EVT EVT Thermal Management & Cooling Systems 1 — Questions and Answers
Question 1: What is the primary purpose of the Battery Thermal Management System (BTMS) in an electric vehicle?
- Increase battery charging speed by reducing resistance
- Maintain battery pack temperature within an optimal operating range to maximize life and performance (Correct answer)
- Cool the electric motor windings during regenerative braking
- Pre-heat cabin air using waste heat from the battery
Correct answer: Maintain battery pack temperature within an optimal operating range to maximize life and performance
The BTMS keeps the battery cells within their optimal temperature window—typically 15–35 °C—to preserve capacity, cycle life, and safe operation.
Question 2: A liquid-cooled battery pack uses ethylene glycol–water (EGW) coolant. What is the MAIN advantage of liquid cooling over air cooling for high-capacity packs?
- Lower system weight
- Higher heat transfer coefficient enabling tighter temperature uniformity across cells (Correct answer)
- Simpler maintenance with no pump required
- Lower manufacturing cost
Correct answer: Higher heat transfer coefficient enabling tighter temperature uniformity across cells
Liquid coolants have far higher thermal conductivity than air, allowing more efficient heat removal and tighter cell-to-cell temperature variation (typically <5 °C delta).
Question 3: Which component in an EV thermal system transfers heat between the refrigerant circuit and the battery coolant loop without mixing the fluids?
- Expansion valve
- Chiller (refrigerant-to-coolant heat exchanger) (Correct answer)
- Condenser
- Accumulator
Correct answer: Chiller (refrigerant-to-coolant heat exchanger)
The chiller is a refrigerant-to-coolant heat exchanger that cools the glycol-water battery coolant loop by evaporating refrigerant on the other side.
Question 4: During a hot summer day, a technician notes the EV's available charge rate drops significantly. What is the most likely cause?
- Low 12V auxiliary battery voltage
- Battery thermal management system limiting charge rate to prevent overheating (Correct answer)
- Software update pending restart
- Worn motor brushes increasing resistance
Correct answer: Battery thermal management system limiting charge rate to prevent overheating
High ambient temperatures cause the BTMS to throttle charge current to keep cell temperatures within safe limits, resulting in reduced charge acceptance.
Question 5: What does a negative temperature coefficient (NTC) thermistor do as its temperature increases?
- Its resistance increases proportionally
- Its resistance decreases (Correct answer)
- Its voltage output increases linearly
- Its capacitance increases
Correct answer: Its resistance decreases
An NTC thermistor decreases in resistance as temperature rises, and this predictable change is used by the BMS to calculate battery pack temperature.
Question 6: A technician replaces coolant in a liquid-cooled battery pack. What is a critical step BEFORE refilling?
- Discharge battery to 0%
- Pressurize the pack to 30 PSI to check for leaks
- Flush the system with distilled water and verify no contamination or air pockets remain (Correct answer)
- Remove all 12V fuses
Correct answer: Flush the system with distilled water and verify no contamination or air pockets remain
Flushing ensures old degraded coolant and any debris are removed, and purging air prevents hot spots from air pockets that reduce heat transfer.
EVT EVT Thermal Management & Cooling Systems 1
What is the primary purpose of the Battery Thermal Management System (BTMS) in an electric vehicle?