Diagnostics Maintenance & Safety Standards Flashcards
7 cards from real BMS practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Diagnostics Maintenance & Safety Standards flashcards as text
Which PPE is mandatory when handling a swollen (bloated) lithium-ion pouch cell during removal?
Answer: Chemical splash goggles, acid-resistant gloves, and face shield
Swollen pouch cells contain pressurized electrolyte vapor and flammable gases; chemical splash goggles, acid-resistant gloves, and a face shield protect against electrolyte splash and potential venting.
A BMS uses a current interrupt device (CID) as a safety mechanism in cylindrical cells. The CID activates when:
Answer: Internal cell pressure exceeds a preset threshold
The CID is a mechanical pressure-activated device built into the cell cap that permanently opens the circuit when internal gas pressure exceeds a safe limit.
When diagnosing a BMS communication fault on a CAN bus, a technician measures 2.5V on both CANH and CANL with no differential voltage. This indicates:
Answer: A short circuit between CANH and CANL
CAN bus recessive state shows ~2.5V on both lines (0V differential); a hard short between CANH and CANL collapses the differential to zero and prevents any dominant bit from forming.
Under OSHA 29 CFR 1910.305(j)(7), when must battery rooms or enclosures have ventilation?
Answer: Whenever hydrogen gas accumulation could create a flammable atmosphere
OSHA requires ventilation in battery areas whenever charging or battery operation could produce hydrogen gas at concentrations approaching the 4% lower flammable limit.
A technician is performing preventive maintenance on a battery energy storage system (BESS). Which torque check is most critical for preventing high-resistance joint faults?
Answer: Busbar-to-cell terminal bolted connections
Loose busbar-to-terminal connections develop high resistance, cause localized heating, and can lead to thermal runaway; torque verification is therefore the highest-priority mechanical PM task.
During post-incident analysis of a battery fire, investigators find that the BMS logged a ground fault 48 hours before thermal runaway occurred. This sequence suggests:
Answer: An unaddressed insulation fault allowed current leakage that progressively damaged cells
A pre-existing ground fault permits leakage current through degraded insulation, which can cause localized heating and electrolyte decomposition, eventually initiating thermal runaway.
What is the purpose of the 'balance charge' maintenance procedure recommended for Li-ion battery packs after extended storage?
Answer: To bring all cells to equal SOC after self-discharge differences developed during storage
Extended storage allows different self-discharge rates to create SOC divergence among cells; a balance charge (or slow top-balance) equalizes cell voltages before return to service.