Murphy A900 User Manual

SERIES A900

MURPHYMATIC

®

GENERATOR

ENGINE CONTROL SYSTEM

DESIGN, INSTALLATION

AND OPERATING MANUAL

A900-9025N

Revised 10-99

Section 40

(00-02-0197)

BEFORE BEGINNING

INSTALLATION OF THIS

MURPHY PRODUCT

✔ Disconnect all electrical

power to the machine.

✔ Make sure the machine

cannot operate during
installation.

✔ Follow all safety warnings of

the machine manufacturer.

✔ Read and follow all

installation instructions.

Certain danger to human safety and to equipment
may occur if some equipment is stopped without pre­warning. It is recommended that monitored functions
be limited to alarm-only or to alarm before shutdown.

WARNING

Table of Contents

Section 1: Introduction page 1

1-1 System 1
1-2 Models 1
1-3 Purpose 1
1-4 Definitions 1
1-5 How To Use This Manual 1

Section 2: Specifications 1

2-1 Enclosure Type 1
2-2 Power Requirements 1
2-3 Input Ratings 1
2-4 Output Ratings 1
2-5 Field Wiring Connections 1
2-6 Operating Temperature 1

Section 3: Model Identification 1

3-1 Model Numbers 1
3-2 A901 2
3-3 A901-2 5
3-4 A902 7
3-5 A902-2 8

3-6 A903 10
3-7 A903-2 12

Section 4: Installation 14

4-1 Location 14
4-2 Wiring 14
4-3 Crank Disconnect 19
4-4 Pre-Operational Check-Out 19

Section 5: Operation 21

5-1 Operator Controls 21
5-2 Operating Modes 21

Section 6: Routine Maintenance and Operational Tests 21

6-1 Routine Maintenance 21
6-2 Operational Tests 21

Section 7: Troubleshooting and Repair 21

7-1 Tools Required 21
7-2 A900 SELECTRONIC®Control Operation and Shutdown 21
7-3 A900 SELECTRONIC®Control Alarm Circuit Operation 23

Section 8: Service Parts 24

8-1 Table 8-1: Replacement Components of the A900 Series Generator Controls 24
8-2 Table 8-2: Replacement Components of the A900 Controls for Detroit Diesel 24

Section 1: Introduction

1-1 System.
1-1.1 The MURPHYMATIC®Generator Engine Control System,

Series A900 is designed to meet the requirements of the engine
control, shutdown and alarm section of NFPA-110 “Emergency
And Standby Power Systems” specification. The controller also
meets the minimum requirements of NFPA99 “Health Care
Facilities” and the Canadian standard CAN/CSA-C282-M89
“Emergency Electrical Power Supply for Buildings” for engine
control, shutdown and alarm systems. By combining one of the
A900 series controls with generator instruments, a complete engine
generator control panel meeting the above specifications can be
provided.

1-2 Models.
1-2.1 The Series A900 is available in three basic configurations:
1-2.1.1 Model A901 for automatic start and stop generator sets

which includes the minimum shutdowns and alarms per NFPA­110 Level 1.
1-2.1.2 Model A902 for automatic start and stop generator sets
which includes the minimum shutdowns and alarms per NFPA­110 Level 2.
1-2.1.3 Model A903 for automatic start and stop generator sets
which includes the minimum shutdowns and alarms per NFPA­110 Level 2 and seven unlabeled alarm lights for additional
customer specified alarms.

1-2.2 All models are available for 12 or 24 V DC operation.
1-2.3 All models are available for use on either two cycle or four

cycle engines. Models for two cycle engines include an alarm
light for “Air Damper Closed” and an “Overspeed Relay” to
operate the air shutoff solenoid for overspeed shutdown.
1-2.4 Each model is made up of two parts, a Control/Display
module and a Relay module.

1-3 Purpose.
1-3.1 This manual is directed to the installation, maintenance and

operating personnel who will be in day to day contact with the
A900 system. However the basic knowledge gained with this
material will allow those personnel to easily adjust to special
circumstances.

