A typical 10Si series wiring diagram is illustrated in Figure 3. The basic operating principles are explained as follows.
The No. 2 terminal is connected to the battery, and the base-emitter of transistors TR4 and TR1 is connected to the battery through resistor R5, thus turning these transistors on. Also, resistors R2 and R3 are connected to the battery through terminal No. 2, but the discharge current of the battery is very low because of the resistance values of R2, R3, R5, TR1 and TR3.
When the switch is closed, current from the battery flows through the indicator lamp to the alternator No. 1 terminal, through resistor R1, and transistors TR3 and TR1 to ground, and then back to the battery. The indicator lamp then turns on.
With the generator operating, AC voltages are generated in the stator windings, and the stator supplies DC field current through the diode trio, the field, TR1, and then through the grounded diodes in the rectifier bridge back to the stator. Also, the six diodes in the bridge rectifier change the stator AC voltages to a DC voltage which appears between ground and the generator " BAT " terminal. As alternator speed increases, current is provided for charging the battery and operating electrical accessories. Also, with the alternator operating, the same voltage appears at the " BAT " and No. 1 terminals, and the indicator lamp goes out to indicate the alternator is producing voltage.
If an open should occur in the No. 2 terminal circuit, TR3 and TR1 will turn off, and no field current will flow to prevent overcharge. As the alternator speed and voltage increase, the voltage between R2 and R3 increases to the point where Zen er diode D1 conducts. Transistor TR2 then turns on and TR3 and TR1 turn off. With TR1 off, the field current and system voltage decrease, and D1 then blocks the current flow, causing TR3 and TR1 to turn back on. The field current and system voltage increase, and this cycle then repeats many times per second to limit the alternator voltage to a preset value.
Capacitor C1 smooths out the voltage across R3, resistor R4 prevents excessive current through TR1 at high temperatures, and diode D2 prevents high-induced voltages in the field windings when TR1 turns off. Resistor R2 is a thermistor which causes the regulated voltage to vary with temperature, thus providing the optimum voltage for charging the battery.