Carolina CAT Construction Equipment• Fall• 1. HET 127 Shop Rules and regulations 1 • 2. HET 110C Diesel Engines 6 • 3. HET 112C Diesel Electrical Systems 5 • 4. HET 125C Preventive Maintenance 2• 5. ENG 111 Expository Writing 3• Spring • 6. HET 116C Heating /Air conditioning Systems 2 • 7. HYD 112C Hydraulics/Medium/Heavy Duty 2 • 8. HYD 134C Hydraulic/Hydrostatic Construction 4 • 9. AUB 134C Auto body MIG welding 3 • 10. MAT 115 Mathematical Models 3 • Summer • 11. HET 114C Power Trains 5 • 12. HET 115C Electronic Engines 3 • 13. HYD 210C Advanced Hydraulics 2 • Fall • 14. COE 112R Co-op work Experience I* (or HET128C) 2 • 15. HET 128C Med/Heavy duty tune up* (or COE112r) 2 • Graduation Requirements: 43

Cranking Systems

HET112C Diesel Electrical Systems

Objectives• Identify the components in a Construction cranking

circuit.• Explain the operating principles of magnetic switches,

solenoids, and starter motors.• Describe the operating principles of lightweight,

planetary gear reduction starter motors.• Test and troubleshoot a cranking circuit using voltage

drop testing

( Objectives cont.)• Disassemble a heavy-duty Construction starter motor.• Test an armature for shorts using a growler.• Test an armature for grounds and opens.• Use a test light to check out field coils.• Outline the procedure required to rebuild a Delco-

Remy 42MT starter motor.

INTRODUCTION The cranking system in any vehicle is designed to turn

the engine over until it can operate under its own power. A cranking system can be divided into two sub-circuits known as the control circuit and the starter circuit. The objective of the cranking system is to energize a starter motor using energy from the vehicle batteries.

STARTING CIRCUIT COMPONENTS• Battery• Key switch (or starter button)• Battery cables• Magnetic switch• Starter motorA starter motor draws high current from the

batteries, typically 300 to 400 amperes.

GROUND AND INSULATED CIRCUITS Almost all current highway vehicles use negative

chassis ground electrical circuits. In such a system, the entire chassis is used as the ground or negative path for current flow. This is known as the ground circuit. An advantage of chassis negative ground systems is that only the positive side of the current path to components has to be insulated.

CRANKING CIRCUITCOMPONENTS

• BATTERY TERMINALS• CABLES• STARTER MOTOR• MAGNETIC SWITCH• CONTROL CIRCUIT

MAXIMUM VOLTAGE DROPSPECIFICATIONS

Insulated circuit voltage drop (VD) maximums:

Cranking Circuit Component Max VDStarter cable 0.2 voltEach cable connection 0.1 voltStarter solenoid 0.3 voltMaximum total permissible voltage loss 0.5 volt

IGNITION SWITCH The ignition switch gets its name from the automobile

key circuit. The term ignition switch is commonly used to describe the switch that energizes the control circuit in the cranking system. There are two types.

The first type is integral with the ignition key: To close the control circuit to initiate cranking, the key is turned. The second type is a push-button and requires that the ignition key circuit be closed before the push-button starter is powered.

STARTER RELAY

STARTER MOTORS

Shop Talk Starter motors can only operate for short periods

without rest. The high current needed to operate the starter creates considerable heat, and continuous operation will cause overheating. A starter motor should never operate for more than 30 seconds at a time and should rest for 2 minutes between cranking cycles. This permits the heat to dissipate without damage to the unit.

STARTER MOTOR CONSTRUCTION

Field Coils

Armature

Commutator

OPERATION

Current Flow

STARTER SOLENOIDS

Solenoid Windings

Shop Talk In almost all diesel engine starters, the solenoid

performs the function of a relay. The control circuit is wired to the windings of the solenoid. Battery current is routed directly to the starter motor through the drive solenoid.

Initiating Cranking

Overrunning Clutches

Thermostats Some starter motors are equipped with a thermostat

(see Figure 9-2B). The thermostat monitors the temperature of the motor. If prolonged cranking causes the motor temperature to exceed a safe threshold, the thermostat opens and the starter current is interrupted. The starter motor, then, will not operate until the motor cools and the thermostat closes.

CONTROL CIRCUIT The control circuit allows the driver to use a small

amount of battery current to control the flow of a large amount of current in the starting circuit. It consists of the following components.

• Ignition Switch• Neutral Safety Switch• Starter Relays

REDUCTION-GEARING STARTERMOTORS

Shop Talk The starter should not be operated if the voltage at

the battery is below 9.6 volts. Some leasing companies now use a voltage sensing module to prevent starter operation if voltage is below 9.6 volts to prevent drivers from destroying starters.

Testing Cranking Current

Shop Talk If the analyzer uses an inductive pickup (amp clamp),

ensure that the arrow on the inductive pickup is pointing in the right direction as specified on the ammeter. Then crank the engine for 15 seconds and observe the ammeter reading.

WARNING: When performing this test, do not operate the

solenoid for extended periods because severe overheating will result.

Starter Circuit Testing

Shop Talk When testing starter circuits, use the OEM

recommended method of preventing the engine from starting. When performing voltage drop tests, make sure you record the results to two decimal places. Record the results by writing them down so you can easily check them to spec afterwards.

NO-LOAD TESTS

STARTER REBUILD• DISASSEMBLY• INSPECTION• REASSEMBLY

ADJUSTING PINION CLEARANCE

Summary• The vehicle cranking circuit functions to crank the

engine until it can operate under its own power.• A cranking circuit is managed by a control circuit that

uses low current to switch and energize a high-current starter motor circuit.

• A starter motor converts the electrical energy of the vehicle batteries into mechanical energy for cranking the engine.

Summary (cont.)• A powerful electromagnetic field in the starter motor

field coils is used to rotate the armature assembly in a typical starter motor.

• Most starter motors are series wound, so there is only one path for current flow through the assembly. This means that all of the current flowed through the field coils also flows through the armature, providing the conditions that along with the absence of CEMF produce peak torque at close to stall speeds.

Summary (cont.)• CEMF works in opposition to battery current inan armature. It rises proportionally witharmature speed. For this reason, CEMF helpslimit starter overspeed.• A new generation of lightweight, high-torquestarter motors uses planetary gear reduction tomultiply cranking torque and greatly reducemotor weight.

Summary (cont.)• Voltage drop testing should be used to troubleshoot

a cranking circuit malfunction because it does so dynamically.

• A heavy-duty Construction starter motor found to be defective should be removed from the engine and either rebuilt or replaced.

Summary (cont.)• A growler is used to test an armature for shorts:A steel strip such as a hacksaw blade is placedon top of the armature during testing and if itvibrates, a short is indicated.• A test light is used to test an armature forgrounds and opens.

Summary (cont.)• Field coils should be checked usinga test light.• After reassembling a starter motor, the pinionclearance should be checked with thicknessgauges and adjusted if necessary.

Any Questions ?