to the table for examples.
(c)Voltages less than battery also may vary due to tolerances of the electronic components in the A900. Minor variations, 1 or 2 volts, normally will have no effect on the A900 operation.
(d)The AC voltage at terminal 29 must be a minimum of 2 VAC to drive the speed sensing circuits of the A900.
7-2.2With power applied and the Mode Selector switch in AUTO, the following occurs when a switch is closed from terminal 28 to ground.
7-2.2.1The fuel relay is energized, which opens the circuits at terminal 5 and 7, and closes the circuits at terminal 6 and 8. This applies battery power to the run solenoid and to the exciter terminal of the alternator.
7-2.2.2At the same time, the crank relay driver provides battery voltage at terminal 17, thru the auxiliary crank disconnect relay contact to the auxiliary starter solenoid. This output is controlled by the crank and rest timer but it can be overridden by the crank disconnect speed switch and / or the auxiliary crank disconnect circuit. The output will remain on until the crank time expires or the crank disconnect circuits detect that the engine has started.
7-2.2.3If the engine does not start during the crank time, the rest timer will prevent cranking until it has timed out. After the rest time, the engine will begin cranking again. This sequence will repeat until the engine starts or the overcrank shutdown circuit trips.
7-2.2.4Engine speed is detected by an AC signal from a magnetic pickup wired to terminal 29. When this frequency exceeds the setting of the crank disconnect speed switch,
(a)Cranking is terminated.
(b)A time delay starts timing during which the oil pressure and water temperature shutdown circuits are locked out.
(c)The overcrank counter is reset to zero.
(d)The overspeed shutdown circuit is activated.
7-2.2.5An engine run signal closes to ground at terminal 19 when the engine starts.
7-2.3With the engine running, the six shutdown TATTLETALE® circuits are activated and will operate anytime a switch closes from ground to their inputs.
Circuit | Input | Output |
(a) Remote Stop | Terminal 33 | Terminal 41 |
(b) Oil Pressure | Terminal 30 | Terminal 39 |
(c) Water Temp | Terminal 32 | Terminal 40 |
(d) Overspeed | Int. Speed Switch | Terminal 38 |
(e) Loss of Speed Signal | Int. Circuit | Terminal 43 |
(f) Spare Shutdown | Terminal 11 | Terminal 42 |
7-2.3.1Each circuit has a indicating light and a transistor output that closes to ground to operate an individual remote indicating light.
7-2.3.2When any of the six shutdown functions trip, the shutdown relay K-2, pulls in and applies battery power to terminal 9. At the same time, the fuel relay, K-1 drops out and if the shutdown was due to overspeed, the overspeed relay, K-3 pulls in to signal an air shut off solenoid, terminal 10 to close.
7-2.3.3The six shutdown circuits, paragraph 7-2.3, are first out latching type TATTLETALE® . That is, only one of the six may trip at one time and it must be reset before the A900 will operate again.
7-2.3.4If one of the TATTLETALE® circuits trip, the following occurs to shutdown the engine and generator.
(a) The TATTLETALE® light for that function turns on.
(b)Shutdown relay K-2 is energized, closing its contacts at terminal 9. These contacts can be wired to a shunt trip solenoid in the generator circuit breaker if required.
(c)The fuel relay drops out, removing battery voltage from the run solenoid, terminal 6, and from the alternator exciter, terminal 8. The circuits at terminal 5 and 7 will close to reconnect the battery positive to these terminals.
(d)The run signal, terminal 19 turns off.
(e)If the shutdown is due to overspeed, the overspeed relay operates and applies battery positive to terminal 10 to close an air shutoff solenoid if the engine is so equipped.
7-2.3.5If the engine is shutdown by the remote stop circuit, no TATTLETALE® light is provided. Otherwise a TATTLETALE® light will show the cause of shutdown.
7-2.3.6In the A900, the Loss of Speed signal TATTLETALE® can be either a shutdown or an alarm. It is connected to a circuit that monitors the magnetic pickup input at terminal 29. If the input from the pickup fails, drops below the minimum voltage, or is disconnected while the engine is running, the Loss of Speed Signal TATTLETALE® circuit will activate and shutdown the engine or operate the alarm circuit. It is recommended that the shutdown circuit is used since this prevents the generator set from running without overspeed protection. If this circuit is used as an alarm, the auxiliary crank disconnect input MUST be supplied to prevent malfunction of the shutdown circuits.
7-2.3.7To reset the circuits, the Mode Selector switch must be turned OFF and back on to either the AUTO or TEST position.
7-2.4Normally, the engine will run until the start signal is removed from terminal 28.
7-2.4.1When the signal is removed, the following occurs to stop the engine;
(a)The fuel relay drops out, removing battery voltage from the run solenoid, terminal 6, and from the alternator exciter, terminal 8. The circuits at terminal 5 and 7 will close to reconnect the battery positive to these terminals.
(b)The run signal, terminal 19 turns off.
(c)The four engine function TATTL TALE® circuits are locked out as soon as the fuel relay drops out. This prevents any TATTLETALE® from tripping while the engine coasts to a stop.
7-3 A900 SELECTRONIC® Control Alarm Circuit
Operation.
7-3.1The A900 alarm circuits perform the following functions;
(a)Turns on individual alarm lights based on input switch closures.
(b)Provides lamp test function for all alarm and shutdown lights.
(c)Activates either the local audible alarm relay, K-4, and remote visual alarm relay, K-6, or the local audible alarm relay, K-4, the remote audible alarm relay, K-5, and the remote visual alarm relay, K-6, depending on the requirements of NFPA-110 1988 paragraph 3-5.5.1 (d).
(d)Provides the audible alarm silence circuit.
7-3.2A contact closure to ground, at the alarm circuit
input terminal, will cause the associated TATTLETALE® light to turn on and an output transistor to close to ground and turn on a remote indicating light.
7-3.2.1The alarm circuits also operate the three relays for local audible alarm, remote audible alarm and remote visual alarm as required by NFPA-110. The normally open dry relay contacts,
