Generator Set Control Panel for Switchgear Conversion 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. If a warning indicator for the charging system is ON, see Service Magazine, SEBD1751, "Difference Between Alternator Indicator In Electronic Monitoring System (EMS) And Low Voltage Indicator In Operating Monitoring System (OMS)". When a problem with the charging system is suspected, then complete the testing that is outlined in this Special Instruction. See "Initial Troubleshooting Procedure" in order to begin troubleshooting. The procedures in this Special Instruction are designed to guide you to the problem with as little testing as possible. In most cases, you will only use a few of the tests to diagnose a problem.

Initial Troubleshooting Procedure

1. CHECK THE RESISTANCE OF THE EXCITATION CIRCUIT (Check 1). 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 Step 3 if your alternator is self-excited. Go to Step 2 if your alternators excitation terminal is labeled with "IG".

   1. If the generator set is equipped with a disconnect switch, turn the disconnect switch to the ON position.

   2. 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. The ground source is the alternator case ground.

   3. Read the voltage that is shown on the multimeter.

      Expected Result - The voltage reads at least 0.2 V.

      Results -

      • OK: The voltage reads 0.2 V or more. The excitation circuit is correct. Proceed to Step 3.

      • NOT OK: The voltage is less than 0.2 V. 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.

2. CHECK THE RESISTANCE OF EXCITATION CIRCUIT (Check 2). 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 Step 3 if your alternator is self-excited.

   1. Turn the disconnect switch to the ON position.

   2. 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).

   3. Read the voltage that is shown on the multimeter.

      Expected Result - The voltage is within 0.5 V of the battery voltage.

      Results -

      • OK: The voltage reads battery voltage. The excitation circuit is correct. Proceed to Step 3.

      • NOT OK: The voltage is below battery voltage by more than 0.5 DCV. 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.

3. CHECK THE SYSTEM VOLTAGE.

   1. Before starting 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.

      Expected Result - This voltage should be system voltage.

      Results -

      • OK: The voltage is system voltage. Go to Step 4

      • NOT OK: The voltage is less than system voltage. Verify that the batteries are good and verify that battery connections are good. If the batteries are good, go to "Test 4 (Alternator Drive System Test)".

4. INITIAL CHECK OF ALTERNATOR OPERATION

   1. The voltmeter remains connected in the configuration from Step 3.

   2. 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 that was recorded in the previous Step 3.

      Results -

      • OK: The voltage is higher than the voltage that was observed in 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 "Test 1 (Alternator Output Test)".

      • OK: The voltage is higher than the voltage that was observed in 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 "Test 8 (Alternator Overcharging Test)".

      • NOT OK: The voltage is not higher than the voltage that was observed in Step 3. Proceed to "Test 4 (Alternator Drive System Check)".

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 charging will begin. Alternator output can be low at idle.

Illustration 1	g00508188

Test 1

Alternator Output Test

1. Ensure that the batteries are NOT fully charged.

   1. Fully charged batteries have open circuit voltage of 25 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. As an alternative, operate the lights for 10 minutes while the engine is off.

2. 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 clamping the probe around the wire, ensure that the probe is "zeroed".

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

4. 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 "Test 2 (Electrical System Current Test)".

   • NOT OK: The current is less than 90% of the specified peak output. Go to "Test 4 (Alternator Drive System Check)".

Test 2A

Test For A Generator Set That Is Equipped With A Main Disconnect Switch

1. Turn off all of the accessories. Disconnect the battery voltage supply to the EMCP II+.

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. Read the current.

   Expected Result - The current is below 2 A.

   Results -

   • OK: The current is below 2 A. Continue to Step 3.

   • NOT OK: The current is above 2 A. There is a current draw in the system. Go to "Test 5 (Alternator Current Test)".

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.

4. Turn off the disconnect switch and read the current.

   Expected Result - The current is below 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 -

   • OK: The current is below 50 mA. 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.

   • NOT OK: The current is above 50 mA. There is a draw in the system. Go to "Test 5 Alternator Current Test".

Test 2B

Test For Any Generator Set

1. Turn off all accessories. Also, disconnect the battery voltage supply to the EMCP II+.

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 around the wire. Read the current.

