Initial Troubleshooting Procedure
- CHECK THE RESISTANCE IN THE EXCITATION CIRCUIT. This step is only for alternators with external excitation when the terminal for excitation is labeled: "1", "REG" and "D+". See "Alternator Specifications" if the method of excitation is unknown. Go to 3 if your alternator is self-excited. Go to 2 for alternators that have an "IG" excitation terminal.
- If the generator set is equipped with a disconnect switch, then turn the disconnect switch to the ON position.
- Verify voltage at the excitation terminal. Connect the red lead from a multimeter to the excitation terminal. Connect the black lead to a ground source (alternator case ground).
- Read the voltage that is shown on the multimeter.
Expected Result: The voltage reads at least .2 volts.
Results:
- YES - The voltage reads .2 volts or more. The excitation circuit is correct. Proceed to 3.
- NO - The voltage is less than .2 volts. There is a fault in the wiring harness to the alternator or there is a poor electrical connection. Correct the problem. Watch for a recurrence of the problem.
- YES - The voltage reads .2 volts or more. The excitation circuit is correct. Proceed to 3.
- CHECK THE RESISTANCE IN THE EXCITATION CIRCUIT. This step is only for alternators with external excitation when the terminal for excitation is labeled: "IG". See "Alternator Specifications" if the method of excitation is unknown. Go to 3 if your alternator is self-excited.
- Turn the disconnect switch to the ON position.
- Verify voltage at the excitation terminal. Connect the red lead from a multimeter to the excitation terminal. Connect the black lead to a ground source . This is often the case of the alternator.
- Read the voltage that is shown on the multimeter.
Expected Result: The voltage is within .5 volts of battery voltage.
Results:
- YES - The voltage reads battery voltage. The excitation circuit is correct. Proceed to 3.
- NO - The voltage is more than .5 volts less than battery voltage. There is a fault in the wiring harness to the alternator or there is a poor electrical connection. Correct the problem. Watch for a recurrence of the problem.
- YES - The voltage reads battery voltage. The excitation circuit is correct. Proceed to 3.
- CHECK THE SYSTEM VOLTAGE.
- 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.
- Turn the disconnect switch to the ON position but do not start the engine.
Expected Result: This voltage should be system voltage.
Results:
- YES - The voltage is system voltage. Go to 4
- NO - The voltage is less than system voltage. Verify that the batteries are good and verify that battery connections are good. Go to "T4 Alternator Drive System - Check" if the batteries are good.
- YES - The voltage is system voltage. Go to 4
- CHECK OF THE INITIAL OPERATION OF THE ALTERNATOR.
- The voltmeter remains connected in the configuration from 3.
- Start the engine. Set the throttle to at least 75%. Read the voltage on the voltmeter.
Expected Result: The voltage is higher than the voltage recorded in the previous Step 3.
Results:
- YES - The voltage is higher than the voltage observed in the previous Step 3. The voltage is also lower than the maximum voltage that is listed in the specifications for the alternator. The alternator is partially charging. See the following diagnostic flow chart for reference in continued testing. Proceed to "T1 Alternator Output - Test".
- YES - The voltage is higher than the voltage observed in the previous Step 3. The voltage is also higher than the maximum voltage that is listed in the specifications for the alternator. The alternator is over charging. Proceed to "T8 Alternator Overcharging - Test".
- NO - The voltage is not higher than the voltage observed in 3. Proceed to "T4 Alternator Drive System - Check".
- YES - The voltage is higher than the voltage observed in the previous Step 3. The voltage is also lower than the maximum voltage that is listed in the specifications for the alternator. The alternator is partially charging. See the following diagnostic flow chart for reference in continued testing. Proceed to "T1 Alternator Output - Test".
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. Most of the alternators in Caterpillar applications are self-excited. These alternators must exceed a turn-on speed before the charging will begin. Alternator output can be low at idle.
Illustration 1 | g00508188 |
T1 Alternator Output - Test
- Ensure that the batteries are NOT fully charged.
- Fully charged batteries have open circuit voltage of 25 V on 24 V systems.
- If the batteries are fully charged, then crank the engine for 30 seconds. This action reduces the battery voltage. Operate the lights for 10 minutes while the engine is off as an alternative.
