Generac Power Systems QT100, Owner'S Manual, Page: 8 / 80

ENGINE PROTECTIVE DEVICES
The Stationary Emergency Generator may be required to operate
for long periods of time without an operator on hand to monitor
such engine conditions as coolant temperature, oil pressure or
rpm. For that reason, the engine has several devices designed to
protect it against potentially damaging conditions by automatically
shutting down the unit when the oil pressure is too low, the coolant
temperature is too high, the coolant level is too low, or the engine
is running too fast.
NOTE:
Engine protective switches and sensors are mentioned here for
the reader's convenience. Also refer to the applicable control
panel manual for additional automatic engine shutdown infor-
mation.
COOLANT TEMPERATURE SENSING
An analog Water Temperature Sender (WTS) is located in the
engine's cooling system. This sender is connected to the panel
and allows the panel to monitor and display the temperature of the
coolant system.
The WTS is a resistive device whose resistance changes based
on coolant temperature. The resistance of the sender results in a
voltage being developed across the sender. As the Coolant tem-
perature increases, the resistance will decrease, causing the volt-
age to decrease. This changing voltage is converted to 4-20mA
signal by a signal conditioner module. The corresponding 4-20mA
signal is read by the control panel and displayed as the coolant
temperature.
The control panel will monitor and display the coolant temperature
anytime the DC input to the control panel is present.
If the temperature exceeds approximately 140° C (284° F), the
engine shutdown will be initiated. The generator will automatically
restart and the display will reset once the temperature has returned
to an operating level.
LOW COOLANT LEVEL
A Low Coolant Level (LCL) sensor is placed in the generators cool-
ant system. This sensor allows the panel to detect a Low Coolant
Level condition.
The LCL is a resistive device whose resistance changes rapidly
based on the presence or absence of coolant.
The resistance of the LCL results in a voltage being developed
across the LCL. This voltage changes as the resistance changes.
This changing voltage is converted to 4-20mA signal by a signal
conditioner module. The corresponding 4-20mA signal is read by
the control panel and displayed as the low coolant level.
If the level of the engine coolant drops below the level of the low
coolant level sensor, the engine shutdown will be initiated.
OIL PRESSURE SENSING
An analog Oil Pressure Sender (OPS) is used for monitoring the
engine oil pressure. This sender allows the control panel to mea-
sure and display the Engine oil pressure.
The OPS is a resistive device, whose resistance changes based
on engine oil pressure. The resistance of the sender results in a
voltage being developed across the sender. As the oil pressure
increases, the resistance will decrease, causing the voltage to
decrease. This changing voltage is converted to 4-20mA signal by
a signal conditioner module. The corresponding 4-20mA signal is
read by the control panel and displayed as the oil pressure.
The control panel will monitor and display oil pressure anytime the
DC input to the control panel is present.
Should the oil pressure drop below the 8 psi range, the engine
shutdown is initiated. The unit should not be restarted until oil is
added. Turn the AUTO/OFF/ MANUAL switch to the OFF position,
then back to AUTO to restart.
OVERCRANK SHUTDOWN
When the control panel receives a start signal, it initiates the pro-
grammed starting sequence. The start sequence consists of the
number of crank attempts, the length of each crank attempt, and
the rest time between each crank attempt. If the engine has not
started by the end of the final crank attempt, an Overcrank alarm
is generated, the control panel will sound the alarm and display the
message "Failed to start".
OVERSPEED SHUTDOWN
A speed circuit controls engine cranking, start-up, operation and
shutdown. Engine speed signals are delivered to the circuit board
whenever the unit is running. Should the engine over speed above
a safe, preset value, the circuit board initiates an automatic engine
shutdown. Contact the nearest Authorized Dealer if this failure
occurs.
RPM SENSOR LOSS SHUTDOWN
If the speed signal to the control panel is lost, engine shutdown
will occur.
DC FUSE
This fuse is located inside of the control panel. It protects the panel
wiring and components from damaging overload. Always remove
this fuse before commencing work on the generator. The unit will
not start or crank if the fuse is blown. Replace the fuse with one of
the same size, type, and rating. (See the exploded views and parts
lists at the end of this manual for replacement part number.)
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EngProt002 R ev. D 06/10
Engine Protective Devices