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T1510(E)(D1)T NOVEMBER EXAMINATION

NATIONAL CERTIFICATE

MOTOR ELECTRICAL THEORY N2

(11040612)

1 December 2016 (X-Paper) 09:00–12:00

This question paper consists of 7 pages and 1 formula sheet.

(11040612) -2- T1510(E)(D1)T

Copyright reserved

DEPARTMENT OF HIGHER EDUCATION AND TRAINING REPUBLIC OF SOUTH AFRICA

NATIONAL CERTIFICATE MOTOR ELECTRICAL THEORY N2

TIME: 3 HOURS MARKS: 100

INSTRUCTIONS AND INFORMATION 1. 2. 3. 4.

Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. Write neatly and legibly.

(11040612) -3- T1510(E)(D1)T

Copyright reserved

QUESTION 1 1.1 12 volt lead-acid batteries consist of six cells that are connected in series.

Determine the total voltage of the following combinations:

1.1.1 Two 12 volt batteries connected in parallel (2) 1.1.2 Two 12 volt batteries connected in series (2) 1.1.3 Total voltage of the arrangement in FIGURE 1 below (4)

FIGURE 1

(11040612) -4- T1510(E)(D1)T

Copyright reserved

1.2

FIGURE 2

The information given below is for the fog light circuit in FIGURE 2 above.

Wattage per fog lamp = 100 W Wattage for indicator lamp = 5 W Potential difference of battery = 14 V

Calculate the following during the operation of the circuit: 1.2.1 Total wattage of the circuit (2) 1.2.2 Total current flow through the circuit (2) 1.2.3 Operating resistance per fog lamp (2) 1.2.4 Operating resistance of indicator lamp (2) 1.2.5 Total operating resistance (4) 1.3 Explain the purpose of the fuse holder that is connected between the battery

and the relay in FIGURE 2 above.

(2) [22]

(11040612) -5- T1510(E)(D1)T

Copyright reserved

QUESTION 2 2.1 Name the type of motor shown in FIGURE 3 below, and name TWO devices

that use this type of motor in a vehicle.

FIGURE 3

(4) 2.2

Make a labelled sketch to illustrate an experiment that shows the principle of self-induction.

(3)

2.3

Make use of the sketch made in QUESTION 2.2 to explain the principle of self-induction.

(3)

2.4 State TWO negative effects of self-induction in unprotected electrical circuits. (2) 2.5

Mutual induction is the production of an EMF between two coils. Name ONE component in a vehicle that operates on this principle.

(1) 2.6

List FOUR requirements/components needed by a device (for example a generator) to produce an EMF that uses the principle of electromagnetic induction.

(4) [17]

(11040612) -6- T1510(E)(D1)T

Copyright reserved

QUESTION 3 3.1 The diagram in FIGURE 4 below shows the internal connections and

components of a pre-engaged-type starter motor. Name all the numbered parts. Write only the answer next to the question number (3.1.1–3.1.10) in the ANSWER BOOK.

(10)

FIGURE 4

3.2 Explain in detail the operation of a pre-engaged-type starter motor used to

turn a vehicle engine, in order for the engine to start.

(6) 3.3 Give THREE possible faults that may produce the non-operation of the starter

motor in a vehicle that has a functional starter motor.

(3) 3.4 Make a neat sketch of a rectangular-type starter motor brush that has an eye

terminal at the lead end.

(3) [22]

QUESTION 4 4.1 The optimum efficiency of a petrol engine vehicle that uses the conventional

type ignition system is dependent on the correct spark timing. Explain in detail the procedure to set the dynamic timing of a petrol engine.

(5)

3.1.7

3.1.8

3.1.9

3.1.10

3.1.1

3.1.6

3.1.2

3.1.4

3.1.5

3.1.3

(11040612) -7- T1510(E)(D1)T

Copyright reserved

4.2 Name the type of timing that is conducted on the following: 4.2.1 Engine that is in operation on the vehicle 4.2.2 Engine that has been rebuilt

(2 × 2)

(4) 4.3 Explain what is understood by the dwell angle of the contact breaker points

fitted within the distributor of the coil ignition system.

(2) 4.4 The conventional coil ignition system has been replaced with a more

advanced ignition system. Give the name of the more advanced ignition system.

(2) [13] QUESTION 5 5.1 A DC power supply is a device that reduces the AC input voltage and then

converts the output to direct current. Draw a neat, labelled diagram of a four-diode power supply. The output is required to have a filtered DC output.

(8) 5.2 Draw a labelled graph that shows the forward and reverse characteristics of a

germanium diode and a silicon diode on the same axis. Clearly indicate the reverse breakdown point, the forward break-over voltage points and the break-over voltage values for each type of diode.

(6) 5.3 Transistors are reliable, efficient switching devices that are used in various

electrical and electronic systems. Make a labelled sketch of an NPN-transistor that is used as a switch to switch a high-voltage DC output to a DC load when connected to a low-voltage DC input supply.

(5) 5.4 Explain in detail the process that is used to convert a semi-conductor material

to a P-type or N-type material. Give a reason for this conversion process.

(4) 5.5 Name any THREE systems that are maintained by an auto-electrician. (3)

[26] TOTAL: 100

(11040612) -8- T1510(E)(D1)T

Copyright reserved


FORMULA SHEET

1. )(AR

VI

2. )(. WVIP

3. )(321 nRRRRRt

4. )(11111 1

321

nt RRRRR

5. )(. vrIEV

6. )(.. VvBE

7. )(.. NIBF



NOVEMBER EXAMINATION


1 DECEMBER 2016

This marking guideline consists of 6 pages.