1-4 Definitions.
1-4.1 Throughout this manual, reference is made to organi-

zations, trade names and trademarks which may not be familiar to
the reader. Some of these are:

1-4.1.1 CSA: Canadian Standards Association.
1-4.1.2 CAN/CSA-C282-M89: The standard for Emergency

Electrical Power Supply for Buildings, 1989 Edition.

1-4.1.3 NFPA: National Fire Protection Association.
1-4.1.4 NFPA-70: The National Electrical Code.
1-4.1.5 NFPA-99-1990: The standard for Health Care Facilities,

1990 Edition.
1-4.1.6 NFPA-110-1988: The standard for Emergency And
Standby Power Systems, 1988 Edition.
1-4.1.7 Several terms used in this manual are registered
trademarks of Frank W. Murphy Mfr .

(a) MURPHYMATIC®: Refers to all Murphy automatic controls.
(b) SELECTRONIC®: A name that is applied to all electronic

controls manufactured by Murphy.
(c) SWICHGAGE®: A combination indicating gauge and switch.
(d) T ATTLET ALE®: A term that refers to a shutdown indicating

device or circuit in the control panel.

1-5 How to use this manual.
1-5.1 Section 1, 2, 4, 5, 6 and 7 contain general information that

applies to all A900 models.
1-5.2 Section 3, Model Identification, is broken into seven sub
sections. Section 3-1 allows you to chose the model that best
fits your requirements and Section 3-2 through 3-7 explain each
models features in detail.

Section 2: Specifications

2-1 Enclosure Type.
2-1.1 The A900 Series enclosure is designed to be mounted in a

standard electrical enclosure for indoor use.

2-2 Power Requirements.
2-2.1 The engine controls, shutdown circuits, alarm and shut-

down indicators are powered from the engine starting battery.
The A900 series is available in either 12 or 24 V, negative ground.

2-2.2 The A900 is fused for 3 A maximum current.
2-3 Input Ratings.

2-3.1 All input switches should be dry contact type, maximum

current is 2 mA, 8 V DC or less.
2-3.2 Frequency signal for the speed sensing circuit requires a
minimum input of 2 V rms from a magnetic pickup (preferred) or
from the tachometer terminal of the battery charging alternator .
2-3.2.1 Frequency range of the speed sensing circuits is 25 Hz to
10,000 Hz.

2-4 Output Ratings.
2-4.1 The A900 Control / Display Module has outputs for remote

indication of alarm and shutdowns. These outputs are transistors
that close to the negative supply (sink) and are rated at 1 amp, 30
V DC maximum.
2-4.2 The Control / Display Module also has an output for an
auxiliary starter contactor which is rated 1 A, 30 V DC maximum.
This is a transistor that closes to the positive supply (source).
2-4.3 The Relay Module includes 3 engine control relays with
contact ratings of 7 A, 30 V DC inductive. These powered
contacts must be supplied from an 8 A fuse or circuit breaker
(customer supplied). The 3 alarm relays have dry contacts, also
rated at 7 A, 30 V DC maximum.

2-5 Field Wiring Connections.
2-5.1 All field wiring connections are barrier terminal blocks, UL

rated for 15 A, 300 V.

2-6 Operating Temperature.
2-6.1 The operating temperature range of the A900 is -4°F to

158°F (-20°C to 70°C.)

Section 3: Model Identification

3-1 Model Numbers.
3-1.1 A901-12 and A901-24: These models are designed for an

automatic start four cycle engine driven generator, and
include the shutdown and alarm points recommended in NFPA­110-1988 “Emergency and Standby Generator Systems” for Level
1 installations. These controllers also meet or exceed the
minimum requirements of NFPA99-1990 “Health Care Facilities”
and with the addition of a Low Water Level alarm, the Canadian
standard CAN/CSA-C282-M89 “Emergency Electrical Power
Supply for Buildings”. The suffix numbers -12 and -24 indicate
the engine starting battery voltage.
3-1.2 A901-2-12 and A901-2-24: These models are designed for

