Murphy MC-900 Series manual

3-2 MC-900.

3-2.1Control / 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.

6-15/32 in.

(164 mm)

	Overcrank	Oil Pressure
	Overspeed	Water
		Temperature
	Lamp Test
	OFF
9-3/4 in.	RUN
	START
(248 mm)

Figure 3-2.1

3-2.1.1Mode 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.

3-2.1.2Lamp Test Pushbutton: Tests the lights on the MC-900 module when the Mode Selector Switch is in the RUN position.

3-2.1.3The 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.

3-2.1.4Eight (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.

3-2.2Relay 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:

3-2.2.1Fuel Relay; this relay provides two outputs, one to energize the engine fuel solenoid and a separate circuit to energize the battery charging alternator field.

3-2.2.2Shutdown 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.

3-2.3Status Signal; The relay module also includes an output that can be used with external circuits for signaling or control functions.

3-2.3.1The Run signal at terminal 17 is on (closed to negative) as long as the Mode Selector Switch is in either Run

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