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Punjab PSEB Matric NSQF Automotive (EV Service Assistant) study materials
Punjab PSEB Matric NSQF Automotive (EV Service Assistant) study resources

Punjab PSEB Matric NSQF Automotive (EV Service Assistant) practice questions

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Question 1Introduction to the Automotive Sector and EV Ecosystem

In the automotive value chain, which activity is classified as part of the after-sales segment of the EV ecosystem?

  1. Stamping of body panels at the vehicle assembly plant
  2. Manufacturing of cathode material for lithium-ion cells
  3. Designing the vehicle's infotainment software architecture
  4. Scheduled battery health inspection at an authorised service centre Correct answer.

Explanation

The after-sales segment covers everything that happens after the vehicle is sold, including periodic maintenance, diagnostics and repair work such as battery health inspection. Stamping, software design and cell material manufacturing all occur upstream in manufacturing or design.

Question 2Introduction to the Automotive Sector and EV Ecosystem

A workshop assistant is asked to explain why electric vehicles are described as having fewer moving parts in the drivetrain than conventional cars. Which reason is technically correct?

  1. EVs use hydraulic valve lifters to reduce engine vibration
  2. EVs use a single-speed reduction gearbox instead of a multi-ratio gearbox and clutch Correct answer.
  3. EVs replace the traction motor with a belt-driven alternator
  4. EVs eliminate the need for any braking system

Explanation

A battery electric vehicle typically drives through a fixed-ratio reduction gear and has no clutch, torque converter or multi-speed gearbox, which removes many components from the drivetrain. This is the main reason for the lower part count and reduced routine servicing.

Question 3Introduction to the Automotive Sector and EV Ecosystem

Which document must a Punjab service workshop check before accepting a high-voltage EV for repair, to confirm the vehicle's category and technical particulars?

  1. The vehicle's insurance premium receipt
  2. The owner's driving licence
  3. The workshop's NSQF certificate
  4. The vehicle's registration certificate Correct answer.

Explanation

The registration certificate records the vehicle category, fuel or power type and technical particulars, which the workshop needs to confirm the vehicle is an electric vehicle and to identify its class. The driving licence, staff certificate and premium receipt do not describe the vehicle's technical specification.

Question 4Introduction to the Automotive Sector and EV Ecosystem

Which component converts the direct current stored in the high-voltage traction battery into alternating current for the traction motor in a typical electric car?

  1. The DC-DC converter
  2. The onboard charger
  3. The battery management system
  4. The inverter Correct answer.

Explanation

The inverter switches DC from the traction battery into controlled three-phase AC that drives the motor, and it also rectifies current during regeneration. The other devices handle charging, auxiliary supply and cell monitoring rather than motor phase current.

Question 5Introduction to the Automotive Sector and EV Ecosystem

Which statement best describes the difference between a hybrid electric vehicle and a battery electric vehicle?

  1. A hybrid carries an engine that can drive the wheels or charge the battery, while a battery EV relies only on the traction battery Correct answer.
  2. A hybrid uses only a fuel cell, while a battery EV uses only a motor
  3. A hybrid has no traction battery, while a battery EV always has one
  4. A battery EV can run on petrol when the battery is empty, while a hybrid cannot

Explanation

A hybrid combines an internal combustion engine with electric drive, and the engine may propel the vehicle or generate electricity. A battery electric vehicle has no engine and draws all its energy from the traction battery charged from an external supply.

Question 6Introduction to the Automotive Sector and EV Ecosystem

A customer reports that the range of a two-year-old electric scooter has dropped noticeably in winter. Which explanation should a service assistant give first?

  1. The traction motor has permanently lost half its magnets
  2. Cold temperatures temporarily reduce usable battery capacity and increase internal resistance Correct answer.
  3. The tyres have changed their rubber compound
  4. The horn circuit is drawing excessive current

Explanation

Lithium-ion cells deliver less usable capacity and higher internal resistance at low temperature, so range falls in winter and usually recovers in warmer weather. This is a normal, temporary effect rather than a permanent motor or wiring fault.

