Generac 86640 - Manual (Page 7)

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□ The VOLTAGE REGULATOR will continue to increase
or decrease direct current flow to the ROTOR, In an
attempt to maintain STATOR AC POWER WINDING
voltage at the same value as the REGULATOR’S preset
REFERENCE voltage.
□ When the STATOR AC POWER WINDING circuit is
completed by connecting a load to the winding's AC
output leads, current will flow through the windings and
to the load.
Rotor Residual Magnetism
The Rotor may be considered a permanent magnet since
some residual magnetism is always normally present In the
Rotor windings. As a general rule. Rotor residual magnetism
atone (without regulated excitation current and without field
boost current) will produce a STATOR AC POWER WINDING
output of approximately 2 to 7 volts.
Field Boost
When the engine Is being cranked, direct current is
delivered to the Rotor windings from a source other than the
Stator excitation windings and Voltage Regulator. This direct
current, in effect, Hashes the field" every time the engine is
cranked. By applying field boost current to the Rotor during
cranking, an early "pickup" voltage Is induced into the Stator
windings to turn the Regulator on sooner and provide AC
output more quickly.
Failure of the field boost circuit rrray or may not result In
toss or dropout of AC power winding output voltage, depend­
ing on the characteristics of the Individual generator. The
following general rules apply:
D If Rotor residual magnetism atone (without field boost) is
sufficient to turn the Voltage Regulator on and provide
the required pickup voltage, the generator will operate
normally with normal AC output voltage.
G If Rotor residual magnetism atone (without field boost) Is
NOT sufficient to turn the Regulator on and provide the
needed pickup voltage, generator AC output voltage will
not build and will be commensurate with Rotor residual
magnetism (about 2 to 7 volts AC).
G If regulated excitation current to the Rotor is lost. Stator
AC power winding output voltage will drop to a value that
is commensurate with Rotor residual magnetism (2 to 7
volts AC). The magnetic field strength created by field
boost current cannot be considered since it is available
only while cranking.
UNITS WITH GASOLINE FUEL SYSTEM;
See Figure 6. Units equipped with a gasoline fuel system
use a choke module (CM) which closes and opens a choke
solenoid (CS) during engine cranking to open and close the
carburetor choke.
UNITS WITH LP GAS FUEL SYSTEM:
Units equipped with a gaseous fuel system do not require
a carburetor choke and do not have a choke module. The field
boost circuit for such units Is shown in Rgure 7. While
cranking, battery voltage is delivered to Terminal No. 8 of an
engine control circuit board, to Wire No. 9, a field boost
assembly. Wire No. 4, and to the Rotor via brushes and slip
rings.
The field boost assembly, shown In Figure 8, consists of
a 100 ohm, 1 watt resistor (1^) and a 200 volt, 1 amp diode
(D2). The diode ensures that current will flow in one direction
only in the circuit. The resistor reduces the battery voltage
(12 volts DC) to approximately 9-10 volts DC.
Figure 6. Field Boost Circuit (Gasoline Fuel System)
STARTER
CONTACTOR
§
° 1 FROM
BATTERY
*
-Q)
ENGINE CONTROL
CIRCUIT BOARD
TO ROTOR •
-TO STARTER
11 CHOKE
* MODULE
DIODE
AMP
Y 1 AMf
L a / v -J
RESISTOR
47 OHM. 2 WATT
Figure 7. Field Boost Circuit (LP Gas Fuel System)
TO IGNITION COIL
9 RESISTOR ^9°^
W-
9
9-----W\ T-
too OHM 200V.
1 WATT 1 WATT
ENGINE CONTROL
CIRCUIT BOARD
TO
ROTOR