MARKING GUIDELINE

MARKING GUIDELINE -2- T1560(E)(D1)T MOTOR ELECTRICAL THEORY N2


QUESTION 1 1.1 1.1.1 12 V (2) 1.1.2 24 V (2) 1.1.3 12 + 12 + 12 + 12 = 48 V (4) 1.2 1.2.1 205 W (2) 1.2.2

I = 205 = 14,643 A 14

(2)

1.2.3

R = 14 = 0,956 Ω 14,643

(2)

1.2.4

R = 142 = 39,2 Ω 5

(2)

1.2.5 Rt = 14 = 0,956 Ω

14,643

(4) 1.3 To protect/insulate the fuse and contacts against short-circuiting. (2)

[22] QUESTION 2 2.1 Shunt type motor

Wiper motor

Fan motor

(4)

2.2

(3)



2.3

Closing the switch produces a magnetic field across the coil.

The lamp remains off due to the lower resistance of the coil.

When the switch opens the collapsing magnetic field of the coil produces a voltage that causes the lamp to flash, proving that self-induction occurred.

(3) 2.4

Damage to sensitive electronic components

Damage to surfaces of contact points

(2)

2.5 Ignition coil (1) 2.6

Magnetic field

Conductors

Rotation between conductor and magnetic field

Field coils/Permanent magnets

(4)

[17] QUESTION 3 3.1 3.1.1

3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.1.7 3.1.8 3.1.9 3.1.10

Plunger Coil winding Shift lever Drive gear Clutch Armature/Armature core Earth Commutator Armature shaft Field coil

(10 × 1)

(10) 3.2

The turning of the ignition switch passes current to the pull-in and hold-in coils of the solenoid that moves the plunger forward. The lever moves the drive gear in a twisting action into the gears of the ring gear, while at the same time the moving contact of the solenoid connects the battery to the motor that turns the engine.

(6) 3.3 Faulty ignition switch

Faulty starter motor relay

Faulty battery

(3)



3.4

(3) [22]

QUESTION 4 4.1 Remove vacuum pipe and loosen distributor.

Mark timing indicators on the engine pulley and pointer.

Connect timing light to battery and high tension lead.

Start vehicle – hold revolutions at specified speed.

Point light to pointer – move the distributor to the position that aligns the timing marks.

Tighten distributor and recheck.

Refit the vacuum pipes.

Check vacuum advance and centrifugal advance to specifications. (Any 5 × 1)

(5) 4.2 4.2.1 Dynamic timing 4.2.2 Static timing

(2 × 2)

(4) 4.3 Dwell angle is the duration that the contact points remain closed and it is

measured in degrees.

(2) 4.4 Electronic ignition system (2)

[13]



QUESTION 5 5.1

(8) 5.2

(6)


Copyright reserved

5.3

High voltage lamp High voltage Transistor Low voltage

(5) 5.4 The process that is called doping involves the adding of pentavalent or

trivalent materials to semi-conductor materials for a more positively or more negatively charged type of material.

The reason is to improve the conducting characteristics of the material. (2 × 2)

(4) 5.5 Charging system

Starting system

Lighting system

(3) [26]

TOTAL: 100


T1130(E)(A4)T

APRIL EXAMINATION



(11040612)

4 April 2016 (X-Paper) 9:00–12:00

Calculators and drawing instruments may be used.


(11040612) -2- T1130(E)(A4)T





INSTRUCTIONS AND INFORMATION 1. 2. 3. 4. 5.

Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. Start each question on a NEW page. Write neatly and legibly.

(11040612) -3- T1130(E)(A4)T


QUESTION 1 1.1 Electrical circuits require various quantities to be of precise values, in order

for the circuit to produce the required outcome. State the definitions for the following quantities:

1.1.1 Electromotive force 1.1.2 Power 1.1.3 Internal resistance

(3 × 2)

(6) 1.2 A starting circuit has the following information: One 12 V lead acid battery

Emf per cell = 2,3 V Internal resistance per cell = 0,017 Ω Current draw from starter motor = 30 A

1.2.1 Calculate the total emf of supply. (2) 1.2.2 Calculate the total internal resistance of the battery. (2) 1.2.3 Calculate the voltage drop for the closed circuit. (2) 1.2.4 Calculate the starter motor resistance during operation. (2) 1.2.5 Calculate the rated power of the starter motor. (2) 1.2.6 Make a labelled sketch of the circuit. Indicate all given and

calculated quantities.

(4) [20]

(11040612) -4- T1130(E)(A4)T


QUESTION 2 2.1 The ignition coil of the coil ignition system operates on the principle of mutual

induction. Make a labelled sketch to illustrate mutual induction.

(3)

2.2 Explain the process of mutual induction. Refer to the sketch in

QUESTION 2.1.

(3) 2.3 Self-induction is a result of the collapsing magnetic field across a coil.

State TWO negative effects of self-induction.

(2)

2.4 Give TWO methods that may be used to overcome the negative effects of

self-induction.

(2) [10]

QUESTION 3 3.1 A starter motor armature fits centrally within the starter motor and produces a

high torque. Draw a neat, labelled sketch of a starter motor armature.

(6)

3.2 State the function of the field coils of the starter motor. (2) 3.3 Describe the starter motor drive of the pre-engaged type of starter motor. (4) 3.4 During examination of a defective starter motor, it was found that the field

windings and armature windings were burnt. Give TWO possible causes for this condition.

(2)

3.5 List any FOUR specifications that are required to test a starter motor on a test

bench.

(4) 3.6 Explain the function of the solenoid of a pre-engaged type of starter motor. (2)

[20]

(11040612) -5- T1130(E)(A4)T


QUESTION 4

4.1 A stroboscopic timing light assists in setting the correct engine timing.

Make a labelled sketch of this device.

(4)

4.2 List any FOUR types of equipment that use a magneto to produce a high-voltage spark at the spark plug.

(4)

4.3 The accuracy of the engine timing depends on the accurate setting of the contact breaker gap that determines the correct dwell angle.

Explain the relationship between the point gap, dwell angle and the ignition timing, with reference to the point gap being too large, or too small.

(4)

4.4 List any SIX components of the conventional coil ignition system. (6) [18]

QUESTION 5

5.1 Choose a description from COLUMN B that matches an item in COLUMN A. Write only the letter (A–J) next to the question number (5.1.1–5.1.10) in the ANSWER BOOK.