1

an automatic-start, two-cycle, engine-driven generator, and
include the shutdown and alarm points recommended in NFPA­110-1988 “Emergency and Standby Generator Systems” for
Level 1 installations. These controllers also meet or exceed the
minimum requirements of NFPA-99-1990 “Health Care
Facilities” and with the addition of a Low Water Level alarm,
the Canadian standard CAN/CSA-C282-M89 “Emergency
Electrical Power Supply for Buildings”. The suffix numbers -12
and -24 indicate the engine starting battery voltage.
3-1.2.1 The A901-2 series control includes an “Air Damper
Closed” light and “Overspeed Relay” to trip the air shut-off
solenoid on overspeed of a two-cycle engine.
3-1.3 A902-12 and A902-24: These models are designed for an
automatic-start, four-cycle, engine-driven generator, and include
the shutdown and alarm points recommended in NFPA-110­1988 “Emergency and Standby Generator Systems” for Level 2
installations. The suffix numbers -12 and -24 indicate the
engine starting battery voltage.
3-1.4 A902-2-12 and A902-2-24: These models are designed
for an automatic-start, two-cycle, engine-driven generator, and
include the shutdown and alarm points recommended in NFPA­110-1988 “Emergency and Standby Generator Systems” for
Level 2 installations. The suffix numbers -12 and -24 indicate
the engine starting battery voltage.
3-1.4.1 The A902-2 series control includes an “Air Damper
Closed” light and “Overspeed Relay” to trip the air shut-off
solenoid on overspeed of a two-cycle engine.
3-1.5 A903-12 and A903-24: These models are designed for an
automatic-start, four-cycle, engine-driven generator, and include
the shutdown and alarm points recommended in NFPA-110­1988 “Emergency and Standby Generator Systems” for Level 2
installations plus seven unlabeled alarms that the user may
specify and an “Alarm Silence Switch”. The suffix numbers -12
and -24 indicate the engine starting battery voltage.
3-1.6 A903-2-12 and A903-2-24: These models are designed for
an automatic-start, two-cycle, engine driven generator, and
include the shutdown and alarm points recommended in NFPA­110-1988 “Emergency and Standby Generator Systems” for
Level 2 installations plus seven unlabeled alarms that the user
may specify and an “Alarm Silence Switch”. The suffix numbers

-12 and -24 indicate the engine starting battery voltage.
3-1.6.1 The A903-2 series control includes an “Air Damper
Closed” light and “Overspeed Relay” to trip the air shut-off
solenoid on overspeed of a two-cycle engine.
3-1.7 Table 3-1.7 illustrates the alarm and shutdown require­ments of NFPA-110, NFPA99 and CAN/CSA-C282-M89 and
compares the features of the A900 series controls to those
requirements.

3-2 A901.
3-2.1 Control / Display Module. The Control / Display Module,

figure 3-2.1, includes the control and test switches, the solid state
logic elements, shutdown and alarm TATTLETALE®lights that
make up the generator engine control for a four-cycle engine.
3-2.1.1 Mode Selector Switch, OFF-AUTO-TEST :

(a) OFF; turns off the control system and resets any shutdown

circuits.

(b) AUTO; turns on the engine controls and shutdown circuits.

System is on standby waiting for a contact closure to start
engine.

(c) TEST; turns on the engine controls and shutdown circuits.

A start signal is applied to the automatic control and the
engine start sequence begins.

3-2.1.2 Lamp Test Pushbutton: Tests the lights on the A901
module.
3-2.1.3 Alarm Silence Pushbutton: Turns off any audible alarm
that is connected to the Local or Remote Audible Alarm Relays.
The indicating light will remain on as long as the condition
exists. If the Alarm Silence pushbutton is not operated, the
audible alarm will turn off when the alarm contact clears.
3-2.1.4 The A901 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 can be selected 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.

(c) Auxiliary Crank Disconnect Circuit; this circuit, required by

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.

Low Water

Temperature

AUTO

OFF

TEST

Loss of Speed

Signal

Lamp Test

Water

Temperature

Low Battery

Voltage

Alarm Silence

High Battery

Voltage

Low Fuel

Level

High Water Temp.

PreAlarm

Battery Charger

AC Failure

Switch

Not In AUTO

Low Oil Pressure

PreAlarm

Oil Pressure

Overspeed

Overcrank

6-1/2 in.

(165 mm)

9-3/4 in.

(248 mm)

Figure 3-2.1

2

Table 3-1.7

3

Level 1

C.V.

