HEAD 6E4974 - Caterpillar

All SR4 GeneratorsReports indicate the life of the exciter field windings may not be satisfactory when the generator is operating in a humid, salty environment (usually a marine application). The presence of salt water on the surface of the exciter field can allow electrolysis to occur. Electrolysis will remove copper from the field windings until the wire is severed. Two methods of extending field winding life are available for generators that must operate in humid, salty environments. One method is to provide electrical isolation for the exciter field windings. The other method is to put an electrical ground on the positive side of the exciter field winding.
Illustration 1. Location of the wire between terminal (G) and terminal (1) or (3) on TS400.
Illustration 2. Location of new 7W8888 Resistor.The 7W9833 Isolation Transformer Kit is available to provide electrical isolation for the field exciter windings. This kit can be used on all SR4 Generators using A1 module type regulators except the 689 Frame Generators used on 3500 Series Engines. The exceptions include 5N7248 and 5N7249 Generator Groups. The 7W9833 Isolation Transformer Kit can be field installed. The kit consists of 3 transformers mounted in a steel box that can be installed on top of the generator. A conduit and wiring harness are also included. Special Instruction, Form SELS0091, packaged with the kit, gives installation instructions.
On larger SR4 generators with multiple card-type regulators, the electrically grounded terminal of the exciter field winding can be switched and a 7W8888 Resistor added to the circuit. See Illustrations 1 and 2. To switch the grounded side of the field winding and add the 7W8888 Resistor, use the procedure that follows.
1. Locate the wire that goes from terminal (G) on the regulator terminal strip to terminal (1) or (3) of TS400 (TS400 is located on the M4 Board). See Illustration 1.2. Disconnect that wire from terminal (1) or (3) and terminal (G). Be sure to leave the other wires connected to terminals (1), (3) and (G).3. Connect the 7W8888 Resistor (10K ohm, 25 watt) between terminals (G) and (F1) as shown in Illustrations 2 and 3.
Illustration 3. Location of new 7W8888 Resistor.