COLUMN A COLUMN B

5.1.1 5.1.2 5.1.3 5.1.4 5.1.5 5.1.6 5.1.7 5.1.8 5.1.9 5.1.10

Semi-conductors Rectifier Diode Regulator Fuse Semi-conducting materials Electrolyte Step-down transformer Timer Overload protection device

A

B

C

D

E

F

G

H

I

J

controls the battery charger output current

silicon and germanium

a mixture of sulphuric acid and purified water

disconnects supply to battery charger when the output current exceeds the rated value

combination of diodes that converts AC to DC

diodes and transistors

device that controls the direction of current flow

opens a circuit due to excessive current flow

reduces the input voltage to a required value

determines the charging period for a battery charger

(10 × 1) (10)

(11040612) -6- T1130(E)(A4)T

Copyright reserved

5.2 Explain the difference between the intrinsic state and the extrinsic state of a

semi-conducting material.

(4) 5.3 A sulphated lead acid battery may produce hard starting and other electrical

problems in a vehicle. Fully explain the procedure that is used to test a lead acid battery for a sulphated condition.

(4)

5.4 Give the reason that leads to a diode reaching breakdown point. (2)

[20] QUESTION 6 6.1 Make neat, labelled sketches of an NPN-type and a PNP-type transistor.

Indicate clearly the electrode polarities.

(4) 6.2 A common emitter-type amplifier is found in many audio devices.

Make a labelled sketch of a common emitter amplifier. Show clearly, the input and output waveforms.

(5)

6.3 Explain the procedure that is used to test an NPN-type transistor. (3)

[12] TOTAL: 100

(11040612) T1130(E)(A4)T

Copyright reserved


FORMULA SHEET

Rt = R1 + R2 + ……..Rn

= + + ………Rn

I =

I =

P = VI

P = I2R

V = E + Ir

E = blv Sin

F = bli



APRIL EXAMINATION


4 APRIL 2016


MARKING GUIDELINE

MARKING GUIDELINE -2- T1140(E)(A4)T MOTOR ELECTRICAL THEORY N2


QUESTION 1 1.1 1.1.1 The higher voltage value or a circuit that has no current flow 1.1.2 The rate of doing work 1.1.3 The small resistance to current flow that is a characteristic of a cell

due to the size of the cell (3 × 2)

(6)

1.2 1.2.1 Et = 2,3 x 6 = 13,8 V (2) 1.2.2 rt = 0,017 x 6 = 0,102 Ω (2) 1.2.3 V = 13,8 – (30 x 0,102) = 10,74 V (2) 1.2.4 R = 10,74 = 0,358 Ω

30

(2) 1.2.5 P = 10,74 x 30 = 322,2 W (2) 1.2.6 V = 10,74 V

S.M → I = 30 A rtl = 0,102 Ω Et = 13,8 V

(4) [20]



QUESTION 2 2.1

(3)

2.2 The alternating voltage source V1 produces a changing magnetic field across

the first coil. This magnetic field is intercepted by the turns of the second coil, thus producing an emf across the second coil.

(3)

2.3 Damage to contact breaker points

Damage to sensitive electronic components

Delay in loss of current in a circuit (Any 2 x 1)

(2)

2.4 Connect a resistor across the load.

Connect a capacitor across the load.

(2) [10]

QUESTION 3 3.1 Twisted spline Groove

Steel shaft Commutator

Iron core

(6)

3.2 The field coils produce a cylindrical attracting and repelling magnetic torque,

in correspondence with the armature magnetic torque.

(2)



3.3 The starter motor drive consists of a solid steel shaft with an internal twisted

spline. A toothed gear fits within an overrunning clutch on the front of the shaft. A centralising bush fits inside the front of the shaft. A shift disc and return spring fits at the rear of the shaft.

(4)

3.4 Continuously cranking the engine that does not start due to a technical

fault.

Continuously cranking a tight rebuilt engine.

(2)

3.5 Off-load current draw

On-load current draw

Off-load voltage

On-load voltage

Off-load torque

On-load torque

Off-load speed

On-load speed (Any 4 × 1)

(4)

3.6 The solenoid levers the drive into the ring gear and connects the battery to

the motor.

(2) [20]

QUESTION 4 4.1

Strobe lamp Switch Connecting cables

(4)

4.2 Outboard motorboat engine

Lawn mower engine

Off-road motorcycle engine

Model-type car engine

(4)

4.3 Point gap too large – small dwell angle – advanced timing

Point gap too small – large dwell angle – retarder timing

(4)



4.4 Distributor

Distributor cap

Rotor

Ignition coil

Contact breaker points

Capacitor

High-tension leads Low-tension leads (Any 6 x 1)

(6) [18]

QUESTION 5 5.1 5.1.1

5.1.2 5.1.3 5.1.4 5.1.5 5.1.6 5.1.7 5.1.8 5.1.9 5.1.10

F E G A H B C I J D (10 x 1)

(10)

5.2 Intrinsic state is a pure state of the material that has not been doped.

Extrinsic state is an impure state of the material that has been doped.

(4) 5.3 Record initial voltage.

Check specific gravity of the electrolyte with a hydrometer; should show discharged for all cells.

Connect a battery charger to the battery.

Select charge rate at 30 A for three minutes.

Record final voltage.

An increase of between three and five volts shows a possible sulphated battery. (4 x 1)

(4)

5.4 The reverse voltage exceeded the rated reverse voltage. (2)

[20]


Copyright reserved

QUESTION 6 6.1

NPN transistor PNP transistor (4) 6.2

(5)

6.3 Select diode test on a digital meter.

Connect positive lead to collector and negative to base; meter to read forward voltage. Reverse leads; meter to read off the scale.

Connect positive lead to emitter and negative to base; meter to read forward voltage. Reverse leads; meter to read off the scale.

