A solid state regulator is installed on the back of the alternator. Two brushes conduct current through two slip rings to the field coil on the rotor. The "steel pole fingers" of the rotor retain residual or permanent magnetism. If the alternator is not used for a long period of time, it may be necessary to electrically restore some of the residual magnetism in the rotor core again. This residual magnetism is needed to excite the alternator in order to start the charging process.
Operation Schematics
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| Illustration 1 | g01054879 |
12V Series Alternators | |
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| Illustration 2 | g01056324 |
24V Series Alternators | |
Charging Circuit
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| 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.
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| 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.