Important Information

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When servicing or repairing electric power generation equipment, do the following: a. Make sure the unit is off-line (disconnected from utility and/or other generators power service), and either locked out or tagged "DO NOT OPERATE". b. Make sure the generator engine is stopped. c. Make sure all batteries are disconnected. d. Make sure all capacitors are discharged. When power generation equipment must be in operation to make tests and/or adjustments, high voltage and current are present. Make sure the testing equipment is designed for and correctly operated for the high voltage and current tests being made. Improper test equipment may fail and present a high voltage shock hazard to its user.

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Do not connect the generator to a utility electrical distribution system, unless it is isolated from the system. Electrical feedback into the distribution system can occur and could cause personal injury or death. Open and secure the main distribution system switch or, if the connection is permanent, install a double throw transfer switch to prevent electrical feedback. Some generators are specifically approved by a utility to run in parallel with the distribution system and isolation may not be required. Always check with your utility as to the applicable circumstances.

Test Equipment

6V7070 Heavy Duty Digital Multimeter

Caterpillar Digital Multimeters measure voltage, resistance, or current up to 10 amps. The diode function checks rectifiers. See Special Instruction SEHS7734 for the operation of 6V7070.

Troubleshooting

SR4 Generator Schematic (10/12 Lead, Self-Excited)

Introduction

Check for loose or corroded terminals. Make sure wire connections are correct. Check the accuracy of the voltmeter and frequency meter/tachometer.

To reduce troubleshooting time, simplify the system or circuit by eliminating non-essential components. If, at this point, it is determined that the basic system is functioning, the circuits or components can be added back in, one at a time until the problem is located.

If elimination of non-essential components does not correct the problem, the troubleshooting procedure will check components in the basic system. If all other basic components (i.e. rotating field assembly, exciter stator etc.) are operating correctly, then replace the VR4 regulator. As a last step after confirming correct operation under no load conditions, operate the generator under a load.

The VR4 regulator will be serviced as a complete unit. Its fuse is the only replaceable part. VR4 regulators must be checked through the bench test before making a claim on warranty (see Bench Test).

Problem List

Problem 1 - No AC Voltage.

Problem 2 - Low AC Voltage.

Problem 3 - High AC Voltage.

Problem 4 - Unstable AC Voltage.

Problem 1 - No AC Voltage

Procedure A - Check AC voltage at regulator between terminals 20 and 22.

* If above 200 volts:

Check meters.

* If 0 volts:

Flash the field. See SR4 Generator Service Manual, SENR3985.

* If 0 to 15 volts:

Go to Procedure B.

Procedure B - Isolate Regulator

Disconnect leads from regulator terminals F1 and F2. Connect a 12 volt automotive type battery across exciter leads F1 (+) and F2 (-). Operate generator at half of the rated speed. Then slowly increase rpm.

* If voltage at regulator terminals 20 and 22 is 0 to 15 volts (AC):

a. Check exciter stator (L1) continuity.

b. Check rotating rectifier block.

c. Check main rotor (L3) continuity.

d. Check exciter rotor (L2) continuity.

NOTE: For more information, see SR4 Generator Service Manual, SENR3985.

* If balanced AC voltage between regulator terminals 20-22-24 increases with rpm:

Go to Procedure C.

Procedure C - Isolate Attachments

Reconnect leads to regulator terminals F1 and F2. Disconnect all attachments such as series boost and remote voltage control.

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

Check all connections to regulator and the regulator fuse.

* If generator output voltage is normal:

Check attachments.

* If voltage at regulator terminals 20 and 22 is 0 to 15 volts:

a. Replace regulator.

b. Bench test the regulator (see Bench Test).

Problem 2 - Low AC Voltage

Procedure A - Check Engine RPM (Frequency)

Procedure B - Adjust Voltage Level With Gain Adjustment Full Counterclockwise

* Voltage level adjustment range should be within +10 to -25% of rated voltage.

a. Check meters.

b. Go to Procedure C.

Procedure C - Check AC Voltage Between Regulator Terminals 20 And 22

* If greater than 200 volts:

Check meters.

* If lower than 200 volts:

Go to Procedure D.

Procedure D - Isolate Regulator

Disconnect leads from regulator terminals F1 And F2. Connect a 12 volt automotive type battery across exciter leads F1 (+) and F2 (-). Operate generator at half of the rated speed. Then slowly increase RPM.

