Murphy Series A900 manual Crank Disconnect, Pre-operational Check-out

current rating that is equal to or greater than the forward current that the coil draws to operate. For example, a relay less than 1 A, use a 1 A diode since they are readily available. The wiring shown in Figures 4-2.3.1, 4-2.3.2 and 4-2.3.3 have examples of the places that a reverse diode is required.

4-3 Crank Disconnect.

4-3.1A magnetic pickup is recommended to supply the speed signal for the A900 series primary crank termination circuit and for the overspeed switch. This pickup will be mounted in the flywheel housing in line with the ring gear on the flywheel and wired to the A900 using either a twisted pair or a shielded cable to reduce the possibility of electrical noise pickup in the wiring.

4-3.1.1The tachometer terminal, of the battery charging alternator, may be used for the speed signal but a broken drive belt will disable this source and some alternators have electrical noise which will cause the speed switches to operate at speeds well below the desired RPM.

4-3.2An auxiliary crank disconnect circuit, required by NFPA-110, is provided in the A900. Any signal that detects when the engine is running and provides a contact closure between Terminals 4 and 16 can be used. This circuit terminates cranking even if the speed signal fails. The “Loss Of Speed” shutdown / alarm on the A900 will indicate if the speed signal is lost while the engine is running by either shutdown of the engine or operation of the alarm circuit. “Loss Of Speed” alarm will only operate if the auxiliary crank disconnect circuit is used. Provision is also made for a second N.C. contact between Terminals 17 and 18 to interrupt the output to the auxiliary starter solenoid. This would disconnect cranking even if both crank disconnect circuits in the A900 should fail. If this contact is not provided, you must jumper Terminals 17 and 18 for the start signal to reach the auxiliary starter solenoid. A voltage sensing relay wired to one output phase of the generator is one way to provide both of these contacts.

4-4 Pre-operational Check-out.

4-4.1After installation is complete, it is necessary to make some adjustments to the A900 SELECTRONIC® Control before the system is operational. All shutdown and alarm circuits also should be tested. Table 4-4.1 lists the standard factory setting of the adjustable functions on the A900 series control. To

Table 4-4.1

		Standard		Adjustment	Adjustment
	Function
		Setting		Range	Type
Crank/Rest		15	10, 15, 20, 25
					Switch
Time		seconds		and 30 Seconds
				1, 2, 3, 4, 5, 6 and
Overcrank		3 cranks			Switch
				No overcrank
Crank					Turn CW
		1180 Hz		25 to 2 KHz
Disconnect					to increase
					Turn CW
Overspeed		3894 Hz		300 to 10 KHz
					to increase
Cooldown				Fixed 5 minute	ON-OFF switch
		OFF
Loss of speed				Shutdown or
		Shutdown
					Switch
Signal				Alarm
Air Damper Closed		ON with		Internal switch ON
					Switch
Alarm on 2 Cycle		Overspeed		External switch OFF
Engines only		shutdown

determine if the frequency of the speed switches must be changed, calculate the required setting using the following formulas:

	Set point		=	No. of Gear Teeth x RPM set points
frequency in HZ					60
			OR
Set point	=	Pulley ratio x No. of Alternator Poles x RPM set points
frequency in HZ				60

Refer to Table 4-4.1 to determine if the speed switch settings are below the factory settings listed. If required frequency will be higher than the standard, increase the setting before proceeding. Turn The Crank Disconnect Set and Overspeed Set pots clockwise to increase setting. The adjustments are 20 turn controls without stops at either end.

4-4.1.1Be sure to have a fully charged battery to do these tests. Low battery voltage can cause improper results during the tests.

4-4.1.2The “Air Damper Closed” alarm on A900 series for 2 cycle engines can be actuated by either an internal circuit that senses the output to the overspeed relay, from the “Overspeed” shutdown circuit or by an external switch wired to terminal 34 of the Control / Display Module. The “Air Damper Closed” switch, Table 4-4.1 must be turned On for internal sensing and Off for external switch. This circuit is a Spare alarm on A900 for 4 cycle engines and the switch must be turned Off to prevent this circuit from operating with the “Overspeed” shutdown.

4-4.1.3All of the adjustments and controls shown in Table 4-4.1 are located on the rear of the control/display module. See Figure 4-4.1.3. Each light and switch is labeled for ease of identification. The LED's are supplied as an aid in installation and troubleshooting of the A900.

4-4.2Crank Disconnect Speed Setting; to set this speed switch, proceed as follows:

(a)Disconnect the run solenoid wire from terminal 6 on the Relay Module.

(b)Check engine to be sure it is safe to crank.

(c)Be sure Mode Selector switch is in OFF position.

(d)Connect battery cables to a fully charged cranking battery.

(e)Turn Mode Selector switch to TEST position and watch the lights on the A900 control module back panel.

1.The engine should start cranking and the “Fuel Relay”, “Crank Relay”, and “Pickup Present” lights turn on.

2.If engine does not crank, check the lights. If green light next to Mode Selector Switch on front panel is not on, check the DC power input wiring and fuse.

3.If green light, “Fuel Relay” and “Crank Relay” lights are on, check wiring from A900 Terminal 18 to auxiliary start solenoid and than on to the starter on engine.

4.With engine cranking, check “Pickup Present” light. It must be on. If off, check the wiring to magnetic pickup and check gap between pickup face and ring gear.

5.If “Crank Disconnect Speed” light comes on and cranking stops, setting of Crank Disconnect Switch is still to low. Turn Mode Selector switch OFF and turn crank disconnect adjustment clockwise 1 or 2 turns and repeat test.

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