- Connect the 9U-5795 Current Probe to a DMM (digital multimeter) or use the 225-8266 Ammeter Tool Gp . The multimeter must have a peak hold feature. Clamp the probe around alternator output wire ("B+"). Before you clamp the probe around the wire, ensure that the probe is "zeroed" .
- Set the digital multimeter to "peak hold" or "max mode" on the "mV" scale.
- Start the engine, 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: This current reading should be at least 90% of the specified peak output.
Results:
- OK - The current is at least 90% of the specified peak output. See "Alternator Specifications" for exact numbers. Go to "T2a Undesired Electrical System Current - Test (For Generator Set Equipped With A Main Disconnect Switch)" or "T2b Undesired Electrical System Current - Test (For Any Generator Set)".
- NOT OK - The current is less than 90% of the specified peak output. Go to "T4 Alternator Drive System - Check".
- OK - The current is at least 90% of the specified peak output. See "Alternator Specifications" for exact numbers. Go to "T2a Undesired Electrical System Current - Test (For Generator Set Equipped With A Main Disconnect Switch)" or "T2b Undesired Electrical System Current - Test (For Any Generator Set)".
T2a - Undesired Electrical System Current - Test (For Generator Set Equipped With A Main Disconnect Switch)
- Turn off all of the accessories. Disconnect the voltage supply to the EMCP II.
- 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.
Expected Result: The current is below 2 A.
Results:
- YES - The current is below 2 A. Continue to 3.
- NO - The current is above 2 A. There is a current draw in the system. Go to "T5 Alternator Current - Test".
- YES - The current is below 2 A. Continue to 3.
- Turn the disconnect switch to the ON position. Connect a multimeter 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. Use the 10A connections in order to avoid damage.
- Turn off the disconnect switch and read the current.
Expected Result: The current is below .050 amperes (50 mA).
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.
Results:
- YES - The current is below 0.050 A. The charging system is currently good. The fault is possibly an intermittent draw in the system. The batteries may be faulty. Check that NO accessories were ON during the test.
- NO - The current is above 0.050 A. There is a draw in the system. Go to "T5 Alternator Current - Test".
- YES - The current is below 0.050 A. The charging system is currently good. The fault is possibly an intermittent draw in the system. The batteries may be faulty. Check that NO accessories were ON during the test.
T2b - Undesired Electrical System Current - Test (For Any Generator Set)
- Turn off all accessories. Disconnect the voltage supply to the EMCP II.
- 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 around the wire. Read the current.
Expected Result: The current is below 2 A.
Results:
- YES - The current is below 2 A. Continue to 3.
- NO - The current is above 2 A. There is a current draw in the system. Go to "T5 Alternator Current - Test".
- YES - The current is below 2 A. Continue to 3.
- Remove the ground cable from the battery terminal. For systems with four batteries, disconnect the ground cables from both negative batteries.
- Connect a multimeter between the disconnected battery ground cable and one of the negative battery terminals. Connect the red positive lead of the multimeter to the cable. The negative lead should be connected to the battery terminal. Use the 10 A connections in order to avoid damage.
Expected Result: The current is below .050 amperes (50 mA).
Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem.
Results:
- YES - The current is below 0.050 A. The charging system is currently good. The fault is possibly an intermittent draw in the system. The batteries may be faulty. Check that NO accessories were ON during the test.
- NO - The current is above 0.050 A. There is a draw in the system. Go to "T5 Alternator Current - Test".
- YES - The current is below 0.050 A. The charging system is currently good. The fault is possibly an intermittent draw in the system. The batteries may be faulty. Check that NO accessories were ON during the test.
Note: The following alternators have a connector for a regulator: 6T-1196 and 9G-6081 . Disconnect the regulator connector from the alternator. Recheck the current that was found in the previous Step. If the current is below 0.050 A (50 mA), the regulator is faulty.
T3 Charging System - Test
- Verify that the alternator B+ terminal nut is tight and verify that the wire has a good connection to the B+ terminal.
- Start the engine and set the throttle to at least 75 percent. Allow the engine to run for at least 3 minutes before you continue to 3. The following table will assist in making calculations during this test.