(3) [12]

TOTAL: 100

Copyright reserved

T1130(E)(A17)T

APRIL EXAMINATION



(11040612)

17 April 2015 (Y-Paper) 13:00–16:00

Calculators may be used.


(11040612) -2- T1130(E)(A17)T

Copyright reserved




INSTRUCTIONS AND INFORMATION 1. 2. 3. 4. 5. 6.

Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. Start each question on a NEW page ALL diagrams and sketches must be of a reasonable size, neat, clear and fully labelled. Write neatly and legibly.

(11040612) -3- T1130(E)(A17)T

Copyright reserved

QUESTION 1 1.1 In the sketch below, the illustration is of a reverse light and buzzer circuit.

Note the following features: The wattage of the lamp is 18 watts. The wattage of the buzzer is 5 watts. The potential difference of the supply is 11,45 volts.

1.1.1 Indicate the type of connection between the lamp and buzzer

(series or parallel).

(2) 1.1.2 Calculate the closed circuit current flow through the lamp. (2) 1.1.3 Calculate the closed circuit current flow through the buzzer. (2) 1.1.4 Calculate the combined resistance of the lamp and buzzer. (3) 1.1.5 Calculate the total power produced by the closed circuit. (2) 1.2 Study the diagram given below:

Calculate the THREE unknown voltages and write the answers in the

ANSWER BOOK.

(4) 1.3 With the aid of TWO sketches, explain the difference between electromotive

force and potential difference. Use values of 14 V and 12 V.

(4) [19]

Reverse lamp

Reverse warning buzzer

Reverse lamp

switch

lgn. Sw

(11040612) -4- T1130(E)(A17)T

Copyright reserved

QUESTION 2 2.1 The following diagram shows a single conductor moving within a magnetic

field:

Explain using the principle of electromagnetic induction the generation of

e.m.f. within the conductor. Name the TWO angles at the maximum produced e.m.f.

(5)

2.2 Mutual induction is a principle that is used in transformers.

Make a sketch to show the principle of mutual induction. Make use of the sketch to explain the generation of an e.m.f. across the secondary circuit.

(6)

2.3 Calculate, in metres per second, the velocity of a conductor that is rotating at

36 kilometres per hour within a magnetic field of a generator.

(2) 2.4 Make a neat labelled sketch of a series wound type motor. (2) 2.5 Explain the difference in the field windings of a generator and a starter motor. (2) [17]

(11040612) -5- T1130(E)(A17)T

Copyright reserved

QUESTION 3

3.1 Describe the commutator of an armature and name TWO types of material that are used.

(5)

3.2 The device shown below is a pre-engaged type starter motor:

Identify ALL the indicated parts and write the correct answers next to the question numbers (3.2.1–3.2.8) in the ANSWER BOOK.

(8)

3.3 A starter motor is part of the starting system. List FOUR other components that are used in the starting system.

(4)

3.4 List any THREE types of starter motors (not the brand name). (3)

3.5 Explain the reason that a series type motor is used for a starter motor. (2) [22]

QUESTION 4

4.1 A point gap that is set to the correct specifications will produce the specified dwell angle. Explain the procedure that is used to set the point gap with a dwell meter.

(4)

4.2 Magnetos are efficient devices that produce a high voltage that produces a spark at the spark plug of a petrol engine. List FOUR types of machinery or equipment that makes use of a magneto.

(4)

4.3 Explain the importance of accurately setting the ignition timing of the conventional ignition system.

(2)

4.4 List THREE specifications that are required to conduct the ignition timing when using a stroboscopic timing light.

(4)

[14]

3.2.1 3.2.2 3.2.3

3.2.4

3.2.5

3.2.6 3.2.7

3.2.8

(11040612) -6- T1130(E)(A17)T

Copyright reserved

QUESTION 5 5.1 Draw on one axis a fully labelled graph to show the forward and reverse

characteristics of a silicon and germanium diode. Also indicate on the graph the minimum conducting voltage of each type of diode.

(6)

5.2 State the name of the components that smoothens a rectified output. (1) 5.3 The following diagram shows a motor-generator battery charging system:

Explain the operation of the system and indicate a type of business that may

use this type of system.

(4) 5.4 A defective diode will cause a malfunction with the electronic device that the

diode is fitted to. Explain fully the procedure that is used to test a pn diode.

(4)

[15] QUESTION 6 6.1 List any FOUR devices that use electronic components in a motor vehicle's

electrical systems.

(4) 6.2 Explain the duties of an auto-electrician. (2) 6.3 A transistor amplifier may be designed to produce a high voltage gain.

Make a labelled sketch of a common emitter amplifier showing the input, output and other relevant components.

(4)

6.4 Indicate ONE use of the type of amplifier referred to in QUESTION 6.3. (3) [13]

TOTAL: 100

(11040612) -7- T1130(E)(A17)T

Copyright reserved

FORMULA SHEET

Rt = R1 + R2 + ……..Rn

= + + ………Rn

I =

I =

P = VI

P = I2R

V = E + Ir

E = blv Sin

F = bli



APRIL EXAMINATION


17 APRIL 2015


MARKING GUIDELINE



QUESTION 1

1.1 1.1.1 Parallel (2)

1.1.2 1,572A

11,45

18

V

PI

(2)

1.1.3 0,436A

11,45

5

V

PI

(2)

1.1.4 5,7Ω

518

11,45

P

VR

22

(3)

1.1.5 23W

185

WWP 21

(2)

1.2 4A

30

120I

V1 = 4 x 5 = 20v V2 = 4 x 10 = 40v V3 = 4 x 15 = 60v

(4)

1.3 Electromotive force is the off load voltage in a circuit, example 14V. Electromotive force is the on load voltage in a circuit, example 12V.

(4)

[19]

QUESTION 2

2.1 The rotating conductor within the magnetic flux cuts the magnetic flux thus producing an e.m.f. within the conductor. Maximum output is at 90 and 270 degrees.

