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HET Period 4 > Electrical > Flashcards

Electrical Flashcards

1
Q

What is the internal resistance of a typical 5 pole relay?

A

70-110 Ohms

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2
Q

In a series circuit, what is true of Voltage, Resistance and Amperes?

A

Resistance is the sum of all added together
Voltage will be equal to the sum of all Voltage Drops across a load
Amperes will be equal to the Voltage Supplied divided by the Total Resistance

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3
Q

What does Ohms Law State?

A

One volt is required

to push one ampere through one one ohm.

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4
Q

In a parallel circuit, what is true of voltage, resistance and amperes?

A

Total resistance will be less than the lowest resistance in the circuit
Total voltage will be equal across the circuit
Total amperage is equal to each section added together.

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5
Q

When testing with a hydrometer, how much variation is allowed between cells?

A

When testing for specific gravity, 1.265 indicates a fully charged battery. A Difference of 0.050 between cells

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6
Q

What is the definition of multiplexing?

A

To send multiple electronic messages through the same signal path at the same time.

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7
Q

What is the typical current circuit protection within a control module?

A

20 amperes.

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8
Q

What is the minimum impedence rating of a multimeter when working with electronic circuits?

A

10 Megaohms of internal resistance

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9
Q

What are three key factors in the severity of a vehicle collision?

A

Speed
Angle at which it hits
What did it hit

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10
Q

What is the discharge time for an airbag once disconnected from a system?

A

2 minutes or manufacturer specification.

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11
Q

What is used within an SRS system connector in order to protect the circuit from being shorted.

A

Shorting bars are used within the connector, so that if voltage was accidentaly applied, it would take path of least resistance through the shorting bar to the other wire and dissipate.

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12
Q

While operating your vehicle in the dark, your headlights go out, then shortly after come back on. This repeats itself until you pull over, what is happening with what component?

A

Your type 1 circuit breaker used in the headlight circuit is overloading due to an electrical issue downstream. As the circuit breaker cools, the circuit reconnects then heats and disconnects again repeatedly.

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13
Q

When operating down the road, your marker lights fail, what component and style would you check first?

A

Type 2 circuit breaker inside the fuse box has popped and opened the circuit due to an electrical issue.

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14
Q

When installing a Fusible Link on a starter circuit, what size and length of wire can be used?

A

Fusible links must be sized 4 gauges smaller than supplied, and a maximum of 4-6” in length

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15
Q

When using a vehicle with daytime running lights, what voltage does the circuit see, why?

A

Daytime running lights run 2-3Volts lower than supplied to the system, in order to prevent blinding other drivers.

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16
Q

If you are asked to install aftermarket high beam auxiliary lights on the front of the vehicle, what must be included in the circuit?

A

A switch preventing the lights from getting powered unless the high beam lights are illuminated.

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17
Q

What colours must be used for marker lights on a vehicle/trailer on what sections?

A

Amber marker lights along the sides, and Red marker lights on the back.

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18
Q

How do you control the intensity of dash lights in the series circuit?

A

Insert a variable rheostat in series to vary the circuit resistance lowering the voltage supplied to the lights.

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19
Q

If servicing an older vehicle with fibre optic lighting circuits for the dash, and you find that the outer sheathing has become damaged. What is the repair?

A

The repair is to replace the entire length of cable.

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20
Q

Within unit electrical circuits, what are the two main sources of power to supply other circuits?

A

Ignition power

Constant Power Bus Bar

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21
Q

Operator complaint, that his interior cab lights will not go off. What type of circuit and failure has happened?

A

Cab light circuits use three normally open switches that are closed with the doors opened. One of the switches has failed closed, allowing the circuit to become energized leaving the lights on all the time.

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22
Q

Operator complaint, the sleeper lights are on all the time. What type of circuit and failure has happened?

A

Sleeper light circuits use two normally closed switches, opened by the door. One of the switches has failed internally in the closed position.

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23
Q

When talking about solenoids, what are the three types and their basic properties.

A

Discrete: Two position, fully extended or retracted. Used in door latch circuits with a return spring to original position.
Proportional: Infinite number of programmable positions, used in HVAC vent positioning.
Latching Solenoid: A Discrete solenoid, that remains magnetically locked at either end of its travel once de-energized. Used in door lock circuits, after circuit deenergizes, door lock stays in requested position.

24
Q

What are the two methods used to reduce self induced voltage spikes in a solenoid circuit?

A

Resistors can be placed in parallel to give another path for the voltage to take rather than pushing through the high resistance of the switch contacts.
Clamping Diodes are placed in parallel, to allow one direction of travel for the voltage spike.

25
Q

When running an electrical motor circuit, is it possible to overheat the system without blowing the fuse?

A

DC Motors running at a slower speed, with no spikes occuring, will increase in heat due to current flow and CEMF, this can cause a failure in the motor somewhere before the fuse blows.

26
Q

How are field coils connected inside a Shunt Motor?

