - The voltage output does not rise.

  Repair: There is an internal problem with the alternator. Repair the alternator or replace the alternator.

  STOP

Test Step 10. TEST FOR UNDESIRABLE CURRENT FLOW IN THE ALTERNATOR CHARGING SYSTEM.

1. Turn the disconnect switch to the OFF position.

2. 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 you clamp the probe around the wire. Read the current on the meter. Make a note of the current that was measured.

Expected Result:

The current is below 2 A. The "YES" selection is dependent on the presence of a main disconnect switch on the generator set that is being tested.

Results:

• YES - WITH DISCONNECT SWITCH - The current is below 2 A. For generator sets with a main disconnect switch, proceed to test step 11.

• YES - WITHOUT DISCONNECT SWITCH - The current is below 2 A. For generator sets without a main disconnect switch, proceed to test step 12.

• NO - The current is above 2 A. There is a current draw in the system. Proceed to test step 13.

Test Step 11. MEASURE THE CURRENT OF THE SYSTEM BY USING THE MAIN DISCONNECT SWITCH.

1. Turn the disconnect switch to the ON position.

2. Connect an ammeter across the disconnect switch terminals. Connect the red lead to the terminal on the frame side. Connect the black lead to the terminal on the battery side. If a multimeter is being utilized for this test, use the 10A connections in order to avoid damage.

3. Turn the disconnect switch to the OFF position and read the current. Make a note of the measured current.

Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem. Contact a Caterpillar dealer for more information.

Expected Result:

The current is below 0.050 A (50 mA).

Results:

• YES - The current is below 0.050 A. The charging system is functioning properly at this time. The failure is possibly an intermittent draw in the system. The batteries may have failed. Ensure that NO accessories were ON during the test. Exit this procedure and retest the alternator charging system.STOP

• NO - The current is above 0.050 A. There is a draw in the system. Proceed to test step 13.

Test Step 12. MEASURE THE CURRENT OF THE SYSTEM BY REMOVING THE NEGATIVE BATTERY CABLE.

1. Disconnect the ground cable from the negative battery post. There may be more than one battery that is connected to ground. Disconnect all of the batteries that are connected to ground. Do not disconnect cables that are between batteries that are connected in series.

2. Connect an ammeter between the disconnected battery ground cable and one of the negative battery terminals. Connect the red positive lead of the ammeter to the cable. The negative lead should be connected to the battery terminal. If a multimeter is being utilized for this test, use the 10 A connections in order to avoid damage.

Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem. Contact a Caterpillar dealer for more information.

Expected Result:

The current is below .050 A (50 mA).

Results:

• YES - The current is below 0.050 A. The charging system is currently good. The problem is a possible intermittent current draw in the system. The batteries may have failed. Check that NO accessories were ON during the test.STOP

• NO - The current is above 0.050 A. There is excessive current flow in the system. Proceed to test step 13.

Test Step 13. TEST THE CURRENT OF THE ALTERNATOR OUTPUT BELOW 2 AMPERES.

1. Turn the disconnect switch to the OFF position.

2. Connect the 9U-5795 Current Probe to a DMM (digital multimeter) or use a 225-8266 Ammeter Tool Gp . Clamp the probe around the "B+" wire of the alternator. Before you clamp the probe around the wire, ensure that the probe is "zeroed".

3. Read the current on the meter. Make a note of the current that was measured.

Expected Result:

The current is under 2 A.

Results:

• YES - The current is under 2 A. Proceed to test step14.

• NO - The current is over 2 A.

  Repair: There is an internal problem with the alternator. Repair the alternator or Replace the alternator.

  STOP

Test Step 14. TEST THE OUTPUT CURRENT OF THE ALTERNATOR BELOW 0.015 AMPERES.

1. 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 generator set. Proceed to test step 15.

• NO - The current is over 0.015 A.

  Repair: There is an internal problem with the alternator. Repair the alternator or replace the alternator.

  STOP

Test Step 15. IDENTIFY THE SOURCE OF EXCESSIVE CURRENT DRAW.

1. Make sure that every electrical component is turned OFF. Make sure that the disconnect switch is turned OFF.

2. 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.

3. 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.

4. Check if any components on the circuit are ON.

5. If everything is OFF, then disconnect electrical components on the circuit one at a time. Monitor the current after each component is disconnected.

6. 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. Contact a Caterpillar dealer for more information.

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.

1. Verify that the nut on the "B+" alternator terminal is tight. Also, verify that the wire has a good connection to the "B+" terminal.

2. Start the engine and set the throttle to at least 75 percent. Allow the engine to run for at least 3 minutes before continuing.

3. 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.

4. 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 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. Repair the alternator or replace the alternator.

  STOP

• NO - The voltage at the battery is less than the voltage at the alternator. However, the difference in voltages 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.

1. Measure the voltage between the frame of the generator set and the "B+" terminal of the alternator. Make a note of the voltage that was measured. Perform the next measurement immediately.

2. Measure the voltage between the frame of the generator set 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.

Results:

• VOLTAGE OK . - The voltage difference does not exceed the tolerance. The positive circuit is good.

  Repair: There is an internal problem with the alternator. Repair the alternator or replace the alternator.

  STOP

• VOLTAGE EXCESSIVE - 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.

  • A circuit breaker has failed.

  Correct the problem. Exit this procedure and retest the alternator charging system.

  STOP