Vo

(5)

2.2 The opening and closing of the switch produces a pulsating magnetic field across the left coil. This magnetic field is intercepted by the right side coil thus producing an e.m.f. across the right coil.

(6)

2.3 V = 36 000 = 10 m/s 3 600

(2)



2.4

(2) 2.5 A generator has thin windings with many turns.

A starter motor has thick windings with few turns.

(2)

[17] QUESTION 3 3.1 The commutator is made of flat segments of copper that is fitted in a

cylindrical form around a fibre core. The segments are insulated with mica.

(5) 3.2 3.2.1 Plunger 3.2.2 Solenoid 3.2.3 Spring 3.2.4 Shift lever 3.2.5 Drive unit 3.2.6 Armature 3.2.7 Pole shoe 3.2.8 Brush assembly

(8 x 1)

(8) 3.3 Battery

Ignition switch

Battery cables

Relay

Wiring (Any 4 x 1)

(4) 3.4 Inertia type

Sliding armature type

Pre-engaged type

Reduction gear type (Any 3 x 1)

(3) 3.5 The series motor conducts large current to produce a high torque at the

required speed.

(2) [22]

http://www.google.co.za/imgres?q=sketch+circuit+simple+series+wound+motor&hl=en&safe=off&biw=1366&bih=628&tbm=isch&tbnid=hZTZ_MdI_s9k7M:&imgrefurl=http://alihassanelashmawy.blogspot.com/2012/05/classification-of-electric-motors.html&docid=mZmwic6P8S4XsM&imgurl=http://3.bp.blogspot.com/-ZWMIEVNN5lE/T6_qqwxr5qI/AAAAAAAAB_8/-1uTzGN_86U/s400/series+wound.JPG&w=380&h=252&ei=jUCIUISaMY-6hAfB1IGICw&zoom=1&iact=hc&vpx=1047&vpy=133&dur=4064&hovh=183&hovw=276&tx=140&ty=118&sig=101766563954982100143&page=2&tbnh=151&tbnw=215&start=18&ndsp=23&ved=1t:429,r:20,s:20,i:188



QUESTION 4

4.1 Remove distributor cap.

Connect dwell meter to distributor.

Operate engine, adjust point gap to required dwell angle read off meter.

Tighten contact breaker screw and recheck. (4 x 1)

(4)

4.2 Motor boat

Motor bike

Quad bikes

Small aircraft

Petrol lawnmowers/ride on lawnmowers

Chainsaw (Any 4 x 1)

(4)

4.3 To ensure that the spark occurs when the piston of the engine cylinder is at the specified position.

(2)

4.4 The before top dead centre specifications in degrees.

The centrifugal advance angle in degrees.

The vacuum advance unit angle in degrees.

The engine revolutions.

The dwell angle. (Any 4 x 1)

(4) [14]

QUESTION 5

5.1 If Si Vbr Vr ∙ ∙ Vf 0.2v 0.6v

(6)

5.2 A filter/smoothing capacitor. (1)

5.3 The motor turns the generator at the required speed. The generator produces the required current to charge batteries.

Transport companies or any type of business that need to charge many batteries simultaneously.

(4)

5.4 Set a multimeter to diode test.

Connect the positive lead to anode and the negative lead to the cathode.

The reading should be 0,6 volts.

Reverse the leads the reading should read off the scale.

(4) [15]


Copyright reserved

QUESTION 6 6.1 Flasher unit

Electronic ignition control unit

Central locking control unit

ABS control unit

Alarm control unit (Any 4 x 1)

(4) 6.2 To diagnose and repair faults in the electrical system of various types of

vehicles and mobile machinery.

(2) 6.3

+ DC c - b e Vin

(4) 6.4 Audio systems. (3) [13]

TOTAL: 100


T1120(E)(N12)T




(11040612)

12 November 2014 (Y-Paper) 13:00–16:00


Candidates will require drawing instruments.


(11040612) -2- T1110(E)(N12)T





INSTRUCTIONS AND INFORMATION 1. 2. 3. 4. 5. 6.

Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. All diagrams and sketches must be of a reasonable size, neat, clear and fully labelled. Answer a new question on a NEW page. Write neatly and legibly.

(11040612) -3- T1110(E)(N12)T


QUESTION 1 1.1 Series-parallel circuits are essential to provide the required current and

voltage for components that are used in electrical circuits. Make use of the following information for a series-parallel circuit to answer the questions that follow. A single resistor of 180Ω is connected in series to two parallel connected resistors of 200Ω and 300Ω. This circuit is connected across a potential difference of 60V.

1.1.1 Make a neat labelled sketch of the circuit. (4) 1.1.2 Calculate the total circuit resistance. (3) 1.1.3 Calculate the total current flow. (2) 1.1.4 Calculate the voltage across the parallel resistors. (2) 1.1.5 Calculate the current flow through the 200Ω resistor. (2) 1.1.6 Calculate the power produced by the complete circuit. (2) 1.2 Explain what is understood by the following electrical principles. 1.2.1 Internal resistance of a circuit. 1.2.2 Electromotive force. 1.2.3 A short circuit. (3 x 2) (6) [21]

(11040612) -4- T1110(E)(N12)T


QUESTION 2 2.1 Fleming's hand rules assist in the design of motors and generators.

Explain Fleming's left hand rule.

(4)

2.2 Calculate the EMF produced by a generator having 200 parallel conductors

with a length of 150mm each. The conductors move at right angles to a magnetic flux of 25 milliteslas at a velocity of 30 m/s.

(4)

2.3 Explain the following electrical principles and give one example where that

principle is used in a motor vehicle.

2.3.1 Self-induction 2.3.2 Mutual induction 2.3.3 Faraday's law of electromagnetism 2.3.4 Polarity (4 x 3) (12) [20] QUESTION 3 3.1 The following component is a part of a starter motor.

3.1.1 Give the name of the component. (1) 3.1.2 Explain the function of the component. (2) 3.1.3 State the name of the insulating material that is found between the

commutator segments.