   Expected Result - The current is below 2 A.

   Results -

   • OK: The current is below 2 A. Continue to Step 3.

   • NOT OK: The current is above 2 A. There is a current draw in the system. Go to "Test 5 (Alternator Current Test)".

3. Remove the ground cable from the battery terminal. For systems with four batteries, disconnect the ground cables from both negative batteries.

4. 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 50 mA.

   Note: The standard acceptable current draw is 50 mA. A current draw above 50 mA usually indicates a problem.

   Results -

   • OK: The current is below 50 mA. 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.

   • NOT OK: The current is above 50 mA. There is a draw in the system. Go to "Test 5 (Alternator Current 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 50 mA, the regulator is faulty.

Test 3

Charging System Test

1. Verify that the alternator B+ terminal nut is tight and 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 to Step 3. The following table will assist in making calculations during this test.
   Show/hide table

   Table 1

   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
   8		1.0 V

3. Measure the voltage between the alternator B+ terminal and the alternator case ground.

4. Measure the voltage across the battery. Put the red lead on the + battery terminal. Put the black lead on the - battery terminal. Step 4 should be completed as quickly as possible after Step 3.

   Expected Result - On 24 V systems, the voltage is within 2 V.

   Results -

   • OK: On 24 V systems, the voltage in Step 3 is not more than 2 V higher than the voltage in Step 4. This test is complete and the related wiring is correct at this time. Replace the alternator or disassemble the alternator and repair.

   • NOT OK: On 24 V systems, the voltage in Step 3 is more than 2 V higher than the voltage in Step 4. There is high circuit resistance. High circuit resistance can be caused by one of the following conditions: corrosion, loose connections and damaged wiring. Continue to Step 5.

5. Check the voltage between the frame and the alternator B+ terminal. Record the voltage.

6. Check the voltage between the frame and the + battery post. Step 6 should be completed as quickly as possible after Step 5.

   Expected Result - The voltage difference between Step 5 and Step 6 does not exceed 1 V on 24 V systems.

   Results -

   • OK: The voltage difference does not exceed the tolerance. The charging circuit is good. Go to Step 7.

   • NOT OK: 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.

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 -

   • OK: The voltage difference does not exceed the tolerance. The ground circuit is good. There is an internal problem with the alternator. Go to "Test 6 (Residual Magnetism Restoration)".

   • NOT OK: 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.

Test 4

Alternator Drive System Check

1. 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.

2. Check the tension of the alternator drive belt. If the tension is off, adjust the tension.

3. Check the nut on the alternator pulley. If the nut is loose, tighten the nut and retest the system.

4. If all of the previous steps find no problems, go to "Test 3 (Charging System Test)".

Test 5

Alternator Current Test

1. Disconnect all the loads from the battery. Disconnect the battery voltage supply to the EMCP II+.

2. 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 clamping the probe around the wire, ensure that the probe is "zeroed" .

3. Read the current.

   Expected Result - The current is under 2 A.

   Results -

   • OK: The current is under 2 A. Continue to Step 4.

   • NOT OK: The current is over 2 A. There is an internal problem with the alternator. Go to "Test 6 (Residual Magnetism Restoration)".

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 alternators B+ terminal. Set the multimeter on the 10 amp scale. Read the current.

   Expected Result - The current is under 15 mA.

   Results -

   • OK: The current is under 15 mA. The alternator is operating correctly. There is a current draw on the generator set. Go to "Test 7 (Identifying Source Of Current Draw Test)".

   • NOT OK: The current is over 15 mA. There is an internal problem with the alternator. Go to "Test 6 (Residual Magnetism Restoration)".

Test 6

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.

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. If a wire is connected, disconnect the wire from the "R" terminal.

   Expected Result - The voltage remains constant.

   Results -

   • OK: The voltage remains constant. Continue to Step 4.

   • NOT OK: The voltage rises and the alternator started 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.

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

5. Connect the other end of the jumper wire to the "R" terminal ("D+" terminal for Bosch) 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. Disassemble the alternator and repair the alternator. If the alternator cannot be repaired, replace the alternator.

6. 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 -

   • OK: 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.

   • NOT OK: The voltage output does not rise. Disassemble the alternator and repair the alternator. If the alternator cannot be repaired, replace the alternator.

