Operational Analysis - Guardian 4389 Repair Manual

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AC GENERATORS

ROTOR RESIDUAL MAGNETISM

The generator revolving field (rotor) may be consid-

ered to be a permanent magnet. Some "residual"

magnetism is always present in the rotor. This resid-

ual magnetism is sufficient to induce a voltage into

the stator AC power windings that is approximately 2-

12 volts AC.

FIELD BOOST

FIELD BOOST CIRCUIT:

When the engine is cranking, direct current flow is

delivered from a circuit board to the generator rotor

windings, via Wire 4.

The field boost system is shown schematically in

Figure 2. Manual and automatic engine cranking is

initiated by circuit board action, when that circuit

board energizes a crank relay (K1). Battery voltage is

then delivered to field boost Wire 4 (and to the rotor),

via a field boost resistor and diode. The crank relay,

field boost resistor and diode are all located on the

circuit board.

Notice that field boost current is available only while

the crank relay (K1) is energized, i.e., while the

engine is cranking.

PART 2

Figure 1. Operating Diagram of AC Generator