Question 7Introduction to the Automotive Sector and EV Ecosystem

During a pre-service safety briefing, a technician must identify the colour coding used on high-voltage cables in most electric vehicles. Which colour is conventionally used to warn of high voltage?

  1. Orange Correct answer.
  2. White
  3. Blue
  4. Green

Explanation

High-voltage wiring in electric and hybrid vehicles is conventionally identified by orange conduit or sleeving so that anyone working on the vehicle recognises the hazard immediately. Other colours are used for low-voltage circuits and carry no high-voltage warning meaning.

Question 8Introduction to the Automotive Sector and EV Ecosystem

A trainee is comparing career paths in the EV sector. Which role is most directly responsible for diagnosing high-voltage faults and authorising repairs on customer vehicles?

  1. Battery cell research scientist
  2. EV service technician Correct answer.
  3. Charging network site planner
  4. Vehicle styling designer

Explanation

The EV service technician works on customer vehicles, using diagnostic equipment and approved procedures to locate and repair high-voltage faults. The other roles are involved in research, design or infrastructure planning and do not authorise repairs on customer vehicles.

Question 9Introduction to the Automotive Sector and EV Ecosystem

A service centre receives an electric car whose 12-volt auxiliary battery is flat although the traction battery shows 60 percent state of charge. Which component should be checked first?

  1. The traction motor stator
  2. The DC-DC converter Correct answer.
  3. The charge port locking actuator
  4. The reduction gearbox

Explanation

In an EV the auxiliary battery is maintained by the DC-DC converter, which steps traction voltage down to about 12 volts. If the traction pack is charged but the small battery is flat, the converter or its control circuit is the first suspect.

Question 10Introduction to the Automotive Sector and EV Ecosystem

Which statement correctly describes the purpose of regenerative braking in an electric vehicle?

  1. The motor acts as a generator so kinetic energy charges the traction battery while the vehicle slows Correct answer.
  2. The motor is reversed in direction to push the vehicle backwards
  3. The friction pads are replaced by electromagnets that stop the wheels
  4. The battery is disconnected during braking to protect the cells

Explanation

During regenerative braking the traction motor is driven by the wheels and works as a generator, converting kinetic energy into electrical energy that is fed back into the traction battery. This recovers energy and reduces wear on the friction brakes, but the conventional brakes remain fitted.

Question 11Introduction to the Automotive Sector and EV Ecosystem

A customer asks which charging method is generally the slowest for an electric car. Which answer is correct?

  1. Connection to a DC fast charger at a highway location
  2. Connection to a 50-kilowatt DC charger at a mall
  3. Connection to a domestic 230-volt AC socket through the onboard charger Correct answer.
  4. Connection to a 22-kilowatt AC public charger

Explanation

A domestic socket supplies only a few kilowatts, so the onboard charger can add energy slowly and a full charge may take many hours. DC fast chargers and higher-rated AC chargers deliver considerably more power and reduce charging time.

Question 12Introduction to the Automotive Sector and EV Ecosystem

Why does the battery management system balance individual cells within a traction pack?

  1. To keep cell voltages close so that no cell is over-discharged or over-charged and pack life is preserved Correct answer.
  2. To convert the pack from direct current to alternating current
  3. To increase the nominal voltage of the whole pack above its design value
  4. To reduce the physical weight of the battery enclosure

Explanation

Cells drift apart in voltage and capacity over time, and balancing keeps them within a narrow band so that the weakest cell does not limit the pack and no cell is pushed beyond safe limits. This protects capacity and service life.

Question 13Introduction to the Automotive Sector and EV Ecosystem

A workshop plans to add EV servicing to its existing petrol-car workshop. Which change is most essential before high-voltage work begins?

