Murphy A900 Series manual fOverspeed Speed Switch

(d)Overcrank circuit; will stop automatic cranking and indicate overcrank if engine fails to start after 3 attempts. The number of cranks are selectable for 1, 2, 3, 4 or 5 cycles before shutdown. The overcrank circuit may also be turned off so no overcrank shutdown occurs.

(e)Shutdown Time Delay Bypass; this delay prevents the oil pressure, water temperature and loss of speed signal shutdown circuits from operating for 15 seconds after the engine starts as detected by the crank disconnect circuit. This same delay also locks out the Low Oil Pressure Pre- alarm and High Water Temperature Pre-alarm circuits when the engine is not running.

(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 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.

3-2.1.5Seven (7) First-out Shutdown Circuits; provide first-out indication of cause of shutdown. These circuits deactivate the fuel relay and lockout the A901 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

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.

3-2.1.6Nine (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. 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)Spare Alarm; operated by an external switch. This circuit is provided for an additional alarm that may be required by the user.

(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 a relay contact in the Battery Charger.

3-2.2Relay Module. The Relay Module, figure 3-2.2, 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. Five (5) 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

Figure 3-2.2

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

1A

4

5

6

7

8

9

3A Fuse

RH2V2	RH2V2
-U	-U
DC12V	DC12V
RH2V2	RH2V2
-U	-U
DC12V	DC12V
	RH2V2
	-U
	DC12V

16

17

18

19

20

21

22

23

24

25

6-1/4 in.

(159 mm)

frequency signal for the speed switches while the engine

is still running. Since the Overspeed shutdown circuit is

4-1/2 in.

(114 mm)

4