Introduction

NOTE: For Specifications with illustrations, make reference to Specifications for 3306B Generator Set Engine Attachments, SENR1077. If the Specifications in SENR1077 are not the same as in the Systems Operation, Testing & Adjusting, look at the printing date on the front cover of each book. Use the Specifications given in the book with the latest date.

Electrical System

The engine electrical system has three separate circuits: the charging circuit, the starting circuit and the low amperage circuit. Some of the electrical system components are used in more than one circuit. The battery (batteries), disconnect switch, circuit breaker, ammeter, cables and wires from the battery are all common in each of the circuits.

The charging circuit is in operation when the engine is running. An alternator makes electricity for the charging circuit. A voltage regulator in the circuit controls the electrical output to keep the battery at full charge.

If the engine has a disconnect switch, the starting circuit can operate only after the disconnect switch is put in the ON position.

The starting circuit is in operation only when the start switch is activated.

The low amperage circuit and the charging circuit are both connected to the same side of the ammeter. The starting circuit connects to the opposite side of the ammeter.

Charging System Components

Alternator (7G7889, 5N5692, 3T6352, 4N3986, And 112-5041)

The alternator is driven by V-belts from the crankshaft pulley. This alternator is a three phase, self-rectifying charging unit, and the regulator is part of the alternator.

This alternator design has no need for slip rings or brushes, and the only part that has movement is the rotor assembly. All conductors that carry current are stationary. The conductors are: the field winding, stator windings, six rectifying diodes, and the regulator circuit components.

The rotor assembly has many magnetic poles like fingers with air space between each opposite pole. The poles have residual magnetism (like permanent magnets) that produce a small amount of magnet-like lines of force (magnetic field) between the poles. As the rotor assembly begins to turn between the field winding and the stator windings, a small amount of alternating current (AC) is produced in the stator windings from the small magnetic lines of force made by the residual magnetism of the poles. This AC current is changed to direct current (DC) when it passes through the diodes of the rectifier bridge. Most of this current goes to charge the battery and to supply the low amperage circuit, and the remainder is sent onto the field windings. The DC current flow through the field windings (wires around an iron core) now increases the strength of the magnetic lines of force. These stronger lines of force now increase the amount of AC current produced in the stator windings. The increased speed of the rotor assembly also increases the current and voltage output of the alternator.

The voltage regulator is a solid state (transistor, stationary parts) electronic switch. It feels the voltage in the system and switches on and off many times a second to control the field current (DC current to the field windings) for the alternator to make the needed voltage output.

Alternator (7G7889, 5N5692, 3T6352, 4N3986, And 112-5041) (Typical Example)
(1) Regulator. (2) Roller bearing. (3) Stator winding. (4) Ball bearing. (5) Rectifier bridge. (6) Field winding. (7) Rotor assembly. (8) Fan.

Alternator (7N9720 And 100-5046)

The alternator is driven by V-belts from the crankshaft pulley. This alternator is a three phase, self-rectifying charging unit. The regulator is part of the alternator.

Alternator (7N9720 And 100-5046)
(1) Fan. (2) Stator winding. (3) Field winding. (4) Regulator. (5) Ball bearing. (6) Roller bearing. (7) Rotor. (8) Rectifier assembly.

This alternator design has no need for slip rings or brushes, and the only part that has movement is the rotor assembly. All conductors that carry current are stationary. The conductors are: the field winding, stator windings, six rectifying diodes, and the regulator circuit components.

The rotor assembly has many magnetic poles like fingers with air space between each opposite pole. The poles have residual magnetism (like permanent magnets) that produce a small amount of magnet-like lines of force (magnetic field) between the poles. As the rotor assembly begins to turn between the field winding and the stator windings, a small amount of alternating current (AC) is produced in the stator windings from the small magnetic lines of force made by the residual magnetism of the poles. This AC current is changed to direct current (DC) when it passes through the diodes of the rectifier bridge. Most of this current goes to charge the battery and to supply the low amperage circuit, and the remainder is sent to the field windings. The DC current flow through the field windings (wires around an iron core) now increases the strength of the magnetic lines of force. These stronger lines of force now increase the amount of AC current produced in the stator windings. The increased speed of the rotor assembly also increases the current and voltage output of the alternator.

