RING-WEAR 8C9120 - Caterpillar

Introduction
For Rewind Data and Connection Diagrams, see Rewind Data for SR 4 Generators, Form No. SENR2924.Troubleshooting
General
Before working inside the generator, make sure that the starter motor can not be activated by any automatic or manual signal.
When the engine-generator is operating, voltages up to 240 are present on the regulator terminal board. The heat sinks and other regulator components have an electric charge. Components will be damaged if a metal contact is made between the generator frame and the heat sinks or other regulator parts. Safety procedures must be followed.
A large percent of the electrical problems are caused by mechanical defects. Take time to carefully inspect the total installation. Keep the mechanical defects separate from the electrical defects.For practical purposes, the generator is a constant speed unit. RPM that is 5 to 10 percent higher or lower than the rated rpm can cause terminal voltages that are 5 to 10 percent higher or lower than the rated output.Generator heat is caused by line current. The higher the line current, the hotter the generator will become.A voltmeter and ammeter or KW meter does not necessarily show the KVA load on a generator because of the power factor of the load.Before working on the generator, be sure you understand the operating principles.Find the operating trouble and use the wiring diagram and troubleshooting guide to find the probable cause.When troubleshooting for voltage, a generator can normally be operated at a low rpm. Voltage and frequency will change directly with rpm. A four-pole, 60 Hertz, 240 volt, 1800 rpm generator at a low idle of 1200 rpm will have an output of 160 volts at 40 hertz. For information on mechanical and electrical characteristics of SR 4 generators, make reference to the section INDUSTRIAL DIVISION DATA SHEETS: No. 70.0.1 and the TECHNICAL INFORMATION FILE (TIF).Test Instruments
A volt-ohm-milliammeter with scales of approximately the following values: AC volts ... 0-12, 0-100, 0-300DC volts ... 0-50, 0-100, 0-150Ohms ... X1, X10, X100, X1000DC Amps ... 0-3The 6V3030 Digital Multimeter can also be used. By itself or with other tools, it can do the following: 1. Test rectifiers with the special diode function.2. Measures resistance of the revolving field and stator winding of the generator or exciter winding.3. With the 6V4960 AC Current Probe, the multimeter can measure current in the range 10A to 1000A rms (at a circuit-to-ground voltage of 650 V rms maximum.) See Special Instruction, Form SEHS8011 for warnings and more information on how to use the current probe.
6V3030 DIGITAL MULTIMETERA circuit continuity tester, similar to the 8S4627 (circuit continuity tester) can be used for checking low resistance continuity. This tool can also be used to check rectifiers and controlled rectifiers. It uses a 3-volt battery source. This is all that is needed to activate the gate of a controlled rectifier.A Kelvin or Wheatstone bridge can be used to measure the resistance of the revolving field and stator winding of the generator or the exciter armature.A 500 to 1000 volts megohmeter is needed to