Starting Systems from caterpillar .pdf

Lesson 3: Starting System

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Introduction

The starting system converts electrical energy from the battery intomechanical energy to start the engine. This lesson explains thestarting system and describes the starting system components.Starting system testing is also coveredObjectives

At the completion of this lesson, the student will be able to:

Explain the operation of the starting system by selecting thecorrect response to questions on a multiple choice quiz.

Given a training aid or a machine and the appropriate tools,test the starting circuit on the training aid or machine andcorrectly answer the lab questions regarding starting circuittesting.

Given a starting motor and a digital multimeter, test theelectrical components of the starting motor on the bench andcorrectly answer the lab questions regarding starting motortesting.

MACHINE ELECTRICALSYSTEMS

• Starting System

• Battery• Charging System

References

Service Magazine Article "Limitations on Engine Cranking Time"March 27, 1989.

Video "Testing the Starter on the Engine" SEVP1591

Tools

8T0900 Clamp-0n Ammeter

9U7330 Digital Multimeter

Unit 4 4-3-2 Electrical FundamentalsLesson 3

How the Starting System Works

A basic starting system has four parts:

- Battery: Supplies energy for the circuit

- Starter switch: Activates the circuit

- Solenoid (motor switch): Engages the starting motor drive withthe flywheel

- Starting Motor: Drives the flywheel to crank the engine

When the starter switch is activated a small amount of current flowsfrom the battery to the solenoid and back to the battery through theground circuit.

The solenoid performs two functions. The solenoid engages thepinion with the flywheel and closes the switch inside the solenoidbetween the battery and starting motor, which completes the circuitand allows high current to flow into the starting motor.

The starting motor takes the electrical energy from the battery andconverts it into rotary mechanical energy to crank the engine. It issimilar to other electric motors. All electric motors produce a turningforce through the interaction of magnetic fields inside the motor.

The battery was previously covered in lesson 1 since it serves theentire electrical system. In this lesson we will focus on the otherelements of the starting system beginning with the starting motor.

BATTERY

SOLENOID(MOTOR SWITCH)

STARTERSWITCH

STARTINGMOTOR

FLYWHEEL

Fig. 4.3.1 Basic Starting Circuit


S

N

CURRENT

FLOW

Fig. 4.3.2 Forces on a Coil

Starting Motor

Before learning the basic operating principles of starting motors let'sreview some basic rules of magnetism:

- Like poles repel, unlike poles attract

- Magnetic flux lines are continuous and exert force

- Current-carrying conductors have a magnetic field that surroundsthe conductor in a direction determined by the direction of thecurrent flow.

Remember, if a conductor has a current passed through it, there willbe a magnetic field formed. A permanent magnet has a field betweenthe two poles. When the current-carrying conductor is placed in thepermanent magnetic field, there will be a force exerted on theconductor because of the magnetic field. If the conductor is formedin a loop and placed in the magnetic field, the result is the same.Since current flow is in opposite directions in the coil, one side willbe forced up while the other side is forced down This will provide arotational or torque effect on the coil.


POLE PIECES

MAGNETICFIELD

Fig. 4.3.3 Pole Pieces

FIELDWINDING

Fig. 4.3.4 Field Winding

If a wire, called a field winding, is wrapped around the pole piecesand current is passed through it, the strength of the magnetic fieldbetween the pole pieces increases.

Starting Motor Principles

The pole pieces in the field frame assembly can be compared to theends of a magnet. The space between the poles is the magnetic field.


Fig. 4.3.5 Wire Loop

Fig. 4.3.6 Wire Loop in a Field

If the loop of wire is placed in the magnetic field between the twopole pieces and current is passed through the loop, a simple armatureis created. The magnetic field around the loop and the field betweenthe pole pieces repel each other, causing the loop to turn.

If we feed current from the battery into a loop of wire, a magneticfield is also formed around the wire.


A commutator and several brushes are used to keep the electric motorspinning by controlling the current passing through the wire loop.The commutator serves as a sliding electrical connection between thewire loop and the brushes. The commutator has many segments,which are insulated from each other.