  1. Extending the petrol storage area to serve both vehicle types
  2. Buying additional engine oil in bulk for the new EV customers
  3. Training staff to NSQF EV competencies and installing insulated tools, PPE and a demarcated high-voltage bay Correct answer.
  4. Increasing the number of mechanical hoists without any electrical work

Explanation

High-voltage work requires qualified personnel, insulated tools, rated personal protective equipment and a clearly marked work area with appropriate isolation procedures. Without these controls the risk of electric shock is unacceptable, regardless of other workshop upgrades.

Question 14Introduction to the Automotive Sector and EV Ecosystem

An electric car is involved in a collision and the high-voltage system may be damaged. Which first action is appropriate for the attending service team?

  1. Immediately wash the battery pack with water to cool it
  2. Start the vehicle and drive it to confirm the fault
  3. Isolate the high-voltage system following the manufacturer's procedure and treat the vehicle as energised until proved otherwise Correct answer.
  4. Remove the service plug and leave it on the workshop floor

Explanation

A damaged EV must be treated as live until the high-voltage system has been properly isolated and verified, because contactors may have welded or insulation may be breached. The manufacturer's isolation procedure protects both the technician and bystanders.

Question 15Introduction to the Automotive Sector and EV Ecosystem

A fleet operator compares total cost of ownership of an electric delivery van with a diesel van of similar size. Which combination of factors most accurately explains why the electric van may cost less to run over several years?

  1. Higher energy cost per kilometre but free insurance for all electric vehicles
  2. Lower energy cost per kilometre and fewer scheduled engine-related services, offset by higher purchase price and battery replacement risk Correct answer.
  3. No maintenance of any kind because electric vehicles have no wearing parts
  4. Zero purchase cost and no requirement for tyres or brakes

Explanation

The running advantage of an electric van comes from cheaper energy per kilometre and the absence of engine-related servicing such as oil and filter changes. This must be weighed against a higher initial price and the possibility of battery degradation or replacement later in life.

Question 16Introduction to the Automotive Sector and EV Ecosystem

A service assistant must decide whether a complaint about a burning smell from an electric scooter's battery compartment can be handled as routine work. Which reasoning is correct?

  1. A burning smell near the battery suggests a possible thermal event, so the vehicle should be isolated in a safe area and escalated to a qualified high-voltage technician Correct answer.
  2. The scooter should be charged immediately to confirm whether the smell disappears
  3. A burning smell is normal for lithium batteries and can be ignored until the next scheduled service
  4. The battery compartment should be opened with ordinary steel tools while the scooter is switched on

Explanation

A burning smell from a battery compartment can indicate overheating, cell failure or a short circuit and is a potential thermal runaway warning. The correct response is to stop work, isolate the vehicle in a safe outdoor area and refer it to a qualified high-voltage technician.

Question 17Electrical and Electronics Fundamentals for EVs

In an EV, which component converts the DC stored in the traction battery into a variable-frequency three-phase AC supply for the drive motor?

  1. The battery management system
  2. The inverter Correct answer.
  3. The DC-DC converter
  4. The on-board charger

Explanation

The inverter switches DC from the pack into three-phase AC of controlled frequency and voltage, which sets motor speed and torque. The other units handle charging, auxiliary supply or cell monitoring, not motor drive.

Question 18Electrical and Electronics Fundamentals for EVs

A technician measures 12.4 V across a nominally 12 V lead-acid auxiliary battery at rest. What does this reading most likely indicate?

  1. The battery is being fast-charged
  2. The battery is fully charged and healthy Correct answer.
  3. The battery has an internal short circuit
  4. The battery is deeply discharged

Explanation

A healthy 12 V lead-acid battery at rest typically shows about 12.6 V when fully charged and around 12.4 V at roughly 70-75 percent state of charge, so the reading is a normal, serviceable value. Values near 11.8 V or lower would point to discharge.

Question 19Electrical and Electronics Fundamentals for EVs

Which unit of measurement is used for electrical resistance?

  1. Watt
  2. Ohm Correct answer.
  3. Ampere
  4. Volt

Explanation

Resistance is measured in ohms, symbol omega, and expresses how strongly a material opposes current flow. Ampere measures current, volt measures potential difference and watt measures power.