Show/hide table
Table 1 Test Step     Voltage Reading     The Voltage should be less than this column for a 24 V system.     3         4         3 minus 4 =         2.0 V     5             6         5 minus 6 =         1.0 V     7         1.0 V    
- Measure the voltage between the alternator B+ terminal and the alternator case 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. 4 should be completed as quickly as possible after 3.
Expected Result: On 24 V systems, the voltage is within 2 V.
Results:
- YES - If the voltage in 3 is not more than 2 V for 24 V systems higher than the voltage in 4, this test is complete and the related wiring is correct at this time. Replace the alternator or disassemble the alternator and repair.
- NO - If the voltage in 3 is more than 2 V for 24 V systems higher than the voltage in 4, there is high circuit resistance: corrosion, loose connections and damaged wiring. Continue to 5.
- YES - If the voltage in 3 is not more than 2 V for 24 V systems higher than the voltage in 4, this test is complete and the related wiring is correct at this time. Replace the alternator or disassemble the alternator and repair.
- Check the voltage between the frame and the alternator B+ terminal. Record the voltage.
- Check the voltage between the frame and the + battery post. Step 6 should be completed as quickly as possible after 5.
Expected Result: The voltage difference between 5 and 6 does not exceed 1 V on 24 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. Go to 7.
- NO - The voltage difference exceeds the tolerance. There is high resistance in the charging circuit: loose cables, corroded cables, damaged cables and faulty circuit breaker. Correct the problem and retest the system.
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. Go to 7.
- 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 ground circuit is good. There is an internal problem with the alternator. Go to "T6 Residual Magnetism Restoration".
- NO - The voltage difference exceeds the tolerance. There is high resistance in the ground circuit: loose cables, corroded cables, loose alternator mounting and poor engine ground. Correct the problem and retest the system.
- YES - The voltage difference does not exceed the tolerance. The ground circuit is good. There is an internal problem with the alternator. Go to "T6 Residual Magnetism Restoration".
T4 Alternator Drive System - Check
- Check the condition of the alternator drive belt. If the drive belt is oily, clean the pulleys. Replace the drive belt, and retest the system. If the drive belt is wet, dry the belt and retest the system. If the drive belt is worn, replace the belt and retest the system.
- Check the tension of the alternator drive belt. If the tension is off, adjust the tension.
- Check the nut on the alternator pulley. If the nut is loose, tighten the nut and retest the system.
- If all of the previous steps find no problems, go to "T3 Charging System - Test".
T5 Alternator Current - Test
- Disconnect all the loads from the battery. Disconnect the voltage supply to the EMCP II.
- Connect the 9U-5795 Current Probe to a DMM (digital multimeter) or use the 225-8266 Ammeter Tool Gp . Clamp the probe around the alternator output wire ("B+"). Before you clamp the probe around the wire, ensure that the probe is "zeroed".
- Read the current.
Expected Result: The current is under 2 A.
Results:
- YES - The current is under 2 A. Continue to 4.
- NO - The current is over 2 A. There is an internal problem with the alternator. Proceed to "T6 Residual Magnetism Restoration".
- YES - The current is under 2 A. Continue to 4.
- Disconnect the B+ terminal wire from the alternator. 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. Set the multimeter on the 10 amp scale. Read the current.
Expected Result: The current is under 0.015 A.
Results:
- YES - The current is under 0.015 A. The alternator is operating correctly. There is a current draw on the generator set. Go to "T7 Identifying Source Of Current Draw - Test".
- NO - The current is over 0.015 A. There is an internal problem with the alternator. Go to "T6 Residual Magnetism Restoration".
- YES - The current is under 0.015 A. The alternator is operating correctly. There is a current draw on the generator set. Go to "T7 Identifying Source Of Current Draw - Test".
T6 Residual Magnetism Restoration
This test is only for self-excited alternators. See Service Magazine, SEBD1672 July 1986, "Brushless Alternators May Not Charge In Certain Conditions" for additional information.
- Start the engine and set the throttle to at least 75%.
- Connect a voltmeter between the "B+" terminal and the alternator case ground.
- If a wire is connected, disconnect the wire from the "R" terminal.
Expected Result: The voltage stays the same.
Results:
- YES - The voltage stays the same. Continue to 4.
- NO - The voltage rises and the alternator begins charging. The wire to the "R" terminal is shorted. Repair the wiring or replace the wiring. Go to "Initial Troubleshooting Procedure" and retest the system.
