In battery engineering and battery safety, severe failures are rarely random. They usually come from progressive degradation mechanisms that develop silently over time.
In a recent investigation of a thermal event in the power distribution (PJB) section of a heavy-duty battery pack fleet in the automotive industry, what first looked like a local issue turned out to be a deeper systemic problem. The root cause was not a single mistake, but a chain of interacting design weaknesses.
The engineering reality: a domino effect
Insulation coordination. Clearance and creepage distances were not sufficiently robust for the application, against principles in standards like IEC 60664-1 and ISO 6469-3. This increased localized electrical stress and enabled conditions for arcing to develop during operation.
Limits of conventional monitoring. Some degradation mechanisms do not become clearly visible under static isolation monitoring. Under load or transient electrical stress, local effects can grow internally without being detected.
Thermal-electrical interaction. Electrical stress turned into thermal stress through conductive paths. This caused connection weakening, higher local resistance and the formation of a self-reinforcing hotspot.
The silent gap: missing observability
The system was effectively blind at hotspot-prone nodes. Missing or misplaced thermal sensors meant the system appeared healthy while a major failure mechanism was already developing inside the pack.
The eMOBINO resolution strategy
We did not just fix the symptom. We strengthened the architecture against recurrence through a structured design review. Each failure was turned into a design improvement.
- Enhanced insulation strategy: improved spacing and insulation coordination for real operating conditions
- Structured thermal management assessment: systematic identification and validation of critical nodes
- Targeted sensing: strategic placement of sensors to enable early detection of thermal deviations
- Integrated safety upgrade: combined hardware and control updates for more proactive fail-safe behavior
Key takeaway
A system can look perfectly healthy while failure is already in progress. If critical nodes are not observable, failure does not start suddenly, it progresses unnoticed.
The best moment to address these risks is before they become field incidents. If you are developing EV, battery or energy storage systems and want to challenge your architecture through an independent technical design review, you can always reach us. We just prefer to meet before things start heating up.