A

Field coils are connected in parallel to shunt motors, sometimes called parallel wound motors.

27
Q

How is direction of rotation changed in a parallel connected shunt motor?

A

Switches are added to change direction of power supplied to the field windings but not the armature, creating a difference in magnetic field.

28
Q

As per CMVSA guidelines, how is cruise control disengagement controlled?

A

There must be three methods,
Brake Switch
Clutch
Cruise Switch

29
Q

When starting a unit, your wiring harness smokes out. What happened?

A

The starter circuit has found another circuit to get power to the starter, from an accessory circuit.

30
Q

You are getting feedback within your radio, what can be done to fix this issue?

A

Install a filter in series

or a Capacitor in parallel.

31
Q

What are the three most common systems used for truck positioning systems? (For Accidents)

A

Collision Warning System
Adaptive Cruise Control
Collision Mitigating System

32
Q

How fast is your radar sensor sensing objects during travel?

A

500 Feet

33
Q

If your safety equipment decides that you need to brake, how much braking effort can the computer give?

A

50% of full braking power can be used to slow the vehicle.

34
Q

How much of a following distance does adaptive cruise control try to maintain?

A

3.6 seconds of following distance from the vehicle in front of you

35
Q

What is the simplest type of electrical sending unit?

A

Diaphragm sending units, that utilize pressure to change the position of the internal resistor, causing higher or lower voltage output - signal.

36
Q

What is an example of a Variable Resistor sending unit?

A

Fuel Sending units with a float on a resistor track.

37
Q

How does a Thermistor function?

A

Thermistors have varying internal resistance depending on temperature applied.

38
Q

What is the difference between a positive and negative type thermistor?

A

Positive coefficient Thermistors resistance increases with temperature increase
Negative is opposite to this

39
Q

How can road speed be measured to give a signal for the speedometer?

A

Transmission output shaft speed sensor, or ABS wheel speed sensors.

40
Q

When was multiplexing first introduced to on highway truck systems?

A

the 1980’s

41
Q

What are the 4 classes of Baud Rate?

A

A - 10Kb/s
B - 10 to 125 kb/s
C - 125kb - 1mb/s
D - 1 - 10MB/s

42
Q

In a multiplexed can network, what is a Stub?

A

Stubs are the chunk of multiplexed cable, off the backbone to the Node or Module

43
Q

What is the basic protocol language that networks use to communicate?

A

J1587 or CAN

44
Q

If a truck is using a J1587 system, what is its communication speed, max nodes, length of backbone and physical construction?

A

9.6kb/s
20 Nodes
40 Metre
Unshielded plain twisted pair

45
Q

If a truck is using a J1939 Type 11 system, what is its communication speed, max nodes, length of backbone and physical construction?

A

250 kb/s
30 Nodes
40M with 1 M stubs
Heavy Gauge shielded twisted pair w/ Terminating Resistor

46
Q

If a truck is using a J1939 Type 15 system, what is its communication speed, max nodes, length of backbone and physical construction?

A

250 kb/s
10 Nodes
40M with 3 M stubs
Unshielded Twisted Pair Terminating Resistors

47
Q

Utilizing multiplexing, how much have engineers been able to reduce wiring on modern trucks?

A

40%

48
Q

What are the two common paired multiplexed systems on a unit?

A

J1587 - J1708

J1939 - CAN

49
Q

What is a major disadvantage of the J1587 system?

A

If one part of the system fails, being a circular communication style, it all fails.
It is also very slow, limiting how many devices you can use.

50
Q

What do the terms MID, PID and Checksum mean in regards to a 1587 system?

A

MID - Message Identifier - Where its going
PID - What it is trying to communicate - Example, Oil Pressure System
Checksum is the end to the message.

51
Q

At what point in industry did the 6 Pin Deutsch connector become standard?

A

1996-2001

52
Q

At which point did the 9 Pin Deutsch become standard?

A

2001

53
Q

When diagnosing a communications issue with the 1587/1708 system, what are the 4 steps?

A

Check for power at the connector
Check HI for 3.2-3.9 VDC
Check LO for 0.7-2.0 VDC
Disconnect all nodes except the engine, then start reconnecting to determine which component is failing the system.

54
Q

In a 1939-CAN networked system, what do the terms PGN, SPN and FMI mean?

A

PGN - Identifies the message
SPN - What system
FMI - What fault

55
Q

When measuring the internal resistance of a Multiplexed 1939 system, what should you find, why?

A

60 Ohms of resistance, as there is two 120 Ohm resistors wired in parallel.

56
Q

When pin testing a 1939 connector, what are the steps you should follow?

A 
Check A to B for Source Power
Check A - C(Hi) for 2-4V
Check A - D(Lo) for 2-4V
Check Resistance A-C for OL
Check Resistance A-D for OL
Check Resistance C-D for 55-65 Ohms

HET Period 4 (5 decks)

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