The voltage regulator is a solid state (transistor, stationary parts) electronic switch. It feels the voltage in the system and switches on and off many times a second to control the field current (DC current to the field windings) for the alternator to make the needed voltage output.

Alternator (6T1395 And 6T1396)

The alternator is a three phase, self-rectifying charging unit that is driven by V-belts. The only part of the alternator that has movement is the rotor assembly. Rotor assembly (4) is held in position by a ball bearing at each end of the rotor shaft.

The alternator is made up of a front frame at the drive end, rotor assembly (4), stator assembly (3), rectifier assembly, brushes and holder assembly (5), slip rings (1) and rear end frame. Fan (2) provides heat removal by the movement of air through the alternator.

Rotor assembly (4) has field windings (wires around an iron core) that make magnetic lines of force when direct current (DC) flows through them. As the rotor assembly turns, the magnetic lines of force are broken by stator assembly (3). This makes alternating current (AC) in the stator. The rectifier assembly has diodes that change the alternating current (AC) from the stator to direct current (DC). Most of the DC current goes to charge the battery and make a supply for the low amperage circuit. The remainder of the DC current is sent to the field windings through the brushes.

Alternator (6T1395 And 6T1396)
(1) Slip rings. (2) Fan. (3) Stator assembly. (4) Rotor assembly. (5) Brush and holder assembly.

Alternator (9G4574 And 100-5045)

The alternator is driven by a V-belt from the crankshaft pulley. It is a 12 volt, 40 ampere unit with a regulator which has no moving parts (solid state). The only part in the alternator which has movement is rotor assembly (9). Rotor assembly (9) is held in position by a ball bearing at each end of rotor shaft (8).

The alternator is made up of a frame (3) on the drive end, rotor assembly (9), stator assembly (5), rectifier assembly (11), brushes (7) and holder assembly, slip rings (13), rear end frame (12) and regulator (6). Drive pulley (1) has a fan (2) for heat removal by the movement of air through the alternator.

Alternator Schematic (With Regulator Attached)
(1) Pulley. (2) Fan. (3) Drive end frame. (4) Stator coils. (5) Stator assembly. (6) Regulator. (7) Brushes. (8) Rotor shaft. (9) Rotor assembly. (10) Field windings. (11) Rectifier assembly. (12) Rear end frame. (13) Slip rings.

Rotor assembly (9) has field windings (10) (wires around an iron core) which make magnetic lines of force when direct current (DC) flows through them. As the rotor turns, the magnetic lines of force are broken by stator assembly (5). This makes an alternating current (AC) in the stator. Rectifier assembly (11) has diodes which change the alternating current (AC) from the stator to direct current (DC). Most of the direct current (DC) goes to charge the battery and make a supply of direct current (DC) for the low amperage circuit. The remainder of the direct current (DC) is sent to field windings (10) through brushes (7).

Alternator Regulator (6T9445 And 6T4156)

Regulator (6T9445 And 6T4156)

The voltage regulator is not fastened to the alternator, but is mounted separately and is connected to the alternator with wires. The regulator is solid state (transistor, stationary parts) electronic switch. It feels the voltage in the system and switches on and off many times a second to control the field current (DC current to the field windings) for the alternator to make the needed voltage output.

Alternator Regulator (7T2798)

Regulator (7T2798)

The regulator is fastened to the alternator by two different methods. One method fastens the regulator to the top, rear of alternator. With the other method the regulator is fastened separately by use of a wire and a connector that goes into the alternator.

The voltage regulator is a solid state (transistor, no moving parts) electronic switch. It feels the voltage in the system and gives the necessary field current (current to the field windings of the alternator) for the alternator to make the needed voltage. The voltage regulator controls the field current to the alternator by switching on and off many times a second. There is no voltage adjustment for this regulator.

Alternator Regulator (9G7567)

Regulator (9G7567)

The voltage regulator is an electronic switch. It feels the voltage in the system and gives the necessary field current (current to the field windings of the alternator) for the alternator to make the needed voltage. The voltage regulator controls the field current to the alternator by switching on and off many times a second.

Starting System Components

Solenoid

A solenoid is a magnetic switch that does two basic operations.

a. Closes the high current starting motor circuit with a low current start switch circuit.

b. Engages the starting motor pinion with the ring gear.