Question 20Electrical and Electronics Fundamentals for EVs

In a series circuit feeding a small EV auxiliary lamp, what happens to the current if a second identical lamp is added in series with the first?

  1. The current increases because more lamps are connected
  2. The current becomes zero because the circuit is broken
  3. The current decreases because total resistance increases Correct answer.
  4. The current stays the same because the supply voltage is unchanged

Explanation

In a series circuit the resistances add, so total resistance rises and, for a fixed supply voltage, Ohm's law gives a smaller current. The same current flows through both lamps.

Question 21Electrical and Electronics Fundamentals for EVs

Which statement correctly describes the role of a contactor in a high-voltage EV battery pack?

  1. It measures the state of charge of each cell
  2. It is an electrically controlled switch that connects or isolates the pack from the vehicle circuits Correct answer.
  3. It converts AC from the motor into DC for regen
  4. It steps the pack voltage down for the 12 V system

Explanation

A contactor is a heavy-duty relay whose coil is energised by the vehicle control system to close or open the high-voltage path. Opening it isolates the pack for safety or shutdown.

Question 22Electrical and Electronics Fundamentals for EVs

Which of the following is the correct relationship between voltage, current and resistance in a DC circuit?

  1. V = I x R Correct answer.
  2. V = I / R
  3. I = V x R
  4. R = V x I

Explanation

Ohm's law states that voltage equals current multiplied by resistance, so V = I x R. The other arrangements misplace the terms and do not give correct units.

Question 23Electrical and Electronics Fundamentals for EVs

Why is a fuse fitted in the low-voltage control circuit of an EV rather than relying on the contactor alone?

  1. The fuse stores charge to keep the controller alive
  2. The fuse converts AC to DC for the control unit
  3. The fuse opens the circuit quickly when current exceeds its rating, protecting wiring from overheating Correct answer.
  4. The fuse boosts the control voltage during cranking

Explanation

A fuse is a sacrificial element that melts and opens the circuit when current exceeds its rating, limiting heat damage to conductors and connectors. A contactor is a switching device and does not by itself limit fault current.

Question 24Electrical and Electronics Fundamentals for EVs

A 48 V auxiliary circuit draws 6 A. What power is being consumed?

  1. 54 W
  2. 288 W Correct answer.
  3. 0.125 W
  4. 8 W

Explanation

Electrical power equals voltage multiplied by current, so 48 V x 6 A gives 288 W. This relationship is used to size wiring and fuses for auxiliary loads.

Question 25Electrical and Electronics Fundamentals for EVs

Two 100 ohm resistors are connected in parallel. What is the equivalent resistance?

  1. 50 ohm Correct answer.
  2. 100 ohm
  3. 200 ohm
  4. 25 ohm

Explanation

For two equal resistors in parallel the equivalent is half of one value, so 100 ohm in parallel with 100 ohm gives 50 ohm. The parallel formula confirms 1/R = 1/100 + 1/100.

Question 26Electrical and Electronics Fundamentals for EVs

A cell group in a traction pack reads 3.2 V while all other groups read 3.7 V. What is the most appropriate interpretation?

  1. The vehicle is in regenerative braking
  2. The whole pack is fully charged
  3. That cell group is weaker and may need balancing or further testing Correct answer.
  4. The BMS is over-reporting all voltages

Explanation

A significantly lower group voltage under similar conditions points to imbalance or a weak cell, which reduces usable capacity and stresses the pack. The BMS balancing function or a capacity test should follow.

Question 27Electrical and Electronics Fundamentals for EVs

What is the main purpose of the DC-DC converter in an electric vehicle?

  1. To supply the low-voltage system from the high-voltage pack Correct answer.
  2. To balance individual cell voltages
  3. To convert AC charging input into DC
  4. To increase motor torque at low speed

Explanation

The DC-DC converter steps the high pack voltage down to around 12-14 V to run lights, controllers and to recharge the auxiliary battery. This lets the vehicle avoid a separate alternator.