(1) 3.1.4 Give the name of the two components (not shown) that keeps the

armature in a centralised linear position.

(2) 3.1.5 Explain a reason that overheats the armature that may lead to the

solder melting at the windings on the commutator.

(2) 3.2 A solenoid consists of a pull-in coil and a hold-in coil. The solenoid levers the

drive into the ring gear of an engine and connects the battery to the motor. Explain clearly the procedure to test the two coils of the solenoid, and indicate the equipment that is used.

(6)

(11040612) -5- T1110(E)(N12)T


3.3 Describe fully the drive unit that is fitted to the starter motor. (4)

3.4 Explain the procedure to test the field coil of a starter motor for an earth fault (windings touching frame) of the type that one end of the coil is riveted to the frame.

(3)

[21]

QUESTION 4

4.1 A point gap that is set to the correct specifications will produce the specified dwell angle. Explain TWO reasons for a fluctuating dwell angle that cannot be set to specifications.

(2)

4.2 Magnetos are efficient devices that produce a high voltage that produces a spark at the spark plug of a petrol engine. List FOUR types of machinery or equipment that makes use of a magneto.

(4)

4.3 The requirements for an engine to operate at maximum efficiency are requires that the ignition contact breaker gap, dwell angle, and ignition timing need to be set to specifications. Explain the relationship between these settings.

(4)

4.4 Give TWO advantages of the magneto when compared to the coil ignition system.

(2)

4.5 Explain the purpose of the inductive probe holder that is part of a stroboscopic timing light.

(2)

[14]

QUESTION 5

5.1 Diodes are commonly used to block reverse current through a circuit or component. Give TWO reasons that silicon diodes are preferred to germanium diodes for the use in battery chargers.

(2)

5.2 List any SIX components of a heavy duty workshop battery charger(not the diodes)

(6)

5.3 List THREE factors that may lead to a sulphated lead-acid battery. (3)

5.4 Explain the purpose of the commutator of a DC generator. (2)

5.5 Explain the function of a regulator in a vehicle charging system. (2) [15]

(11040612) -6- T1110(E)(N12)T


QUESTION 6 6.1 A transistor uses low input current but has the ability to conduct a large output

current. Draw a labelled circuit diagram of an NPN transistor that is connected as a switch to a low voltage d.c. input that conducts high voltage d.c. current through a lamp. Include a relay to the output circuit.

(6)

6.2 A transistor may be used as an amplifier.

List the names of three types of transistor amplifiers.

(3)

[9]

TOTAL: 100

(11040612) -7- T1110(E)(N12)T


FORMULA SHEET

Rt = R1 + R2 + ……..Rn

= + + ………Rn

I =

I =

P = VI

P = I2R

V = E + Ir

E = blv Sin

F = bli





12 NOVEMBER 2013


MARKING GUIDELINE

MARKING GUIDELINE -2- T1110(E)(N12)T MOTOR ELECTRICAL THEORY N2


QUESTION 1 1.1 1.1.1 180Ω 200Ω

300Ω 60v

(4) 1.1.2 R = 180 + 200 x 300 = 300Ω

200 + 300

(3) 1.1.3 I = 60 = 0,2A

300

(2) 1.1.4 Vp = 0,2 x 120 = 24v (2) 1.1.5 I200 = 24 = 0,12A

200

(2) 1.1.6 P = 60 x 0,2 = 12w (2) 1.2 1.2.1 The battery resistance to current flow that is dependent on the size

of the battery.

1.2.2 The value of the supply when a circuit is off. 1.2.3 A condition when the current takes a short return to the supply due

to a cable / winding touching ground. (2 x 3)

(6) [21] QUESTION 2 2.1 Hold the left hand with the two middle fingers and thumb at right angles to

one another. The index finger points to the direction of the magnetic field, the middle points to the direction of current flow and the thumb points to the direction of movement of the motor.

(4) 2.2 E = 0,025 x 0,15 x 30 x 200 = 22,5v (4) 2.3 2.3.1 The ability of a coil to produce its own voltage as the current

through the coil changes. A relay



2.3.2 The ability of one coil to produce an e.m.f. across a second coil

when the current through the first coil changes. Ignition coil

2.3.3 The faster the conductors cut a magnetic field, the higher the e.m.f.

that is generated. Alternator

2.3.4 Connecting the positive and negative of the supply to the

respective positive and negative electrical connections. All componemts and electrical connections.

(3 x 4) (12) [20] QUESTION 3 3.1 3.1.1 Armature (1) 3.1.2 To produce a directional magnetic field when connected to a

supply.

(2) 3.1.3 Mica (1) 3.1.4 Front and rear bushes. (2) 3.1.5 The starter motor overheated due to overload/continuous operation

when the engine fails to start.

(2) 3.2 Use a 12 volt dc supply and two jumper cables connected to the terminals

of the supply.

Hold in coil. Connect the negative to the base of the solenoiod, connect negative to switch terminal. Assist the plunger manually. The plunger should pull in and stay in.

Pull in coil. Connect negative to motor post and positive to switch terminal. The plunger should pull in and stay in without assistance.

(6) 3.3 The drive consists of a steel shaft with an internal twisted spline. A toothed

gear is fitted to an overrunning clutch that is fitted to the shaft. At the rear of the shaft is a damping spring.

(4)

3.4 Remove the rivet to disengage the coil end from the frame. Connect a

multimeter between one end of the coil and the frame. An open circuit indicates no earth fault.

(3)

[21]



QUESTION 4

4.1 Worn distributor shaft

Worn breaker plate

Loose contact breaker points

(2)

4.2 Motor boat

Motor bike

Quad bikes

Small aircraft

Petrol lawnmowers / ride on lawnmowers

chainsaw

(4)

4.3 A bigger than specified contact breaker gap will produce a small dwell angle with advanced timing.

A smaller than specified contact breaker gap will produce a large dwell angle with retarded timing.

