Generac Power Systems 00862-1 - Manual (Page 10)

ENGINE PROTECTIVE DEVICES
AUTOMATIC LOW OIL
PRESSURE SHUTDOWN
The engine is equipped with a normally closed (N.C.)
oil pressure switch (Figure 4).Engine oil pressure
holds the switch open during cranking and operation.
Should oil pressure drop below about 7.5-12 PSI, the
switch contacts close and the engine automatically
shuts down.
Figure 4 — Switches for Engine Shutdown
HIGH TEMPERATURE SHUTDOWN
A temperature switch (Figure 4) with normally closed
(N.C.) contacts is mounted near the oil filter. If the
temperature were to exceed about 284°F (140°C), the
switch contacts close and the engine shuts down.
FIELD BOOST
The Controller Circuit Board houses a field boost
diode and resistor which are not part of the automatic
choke circuit. These two components are part of a
“field boost” circuit (Figure 5). During engine cranking
only, a positive DC (battery) voltage Is delivered
through the diode, resistor, brushes and slip rings,
and to the generator rotor. Application of this voltage
to the rotor “flashes the field” whenever it is started.
Flashing of the field each time the generator is started
makes sure that a sufficiently strong magnetic field is
available to produce the required “pick up” voltage in
the stator windings.
Figure 5 — Field Boost Circuit
OVER VOLTAGE PROTEaiON
A solid state voltage regulator (Figure 6) controls the
generator’s AC output voltage. This regulator controls
an excitation current to the rotor. By regulating the
rotor’s excitation current, the strength of its magnetic
field is regulated and, in turn, the voltage delivered to
connected electrical loads is controlled. When the AC
frequency Is 60 Hz, voltage is regulated at 120 volts
(voltage-to-frequency ratio is 2-to-1).
Figure 6 — Voltage Regulator
„ ~V- SENSING 11—'
TO ROTOR
(.) —1~ (DIRECT CURRENT)
FROM STATOR
EXCnATIONWINDMO
(ALTERNATING CURRENT)
The voltage regulator also incorporates a “voltage
surge protection circuit.” This circuit prevents trouble­
some surges in the generator AC output voltage.
Voltage surge is a common cause of damage to elec­
tronic equipment.
ENGINE OVERSPEED
If engine speed is increased manually or otherwise,
the circuit controller board will disable the system and
shut down the engine.
WARNING: Do NOT attempt to physically adjust or
control the engine speed. Equipment damage or
personal injury may result.