Question 28Electrical and Electronics Fundamentals for EVs

A technician must test a high-voltage cable for continuity. Which practice is correct?

  1. Disconnect the BMS and test while charging
  2. Isolate the high-voltage system, verify zero voltage, then test with the approved meter Correct answer.
  3. Test using a low-impedance test lamp across the terminals
  4. Test with the pack live to save time

Explanation

High-voltage work requires isolation and a verified zero-energy state before any continuity or resistance test. A proving check of the meter on a known source confirms it reads correctly.

Question 29Electrical and Electronics Fundamentals for EVs

Which instrument is used to measure the current flowing in a conductor without breaking the circuit?

  1. Hydrometer
  2. Clamp meter Correct answer.
  3. Insulation tester
  4. Multimeter in volt mode

Explanation

A clamp meter uses a current transformer or Hall sensor around the conductor to measure current without disconnecting it. This is convenient for checking EV auxiliary and charging currents.

Question 30Electrical and Electronics Fundamentals for EVs

In a three-phase AC induction motor used in some EVs, what creates the rotating magnetic field in the stator?

  1. A permanent magnet rotor spinning inside a coil
  2. Three-phase currents in windings spaced 120 electrical degrees apart Correct answer.
  3. A commutator and carbon brushes
  4. A single DC winding energised by the inverter

Explanation

When three-phase currents displaced by 120 degrees flow in stator windings that are also spaced 120 degrees, their fields combine into a rotating magnetic field. This field induces rotor current and produces torque.

Question 31Electrical and Electronics Fundamentals for EVs

A 12 V auxiliary battery is charged by the DC-DC converter at 14.2 V. What does this higher voltage indicate?

  1. The converter has failed and is passing pack voltage
  2. The converter is regulating to a charging voltage above the battery's rest voltage Correct answer.
  3. The battery is being discharged rapidly
  4. The battery is faulty and must be replaced

Explanation

Charging requires a voltage above the battery's rest voltage so current flows into it; around 14 V is typical for a 12 V lead-acid system. This is normal regulation, not a fault.

Question 32Electrical and Electronics Fundamentals for EVs

Which of these best explains why the inverter uses pulse-width modulation (PWM)?

  1. To measure cell temperatures
  2. To synthesise an approximate sine wave by rapidly switching the DC supply Correct answer.
  3. To reduce the weight of the battery pack
  4. To increase the charging rate from the mains

Explanation

PWM switches the DC bus on and off at high frequency with varying duty cycle, so the average output follows a desired waveform. Varying the modulation controls motor voltage and frequency.

Question 33Electrical and Electronics Fundamentals for EVs

A technician reads 0 V at the coil of a contactor that should be closed, while the control fuse is intact and the ignition is on. Which step is most logical next?

  1. Recharge the auxiliary battery immediately
  2. Check the control relay and the coil supply wiring for an open circuit Correct answer.
  3. Replace the high-voltage battery pack
  4. Replace the traction motor

Explanation

With no voltage at the coil and a good fuse, the fault lies upstream in the control path, such as a relay, wiring or connector. Tracing that path with a meter is the correct diagnostic step.

Question 34Electrical and Electronics Fundamentals for EVs

Which statement about the difference between AC and DC is correct for EV charging?

  1. AC charging feeds DC directly to the cells without conversion
  2. DC fast charging requires the on-board charger to invert current
  3. AC and DC charging are identical in the conversion path
  4. AC charging relies on the vehicle's on-board charger to rectify current to DC Correct answer.

Explanation

In AC charging the mains alternating current is converted to DC by the on-board charger before it reaches the pack. In DC fast charging the rectifier is in the external charger, bypassing the on-board unit.

Question 35Electrical and Electronics Fundamentals for EVs

A 60 Ah battery is discharged at a constant 12 A. Approximately how long will it take to reach 50 percent depth of discharge?

  1. 0.2 hours
  2. 2.5 hours Correct answer.
  3. 5 hours
  4. 12 hours

Explanation

Half of 60 Ah is 30 Ah of usable charge to remove. Dividing 30 Ah by 12 A gives about 2.5 hours, ignoring rate and temperature effects.

