SWITCH GP-LIMIT 3573967 - Caterpillar

alternator is a brushless, heavy-duty integral charging system. The alternator has a built-in diode rectifier and a voltage regulator. The system produces DC current for electrical systems.The solid state integrated circuit voltage regulator that is built into the alternator limits the system voltage by switching the ground circuit for the field coil on and off. This is done rapidly in order to control the current that is in the field coil. When the ground circuit for the alternator field is turned ON by the voltage regulator, the field current passes from the diode trio and through the stationary field coil. Nominal regulated voltages of 13.5 to 14.5 volts are available for 12 volt systems. The nominal regulated voltage for the 24 volt system is between 27 and 29 volts.After the engine is started and rpm rises, the excitation circuit is turned on all the time, and generated voltage rises rapidly. If the "I" terminal is not used, the initial field voltages at start-up are generated by residual magnetism. The residual magnetism can be lost. This results in no output. Loss of the residual magnetism can be caused by extended downtime or a severe shock to the alternator. Refer to Troubleshooting, "T6 Residual Magnetism Restoration". As the speed increases and the output increases, the voltage that is available at the diode trio becomes sufficient to supply field current for normal operation. When the voltage at the "B" terminal exceeds the battery voltage current flows into the battery.The 34SI model has an "I" terminal. The terminal CAN be used in order to supply excitation current. The current flows from a source that has a keyswitch through an indicator light. The indicator light provides a verification for alternator excitation and the light also provides a indication of faults. The "I" terminal must have an indicator or a resistor in series between the current source and the "I" terminal. This maintains the normal field current around 0.17 amperes. Once the alternator begins charging, the