- YES - The voltage stays the same. Continue to 4.
- Connect one end of a jumper wire to the "B+" terminal of the alternator.
- Connect the other end of the jumper wire to the "R" terminal ("D+" terminal for Bosch alternators) of the alternator for 2 seconds.
Expected Result: The voltage output rises on the "B+" terminal.
Results:
- OK - The voltage output rises. The alternator is now charging. Go to "Initial Troubleshooting Procedure" and retest the system.
- NOT OK - The voltage output does not rise. There is an internal malfunction in the alternator. See the appropriate service manual or the alternator in order to test the internal components and connections.
- OK - The voltage output rises. The alternator is now charging. Go to "Initial Troubleshooting Procedure" and retest the system.
- Remove the wire that is connected to the "I" terminal. Check for a rise in voltage on the "B+" terminal.
Expected Result: The voltage rises.
Results:
- YES - The voltage rises. There is a short in the wiring to the terminal. Repair the wiring or replace the wiring. Go to "Initial Troubleshooting Procedure" and retest the system.
- NO - The voltage output does not rise. There is an internal malfunction in the alternator. See the appropriate service manual or the alternator in order to test the internal components and connections.
- YES - The voltage rises. There is a short in the wiring to the terminal. Repair the wiring or replace the wiring. Go to "Initial Troubleshooting Procedure" and retest the system.
T7 Identifying Source Of Current Draw - Test
- Disconnect all the loads from the battery. Disconnect the system voltage from the EMCP II.
- 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. Use the current probe if the draw is above approximately 2 A. Use the Ammeter if the draw is below approximately 2 A.
- Monitor the current and remove the following fuses one at a time: "F1", "F4", "F7" and "F8". Check the current after each fuse is removed. After you remove a fuse, observe the current and reinstall the fuse. Start with the main fuses first, and proceed to smaller circuits.
- If a removal of a fuse causes the current to drop, then the problem is in that circuit.
- Check if any components on the circuit are ON.
- If everything is OFF, disconnect electrical components on that circuit one at a time and monitor current.
- After all of the components in that circuit have been disconnected, check the current. If the problem still exists, then check the wiring for corrosion or shorts to ground.
Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem.
T8a - Alternator Overcharging - Test
This test is for alternators that have an "IG" terminal , an "S" terminal, or another sense terminal.
- Clean the connection and tighten the connection to the wiring terminal on the alternator.
- Verify that the alternator B+ terminal nut is tight and verify that the wire has a good connection to the "B+" terminal.
- Start the engine and set the throttle to at least 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 this test.
Show/hide table
Table 2 Test Step     Voltage Reading     Voltage should be less than this column for a 24 V system.     4         5         4 minus 5 =         2.0 V     6             7         6 minus 7 =         1.0 V    
- Measure the voltage between the alternator's "B+" terminal and the case for the alternator.
- 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 4.
Expected Result: On 24 V systems, the voltage is within 2 V.
Results:
- YES - If the voltage in 4 is not more than 2 V for 24 V systems higher than the voltage in 5, this step is complete and the related wiring is correct at this time. Go to 8.
- NO - If the voltage in 4 is more than 2 V for 24 V systems higher than the voltage in 5, there is high circuit resistance: corrosion, loose connections and damaged wiring. Go to 6.
- YES - If the voltage in 4 is not more than 2 V for 24 V systems higher than the voltage in 5, this step is complete and the related wiring is correct at this time. Go to 8.
- Check the voltage between the frame and the alternator B+ terminal. Record the voltage.
- Check the voltage between the frame and the + battery post. Step 7 should be completed as quickly as possible after 6.
Expected Result: The voltage difference between 6 and 7 does not exceed 1 V on 24 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. Go to 8.
- 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 "Initial Troubleshooting Procedure" and retest the system.
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. Go to 8.
- Start the engine and set the throttle to at least 75 percent.
- Measure the voltage between the sense terminal and the case of the alternator.
Expected Result: The voltage at the sense terminal is above the specification.
Results:
- YES - The voltage is over specification. There is an internal malfunction in the alternator. See the appropriate service manual for the alternator in order to test the internal components and connections.