The brushes ride on top of the commutator and slide on thecommutator to carry battery current to the spinning wire loops. Asthe wire loops rotate away from the pole shoes, the commutatorsegments change the electrical connection between the brushes andthe wire loops. This reverses the magnetic field around the wireloops. The wire loop is again pulled around and passes the other polepiece. The constantly changing electrical connection keeps the motorspinning. A push-pull action is set up as each loop moves aroundinside the pole pieces.

Several loops of wire and a commutator with many segments areused to increase motor power power and smoothness. Each wire loopis connected to its own segment on the commutator to provide currentflow through each wire loop as the brushes contact each segment. Asthe motor spins, many wire loops contribute to the motion to producea constant and smooth turning force.

BRUSHES

COMMUTATOR

Fig. 4.3.7 Simple Armature


Fig. 4.3.8 Armature

Fig. 4.3.9 Field Windings

A field winding is a stationary insulated wire wrapped in a circularshape, which creates a strong magnetic field around the motorarmature. When current flows through the field winding, themagnetic field between the pole pieces becomes vary large. It can be5-10 times that of a permanent magnet. As the magnetic fieldbetween the pole shoes acts against the field developed by thearmature, the motor spins with extra power.

A starting motor, unlike a simple electric motor, must produce veryhigh torque and relatively high speed. Therefore a system to supportthe wire loops and increase the strength of each wire loop's magneticfield is needed.

A starter armature consists of the armature shaft, armature core,commutator and armature windings (wire loops). The starting motorshaft supports the armature as it spins inside the starter housing. Thecommutator is mounted on one end of the armature shaft. Thearmatures core holds the windings in place. The core is made of ironto increase the strength of the magnetic field produced by thewindings.


Starting Motor Characteristics

Starters are high capacity intermittent duty electric motors that tendto behave with specific characteristics when in operation:

If they are required to power a certain mechanical component (orload), they will consume specific amount of power in watts.

If the load is removed, speed increases and current draw will godown.

If the load is increased, speed decreases and current draw will go upthey have low resistance and high current flow.

The amount of torque developed by an electric motor increases as theamperes flowing through the motor increases. The starting motor isdesigned to operate for short periods of time under an extreme load.The starting motor produces a very high horsepower for its size.

Counter Electromotive Force (CEMF) is responsible for changes incurrent flow as the starter speed changes. CEMF increases theresistance to current flow from the battery, through the starter, as thestarter speed increases. This occurs because, as the conductors in thearmature are forced to spin, they are cutting through the magneticfield created by the field windings. This induces a counter-voltage inthe armature that acts against battery voltage, this counter-voltageincreases as the armature speed increases. This acts as a speedcontrol and prevents high free-running speeds.

Although most electric motors have some form of current protectiondevice in the circuit, most starter motors do not. Some starters dohave thermal protection, this is provided by a heat sensitivethermostatic switch. The thermostatic switch will open when thestarter temperature rises due to excessive cranking, the switch willautomatically reset when it cools. They are classed as an intermittentoperating motor. If they were a continuous operating motor, theywould need to be almost as large as the engine itself. Because of thehigh torque demands on the starter motor, a great deal of heat isproduced during operation. Extended operation of the starter motorwill cause internal damage due to this high heat. All the parts of thestarter motor’s electrical circuit are very heavy to be able to handlethe heavy current flow associated with its operation.

If higher loads require more power to operate, then each starter motormust have sufficient torque to provide turning speed necessary tocrank the engine. This power is directly related to the strength of themagnetic field, since the strength of the field is what creates thepower.


As previously described, starting motors have a stationary member(field windings) and a rotating member (armature). The fieldwindings and the armature are usually connected together so that allcurrent entering the motor passes both the field and the armature.This is the motor circuit.

The brushes are a means of carrying the current from the externalcircuit (field windings) to the internal circuit (armature windings).

The brushes are contained in brush holders. Normally, half thebrushes are grounded to the end frame and the other half are insulatedand connected to the field windings.

Starter motor fields can be wired together in four differentconfigurations to provide the necessary field strength:

- series- compound (shunt)- parallel- series-parallel

Series wound starters (Figure 4.3.10) are capable of producing a veryhigh initial torque output when they are first engaged. This torquethen decreases as they operate due to counter-electromotive force,which decreases the current flow since all the windings are in series.