Question 36Electrical and Electronics Fundamentals for EVs

Why must the insulation resistance of a high-voltage cable be tested at a high voltage such as 500 V DC?

  1. To confirm the cable's colour coding
  2. To charge the cable capacitance for faster readings
  3. To measure the conductor's current rating
  4. To reveal weak insulation that a low-voltage ohmmeter would not stress enough to detect Correct answer.

Explanation

Insulation faults often appear only when the dielectric is stressed near its working voltage, so a high test voltage exposes leakage paths. A low-voltage ohmmeter may show a healthy reading while the cable still fails in service.

Question 37Electrical and Electronics Fundamentals for EVs

An inverter output shows a distorted waveform with excessive harmonic content. Which consequence is most likely in the drive motor?

  1. Automatic improvement in torque ripple
  2. Higher state of charge in the battery
  3. Increased losses and heating in the motor laminations and windings Correct answer.
  4. Reduced need for cooling in the inverter

Explanation

Harmonics create additional eddy-current and copper losses, raising motor temperature and reducing efficiency. Good waveform quality and filtering are therefore important design goals.

Question 38Electrical and Electronics Fundamentals for EVs

A technician finds that a cell group heats faster than its neighbours only during fast charging, while voltages match at rest. Which explanation is most plausible?

  1. The group has elevated internal resistance, causing extra I-squared-R heating under high current Correct answer.
  2. The group has a higher capacity than the others
  3. The vehicle is not connected to a charger
  4. The temperature sensor is calibrated correctly and shows a normal value

Explanation

Cells with higher internal resistance dissipate more heat at the same current, and the effect is most visible during high-rate charging. Resting voltages can still match because the voltage drop disappears when current stops.

Question 39Electrical and Electronics Fundamentals for EVs

Why is the auxiliary 12 V battery still needed in an EV that has a large traction pack?

  1. It stores regenerative energy from the motor
  2. It powers control electronics and safety systems, and keeps them alive when the high-voltage contactors are open Correct answer.
  3. It supplies traction current during acceleration
  4. It replaces the DC-DC converter

Explanation

The high-voltage system is isolated when the vehicle is off, so low-voltage control units, locks and safety circuits run from the 12 V battery. The DC-DC converter recharges it when the contactors close.

Question 40Electrical and Electronics Fundamentals for EVs

A three-phase motor draws balanced currents, but one phase cable shows a much higher temperature than the others at the same current. Which is the most likely cause?

  1. A higher system voltage on that phase
  2. A fully charged traction battery
  3. A loose terminal on that phase creating contact resistance and local heating Correct answer.
  4. A lower motor speed than commanded

Explanation

A poor connection adds contact resistance, so extra heat develops at the joint even when current is balanced. Thermal inspection and torque checking of terminals is the correct response.

Question 41Battery Technology and Battery Management Systems

In an electric vehicle battery pack, what is the main role of the Battery Management System (BMS)?

  1. To convert DC battery voltage into three-phase AC for the traction motor
  2. To physically lock the charging connector during charging
  3. To step down pack voltage to 12 V for lighting and accessories
  4. To monitor cell voltage, current and temperature and protect the pack within safe limits Correct answer.

Explanation

The BMS is the electronic supervisor of the pack: it measures cell voltages, pack current and temperatures and uses that data to protect the cells from overcharge, over-discharge and overheating. Motor inversion is the job of the inverter, and low-voltage conversion is done by the DC-DC converter.

Question 42Battery Technology and Battery Management Systems

Which cell chemistry is most commonly used in modern electric vehicle traction packs because of its high energy density and long cycle life?

  1. Nickel-iron (NiFe)
  2. Lead-acid
  3. Alkaline manganese
  4. Lithium-ion Correct answer.

Explanation

Lithium-ion cells dominate EV traction packs because they offer high specific energy, high specific power and good cycle life compared with older chemistries. Lead-acid is used mainly for 12 V auxiliary duty, not traction.

