ker88839_ch08.qxd
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Figure 8-4. The output circuit and the field circuit make up the automotive charging system. (DaimlerChrysler Corporation)
Chapter Eight
Figure 8-6. These are the voltage levels induced across the upper half of the conductor during one rotor revolution. (DaimlerChrysler Corporation)
turns. The alternating current caused by a singlephase voltage is called single-phase current.
DIODE RECTIFICATION Figure 8-5. No current flows when the rotor’s magnetic field is parallel to the stator. (DaimlerChrysler Corporation)
current output. Figure 8-6 shows the voltage levels induced across the upper half of the looped conductor during one revolution of the rotor. The constant change of voltage, first to a positive peak and then to a negative peak, produces a sine wave voltage. This name comes from the trigonometric sine function. The wave shape is controlled by the angle between the magnet and the conductor. The sine wave voltage induced across one conductor by one rotor revolution is called a single-phase voltage. Positions 1 through 5 of Figure 8-6 show complete sine wave singlephase voltage. This single-phase voltage causes alternating current to flow in a complete circuit because the voltage switches from positive to negative as the rotor
If the single-phase voltage shown in Figure 8-6 made current travel through a simple circuit, the current would flow first in one direction and then in the opposite direction. As long as the rotor turned, the current would reverse its flow with every half revolution. The battery cannot be recharged with alternating current. Alternating current must be rectified to direct current to recharge the battery. This is done with diodes. A diode acts as a one-way electrical valve. If a diode is inserted into a simple circuit, as shown in Figure 8-7, one-half of the AC voltage is blocked. That is, the diode allows current to flow from X to Y, as shown in position A. In position B, the current cannot flow from Y to X because it is blocked by the diode. The graph in Figure 8-7 shows the total current. The first half of the current, from X to Y, was allowed to pass through the diode. It is shown on the graph as curve XY. The second half of the current, from Y to X, was not allowed to pass through the diode. It does not appear on the graph because it never traveled through the circuit. When the
