DRAIN AS 3726370 - Caterpillar

Operation Schematics
Illustration 1 g01054879
12V Series Alternators
Illustration 2 g01056324
24V Series AlternatorsCharging Circuit
Illustration 3 g01123654
Charging circuit with 120° phase "U" angle.Current for battery charging and for the electrical accessories is taken from the "+" terminal of the alternator. The flow of current for battery charging and electrical accessories at an instant of time (120° phase angle) is shown in Illustration 3.Voltage at the output of winding "U" is positive, while it is negative at "W" and zero at "V" (no voltage). The current path is as follows:Output of winding "U", positive diode, alternator terminal "B+", battery ground, negative diode, output of winding "W", neutral point.
Illustration 4 g01123655
Charging circuit with 150° phase "U" angle.If another instant is chosen (150° phase angle) where none of the voltages are zero, the current would flow as shown in Illustration 4.Equal currents flow from the windings "U" and "V" to the respective positive diodes. They return to the neutral point through the winding "W" negative diode and winding "W". Note that not all the diodes belonging to the various phases are used at the instant of time examined in this example. This remains true for all the other instants of time which could be examined. Individual phase currents change in magnitude and polarity, while the output current to the battery or electrical accessories maintains its uniform direction.Alternator Excitation
Alternator excitation is done through residual magnetism of the rotor. If the alternator sits for a long period of time, the rotor magnetism may be reduced below the level to excite the alternator. Refer to Testing and Adjusting, "Residual Magnetism - Restore" for the procedure to restore the residual magnetism in the alternator.The alternator is turned on through the ignition switch. There is an external wire that connects the regulator to battery when the ignition switch is turned on.Regulator Operation
The voltage regulator is an electronic switching device. It senses the system voltage level and switches the voltage applied to the field in order to maintain proper system voltage. The circuit is a variable duty cycle switch which determines what the average field current in the alternator will be. A high ratio of "on-to-off" time will result in a near full field condition while a low ratio will result in a low field current condition. Alternator rpm and system load conditions are the factors which determine what the field current must be.Both regulator sensing and operating power (including field power) are obtained from the output terminal of the alternator.