Discontinued – Murphy Series A900 User Manual

Page 16

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audible alarm will turn off when the alarm contact clears.
3-7.1.4 The A903-2 SELECTRONIC

Control Module includes

the following engine control features:

(a) Cycle crank circuit; will crank the engine for 15 seconds

then rest for 15 seconds until the engine starts. The
crank/rest time is selectable for either 10, 15, 20, 25 or 30
seconds. If the engine false starts, goes above crank
disconnect speed then drops below that speed, the control
will rest for a fixed 10 second period before cranking again.

(b) Crank Disconnect Speed Switch; this circuit detects

engine speed and terminates cranking when engine speed
rises above the speed switch setting. The speed switch is
adjustable, 25 Hz to 2000 Hz, and is factory set at 1180
Hz. This would be 600 RPM on an engine with 118 teeth
on the flywheel ring gear.

NFPA-110, is provided as a back up for the Crank
Disconnect Speed Switch. It is operated by an external
switch sensing either speed, generator voltage or some other
variable that could be used to terminate cranking. Either
circuit will disconnect the starter when the engine starts.

(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 alarm circuit #7 and #8
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 A903-2 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.

3-7.1.5 Seven (7) First-out Shutdown Circuits; provide first-out
indication of cause of shutdown. These circuits deactivate the
fuel relay and lockout the A903 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.

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.

3-7.1.6 Nine (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
A903-2. All are active when the engine is running, shutdown or
on standby except alarm circuit #7 and #8 which are locked out
until the engine is running. Nine (9) Amber Alarm Indicating
Lights are provided however only three circuits is labeled. The
other 6 are for customer specified alarms.

(a) Low Water Temperature; operated by low water

temperature 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.

TEST mode selector switch.

(d) #4 Spare Alarm; operated by an external switch. This