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
The 'knee point' in a battery's cycle life curve represents:
Answer: The cycle count at which capacity fade accelerates nonlinearly and rapidly
The knee point marks the onset of accelerated, nonlinear capacity fade — often linked to lithium plating, SEI breakthrough, or electrolyte depletion — after which remaining useful life drops quickly.
A BMS performs 'cell voltage sampling' at 10ms intervals during a 2C discharge pulse. What artifact can this introduce if not compensated?
Answer: Aliasing due to switching noise from adjacent power electronics
High-frequency switching in adjacent power electronics generates noise at frequencies that can alias into the 10ms sampling window, causing erroneous voltage readings unless low-pass filtering is applied.
According to UN 38.3, what series of tests must lithium batteries pass before transport as cargo?
Answer: Altitude simulation, thermal test, vibration, shock, external short circuit, impact/crush, overcharge, forced discharge
UN 38.3 specifies eight tests (T1-T8): altitude simulation, thermal, vibration, shock, external short, impact/crush, overcharge, and forced discharge for transport approval.
A battery pack's BMS applies a derating curve that reduces maximum charge current by 50% when cell temperature falls below 10°C. The engineering reason for this is:
Answer: Low temperature slows Li-ion intercalation kinetics, increasing the risk of lithium plating on the anode
At low temperatures, slower Li+ diffusion and higher anode overpotential increase the risk that lithium deposits as metallic plating instead of intercalating safely into graphite.
During a maintenance inspection, a technician discovers that two parallel cell groups in a module have a 150mV voltage difference at rest (3 hours post-charge). The appropriate action is:
Answer: Investigate for cell failure, micro-shorts, or connection faults before returning to service
A 150mV OCV difference between parallel groups at rest is abnormal and indicates possible cell failure, internal short, or connection fault; operation should pause pending root-cause analysis.
What does a high 'calendar aging' rate (capacity loss during storage) typically indicate about a Li-ion cell's condition?
Answer: Elevated storage temperature or high SOC state is causing continuous electrolyte oxidation at the cathode
Calendar aging is primarily driven by high SOC and high temperature, both of which accelerate cathode-electrolyte interface reactions and SEI layer growth on the anode.
When a BMS fault log shows recurring 'precharge timeout' faults during system startup, the technician should first suspect:
Answer: An excessive DC bus capacitance or a short on the output bus causing slow voltage rise
Precharge timeout means the output bus voltage is not rising to pack voltage within the allowed time, which points to excessive capacitive load or a partial short preventing the precharge resistor from charging the bus.