(4)

4.4 Magneto does not require a battery.

Fault diagnosing is easier due to fewer components.

(2)

4.5 To receive the high trigger voltages within the high tension lead and transfer the voltage to the stroboscopic timing light.

(2)

[14]

QUESTION 5

5.1 Silicon diodes have the ability to conduct larger current.

Silicon diodes have the ability to operate at higher temperature.

(2)

5.2 Transformer

Ammeter

Voltmeter

Timer

Current control switch

Connecting leads and clamps

Rectifier

(6)

5.3 Charging current too low.

Battery not serviced and charged when not being used.

Topping up cells with non-purified water.

(3)

5.4 To transfer output current to the system.

To convert alternating current to direct current.

(2)

5.5 To control the output current of the generator/alternator to produce the required charge to the battery.

(2)

[15]



QUESTION 6 6.1

+ DC c b e Vin

(6) 6.2 Common base amplifier

Common emitter amplifier

Common collector amplifier

(3) [9]

TOTAL: 100


T1110(E)(J22)T

AUGUST EXAMINATION



(11040612)

22 July 2014 (Y-Paper) 13:00–16:00


Drawing instruments are required.


(11040612) -2- T1110(E)(J22)T





INSTRUCTIONS AND INFORMATION 1. 2. 3. 4. 5 6

Answer ALL the questions. Read ALL the questions carefully. Number the answers correctly according to the numbering system used in this question paper. All diagrams and sketches must be of reasonable size, neat, clear and fully labelled. Answer each new question on a NEW page. Write neatly and legibly.

(11040612) -3- T1110(E)(J22)T


QUESTION 1 1.1 The following sketch shows a headlamp circuit with a potential difference of

13 volts. Calculate the following values:

55 W To switch 60 W 5 W Pilot lamp To switch High-beam circuit Low-beam circuit

1.1.1 The total current flow through the low-beam circuit when activated (3) 1.1.2 The current flow through the pilot lamp when the high-beam circuit

is activated

(2) 1.1.3 The total current flow through the high-beam circuit when activated (4) 1.1.4 The total resistance of the high-beam circuit (4) 1.1.5 The total power produced by the low beam-circuit when activated (2) 1.2 Give the purpose of each of the following devices used in electrical circuits: 1.2.1 Resistor (2) 1.2.2 Conductor (2) 1.2.3 Overload protection switch (2) 1.2.4 Ampere meter (2) [23]

(11040612) -4- T1110(E)(J22)T


QUESTION 2 2.1 Explain what is understood by the back-EMF of a motor. (2) 2.2 Make a neat, labelled sketch of a simple shunt-wound motor. (4) 2.3 Give TWO examples of the application of a shunt-wound type motor in a

motor vehicle.

(2) 2.4 Make TWO neat, labelled sketches to graphically show the difference

between alternating current and direct current.

(4) 2.5 Name TWO methods that may limit the effects of self-induction. (4) [16] QUESTION 3 3.1 A starter motor consists of an engaging unit, a drive unit, and a high-torque

motor. Explain, in the correct sequence, the operation of the starter motor that leads to turning of the vehicle engine.

(6)

3.2 The components below are components of a starter motor.

Write down the name(s) of the components indicated by the numbers. Write only the corresponding components next to the numbers (1‒6) in the ANSWER BOOK.

(6)

3.3 The insulation of starter motor windings often burns, causing failure of the

starter motor. Give THREE possible causes that may lead to this condition.

(3)

(11040612) -5- T1110(E)(J22)T


3.4 The following components shown below are a set of starter motor brushes.

Explain the purpose of the brushes and indicate the TWO main materials in the composition of the brush.

(4)

3.5 Explain the function of the spiral splines on an armature shaft. (2) [21] QUESTION 4 4.1 A points gap that is set to the correct specifications with a dwell meter will

produce the specified dwell angle. Give FOUR safety precautions to be observed when conducting this procedure.

(4)

4.2 Name any FOUR components of a stroboscopic timing light that is used to set

the ignition timing of the conventional type coil-ignition system.

(4) 4.3 Magnetos are efficient devices producing a high voltage that produces a

spark at the spark plug of a petrol engine. Name any TWO parts of a magneto.

(2)

4.4 Give the reason why static ignition timing is carried out on a stationary engine

of a vehicle.

(2) 4.5 Ignition timing that is too advanced may be disadvantageous to the vehicle's

operation. Name any TWO possible disadvantages.

(2)

[14]

(11040612) -6- T1110(E)(J22)T


QUESTION 5 5.1 Quick charging a lead-acid may be conducted when time does not allow for

slow charging. Explain the procedure that is used to quick charge a lead-acid battery.

(3)

5.2 Give any THREE personal safety precautions that must be observed when

quick charging a lead-acid battery.

(3) 5.3 A sulphated lead-acid battery will cause starting problems for a vehicle.

Explain the procedure that is used to test a lead-acid battery for a sulphated condition.

(4)

[10] QUESTION 6 6.1 Give the reason why a transistor produces better quality switching than a

contact breaker switch.

(2) 6.2 Name the type of transistor that is negative switching, (NPN or PNP) and give

a reason for the answer.

(2) 6.3 Give any TWO characteristics of a common emitter amplifier. (2) 6.4 The diagram shown below is a simple 12-volt battery charger.

Name the type of rectifier that is used, that is, full-wave or half-wave.