Compound motors have three windings in series and one winding inparallel. This produces good initial torque for starting and the benefitof some load adjustment due to the parallel winding. This type ofstarter also has the added benefit of speed control due to the parallelfield.

Parallel wound motors provide higher current flow and greater torqueby dividing the series windings into two parallel circuits.

Series-parallel motors combine the benefits of both the series and theparallel motors.

CURRENTFROM

BATTERY

FIELDWINDING

GROUNDS POLE SHOE

COMMUTATOR

FIELDWINDING

BRUSH

Fig. 4.3.10 Starting Motor Circuits


Many starters have four fields and four brushes. Starters that arerequired to produce very high torque may have up to six fields andbrushes while some light-duty starters may have only two fields.

Many heavy-duty starter motors are not grounded through the case ofthe starter. This type of starter motor is grounded through aninsulated terminal that must be connected to the battery ground forthe starter to work. A ground wire for the solenoid and other engineelectrical devices must also be attached to the starter ground terminalfor proper electrical operation.


Fig. 4.3.11 Starting Motor Drive

Up to this point we've covered the electrical components of thestarting motor. After electrical power is transmitted to the startingmotor, some type of connection is needed to put this energy to work.The starting motor drive makes it possible to use the mechanicalenergy produced by the starting motor.

Although torque produced by the starter motor is high, it does nothave the ability to crank the engine directly. Other means must beused to provide both adequate cranking speed and the necessarytorque.

To provide adequate torque for cranking the engine, the speed of thestarter is altered by the ratio between the pinion gear on the starterand the engine flywheel. This ratio varies from 15:1 to 20:1. Forexample, if the starter drive gear had 10 teeth, the ring gear mighthave 200 to provide a ratio of 200:10 or 20:1.

Starter drive mechanisms

If the starter were left engaged to the flywheel after the enginestarted, damage would occur to the armature due to very high speedscreated as engine rpm increased. At high speed, the armature wouldthrow its windings due to centrifugal force.

The gear that engages and drives the flywheel is called a pinion gear.The gear on the flywheel is called a ring gear. How the starter piniongear engages with the flywheel ring gear depends on the type of driveused.

Starter pinion gears and their drive mechanisms can be of twodifferent types:

- inertia drive- overrunning clutch.

Inertia drives are actuated by rotational force when the armatureturns. This type engages after the motor begins to move. The drivesleeve has a very coarse screw thread cut Into it, which correspondsto threads on the inside of the pinion.

As the motor begins to turn, the inertia created at the drive causes thepinion to move up the threads until it engages with the ring gear onthe flywheel. You can recreate this action by spinning a heavy nut ona bolt and watch the rotary motion change to linear motion as the nutmoves up or down.

One disadvantage of inertia starters is that the pinion is not positivelyengaged before the starter begins to turn. If the drive does notengage with the flywheel, the starter will spin at high speed withoutcranking the engine or if the pinion lags it will strike the gear withheavy force, damaging the teeth.


Fig. 4.3.12 Overrunning clutch

The overrunning clutch drive is the most common type of clutchdrive. The overrunning clutch drive requires a lever to move thepinion into mesh with the flywheel ring gear. The pinion is engagedwith the flywheel ring gear before the armature starts to rotate.

With this type of drive system, a different method must be used toprevent armature over-speeding. A lever pulls the drive out ofengagement while an overrunning clutch prevents over-speeding.

The overrunning clutch locks the pinion in one direction and releasesit in the other direction. This allows the pinion gear to turn theflywheel ring gear for starting. It also lets the pinion gear freewheelwhen the engine begins to run.

The overrunning clutch consists of rollers held in position by springsagainst a roller clutch. This roller clutch has tapered ramps that allowthe roller to lock the pinion to the shaft during cranking.

The torque travels through the clutch housing and is transferred bythe rollers to the pinion gear. When the engine starts and the speed ofthe drive pinion exceeds the speed of the armature shaft, the rollersare pushed down the ramps and permit the pinion to rotateindependently from the armature shaft. Once the starter drive pinionis disengaged from the flywheel and is not operating, spring tensionwill force the rollers into contact with the ramps in preparation forthe next starting sequence. There are various heavy duty designs ofthis drive.