Typical Solenoid Schematic

The solenoid switch is made of an electromagnet (one or two sets of windings) around a hollow cylinder. There is a plunger (core) with a spring load inside the cylinder that can move forward and backward. When the start switch is closed and electricity is sent through the windings, a magnetic field is made that pulls the plunger forward in the cylinder. This moves the shift lever (connected to the rear of the plunger) to engage the pinion drive gear with the ring gear. The front end of the plunger then makes contact across the battery and motor terminals of the solenoid, and the starting motor begins to turn the flywheel of the engine.

When the start switch is opened, current no longer flows through the windings. The spring now pushes the plunger back to the original position, and at the same time, moves the pinion gear away from the flywheel.

When two sets of windings in the solenoid are used, they are called the hold-in windings and the pull-in winding. Both have the same number of turns around the cylinder, but the pull-in winding uses a larger diameter wire to produce a greater magnetic field. When the start switch is closed, part of the current flows from the battery through the hold-in winding, and the rest flows through the pull-in windings to motor terminal, then through the motor to ground. When the solenoid is fully activated (connection across battery and motor terminal is complete), current is shut off through the pull-in windings. Now only the smaller hold-in windings are in operation for the extended period of time it takes to start the engine. The solenoid will now take less current from the battery, and heat made by the solenoid will be kept at an acceptable level.

Starting Motor

The starting motor is used to turn the engine flywheel fast enough to get the engine to start running.

The starting motor has a solenoid. When the start switch is activated, the solenoid will move the starting motor pinion to engage it with the ring gear on the flywheel of the engine. The starting motor pinion will engage with the ring gear before the electric contacts in the solenoid close the circuit between the battery and the starting motor. When the circuit between the battery and the starting motor is complete, the pinion will turn the engine flywheel. A clutch gives protection for the starting motor so that the engine cannot turn the starting motor too fast. When the start switch is released, the starting motor pinion will move away from the ring gear.

Starting Motor Cross Section
(1) Field. (2) Solenoid. (3) Clutch. (4) Pinion. (5) Commutator. (6) Brush assembly. (7) Armature.

Other Components

Circuit Breaker

The circuit breaker is a switch that opens the battery circuit if the current in the electrical system goes higher than the rating of the circuit breaker.

A heat activated metal disc with a contact point makes complete the electric circuit through the circuit breaker. If the current in the electrical system gets too high, it causes the metal disc to get hot. This heat causes a distortion of the metal disc which opens the contacts and breaks the circuit. A circuit breaker that is open can be reset (an adjustment to make the circuit complete again) after it becomes cool. Push the reset button to close the contacts and reset the circuit breaker.

Circuit Breaker Schematic
(1) Reset button. (2) Disc in open position. (3) Contacts. (4) Disc. (5) Battery circuit terminals.

Shutoff Solenoid

The rack shutoff solenoid, when activated, moves the shutoff lever in the governor housing which in turn moves the fuel rack to the fuel closed position. The solenoid is activated by a manual control switch.

Grounded Electrical Systems

These systems are used in applications when it is not necessary to prevent radio distortion and/or chemical changes (electrolysis) of grounded components.

(Regulator Inside Alternator)

Charging System
(1) Ammeter. (2) Alternator. (3) Battery.

Charging System With Electric Starting Motor
(1) Start switch. (2) Ammeter. (3) Alternator. (4) Battery. (5) Starting motor.

(Regulator Separate From Alternator)

Charging System
(1) Ammeter. (2) Regulator. (3) Battery. (4) Pressure switch. (5) Alternator.

Charging System With Electric Starting Motor
(1) Start switch. (2) Ammeter. (3) Regulator. (4) Starting motor. (5) Battery. (6) Pressure switch. (7) Alternator.

(Starting Systems)

Starting System
(1) Start switch. (2) Starting Motor. (3) Battery.

Insulated Electrical Systems

These systems are most often used in applications where radio interference is not desired or where conditions are such that grounded components will have corrosion from chemical change (electrolysis).

(Regulator Inside Alternator)

Charging System
(1) Ammeter. (2) Alternator. (3) Battery.

Charging System With Electric Starting Motor
(1) Start switch. (2) Ammeter. (3) Alternator. (4) Battery. (5) Starting motor.

(Regulator Separate From Alternator)

Charging System
(1) Ammeter. (2) Regulator. (3) Battery. (4) Pressure switch. (5) Alternator.

Charging System With Electric Starting Motor
(1) Start switch. (2) Ammeter. (3) Regulator. (4) Starting motor. (5) Battery. (6) Pressure switch. (7) Alternator.