* If voltage at regulator terminals 20 and 22 is less than 100 volts:

a. Check rotating rectifier block. See SR4 Generator Service Manual, SENR3985.

b. Check exciter stator (L1) resistance between F1 and F2 leads. Exciter stator resistance should be approximately 2 to 6 ohms. See SR4 Generator Service Manual, SENR3985.

* If balanced AC voltage between regulator terminals 20-22-24 increases with RPM:

Go to step E.

Procedure E - Isolate Attachments

Connect exciter stator (L1) leads to regulator terminals F1 and F2. Disconnect all attachments such as series boost and remote voltage control.

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7. Check all connections to the regulator and regulator fuse.

* If generator output voltage is normal:

Check attachments.

* If voltage at regulator terminals 20 and 22 cannot be adjusted to rated voltage and rated frequency at no load:

a. Replace regulator.

b. Bench test the regulator (see Bench Test).

Problem 3 - High AC Voltage

Procedure A - Check Engine RPM (Frequency)

Procedure B - Adjust Voltage Level With Gain Adjustment Full Counterclockwise.

* Voltage level adjustment range should be within +10% to -25% of rated voltage.

a. Check meter.

b. Go to Procedure C.

* Check accuracy of generator set voltmeter.

Procedure C - Check Connections To Regulator.

* If connections are correct:

Go to Procedure D.

Procedure D - Isolate Attachments

Disconnect all attachments such as series boost and remote voltage control. Operate at rated rpm.

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

* If generator output voltage is normal:

Check attachments.

* If voltage cannot be adjusted to rated voltage at rated frequency:

a. Replace regulator.

b. Bench test the regulator (see Bench Test).

Problem 4 - Unstable AC Voltage

Procedure A - Check Engine RPM

* Governor operation is unstable.

a. Correct engine problem. Reference engine service manual.

b. Go to Procedure B.

Procedure B - Check for loose connections.

* If connections are okay:

Go to Procedure C.

Procedure C - Isolate Regulator.

Disconnect leads F1 and F2 from their respective terminals on the regulator. Connect a 12 volt automotive type battery across exciter leads F1 and F2. Operate at half of rated speed and then slowly increase rpm.

* Voltage at regulator terminals 20-22 is unstable.

a. Check connections to rotating rectifier block, main field poles and other connections on the rotating (revolving) field.

b. Check connections to excitor stator.

* If stable balanced AC voltage between regulator terminals 20-22-24 increases with rpm:

Go to Procedure D.

Procedure D - Isolate Attachments

Reconnect leads to regulator terminals F1 and F2. Disconnect attachments such as series boost and remote voltage control. Operate at rated rpm.

NOTE: If remote mounted voltage adjustment is disconnected, connect jumper across terminals 4 and 7.

Check all connections to the regulator and its fuse.

* If generator output voltage is normal:

Check attachments.

* If voltage at regulator terminals 20-22 is unstable at rated frequency with no load:

a. Replace regulator.

b. Bench test the regulator (see Bench Test).

Bench Test

NOTE: An alternative to the following test procedure is available. The 4C4693 Regulator Tester with NEHS0535 Operating Manual can be used to bench test the regulator.

Bench Test Circuit
(1) AC power source. (2) On/Off switch. (3) Voltage level rheostat. (4) Voltage gain rheostat. (5) 100W Light bulb.

1. Construct and connect the bench test circuit. AC power source (1) must be:

60 Hz units ... 220 to 240 VAC

50 Hz units ... 180 to 200 VAC

2. Turn voltage level rheostat (3) and voltage gain rheostat (4) counterclockwise 32 full turns.

NOTE: Voltage level rheostat (3) and voltage gain rheostat (4) are multiple (thirty) turn rheostats. The adjusting screw on the rheostat does not have a fixed stop. To ensure the lowest position, turn the rheostat 32 full turns counterclockwise from the current position. To ensure the highest position, turn the rheostat 32 full turns clockwise from the current position. The adjusting screw can be turned past the rheostat stop (ratchet action) without further changing the rheostats setting.

3. Turn switch (2) to the ON position.

4. Turn voltage level rheostat (3) clockwise until light (5) first turns ON (approximately ten turns). The light should increase and decrease in intensity as rheostat (3) is turned clockwise and counterclockwise respectively. After 10 to 15 seconds at maximum intensity, light (5) should go OFF.

* If light (5) reacts as described:

Regulator is okay.

* If light (5) reacts different than described:

Replace VR4 regulator.