R

CSB ST

OFF

ON

POS NEG

DISCONNECTSWITCH

BATTERIES

STARTSWITCH

STARTRELAY

STARTERMOTOR

POS NEG

Fig. 4.3.13 Starting System Schematic

Starting Circuit Controls

The starting circuit contains control and protection devices. Theseare necessary to allow the intermittent operation of the starter motorand to prevent operation during some machine operation modes forsafety reasons. The starter electrical circuit may consist of thefollowing devices:

- battery- cables and wires- key start switch- neutral safety switch/clutch safety switch (if equipped)- starter relay- starter solenoid.

Battery

The battery supplies all of the electrical energy to the starter enablingit to crank the engine. It is important that the battery be fully chargedand in good condition if the starting system is to operate at fullpotential.

Cables and wires

The high current flow through the starter motor requires cables thatmust be large enough to have low resistance. In a series circuit, anyadded resistance in the circuit will affect the operation of the load dueto a reduction in the total current flow in the circuit.

In some systems, the cables will connect the battery to the relay andthe relay to the starter motor, while in other systems the cable will godirectly from the battery to the starter.

Ground cables must also be large enough to handle the current flow.All connectors and connections in the starting system must have aslittle resistance as possible.

Key Start Switch

The key start switch activates the starter motor by providing power tothe starter relay from the battery. It can be operated directly by keyor button or remotely by linkage from a key-activated control. It canbe mounted in the dashboard assembly or on the steering column.

Fig. 4.3.14 Key Start Switch


Neutral safety switch or clutch safety switch

All vehicles equipped with a power shift or automatic transmissionrequire a neutral safety switch that will only permit starter operationin park or neutral. This switch can be mounted on the transmission,at the shifter or in the linkage. The switch contacts are closed whenthe transmission selector is in park or neutral and open when thetransmission selector is in any gear.

Some vehicles may use a clutch safety switch that is open when theclutch is in the engaged position and closed when the operatordepresses the clutch pedal. This prevents starter operation as long asthe clutch is engaged. Some transmissions also use a neutral gearswitch that will prevent starter operation unless the transmission isplaced in the neutral position.

All safety switches of this type should be maintained in goodoperating condition and should never be bypassed or removed.

Fig. 4.3.15 Starter Relay


Starter relay

The starter relay (magnetic switch) may be used in some startingsystems. It is located between the key start switch and startersolenoid. It is a magnetic switch that is activated by power from thebattery supplied through the key start switch. Relays are usuallyplaced so that the cables between the starter and the battery are asshort as possible.

The starter relay uses a small current from the key start switch tocontrol the larger current to the starter solenoid, which reduces theload on the key start switch. Energizing the relay windings will causethe plunger to be pulled up due to the magnetism caused by thecurrent flow through the windings. The contact disk will also bepulled up and will contact the battery and starter terminal ends.Current will flow from the battery to the starter solenoid.

Fig. 4.3.16 Starter Solenoid

Solenoids combine the operation of a magnetic switch (relay) withthe ability to perform a mechanical task (engage the drive). Thestarter solenoid produces a magnetic field that pulls the solenoidplunger and disc into the coil windings, which completes the startingsystem circuit. The solenoid is mounted on the starter motor so thatlinkage may be attached to the overrunning clutch drive to engage thedrive.

Solenoids contain two different windings for effective operation.When the ignition switch is turned to the start position, current fromthe battery flows through a pull-in winding and a hold-in winding.These windings contain many coils of wire and produce a strongmagnetic field to pull the heavy plunger forward and engage thestarter drive.

When a plunger reaches the end of its travel through the solenoid, itengages a contact disk that will operate like a relay and allow currentto flow to the starter motor from the battery. This also serves todisconnect the series pull-in winding from the circuit and allowcurrent to flow through a shunt hold-in winding only. Only thelighter magnetic field created by the hold-in winding is required tohold the plunger in position. This reduces the amount of controlcurrent required, eliminating heat build-up and provides more currentfor the starter motor.