(Starting Systems)

Starting System
(1) Start switch. (2) Starting motor. (3) Battery.

Indicators And Sending Units

Sending Unit for Water Temperature

Sending Unit For Water Temperature
(1) Connection. (2) Bushing. (3) Bulb.

The sending unit for water temperature is an electrical resistance. It changes the value of its resistance according to the temperature which the bulb (3) feels.

The sending unit is in a series circuit with the electrical indicator. When the temperature is high, the resistance is high. This makes the indicator have a high reading.

The sending unit must be in contact with the coolant. If the coolant level is too low because of a sudden loss of coolant while the engine is running or because the level is too low before starting the engine, the sending unit will not work correctly.

Sending Unit for Oil Pressure

Sending Unit For Oil Pressure
(1) Connection. (2) Bushing.

The sending unit for oil pressure is an electrical resistance. It has a material which changes electrical resistance according to pressure which it feels.

The sending unit for oil pressure is in a series circuit with the electrical indicator. As the pressure on the sending unit changes, the reading on the indicator changes in the same way.

Electric Tachometer Wiring

(1) Magnetic pickup. (2) Terminal Connections - terminals 18 and 19 on load sharing governor control and terminals 7 and 8 on standby governor control. (3) Tachometer. (4) Ground connection - governor control chassis ground. (5) Governor control terminal strip. (6) Wiring connections - for second tachometer circuit if needed. (7) All wire must be 22AWG shielded cable or larger. (8) Dual speed switch terminal strip. (9) Ground connection - ground to engine.

Automatic Start/Stop System - Non-Package Generator Sets

Automatic Start/Stop System Schematic (Hydraulic Governor)
(1) Starting motor and solenoid. (2) Shutoff solenoid. (3) Fuel pressure switch. (4) Water temperature switch. (5) Oil pressure switch. (6) Overspeed contactor. (7) Battery. (8) Low lubricating oil pressure light (OPL). (9) Overcrank light (CL). (10) Overspeed light (OSL). (11) High water temperature light (WTL). (12) Automatic control switch (ACS).

An automatic start/stop system is used when a standby electric set has to give power to a system if the normal (commercial) power supply has a failure. There are three main sections in the system. They are: the automatic transfer switch, the start/stop control panel (part of switch gear) and the electric set.

Automatic Transfer Switch

Automatic Transfer Switch (Typical Example)

The automatic transfer switch normally connects the 3-phase normal (commercial) power supply to the load. When the commercial power supply has a failure the switch will transfer the load to the standby electric set. The transfer switch will not transfer the load from commercial to emergency power until the emergency power gets to the rated voltage and frequency. The reason for this is, the solenoid that causes the transfer of power operates on the voltage from the standby electric set. When the normal power returns to the rated voltage and frequency and the time delay (if so equipped) is over, the transfer switch will return the load to the normal power supply.

Control Panel

Electronic Modular Control Panel (EMCP II)
(1) Optional panel lights. (2) Optional governor switch (shown) or speed potentiometer. (3) Optional starting aid switch. (4) Engine control switch. (5) Optional alarm module (shown) or synchronizing lights module. (6) Voltage adjust rheostat. (7) Emergency stop push button. (8) Generator set control. (9) Optional panel light switch.

The main function of the control panel is to control the start and shutoff of the engine.

The engine control on the automatic start/stop control panel is an automatic engine control switch (ECS) with four positions. The positions of switch (4) are: OFF/RESET, AUTO, MAN./START, and COOLDOWN/STOP. Each light goes ON only when an abnormal condition in the engine stops the engine. The light for the condition in the engine that stopped the engine is ON even after the engine has stopped. Switch (4) must be moved to the OFF/RESET position for the light to go OFF. Each light will go ON, for a light test, when the light is pushed in and held.

When the generator is to be used as a standby electric power unit, the automatic control switch is put in the AUTO position. Now, if the normal (commercial) electric power stops, the engine starts and the generator takes the electric load automatically. When the normal (commercial) electric power is ON again, or the electric load, the transfer switch opens its contacts to the generator, and closes its contacts to the normal (commercial) electric power. After the transfer switch for the generator opens, the engine automatically stops, usually after running for a cooldown time.

