Murphy MC-900 Series - Manual (Page 4)

3-2 MC-900.
3-2.1 Control / Display Module. The Control / Display
Module, figure 3-2.1, includes the control and test switches,
the solid state logic elements and shutdown TATTLETALE
®
lights that make up the generator engine control for a four
cycle engine.
3-2.1.1 Mode Selector Switch, OFF-RUN-START:
(a) OFF; turns off the control system and resets any
shutdown circuits.
(b) RUN; turns on the engine controls and shutdown
circuits. System is on, waiting for the engine to start.
Switch returns to run position from START after starting
engine.
(c) START; turns on the engine start circuit. A start signal is
applied to the auxiliary start solenoid and the engine
starter engages. Releasing the start switch disconnects
cranking.
3-2.1.2 Lamp Test Pushbutton: Tests the lights on the MC-900
module when the Mode Selector Switch is in the RUN
position.
3-2.1.3 The MC-900 SELECTRONIC
® Control Module
includes the following engine control features:
(a) Overcrank circuit; will stop manual cranking and
indicate overcrank if start switch remains closed longer
than the overcrank time setting. The crank time is
selectable for 10, 15, 20, 25 or 30 seconds before
shutdown.
(b) Shutdown Time Delay Bypass; this delay prevents the
oil pressure and water temperature shutdown circuits
from operating for 30 seconds after the engine starts as
detected by the Mode Selector Switch returning to RUN
position. This same delay can also lock out all other
shutdown circuits except Overspeed and Overcrank.
The user may select which circuits are locked out by the
time delay bypass.
(c) Overspeed Speed Switch;
1. Provides a signal to the overspeed shutdown circuit
if the engine exceeds the preset speed. The factory
setting is approximately 3894 Hz, or 1980 RPM on
an engine with 118 teeth on the flywheel ring gear.
The adjustment range is 300 Hz to 10,000 Hz.
2. A push to test switch is provided to allow testing of
the overspeed circuit without overspeeding the
engine. When switch is depressed, the set point of
the speed switch is lowered approximately 10%.
3. The push to test switch can also be used to set the
overspeed switch at approximately 110% of running
speed. Hold the switch depressed while adjusting the
setting until the overspeed trips. When switch is
released, the set point will be 10% above normal
running speed. This is the method used to make the
factory setting. With engine speed at 1800 RPM or
3540 Hz.
3-2.1.4 Eight (8) First-out Shutdown Circuits; provide first-
out indication of cause of shutdown. These circuits deactivate
the fuel relay and lockout the MC-900 until reset. Shutdown
circuits are activated by the Mode Selector Switch and or
Shutdown Time Delay Bypass. Eight (8) Red Shutdown
Indicating Lights are provided.
(a) Overcrank; tripped by the overcrank timing circuit
which times as long as the START switch is closed.
(b) Overspeed; tripped by overspeed switch when engine
exceeds a preset speed.
(c) Oil Pressure; tripped by the oil pressure SWICHGAGE ®
if pressure drops below preset point while the engine is
running.
(d) Water Temperature; tripped by the water temperature
SWICHGAGE ® if engine coolant temperature exceeds
the switch setting.
(e) Spare Shutdowns; tripped by an external switch. These
circuits are provided for additional shutdowns that may
be recommended by the engine supplier or required by
the user.
3-2.2 Relay Module. The Relay Module, figure 3-2.2,
includes all of the control and shutdown relays that are
required to make up the generator engine control. Relays are
available for operation on either 12 or 24 volt battery systems.
Two (2) relays are included for:
3-2.2.1 Fuel Relay; this relay provides two outputs, one to
energize the engine fuel solenoid and a separate circuit to
energize the battery charging alternator field.
3-2.2.2 Shutdown Relay; this relay is operated by the
shutdown circuits of the Control / Display Module and
provides an output that can be used to trip the generator circuit
breaker on an emergency shutdown.
3-2.3 Status Signal; The relay module also includes an output
that can be used with external circuits for signaling or control
functions.
3-2.3.1 The Run signal at terminal 17 is on (closed to
negative) as long as the Mode Selector Switch is in either Run
2
Overcrank
OFF
RUN
START
Lamp Test
Water
Temperature
Oil Pressure
6-15/32 in.
(164 mm)
9-3/4 in.
(248 mm)
Overspeed
Figure 3-2.1
DISCONTINUED