Murphy A900 Series manual 159 mm

(f)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.

(g)Cooldown circuit; this circuit keeps the engine running for five minutes after the transfer switch has removed

the load from the generator and signaled the A901-2 to stop the engine. This feature may be selected (turned On, standard setting is Off) with a switch on the back of the Control / Display Module.

3-3.1.5Seven (7) First-out Shutdown Circuits; provide first-out indication of cause of shutdown. These circuits deactivate the fuel relay and lockout the A901-2 until reset. Shutdown circuits are activated by the crank disconnect circuit and are not active when the engine is stopped. Six (6) Red Shutdown Indicating Lights are provided. The Remote Shutdown circuit does not have an indicator light.

(a)Overcrank; tripped by the overcrank sensing circuit which counts the number of cranking attempts.

(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 Shutdown; tripped by an external switch. This circuit is provided for an additional shutdown that may be recommended by the engine supplier.

(f)Loss of Speed Signal; tripped by an internal sensing circuit that detects the loss of the Magnetic Pickup frequency signal for the speed switches while the engine is still running. Since the Overspeed shutdown circuit is activated by the frequency input, it prevents the engine from running without overspeed protection.

(g)Remote Shutdown; this circuit is provided to shutdown the engine generator from a remote location. No indicating light is provided.

3-3.1.6Nine (9) Alarm Indicating Circuits; provide indication of cause of alarm. These circuits activate the alarm relays. Alarm circuits are active as long as power is applied to the A901-2. All are active when the engine is running, shutdown or on standby except Low Oil Pressure Pre- alarm and High Water Temperature Pre-alarm. Nine (9) Amber Alarm Indicating Lights are provided.

(a)Low Water Temperature; operated by low water temp- erature SWICHGAGE® .

(b)Air Damper Closed; operated by an external switch or by the Overspeed Relay circuit. This circuit is provided with a selector switch to allow the user to determine the source of the signal.

(c)Switch Not In Automatic; operated by the OFF-AUTO- TEST mode selector switch.

(d)Low Fuel Level; operated by level switch on fuel tank.

(e)High Battery Voltage; operated by relay contact in battery charger.

(f)Low Battery Voltage; operated by low voltage sensing device in battery charger.

(g)Low Oil Pressure Pre-alarm; operated by pre-alarm switch in oil pressure SWICHGAGE® .

(h)High Water Temperature Pre-alarm; operated by pre- alarm switch in water temperature SWICHGAGE® .

(i)Battery Charger AC Failure; operated by relay contact in Battery Charger.

3-3.2Relay Module. The Relay Module, figure 3-3.2, includes all of the control, alarm 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. Six (6) relays are included for:

	3A Fuse
1A
4
5	DC12V	DC12V	16
6			17
7			18	6-1/4 in.
8			19	(159 mm)
9			20
	DC12V	DC12V	21
			22
			23
			24
	DC12V	DC12V	25
	4-1/2 in.
	(114 mm)

Figure 3-3.2

3-3.2.1Fuel Relay; this relay provides two outputs, one to energize the engine fuel solenoid and a separate circuit to energize the battery charging alternator field.

3-3.2.2Shutdown 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.

3-3.2.3Overspeed Relay; operates only on an Overspeed shutdown. This relay provides an output to trip an air shut off solenoid to close the air damper on a two-cycle engine.

3-3.2.4Local Audible Alarm Relay; provides a contact closure

6