When the automatic engine control switch (ECS) is moved to the MAN./START position, the engine starts. It may now be necessary for the circuit breaker for the generator electric power to be closed manually to the load. If the generator is a standby electric power unit and the automatic engine control switch (ECS) is in the MAN./START position when normal (commercial) electric power stops, the automatic engine control switch (ECS) can be put into the AUTO position and the engine will stop automatically when the normal (commercial) electric power is ON again.

The engine will be stopped with the automatic engine control switch (ECS) in either the AUTO or MAN./START positions if there is a fault (not normal) condition in the engine. The fault conditions in the engine that can stop the engine are low lubricating oil pressure, high engine coolant (water) temperature or engine overspeed (too much rpm). When any of these conditions stop the engine, the light for the fault condition will stay ON after the engine is stopped. A fourth fault condition light is ON only when the starting motor runs the amount of seconds for the overcrank timer (engine does not start).

Move the automatic engine control switch (ECS) to the OFF/RESET position and the fault condition lights go OFF if the fault condition has been removed.

Electric Set

The components of the electric set are: the engine, the generator, the starting motor, the battery, the shutoff solenoid and signal switches on the engine. The electric set gives emergency power to drive the load.

An explanation of each of the signal components is given in separate topics.

Wiring Diagrams

The following wiring diagrams show the connections of the start/stop components with the engine. The diagrams show available options for the hydraulic governor application and the 2301A governor.

For a more complete explanation of operation of the automatic start/stop control panel, refer to Operation & Maintenance Manual, SEBU6918 for SR4B generators and control panels.

Automatic Start/Stop Wiring

A-DC AmmeterACS-Engine Control SwitchALT-Charging AlternatorAR-Arming RelayARX-Auxiliary RelayASO-Air Shutoff SolenoidOCT-Overcrank TimerCB-Circuit BreakerCCM-Cycle Cranking ModuleCCT-Cycle Crank RelayCDT-Cool Down TimerCDTR-Cool Down Timer RelayCRC-Cycle Crank Logic TimerCTS-Crank Terminate SwitchDSS-Dual Speed Switch (Includes CTS And OSS)GS-Governor SwitchGSM-Governor Synchronizing MotorI-Initiate Contact (Remote Start)MS-Magnetic Switch (Crank Circuit)OCR-Overcrank RelayOP-Oil Pressure Indicator SenderOPG- Oil Pressure IndicatorOPR-Low Oil Pressure RelayOOPS- Oil Pressure SwitchOPT-Optional EquipmentOSR- Overspeed Relay (In DSS)PIL-Panel Illumination LampPLS-Panel Lamp SwitchPS-Pinion SolenoidRR-Run RelaySS-Shutoff SolenoidSM-Starting MotorTDR-Time Delay RelayTDX-Time Delay Auxiliary RelayWT-Water Temperature Indicator SenderWTG-Water Temperature IndicatorWTR-High Water Temperature RelayWTS-Water Temperature Switch^*-Indicates Equipment External To Control Panel0-Terminal Strip Point (Control Panel)[ ]-Terminal Strip Point (Generator Terminal Box)[]-Relay Contact Line Number

Control Panel Wiring Schematic

NOTE A: Terminals 13 and 14 of the generator box will be connected to terminals 13 and 14 of the control panel when the CDT is not supplied.

Note B: Red jumper wire from terminal strip point number 4A to 4 in control panel must be removed when the cycle cranking module (CCM) is used.

NOTE C: Auxiliary relay (ARX) contacts are to be customer wired. See Relay Contact Schematic.

NOTE D: Dotted lines shown on Control Panel Wiring Schematic show engine wiring.

NOTE E: The overcrank timer (OCT) is to be adjusted to the 30 second setpoint (red dot). When cycle cranking (CCM) is used the overcrank timer (OCT) is to be adjusted to the 90 second setpoint (white dot).

NOTE F: ACS switch contacts shown with switch in auto position.

NOTE G: Jumper wire from terminal 72 to terminal 73 must be removed when DC ammeter (A) is used.

NOTE H: Jumper wire from terminal 13 to terminal 133 to be removed if additional fault shutdowns are added. Examples: reverse power relay or remote shutdown. Insert a normally closed switch between terminal 13 and terminal 133.