Question 43Battery Technology and Battery Management Systems

What does the nominal voltage of a single lithium-ion cell of the LFP type typically equal?

  1. 2.0 V
  2. 12 V
  3. 1.2 V
  4. 3.2 V Correct answer.

Explanation

A lithium iron phosphate (LFP) cell has a nominal voltage of about 3.2 V, with a charged rest voltage near 3.3 to 3.4 V. This is lower than the 3.6 to 3.7 V nominal of NMC cells, which affects pack series count.

Question 44Battery Technology and Battery Management Systems

A traction pack is built from cells connected in series. What does increasing the number of series cells mainly increase?

  1. The pack's internal resistance only
  2. The pack's total capacity in ampere-hours
  3. The pack's total voltage Correct answer.
  4. The pack's physical flexibility

Explanation

Series connection adds cell voltages while the current path and ampere-hour capacity stay the same as a single cell. Parallel connection is what raises capacity in ampere-hours.

Question 45Battery Technology and Battery Management Systems

Why must a lithium-ion EV pack be protected against over-discharge by the BMS?

  1. Because over-discharge increases the nominal voltage of the cells
  2. Because over-discharge improves the cycle life of the cells
  3. Because over-discharge makes the pack heavier
  4. Because over-discharge can cause irreversible cell damage and copper dissolution that creates internal short risk Correct answer.

Explanation

Discharging a lithium cell below its lower voltage limit damages the anode structure and can dissolve copper current collector material, which may later cause internal short circuits. The BMS therefore opens the contactors before the limit is reached.

Question 46Battery Technology and Battery Management Systems

Which quantity does a shunt-based current sensor in a battery pack measure directly?

  1. Cell temperature
  2. Pack current by measuring the voltage drop across a known resistance Correct answer.
  3. State of health by chemical analysis
  4. Cell internal pressure

Explanation

A shunt sensor measures the small voltage developed across a precision resistor and uses Ohm's law to calculate current. This current data is integrated over time by the BMS to estimate state of charge.

Question 47Battery Technology and Battery Management Systems

What is the purpose of cell balancing in a battery management system?

  1. To equalise the state of charge of series cells so the weakest cell does not limit pack capacity Correct answer.
  2. To increase the maximum charging current of the charger
  3. To disconnect the pack from the motor inverter
  4. To cool the pack during fast charging

Explanation

In a series string the same current flows through every cell, so the cell with the lowest charge limits usable pack capacity. Balancing moves charge between cells or dissipates excess energy so all cells reach a similar state of charge.

Question 48Battery Technology and Battery Management Systems

Which device in an EV battery pack physically isolates the high-voltage pack from the vehicle when the vehicle is switched off?

  1. The service disconnect fuse
  2. The main contactors Correct answer.
  3. The Hall-effect sensor
  4. The pre-charge resistor

Explanation

Main contactors are high-voltage relays that open to isolate the pack from the vehicle circuits when the vehicle is off or a fault is detected. The pre-charge resistor only limits inrush current when the contactors close.

Question 49Battery Technology and Battery Management Systems

An EV pack has 96 series cells, each with a nominal voltage of 3.7 V. What is the approximate nominal pack voltage?

  1. 740 V
  2. 192 V
  3. 96 V
  4. 355 V Correct answer.

Explanation

For series cells, pack voltage equals cell voltage multiplied by the number of cells: 96 x 3.7 V = 355.2 V. This is the typical nominal voltage of a 400 V class traction pack.

Question 50Battery Technology and Battery Management Systems

A 60 Ah cell is used in a pack with 4 parallel strings. What is the total pack capacity in ampere-hours?

  1. 240 Ah Correct answer.
  2. 15 Ah
  3. 120 Ah
  4. 60 Ah

Explanation

Parallel connection adds capacities, so four 60 Ah strings give 4 x 60 = 240 Ah. The pack voltage is set by the number of series cells in each string, not by the parallel count.