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GENERAL INFORMATION
GENERAL
Standby electric power generators will often run
unattended for long periods of time. Such operating
parameters as (a) battery voltage, (b) engine oil pres-
sure, (c) engine temperature, (d) engine operating
speed, and (e) engine cranking and startup are not
monitored by an operator during automatic operation.
Because engine operation will not be monitored, the
use of engine protective safety devices is required to
prevent engine damage in the event of a problem.
Prepackaged generator engines mount several engine
protective devices. These devices work in conjunction
with a circuit board, to protect the engine against
such operating faults as (a) low battery, (b) low engine
oil pressure, (c) high temperature, (d) overspeed, and
(e) overcrank. On occurrence of any one or more of
those operating faults, circuit board action will effect
an engine shutdown.
LOW BATTERY
The microprocessor will continually monitor the bat-
tery voltage and turn on the Low Battery LED if the
battery voltage falls below 11.0 volts for one (1) min-
ute. No other action is taken on a low battery condi-
tion. Low battery voltage is a non-latching alarm
which will automatically clear if the battery voltage
rises above 11.0 volts. Battery voltage is NOT moni-
tored during the crank cycle.
LOW OIL PRESSURE SHUTDOWN
See Figure 1. An oil pressure switch is mounted on
the engine oil filter adapter. This switch has normally
closed contacts that are held open by engine oil pres-
sure during cranking and startup. Should oil pressure
drop below approximately 8 psi, the switch contacts
will close. On closure of the switch contacts, a Wire
86 circuit from the circuit board will be connected to
ground. Circuit board action will then de-energize a
"run relay" (on the circuit board). The run relay's nor-
mally open contacts will then open and a 12 volts DC
power supply to a Wire 14 circuit will then be terminat-
ed. This will result in closure of a fuel shutoff solenoid
and loss of engine ignition.
HIGH TEMPERATURE SWITCH
This switch's contacts (Figure 1) close if the tempera-
ture should exceed approximately 140° C (284° F),
initiating an engine shutdown. The generator will auto-
matically restart and the LED on the generator control
panel will reset once the temperature has returned to
a safe operating level.
PART 1
ENGINE-GENERATOR PROTECTIVE DEVICES
OVERSPEED SHUTDOWN
During engine cranking and operation, the circuit
board receives AC voltage and frequency signals from
the ignition magneto, via Wire 18. Should the speed
exceed approximately 72 Hz (4320 rpm), circuit board
action will de-energize a "run relay" (mounted on the
circuit board). The relay's contacts will open, to termi-
nate engine ignition and close a fuel shutoff solenoid.
The engine will then shut down. This feature protects
the engine-generator against damaging overspeeds.
NOTE: The circuit board also uses rpm sensing to
terminate engine cranking.
RPM SENSOR FAILURE
During cranking, if the board does not see a valid
RPM signal within three (3) seconds, it will shut down
and latch out on RPM sensor loss.
During running, if the RPM signal is lost for one full
second the board will shut down the engine, wait 15
seconds, then re-crank the engine.
• If an RPM signal is not detected within the first three
(3) seconds of cranking, the control board will shut
the engine down and latch out on RPM sensor loss.
• If the RPM signal is detected the engine will start
and run normally. If the RPM signal is subsequently
lost again, the control board will try one more re-
crank attempt before latching out and flashing the
overspeed LED.
LOW OIL SWITCH
Figure 1. Engine Protective Switches on an
Air-Cooled Engine
SECTION 1.5
HIGH TEMP SWITCH
Page 23
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