ARMATURE FIELD WINDING

BRUSHES

REDUCTIONGEARS

KEY STARTSWITCH BATTERY

SOLENOID

PULL-IN WINDING

PINION

HOLD-INWINDING

OVERRUNNINGCLUTCH

Fig. 4.3.17 Starter Circuit Schematic--Key Start SwitchClosed

ARMATURE

BRUSHES


SOLENOID

FIELD WINDING

REDUCTIONGEARS

PULL-IN WINDING

PINION

HOLD-INWINDING

OVERRUNNINGCLUTCH

Fig. 4.3.18 Starter Circuit Schematic--SolenoidContacts Closed

When the plunger is pulled to the left, the solenoid contacts close. Atthis point the pinion begins to mesh with the flywheel ring gear andthe pull-in winding is shorted, which causes current flow through thesolenoid contacts to the field winding, armature, brushes and toground. Current still flows through the hold-in winding to ground.The starting motor is energized, the pinion engages the flywheel ringgear and the engine begins to crank. At this time the plunger is keptin the pull-in position only by the magnetic force of the hold-inwinding.

The starting system operates as follows:

When the ignition switch is closed, battery current flows in twodirections. Current flows from the battery to the start switch andthen through the pull-in winding, field winding, armature, brushesand to ground.

The activation of the pull-in winding and the hold-in windingproduces a magnetic force. The magnetic force pulls the plungerto the left, which moves the overrunning clutch and pinion towardthe flywheel ring gear.


ARMATUREFIELD COIL

BRUSHESSTARTER DRIVE


SOLENOID

Fig. 4.3.19 Starter Circuit Schematic--Key Start SwitchReleased

As soon as the engine starts, the flywheel ring gear turns the pinionfaster than the starting motor is rotating. The overrunning clutchbreaks the mechanical connection between the clutch and the startingmotor. When the ignition switch is released, current flows throughthe hold-in winding and the pull-in winding is in the same direction,which causes the hold-in winding magnetic force to be reduced. Thesolenoid contacts are opened. The plunger and overrunning clutchare pulled back to their original position by the return spring force.The armature stops and the motor is OFF.

Series-Parallel Systems

Machines with larger diesel engines require high power starters toprovide adequate cranking speed for the engine. To achieve thissome machines use 24V starters. Using 24V allows the starter toproduce the same power with less current flow.

In a series-parallel system the starter operates on 24V but the rest ofthe machine electrical system operates on 12V. A special series-parallel switch is used that connects two or more batteries in parallelfor normal accessory and charging operation and then connects thenin series to the starter when cranking. 12V accessories are preferredbecause they are much less expensive than 24V lights andaccessories.

12/24V electrical systems

In another system of this type, the starter is connected in series withtwo 12V batteries and the alternator charges them with 24V.

Starter System Testing

Accurate testing of a starting system begins with an understanding ofhow the system functions. If your knowledge of the operation iscomplete, you can logically determine the fault through visualinspection and electrical testing.


An organized procedure for testing and inspection is necessary to prevent the replacement of good partsor the unnecessary repair of operational components.

Verify the complaint

Operate the system yourself to see how it functions. Starter system problems will normally fall into thefollowing categories:

- starter spins but does not crank the engine

- engine cranks very slowly

- engine does not crank at all

- the starter motor is too noisy

Do not crank the engine for more than 30 seconds at a time. Allow the starter motor to cool betweencranking periods to prevent damage.

Review the Service Magazine Article "Limitations on Engine Cranking Time" dated March 27,1989.

Define the problem

Determine whether the problem is mechanical or electrical. For instance, if the starter rotates but doesnot crank the engine, the problem is most likely mechanical, since the drive does not seems to beengaging.

Mechanical problems can be corrected by repairing the component or replacing parts as required.

Electrical problems require additional testing to determine the cause of the fault and the repair that willbe required.

Isolate the problem

Regardless of whether the problem is mechanical or electrical, you will have to determine where it isoccurring, so that you can quickly and accurately make your repairs.

The steps involved in testing and isolating a starting circuit are:

1. Test the battery to determine if it is fully charged and capable of delivering sufficient current.2. Test the wiring and switches to determine if they are in good operating condition.3. If the engine, battery and wiring are all OK, but the starter is not operating correctly, the fault must

be with the starter itself.