- NO - The voltage is below that found in the initial tests (B+ to alternator case). The sense circuit in the generator set has high resistance. Correct the problem and retest the system . Go to "Initial Troubleshooting Procedure" at the beginning of this test.
- YES - The voltage is over specification. There is an internal malfunction in the alternator. See the appropriate service manual for the alternator in order to test the internal components and connections.
T8b - Alternator Overcharging - Test (Continued)
This test is for alternators that do not have an "IG" terminal, "S" terminal, or other sense terminal.
- Clean the connection and tighten the connection to the wiring terminal on the alternator.
- Verify that the alternator's "B+" terminal nut is tight. Verify that the wire has a good connection to the "B+" terminal.
- Run the engine at 75 percent. Allow the engine to run for at least 3 minutes before you continue to 4. The following table shows the measurements taken during this test will be used.
Show/hide table
Table 3 Test Step     Voltage Reading     Voltage should be below this reading for a 24 V system     4         5         4 minus 5 =         2.0 V     6             7         6 minus 7=         1.0 V    
- Measure the voltage between the alternator B+ terminal and the alternator case ground.
- Measure the voltage across the battery. Put the red lead on the positive battery terminal, and put the black lead on the negative battery terminal. Step 5 should be completed as quickly as possible after 4.
Expected Result: On 24 V systems, the voltage is within 2 V.
Results:
- YES - If the voltage in 4 is not more than 2 V for 24 V systems higher than the voltage in 5, this step is complete and the related wiring is correct at this time. There is an internal malfunction in the alternator. See the appropriate service manual for the alternator in order to test the internal components and connections.
- NO - If the voltage in 4 is more than 2 V for 24 V systems higher than the voltage in 5, there is high circuit resistance: corrosion, loose connections and damaged wiring. Go to 6.
- YES - If the voltage in 4 is not more than 2 V for 24 V systems higher than the voltage in 5, this step is complete and the related wiring is correct at this time. There is an internal malfunction in the alternator. See the appropriate service manual for the alternator in order to test the internal components and connections.
- Check the voltage between the frame and the alternator B+ terminal. Record the voltage.
- Check the voltage between the frame and the positive battery post. 7 should be completed as quickly as possible after 6.
Expected Result: The voltage difference between 6 and 7 does not exceed 1 V on 24 V systems.
Results:
- YES - The voltage difference does not exceed the tolerance. The charging circuit is good. There is an internal malfunction in the alternator. See the appropriate service manual for the alternator in order to test the internal components and connections.
- 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 "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. See the appropriate service manual for the alternator in order to test the internal components and connections.
Alternator Specifications
Alternator Specifications     | ||
---|---|---|
    | Peak Current Rating (Amps)     | Minimum Peak Current (Amps)     |
24 V Alternators     | ||
2P-1204 , 3Y-8200     | 19     | 17     |
2Y-8310     | 21     | 19     |
6T-1395 , 7T-2095 , OR-3653     | 33     | 30     |
6N-9294 , OR-5217 , OR-3482     | 35     | 32     |
5N-5692 , OR-2698     | 45     | 41     |
5S-9088 , 100-5047 , 112-5041 , OR-5206 , OR-3667 , OR-3668     | 50     | 45     |
109-2362 , 9W-3043 , OR-3652 (D+), 112-8032     |
55     | 50     |
3E-7772 (IG), OR-9437 (IG), 105-3132 (IG), 4N-3986 , OR-5203     | 60     | 54     |
155-7434 , 132-2156 (I), 107-7977 (I), OR-8279 (I)     | 70     | 63     |
107-7976 , 114-2401 , OR-8997 , 3E-7577 , OR-3615     | 75     | 68     |
9X-7803 , OR-3749 , 122-6657     | 100     | 90     |
Parts-Service Only Discontinued 24 V Alternators     | ||
9G-6081 , 6T-1196     | 40     | 36     |
D+ - Diode trio output. Alternator requires external excitation.     | ||
REG - Regulator Terminal. Alternator requires external excitation.     | ||
I - Ignition Terminal. Alternator can be externally excited through this terminal.     | ||
IG - Ignition Terminal. System voltage must be supplied to this terminal to turn on the alternator. Some of these alternators use the IG terminal as a sense terminal.     |