Battery Technology & Energy Storage Flashcards
7 cards from real EVT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Battery Technology & Energy Storage flashcards as text
A technician measures the insulation resistance of an EV high-voltage battery pack and gets a reading of 200 kΩ. What does this indicate?
Answer: The insulation is degraded and the vehicle should not be energized
EV high-voltage systems typically require insulation resistance above 100 Ω/V (often 500 kΩ or more for 400V systems); 200 kΩ on a 400V pack falls below safe thresholds.
What is the primary purpose of cell balancing in a multi-cell battery pack?
Answer: To ensure all cells reach the same state of charge to maximize usable capacity
Cell balancing ensures every cell in the pack operates at the same SOC, preventing weak cells from limiting overall pack capacity and extending pack life.
Which battery chemistry offers the highest energy density by weight, making it preferred for long-range BEVs?
Answer: Nickel manganese cobalt (NMC)
NMC chemistry achieves higher gravimetric energy density than LFP or NiMH, enabling greater range for a given battery weight in long-range BEV applications.
During thermal runaway, in what order do the following events typically occur?
Answer: Heat buildup → venting → cell rupture → fire
Thermal runaway follows the sequence of heat buildup triggering electrolyte decomposition, followed by gas venting, then mechanical rupture, and finally ignition.
What is 'capacity fade' in the context of EV battery aging?
Answer: A gradual reduction in the total energy a battery can store over its lifetime
Capacity fade refers to the irreversible reduction in maximum storable energy that accumulates with cycling and calendar aging due to active material loss and electrolyte degradation.
A battery pack uses passive balancing. What happens to excess energy from high-SOC cells during balancing?
Answer: It is dissipated as heat through resistors
Passive balancing bleeds excess charge from higher-SOC cells by dissipating energy as heat through bleed resistors, equalizing SOC without energy transfer.
What is the significance of the 'knee point' in a battery's capacity vs. cycle-count graph?
Answer: It indicates where capacity fade accelerates rapidly, signaling end of useful life
The knee point marks where the gradual linear capacity fade curve bends sharply downward, indicating accelerated degradation and approaching end-of-life.