Diagnostics Maintenance & Safety Standards Flashcards

Which diagnostic parameter best indicates the beginning of lithium plating in a Li-ion cell during charging?

Answer: Coulombic efficiency dropping below 99.5%

Coulombic efficiency (charge-out/charge-in) dropping below ~99.5% is an early indicator of lithium plating, as plated lithium is not fully recovered on discharge.

A BMS reports a persistent cell voltage divergence that increases during discharge but resets after a rest period. The most likely cause is:

Answer: Cell-to-cell capacity imbalance

Capacity imbalance causes weaker cells to deplete faster under load, creating divergence that recovers at rest as OCV equalizes.

When performing insulation resistance testing on a high-voltage battery pack, what minimum acceptable IR value is typically required per IEC 60664?

Answer: 1,000 Ω/V

IEC 60664 and most EV safety standards require a minimum insulation resistance of 1,000 Ω/V (100 Ω/V for AC systems) relative to system voltage.

A technician uses an EIS (Electrochemical Impedance Spectroscopy) tool and finds the Warburg impedance component has significantly increased. This most likely indicates:

Answer: Electrolyte depletion or lithium-ion diffusion limitation

The Warburg element in an EIS Nyquist plot represents solid-state diffusion; a large Warburg tail indicates slowed Li-ion transport due to electrolyte depletion or concentration polarization.

OSHA 1910.303 requires that electrical equipment in battery rooms must be listed and labeled. What is the primary purpose of this requirement?

Answer: To confirm equipment has been evaluated for safety by a recognized testing laboratory

OSHA requires listing/labeling to confirm that a Nationally Recognized Testing Laboratory (NRTL) has evaluated the equipment for electrical safety hazards.

During a capacity test, a battery pack delivers only 78% of rated capacity at 0.5C but 91% at 0.2C. The technician should conclude:

Answer: High internal resistance is causing significant voltage drop at higher rates

Rate-dependent capacity reduction is characteristic of increased internal resistance; higher current causes greater IR voltage drop, triggering the lower-voltage cutoff earlier.

When replacing a failed cell in a battery module, the replacement cell's SOC should be matched to the existing pack within:

Answer: ±2% SOC

Replacement cells should be within ±2% SOC of the pack to prevent large initial balancing currents and thermal stress during the first charge-discharge cycle.