Test 7

Identifying The Source Of Current Draw Test

1. Disconnect all the loads from the battery. Disconnect the battery system voltage from the EMCP II+.

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. Monitor the current. Remove the following fuses one at a time: "F1", "F4", "F7" and "F8". Check the current after each fuse is removed. After removing a fuse and observing the current, reinstall the fuse. Start with the main fuses first, and proceed to smaller circuits.

4. If a removal of a fuse causes the current to drop, then the problem is in that circuit.

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

   2. If everything is OFF, disconnect electrical components on that circuit one at a time and monitor current.

   3. 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.

Test 8A

Alternator Overcharging Test (Check 1)

This test is for alternators that have one of the following terminals:

• "IG"

• "S"

• any other sense terminal

1. Clean the connection and tighten the connection to the wiring terminal on the alternator.

2. Verify that the alternator B+ terminal nut is tight and verify that the wire has a good connection to the "B+" terminal.

3. 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 continuing to Step 4. The following table will assist in making calculations during this test.
   Show/hide table

   Table 2

   Test Step	Voltage Reading	Voltage should be below this reading for a 24 V system
   5
   6
   5 minus 6 =		2.0 V
   7
   8
   7 minus 8 =		1.0 V

4. Measure the voltage between the alternator B+ terminal and the alternator case ground.

5. 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 24 V systems, the voltage is within 2 V.

   Results -

   • OK: On 24 V systems, the voltage in Step 4 is not more than 2 V higher than the voltage in Step 5. This step is complete and the related wiring is correct at this time. Go to Step 8.

   • NOT OK: On 24 V systems, the voltage in Step 4 is more than 2 V higher than the voltage in Step 5. There is high circuit resistance. High circuit resistance can be caused by the following conditions: corrosion, loose connections and damaged wiring. Go to Step 6.

6. Check the voltage between the frame and the alternator B+ terminal. Record the voltage.

7. Check the voltage between the 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 V on 24 V systems.

   Results -

   • OK: The voltage difference does not exceed the tolerance. The charging circuit is good. Go to Step 8.

   • NOT OK: 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.

8. Start the engine and set the throttle to at least 75 percent.

9. 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 -

   • OK: The voltage is higher than specification. The alternator is faulty or the regulator is faulty. Replace the alternator or repair the alternator.

   • NOT OK: The voltage is below the voltage that was found in the initial tests ("B+" to the 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.

Test 8B

Alternator Overcharging Test (Check 2)

This test is for alternators that have one of the following terminals:

• "IG"

• "S"

• any other sense terminal

1. Clean the alternator wiring terminal connection. Tighten the alternator wiring terminal connection.

2. Verify that the alternators B+ terminal nut is tight. Also verify that the wire has a good connection to the B+ terminal.

3. Run the engine at 75 percent. Allow the engine to run for at least 3 minutes before continuing to Step 4. The following table shows the way that the measurements that were 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
   5
   6
   5 minus 6 =		2.0 V
   7
   8
   7 minus 8 =		1.0 V

4. Measure the voltage between the alternators B+ terminal and the alternator case ground.

5. 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 24 V systems, the voltage is within 2 V.

   Results -

   • OK: On 24 V systems, the voltage in Step 4 is not more than 2 V higher than the voltage in Step 5. This step is complete and the related wiring is correct at this time. Go to Step 8.

   • NOT OK: On 24 V systems, the voltage in Step 4 is more than 2 V higher than the voltage in Step 5. There is high circuit resistance. High circuit resistance can be caused by the following conditions: corrosion, loose connections and damaged wiring. Go to Step 6.

6. Check the voltage between the frame and the alternators B+ terminal. Record the voltage.

7. Check the voltage between the 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 V on 24 V systems.

   Results -

   • OK: The voltage difference does not exceed the tolerance. The charging circuit is good. The regulator is faulty or the alternator is faulty. Replace the suspect component, and retest the system.

   • NOT OK: The voltage difference exceeds the tolerance. There is high resistance in the charging circuit. High resistance in the charging circuit can be caused by the following conditions: 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.

Alternator Specifications

Table 4

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 , 122-6657100	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.