Inspecting and Troubleshooting

Visual inspection

Begin all starting system testing with a thorough visual inspection. Check for:

- loose or corroded battery terminals

- worn or frayed insulation on the battery cables

- corroded solenoid or relay connections

- a damaged starter solenoid or relay

- cracked or broken insulators on the starter relay

- loose engine or chassis grounds

- damaged neutral safety switches

- damaged ignition switch or actuating mechanisms

- loose starter

Battery test

Continue the inspection with a complete test and service of the battery.

Perform all required tests to verify that the battery is in good operating condition. Correct batteryoutput is vital for good starting system operation and for correct diagnosis of the starting system.


Starting System Tests

On machine starting motor tests should be performed first to determine whether the starter must beremoved and tested further. On machine tests include :

- Starting system voltage during cranking

- Current draw during cranking

- Voltage drops during cranking

- Engine rotation

- Starting motor pinion and flywheel ring gear inspection

Bench tests will determine if the starter must be repaired or replaced. Bench tests include a no load testand starting motor component tests.

Discuss the test procedures used in the video. Stress the importance of safety when operating theengine during the testing process.


Lab Objective: Given a machine, a multimeter and a clamp-on ammeter perform a test of the startingsystem.

Tooling:

1. 9U7330 Multimeter or equivalent2. 8T0900 Clamp-On Ammeter or equivalent3. Appropriate Service Manual for machine used for test.

Directions: Determine if the starting problem is related to the battery or the starter by performing thefollowing tests.

1. While cranking the engine, measure the battery voltage at the battery posts. Record the results:______________ volts. (Do not measure the battery voltage at the post clamps, place the metertest leads on the actual battery post).

2. Consult the appropriate service manual for battery voltage specifications: Record the servicemanual specification: __________ volts.

3. If the battery voltage is within specification continue with the next test. If the battery voltage isnot within specification, perform a battery load test to determine condition of the battery.

4. Connect the 8T0900 Clamp-On Ammeter around the positive battery cable. Crank the enginewhile observing the current draw on the system.

5. Consult the appropriate service manual for current draw specifications: Record the servicemanual specification: __________ amps.

6. If the current draw exceeds specification, the starter is shorted or grounded.

The remaining electrical tests should be conducted to actually isolate the starting problem when ithas been determined that the battery and starter are functioning normally. These test will helpisolate other electrical related problems.

7. Measure the voltage drop from the solenoid motor terminal to the starting motor ground. Record the results below.

Voltage drop specification (reference machine Service Manual) ____________ volts

Voltage measured: _________________volts

8. Measure the voltage drop from the battery positive post to the starter positive post. Record theresults below.



Unit 4: Lesson 3 - 1 - Electrical FundamentalsStudent Copy Lab 4.3.1

Starting System Test

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9. Measure the voltage drop from the battery negative post to the starter negative post. Recordthe results below.



10. Measure the voltage drop across the disconnect switch (if equipped). Record the results below.



11. Measure the voltage drop across the start relay contacts. Record the results below.



12. Measure the voltage drop across the solenoid contacts. Record the results below.



13. Are the voltages measured in steps 3 through 8 within specifications? __________________

NOTE: If the voltage drops measured in the above tests are too high, the problems are usuallyassociated with broken wires, excessive corrosion or bad connections.

If the engine still fails to crank, perform the following additional tests.

14. Turn the engine over by hand to ensure it is not locked up. Check oil viscosity and any external loads that would affect engine rotation.

15. If the starting motor does not crank, check for blocked engagement of the pinion and flywheel ringgear.

Unit 4: Lesson 3 - 2 - Electrical FundamentalsLab 4.3.1: Student Copy

Starting System Test

Lab Objective: Given two 12V batteries, a multimeter and a clamp-on ammeter, perform a no-loadtest on the starter motor.

Tooling:

1. 9U7330 Multimeter or equivalent2. 8T0900 Clamp-On Ammeter or equivalent3. Appropriate Service Manual for starter being used for test.4. Test switch (SPST)5. Rpm indicator or photo tach

Directions: Perform No-load test using the Service Manual and the following procedures.