Shutoff And Alarm System Components

Oil Pressure Switch

Micro Switch Type

Oil Pressure Switch (Micro Switch Type)
(1) Locknut. (2) Adjustment screw. (3) Spring. (4) Arm. (5) Spring. (6) Bellows. (7) Latch plate. (8) Button for micro switch. (9) Arm. (10) Projection of arm.

The oil pressure switch is used to give protection to the engine from damage because of low oil pressure. When oil pressure lowers to the pressure specifications of the switch, the switch closes and activates the rack shutoff solenoid.

On automatic start/stop installations, this switch closes to remove the starting system from the circuit when the engine is running with normal oil pressure.

This switch for oil pressure can be connected in a warning system for indication of low oil pressure with a light or horn.

As pressure of the oil in bellows (6) becomes higher, arm (4) is moved against the force of spring (3). When projection (10) of arm (4) makes contact with arm (9), pressure in the bellows moves both arms. This also moves button (8) of the micro switch to activate the micro switch.

Some of these switches have a "Set For Start" button. When the button is pushed in, the micro switch is in the START position. This is done because latch plate (7) holds arm (9) against button (8) of the micro switch and the switch operates as if the oil pressure was normal. When the engine is started, pressure oil flows into bellows (6). The bellows move arm (4) into contact with latch plate (7). The latch plate releases the "Set For Start" button and spring (5) moves it to the RUN Position. This puts the switch in a ready to operate condition.

Pressure Switch

Pressure switches are used for several purposes and are available with different specifications. They are used in the oil system and in the fuel system. One use of the switch is to open the circuit between the battery and the rack shutoff solenoid after the oil pressure is below the pressure specifications of the switch. It also closes when the engine starts.

Another use of the switch is to close and activate the battery charging circuit when the pressure is above the pressure specification of the switch. It also disconnects the circuit when the engine is stopped.

Shutoff Solenoid

A shutoff solenoid changes electrical input into mechanical output. It is used to move the fuel injection pump rack to the off position.

The shutoff solenoid can be activated by any one of the many sources. The most usual are: water temperature contactor, oil pressure switch, overspeed switch and remote manual control switch.

The shutoff solenoid can be either the energized to run or the energized to shutoff type as provided with the engine shutoff control logic.

Mechanical Oil Pressure And Water Temperature Shutoff

Mechanical Shutoff Group
(1) Oil pressure sensing valve. (2) Tee. (3) Water temperature sensing valve. (4) Shutdown cylinder.

The shutdown cylinder (4) is mounted to the rear of the governor housing. the plunger of the cylinder acts on a spring-loaded lever assembly inside the governor housing. When extended, the plunger rotates the lever assembly to allow full movement of the fuel rack. When the plunger is retracted, the lever assembly returns to its original position which moves and holds the fuel rack in the shutoff position.

When starting the engine, the knob on shutdown cylinder (4) must be held in to extend the plunger against the lever assembly inside the governor housing. This will rotate the lever assembly to allow full rack movement. After the engine starts and oil pressure is high enough to hold the plunger extended, the knob can be released. Oil pressure will hold the plunger in this position until there is a low oil pressure condition.

Under normal operating conditions, pressure oil from the engine oil manifold flows to tee (2). Part of the oil from the tee flows through water temperature sensing valve (3) into the pressure inlet end of oil pressure sensing valve (1) where the oil flow is blocked and the oil pressure is monitored. The other part of the oil flow from tee (2) flows to and through the drain end of valve (2) on to shutdown cylinder (4) where the oil flow is blocked and the pressure holds the cylinder plunger extended.

When the oil pressure gets too low the drain end of valve (1) will open causing the pressure oil to cylinder (4) to drain back to the engine block. With no oil pressure in cylinder (4), the lever assembly in the governor returns to its original position pushing the cylinder plunger to the retracted position and moves the fuel rack to the shutoff position to stop the engine.

When the water temperature is too high, the pressure oil that flows through water temperature sensing valve (3) is diverted to drain within the valve body and flows back to the engine block. This causes the oil pressure to become too low and the engine will stop as described above.

Water Temperature Switch

Water Temperature Switch

The contactor switch for water temperature is installed in the water manifold. No adjustment to the temperature range of the contactor can be made. The element feels the temperature of the coolant and then operates the micro switch in the contact when the coolant temperature is too high, the element must be in contact with the coolant to operate correctly. If the cause for the engine being too hot is because of low coolant level or no coolant, the switch will not operate.