S

L.A.

R.A.

R.V.

Level 2

C.V.

S

L.A.

R.A.

R.V.

NFPA-110

NFPA99

C.V.

S

L.A.

R.A.

R.V.

②

CAN/CSA

C282-M89

C.V. S L.A. R.A. R.V.

A901

C.V.

S L.A. R.A. R.V.

A902

C.V. S L.A.

R.A.

R.V.

④ ④

A903

C.V.

S

L.A.

R.A. R.V.

④ ④

a. Overcrank X X X X X X X X O O X X X X X X X X X X X X X X X X X X O O X X X O O

b. Low Water Temperature X — X X X X — X O O X — X X X X — X X X X — X X X X — X O O X — X O O

c. High Engine Temp. Prealarm X — X X X O — O — O X — X X X O — O O O X — X X X — — — — — — X O O

d. High Engine Temperature X X X X X X X X O O X X X X X X X X X X X X X X X X X X O O X X X O O

e. Low Lube Oil Pressure Prealarm X — X X X X X O — O X — X X X O — O O O X — X X X — — — — — — X O O

f. Low Lube Oil Pressure X X X X X X X X O O X X X X X X X X X X X X X X X X X X O O X X X O O

g. Overpeed X X X X X X X X O O X X X X X X X X X X X X X X X X X X O O X X X O O

h. Low Fuel Main Tank X — X X X O — O O O X — X X X X — X X X X — X X X — — — — — — X O O

i. Control Switch not set in Auto X — X X X O — O — O — — — — — X — X X X X — X X X — — O — O — — — —

j. High Battery Voltage X — X — X O — O — O — — — — — — — — — — X — X — X — — O — O — — — —

k. Low VoltageBattery X — X — X O — O — O — — — — — X — X X X X — X — X — — O — O — — — —

l. Lamp Test X — — — X X — — — — — — — — — X — — — — X — — — — X — — — — X — — — —

m. Audible Alarm Silencing switch — — X X — — — — O — — — — — — — — X X — — — — X — — — — O — — — X O —

n. Low Starting Air Pressure X — X — X O — O — O — — — — — X — X X X — — — — — — — — — — — — — — —

o. Low Starting Hydraulic Pressure X — X — X O — O — O — — — — — X — X X X — — — — — — — — — — — — — — —

q. Remote Emergency Stop — X — — — — X — — — — — — — — — O — — — — X — — — — X — — — — X — — —

r. Low Coolant Level — — — — — — — — — — — — — — — X — X X X — — — — — — — — — — — — — — —

s. Battery Charger AC Failure X — X — X O — O — O — — — — — — — — — — X — X — X — — O — O — — — —

③③ ③③ ③

③

③

⑤

⑤

⑤

⑤

⑤

⑤

①

①

KEY

C.V.: Control panel-mounted Visual indication.

S: Shutdown of EPS

L.A.: Local Audible contacts.

R.A.: Remote Audible contacts.

R.V.: Remote Visual contacts.

X: Required

O: Optional

①: Items “N” or “O” apply only when applicable as

a starting method.

②: NFPA99 requires an audible alarm for all alarm and

shutdown functions. May be connected to L.A. contacts.

③: Air Damper Closed and is available on -2 models only.

④: R.A. and R.V. relays not supplied in model A902 or

A903, optional.

⑤: Circuits and indicators supplied without labels.

p. Air shutdown dampner when used X X X X X X X X O O — — — — — X X X — X X X X X O O X O O

(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.

3-2.1.5 Seven (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
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.

3-2.1.6 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 A901. All are
active when the engine is running, shutdown or on standby except
Low Oil Pressure Pre- alarm and High Water Temperature Pre­alarm. 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 .

3-2.2 Relay 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:
3-2.2.1 Fuel Relay; this relay provides two outputs, one to
energize the engine fuel solenoid and a separate circuit to

4

DC12V

3A Fuse

1A

4
5
6
7
8
9

16
17
18
19
20
21
22
23
24
25

RH2V2

-U

DC12V

RH2V2

-U

DC12V

RH2V2

-U

DC12V

RH2V2

-U

DC12V

RH2V2

-U

6-1/4 in.