1. Connect a fully charged 12 volt battery (two fully charged 12 volt batteries for a 24V system) tothe starting motor as shown in the Service Manual. Connect the positive battery cable to the"BAT" terminal of the starting motor solenoid. Connect the negative battery cable to thestarting motor negative terminal.

2. Connect an open switch between the "S" terminal and "BAT" terminal of the solenoid.

3. Connect the multimeter red lead to the "MTR" terminal of the solenoid. Connect the black leadto the starting motor negative terminal.

4. Use an rpm indicator or photo tach to measure armature speed.

5. Close the switch. Record the results below.

No Load Test specification (reference machine Service Manual) ____________ amps

Voltage measured: _________________ voltsCurrent measured: _________________ ampsSpeed measured: _________________ rpm

Analyze the test results. Use the following list of probable causes to determine root cause ofproblem.

6. Low speed and high current indicate: a. Too much friction which could be caused by:

- Tight, dirty, worn bearings- Bent armature- Loose field pole shoes allowing armature to drag

b. Shorted armaturec. Grounded armature or field winding


No-Load Starter Test

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7. Failure to operate with high current draw indicates:- Direct ground on the terminal or field windings- Frozen bearings

8. Failure to operate with no current draw indicates:- Open field windings- Open armature- Broken brush springs

9. Low speed and low current draw indicate:- High internal resistance

10. High speed and high current draw indicate:- Shorted field circuit- Starting Motor Component Tests

11. Write a brief explanation describing the outcome of the above tests. Also, explain the diagnosisor suggested “root” cause of the problem.__________________________________

____________________________________________________________.

The following labs will demonstrate the starting motor component tests that should be performed afterthe starting system has been tested on the machine and the starting motor no-load test (off the machine)has been completed.


No-Load Starter Test continued

Lab Objective: Given a starter motor, a multimeter and a ruler, perform static measurements on thefield windings, armature and brushes.

Tooling:

1. 9U7330 Multimeter or equivalent2. Ruler3. Appropriate Service Manual for starter being used for test.

Directions: Disassemble the starter and perform the following static tests:

Test #1: Field Winding Ground Testa. Set the multimeter to the 20 M scale.b. Touch the meter leads between each field winding lead and the starting motor case. Record

the results below.

Each reading should be greater than 100,000 ohms.Resistance measured: _______________________ ohms

c. Touch the meter leads between the "MTR" terminal lead and the starting motor case. Recordthe results below.


If any of the meter readings are less than 100,000 ohms what does this indicate?______________________________________________________.

Test #2: Field Winding Continuity Test

a. Set the multimeter to the Ω scale.

b. Touch the meter leads between each field winding lead and the "MTR" terminal lead. Record the results below.

Each reading should be between 0 and 0.1 ohm.Resistance measured: _______________________ ohms

If any of the meter readings are less than 0.1 ohm what does this indicate?_______________________________________________________________,

Static check continued on next page


Static Starter Motor Tests

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Test #3: Armature Short Circuit Test

a. Place the armature on the growler tester and turn the tester on.

b. Hold a hacksaw blade against the armature core while slowly rotating the armature

c. The blade should not vibrate or be attracted to the armature core.

If the blade vibrates or is attracted to the core what does this indicate? _________________________________________________________________________.

Test #4: Armature Ground Test

a. Set the multimeter to the 20 M scale.

b. Touch one meter lead on each commutator bar and the other lead on the armature core.

Each reading should be greater than 100,000 ohms.

If any of the meter readings are less than 100,000 ohms what does this indicate?_______________________________________________

Test #5: Brush Holder Check

a. Set the multimeter to the Ω scale.

b. Touch one meter lead to each positive brush holder and the other lead to the brush holder plate. Check both positive brush holders. Record the results below.


_______________________ ohms

If any of the meter readings are less than 100,000 ohms what does this indicate?_________________________________________.

Test #6: Brush Length Check

Measure the brush length for wear

Brush length specification (reference machine Service Manual) ____________ mmLength measured: _________________ mm


Static Starter Motor Tests continued

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Starting Systems from caterpillar .pdf