The switch is connected to the rack shutoff solenoid to stop the engine. The switch can also be connected to an alarm system. When the temperature of the coolant lowers to the operating range, the contactor switch opens automatically.

Circuit Breaker

Circuit Breaker Schematic (Typical Example)
(1) Disc in open position. (2) Contacts. (3) Disc. (4) Circuit terminals.

The circuit breaker gives protection to an electrical circuit. Circuit breakers are rated as to how much current they will permit to flow. If the current in a circuit gets too high it will cause heat in disc (3). Heat will cause distortion of the disc and contacts (2) will open. No current will flow in the circuit.

An open circuit breaker will close (reset) automatically when it becomes cooler.

Electronic Speed Switch (ESS)

Electronic Speed Switch (ESS)
(1) Verify button. (2) Reset button. (3) "LED" overspeed light. (4) Seal screw plug (overspeed). (5) Seal screw plug (crank terminate).

The Electronic Speed Switch (ESS) is designed with controls built into a single unit to monitor several functions at the same time. The functions that the ESS monitors are:

Engine Overspeed (OS)

This is an adjustable engine speed setting (normally 118 percent of rated speed) that prevents the engine from running at a speed that could cause damage. This condition will cause a switch to close that shuts off the fuel to the engine and connects the magneto to ground to stop current flow to the spark plugs.

Crank Termination (CT)

This is an adjustable engine speed setting that signals the starting motor that the engine is firing and cranking must be terminated. When the speed setting is reached, a switch will open to stop current flow to the starting motor circuit. The starting motor pinion gear will now disengage from the engine flywheel ring gear.

Air Starting System

The air starting motor is used to turn the engine flywheel fast enough to get the engine running.

Air Starting System
(1) Starter control valve. (2) Oiler. (3) Relay valve. (4) Air starting motor.

The air starting motor is on the right side of the engine. Normally the air for the starting motor is from a storage tank which is filled by an air compressor installed on the left front of the engine. The air storage tank holds 297 liter (10.5 cu ft) of air at 1720 kPa (250 psi) when filled.

For engines which do not have heavy loads when starting, the regulator setting is approximately 690 kPa (100 psi). This setting gives a good relationship between cranking speeds fast enough for easy starting and the length of time the air starting motor can turn the engine before the air supply is gone.

If the engine has a heavy load which cannot be disconnected during starting, the setting of the air pressure regulating valve needs to be high in order to get high enough speed for easy starting.

The air consumption is directly related to speed, the air pressure is related to the effort necessary to turn the engine flywheel. The setting of the air pressure regulator can be up to 1030 kPa (150 psi) if necessary to get the correct cranking speed for a heavily loaded engine. With the correct setting, the air starting motor can turn the heavily loaded engine as fast and as long as it can turn a lightly loaded engine.

Other air supplies can be used if they have the correct pressure and volume. For good life of the air starting motor, the supply should be free of dirt and water. The maximum pressure for use in the air starting motor is 1030 kPa (150 psi). Higher pressures can cause problems.

Air Starting Motor
(5) Vanes. (6) Gear. (7) Pinion spring. (8) Pinion. (9) Rotor. (10) Piston.

The air from the supply goes to relay valve (3). The starter control valve (1) is connected to the line before the relay valve (3). The flow of air is stopped by the relay valve (3) until the starter control valve (1) is activated. Then air from the starter control valve (1) goes to the piston (10) behind the pinion (8) for the starter. The air pressure on the piston (10) puts the spring (7) in compression and puts the pinion (8) in engagement with the flywheel gear. When the pinion is in engagement, air can go out through another line to the relay valve (3). The air activates the relay valve (3) which opens the supply line to the air starting motor.

The flow of air goes through the oiler (2) where it picks up lubrication oil for the air starting motor.

The air with lubrication oil goes into the air motor. The pressure of the air pushes against the vanes (5) in the rotor (9). This turns the rotor which is connected by the gear (6) to the starter pinion (8) which turns the engine flywheel.

When the engine starts running the flywheel will start to turn faster than the starter pinion (8). The pinion (8) retracts under this condition. This prevents damage to the motor, pinion (8) or flywheel gear.

When the starter control valve (1) is released, the air pressure and flow to the piston (10) behind the starter pinion (8) is stopped, the pinion spring (7) retracts the pinion (8). The relay valve (3) stops the flow of air to the air starting motor.