Section 4.2 - Engine Protective Devices; Introduction; Low Battery Warning; Low Oil Pressure - Generac Power Systems 7 kW NG Repair Manual

Section 4.2
Engine Protective Devices

INTRODUCTION

Standby power generators will often run unattended for long
periods. Such operating parameters as (a) battery voltage,
(b) engine oil pressure, (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.

LOW BATTERY WARNING

The controller will continually monitor the battery voltage and
display a "Low Battery Voltage" message if the battery voltage
falls below 11.9 VDC for 1 minute.
No other action is taken on a low battery condition. The warning
will automatically clear if the battery voltage rises above 12.4
VDC.

LOW OIL PRESSURE

See Figure 91. An oil pressure switch is mounted on the oil
filter adapter. This switch has normally closed contacts that are
held open by engine oil pressure during cranking and startup.
Should oil pressure drop below approximately 5 psi, the switch
contacts will close. On closure of the switch contacts, the Wire
86 circuit from the controller will be connected to ground. The
controller's logic will then de-energize a "run relay" (internal to
the controller). The run relay's contacts will then open and then
the 12 VDC run circuit will then be terminated. This will result in
closure of the fuel shutoff solenoid and loss of engine ignition.

HIGH TEMPERATURE SWITCH

The contacts of this switch (Figure 91) close if the temperature
should exceed approximately 293º F (144ºC), initiating an
engine shutdown. The Generator will automatically restart and
the fault on the LCD display will reset once the temperature has
returned to a safe operating level.
LOW OIL SWITCH
Figure 91. Engine Protective Switches
Page 94
HIGH TEMP SWITCH
OIL FILTER
PART 4

OVERSPEED

During engine cranking and operation the controller receives
AC voltage and frequency signals from the ignition magneto
via Wire 18. Should the speed exceed approximately 72 Hz
(4320 RPM), the controller's logic will de-energize the "run
relay" (internal to the controller). The relay contacts will open
terminating engine ignition and closing the fuel shutoff solenoid;
the engine will then shut down. This feature protects the engine
and alternator against damaging over speeds. During cranking
the RPM signal generated by the magnetos is used 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 shutdown and latch out on "RPM
Sensor Loss."
During running if the RPM signal is lost for one full second
the controller will shutdown 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 controller will shut down 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
controller will try one re-crank attempt before latching out
and the LCD displays "RPM Sensor Loss."
Note: A common cause of RPM Sensor Loss fault is the lack
of engine cranking; this could be a faulty crank circuit or a
faulty starter.

OVERCRANK

This feature prevents the Generator from damaging itself when
it continually attempts to start and another problem, such as no
fuel supply, prevents it from starting. The unit will crank and
rest for a preset time limit. Then, it will stop cranking and the
LCD screen will indicate an "Overcrank" condition. The AUTO-
OFF-MANUAL switch will need to be set to OFF and then back
to AUTO to reset the generator.
Note: If the fault is not repaired, the overcrank fault will
continue to occur.
The system will control the cyclic cranking as follows: 16
second crank, seven (7) second rest, 16 second crank, seven
(7) second rest followed by three (3) additional cycles of seven
(7) second cranks followed by seven (7) second rests.
Choke Operation
1. The 990/999cc engines have an electric choke in the
air box that is automatically controlled by the electronic
control board.
2. The 530cc engines have an electric choke on the divider
panel air inlet hose that is automatically controlled by the
electronic control board.
ENGINE/DC CONTROL