PAD 7J4775 - Caterpillar

Introduction
The K1/N1 Series Bosch Alternator has three phase, full-wave, rectified output. It is the brush-type. See the Bosch Alternator Coverage Chart in Specifications for the list of alternators covered in this module. The 7T-2876 Charging Alternator Gp is referenced throughout this module. The other alternators are similar. The difference between the alternators is noted.Alternator Operation
Illustration 1 g03237077
BOSCH AlternatorThe alternator is an electrical and mechanical component driven by belt rotation from the engine. It is used to charge the storage battery during engine operation. The alternator is cooled by a fan that is part of the alternator. The fan pulls air through the back of the alternator. The air exits the front of the alternator, cooling it in the process.The alternator converts mechanical and magnetic energy to alternating current (AC) and voltage. This process is done by rotating a direct current (DC) electromagnetic field (rotor) inside a three phase stator assembly. The alternating current and voltage (generated by the stator) are changed to direct current (DC) by a three phase, full wave rectifier system. The rectifier system has six silicon rectifier diodes. DC current flows to the alternator output terminal. The rectifier also has three exciter diodes. They rectify the current needed to start the charging process.A solid-state regulator is installed on the back of the alternator. Two brushes conduct current, through two slip rings, to the rotor field. A capacitor, installed on some alternators, smooths alternator DC voltage.These alternators are self-exciting at high speed. That means they have residual magnetism in the rotor. The excitation circuit cannot start the charging process until the pre-excitation circuit produces the required breakdown voltage. The alternator is connected to the battery through the ignition or key start switch. This connection supplies the necessary current to the pre-excitation circuit. This current is available every time the ignition switch is turned on.