(1)

(11040612) -7- T1110(E)(J22)T


6.5 Refer to the diagram in QUESTION 6.4 and answer the following questions: 6.5.1 Name the type of transformer that is used. (2) 6.5.2 Explain the purpose of the transformer. (2) 6.5.3 Explain the process that produces the DC output. (5) [16]

TOTAL: 100

(11040612) -8- T1110(E)(J22)T


FORMULA SHEET Rt = R1 + R2 + ……..Rn

= + + ………Rn

I =

I =

P = VI

P = I2R

V = E + Ir

E = blv Sin

F = bli



AUGUST EXAMINATION


22 JULY 2014


MARKING GUIDELINE

MARKING GUIDELINE -2- T1110(E)(J22)T MOTOR ELECTRICAL THEORY N2


QUESTION 1 1.1 1.1.1 I = 55 x 2 = 8,461 A

13

(3) 1.1.2 I = 5 = 0,385 A

13

(2) 1.1.3 I = 60 x 2 + 0,385 = 9,231 + 0,385 = 9,616 A

13

(4) 1.1.4

Ω3521,125

13

P

VR

22

(4) 1.1.5 P = W1 + W2 =

55 + 55 = 110 W

(2) 1.2 1.2.1 To reduce current flow in a series circuit or to increase current flow

in a parallel circuit

(2) 1.2.2 A device that allows current to flow easily through a circuit (2) 1.2.3 To disconnect a circuit when the amount of current rises over the

rated value

(2) 1.2.4 A measuring device that measures current flow through a circuit (2) [23] QUESTION 2 2.1 The EMF that is generated through the motor that opposes the supply current

due to the windings of the armature that cut the magnetic fields of the field coils.

(2)

2.2

(4) 2.3 Blower motor

Radiator-fan motor

(2)



2.4

(4) 2.5 Fit a resistor across the load.

Fit a capacitor across the load.

(4) [16] QUESTION 3 3.1 The current that flows to the coils of the solenoid produces a magnetic field

that draws the shift lever in, thus moving the drive over the twisted splines into the ring gear. The moving contact connects the motor to the battery. The magnetic fields produced by the armature and field coils produces a rotational attracting and retarding torque that turns the armature thus turning the engine.

(6) 3.2 Drive/front-end bracket or commutator/rear-end bracket

Drive unit/Bendix

Armature

Field coils

Brush assembly

Solenoid

(6) 3.3 Operating the unit continuously on overload when attempting to start a

tight rebuilt engine

The starter remains meshed after the engine starts

Continuously operating the unit when the engine fails to start

(3)

3.4 The brushes transfer current to the commutator segments

Copper and carbon

(4)

http://www.google.co.za/imgres?q=simple+ac+and+dc+electrical+waveforms&um=1&hl=en&safe=off&biw=1366&bih=628&tbm=isch&tbnid=pv-zMsvW4WE-eM:&imgrefurl=http://www.iaei.org/magazine/2011/03/electrical-fundamentals-%E2%80%94-basic-electric-circuit-theory/&docid=DiEgfX04E_NBlM&imgurl=http://www.iaei.org/magazine/wp-content/uploads/2011/05/11b_VidalFig1-300x268.jpg&w=300&h=268&ei=e9SLUOvJKYXKhAfh0oGwDQ&zoom=1&iact=hc&vpx=1085&vpy=133&dur=982&hovh=212&hovw=238&tx=80&ty=92&sig=101766563954982100143&page=2&tbnh=132&tbnw=148&start=19&ndsp=22&ved=1t:429,r:3,s:20,i:137

http://www.google.co.za/imgres?q=simple+ac+and+dc+electrical+waveforms&um=1&hl=en&safe=off&biw=1366&bih=628&tbm=isch&tbnid=pM4PpC1DWITfrM:&imgrefurl=http://www.iaei.org/magazine/2011/03/electrical-fundamentals-%E2%80%94-basic-electric-circuit-theory/&docid=DiEgfX04E_NBlM&imgurl=http://www.iaei.org/magazine/wp-content/uploads/2011/05/11b_VidalFig2-300x260.jpg&w=300&h=260&ei=e9SLUOvJKYXKhAfh0oGwDQ&zoom=1&iact=hc&vpx=174&vpy=59&dur=1277&hovh=208&hovw=240&tx=86&ty=60&sig=101766563954982100143&page=2&tbnh=132&tbnw=152&start=19&ndsp=22&ved=1t:429,r:19,s:0,i:122



3.5 To engage the drive in a twisting motion to enable the gear of the drive to

locate into the engine ring gear.

(2) [21] QUESTION 4 4.1 Ensure that the vehicle cannot move, that the parking brake is engaged.

Ensure that the vehicle is in neutral.

Keep hands, clothing, loose jewellery and loose hair away from moving parts.

Ensure that body parts do not touch heated components.

Keep cables away from moving parts.

(4) 4.2 Inductive connector

Strobe lamp

Trigger switch

Connecting cables

(4) 4.3 Armature

Permanent magnets

Cylindrical magnet housing

(2) 4.4 To ensure that the spark is produced at the required position of the piston in

the engine cylinder

(2) 4.5 Low engine performance

Possible engine misfire

Possible hard starting

High fuel consumption

(2) [14] QUESTION 5 5.1 Charge the battery passing a current of approximately 18 amperes for

between half an hour to one hour. Monitor the procedure as often as possible to ensure that the battery does not overheat.

(3)

5.2 Use the appropriate acid-proof safety clothing.

Ensure that all connections are secure to prevent any sparks.

Ensure that the area is well ventilated to avoid breathing in any toxic gasses.

(3) 5.3 Measure the specific gravity of the cells.

Measure and note the battery voltage.

Charge the battery at 30 amperes for three minutes.

Measure the battery voltage. A significant increase above 15,5 V in 3 minutes confirms a suspected sulphated battery.

(4) [10]



QUESTION 6 6.1 There are no moving parts in a transistor. (2) 6.2 PNP. The base is connected to a negative source.

High voltage gain

(2) 6.3 Input is 180 degrees opposite to the input

High current gain

(2) 6.4 Full-wave (1) 6.5 6.5.1 Centre-tap transformer (2) 6.5.2 To reduce the input voltage (2) 6.5.3 The transformer produces two equal AC outputs that are inputs

to the rectifier.

The upper diode passes a forward current that is blocked by the lower diode.

When the cycles reverse the lower diode passes a forward current that is blocked by the upper diode.

(5) [16]

TOTAL: 100

email: [email protected] questions typical exam ... · fitted within the distributor of the...

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