Generac Power Systems 16 kW NG, 10 kW LP, 13 kW NG Rotor Residual Magnetism, Field Boost 12-20 KW

AC generators

Part 2

Section 2.2 Operational analysis

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 residual magnetism is sufficient to induce a voltage into the stator AC power windings that is approximately 2-12 volts AC.

Field Boost (12-20 KW)

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. 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 is energized, i.e., while the engine is cranking.

	TO LOAD
MLB = MAIN LINE	MLB
CIRCUIT BREAKER

STATOR	STATOR
POWER	POWER
WINDING	WINDING

Field boost voltage is reduced from that of battery voltage by the resistor action and, when read with a DC voltmeter, will be approximately 9 or 10 volts DC.

+12 VDC
	PIN 5	13
		56	TO
			STARTER
	FIELD
	BOOST
DIODE	RESISTOR
	PIN 1
CRANk	FIELD	4	STARTER
RELAY k1			CONTACTOR
	BOOST
BASE	DIODE
TRANSISTOR
		FIELD
		BOOST
CIRCUIT BOARD		TO
		ROTOR

Figure 2. Field Boost Circuit Schematic

TO LOAD

MLB MLB = MAIN LINE CIRCUIT BREAKER

SENSING

	MAGNETIC
	FIELD
ENGINE -
DIRECT	ROTOR
DRIVE
		ENGINE -
	MAGNETIC	DIRECT
	FIELD	DRIVE
	STATOR
	EXCITATION
	WINDING

STATOR	STATOR
POWER	POWER
WINDING	WINDING

MAGNETIC

FIELD

ROTOR

MAGNETIC

FIELD

FIELD BOOST FROM

CONTROL LOGIC

CIRCUIT BOARD

VOLTAGE

REGULATOR

CAPACITOR

STATOR

EXCITATION

WINDING

8/10 kW Units 12-20 kW Units

Figure 1. Operating Diagram of AC Generator

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