(159 mm)

4-1/2 in.

(114 mm)

Figure 3-2.2

energize the battery charging alternator field.
3-2.2.2 Shutdown 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.
3-2.2.3 Local Audible Alarm Relay; provides a contact closure
to operate a local audible alarm as required by NFPA-110, Level
1 and Level 2.
3-2.2.4 Remote Audible Alarm Relay; provides a contact
closure to operate a remote audible alarm as required by NFPA­110, Level 1.
3-2.2.5 Remote Visual Alarm Relay; provides a contact closure
to operate a remote visual alarm as required by NFPA- 110,
Level 1.
3-2.3 Status Signals. The relay module also includes three
outputs that can be used with external circuits for signaling or
control functions.
3-2.3.1 The Control On function at terminal 12 is on (closed
to negative) as long as the Mode Selector Switch is in either
Auto or Test. When the Mode Selector is turned Off, the
Control On signal is open. This can be used to signal switch
position or to reset an external circuit when the Mode Selector
is turned Off.
3-2.3.2 The System Ready signal at terminal 13 is on (closed
to negative) as long as the Mode Selector Switch is in either
Auto or Test and no shutdown Tattletale circuit is latched on.
This can be used to signal that the generator engine is ready to
automatically start or is running in Test.
3-2.3.3 The Control On function at terminal 14 is on (closed
to positive) as long as the Mode Selector Switch is in either
Auto or Test. When the Mode Selector is turned Off, the
Control On signal is open. This can be used to signal switch
position or to reset an external circuit when the Mode Selector
is turned Off.

3-3 A901-2.
3-3.1 Control / Display Module. The Control / Display Module,

figure 3-3.1, includes the control and test switches, the solid state
logic elements, shutdown and alarm TATTLETALE®lights that
make up the generator engine control for a two-cycle engine.
3-3.1.1 Mode Selector Switch, OFF-AUTO-TEST :

(a) OFF; turns off the control system and resets any shutdown

circuits.

(b) AUTO; turns on the engine controls and shutdown

circuits. System is on standby waiting for a contact
closure to start engine.

(c) TEST; turns on the engine controls and shutdown circuits.

A start signal is applied to the automatic control and the
engine start sequence begins.

3-3.1.2 Lamp Test Pushbutton: Tests the lights on the A- 901-2
module.
3-3.1.3 Alarm Silence Pushbutton: Turns off any audible alarm
that is connected to the Local or Remote Audible Alarm Relays.
The indicating light will remain on as long as the condition
exists. If the Alarm Silence pushbutton is not operated, the
audible alarm will turn off when the alarm contact clears.
3-3.1.4 The A901-2 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.

(c) Auxiliary Crank Disconnect Circuit; this circuit, required by

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 the Low Oil Pressure Pre­alarm and High Water Temperature Pre-alarm circuits
when the engine is not running.

Low Water

Temperature

AUTO

OFF

TEST

Loss of Speed

Signal

Lamp Test

Water

Temperature

Air Damper

Closed

Low Battery

Voltage

Alarm Silence

Battery Charger

AC Failure

High Battery

Voltage

Low Fuel

Level

High Water Temp.

PreAlarm

Switch

Not In AUTO

Low Oil Pressure

PreAlarm

Oil Pressure

Overspeed

Overcrank

6-1/2 in.

(165 mm)

9-3/4 in.

(248 mm)

Figure 3-3.1

5

(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.

3-3.1.5 Seven (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 T emperature; 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.

3-3.1.6 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
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 .

3-3.2 Relay 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:

3-3.2.1 Fuel Relay; this relay provides two outputs, one to
energize the engine fuel solenoid and a separate circuit to
energize the battery charging alternator field.
3-3.2.2 Shutdown 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.
3-3.2.3 Overspeed 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.
3-3.2.4 Local Audible Alarm Relay; provides a contact closure

DC12V

3A Fuse

1A

4
5
6
7
8
9

16
17
18
19
20
21
22
23
24
25

DC12V

DC12V DC12V

DC12V DC12V

6-1/4 in.

(159 mm)

4-1/2 in.

(114 mm)

Figure 3-3.2

6