FIELD FAILURE REPORT

Report Number: FFR-2026-0911
Product: 120kW DC Fast Charging Station (Model DC-120)
Failure Date: September 3, 2026
Failure Location: Highway Service Area, Jiangsu Province
Unit Age: 14 months (installed July 2025)
Report Date: September 11, 2026
Prepared By: Electrical Safety Engineering Team

1. Incident Summary

On September 3, 2026, a 120kW DC fast charging station failed during operation. The station was serving an electric vehicle at the time. The failure was characterized by a sudden power loss, followed by smoke and a burning smell from the charging cabinet. The vehicle was not damaged. No injuries were reported.

The station was immediately taken out of service. The operator requested an independent investigation.

Investigation Team:

• Lead engineer: Power electronics specialist

• Supporting engineer: Thermal analysis specialist

• Supporting engineer: Electrical safety specialist

Site Visit Date: September 6, 2026

2. Physical Inspection Findings

2.1 External Condition

The charging cabinet is a standard outdoor unit with IP54 rating. The cabinet exterior was intact. No signs of physical impact. The cooling vents on the sides were partially blocked with dust, pollen, and small debris. The vent blockage was estimated at 40-60% coverage.

The cabinet door was opened. The interior showed evidence of overheating. Soot deposits were visible on the upper section of the cabinet interior. The soot pattern suggested a localized thermal event.

2.2 Power Module Inspection

The power module (Model PM-120) was removed for inspection. The module contains:

2.3 Soot Pattern Analysis

The soot pattern was localized around the IGBT modules and DC bus capacitors. The pattern suggested the failure initiated in this area. The thermal event was concentrated, not distributed. This is consistent with a failure of one or more components, not a general overheating condition.

However, the dust blockage on the heatsink and cooling fan likely contributed to reduced cooling capacity, which increased the operating temperature of the module over time.

3. Thermal Analysis

3.1 Baseline Thermal Performance

The module's thermal design assumes an ambient temperature of 40°C and a cooling airflow of 120 CFM. The IGBT junction temperature target is <125°C.

3.2 Field Conditions

The station is located in a highway service area. Field ambient temperature in summer can reach 38°C. The cabinet is exposed to direct sunlight for part of the day, which can raise the internal cabinet temperature by 5-10°C above ambient.

3.3 Calculated Thermal Impact of Dust Blockage

Based on the observed dust blockage (estimated 40-60% of heatsink fins), the effective cooling capacity is reduced.

Observation: The estimated junction temperature under blocked conditions exceeds the IGBT's maximum rated junction temperature of 150°C. This explains the IGBT failure.

3.4 Thermal Interface Material Degradation

The thermal interface material (TIM) between the IGBT modules and the heatsink was degraded. The TIM was dry, cracked, and discolored. The degradation reduces thermal conductivity and increases thermal resistance.

TIM Degradation Impact:

The combination of dust blockage and TIM degradation caused the IGBT junction temperature to exceed the maximum rating, leading to thermal runaway.

4. Maintenance Records Review

The operator's maintenance records were reviewed.

Observation: The maintenance schedule was not followed. The cooling fan inspection was overdue by 5 months. The heatsink cleaning was overdue by 2 months. The TIM inspection was never performed.

5. Design Review Findings

5.1 Heatsink Access

The heatsink is located at the rear of the cabinet. Access requires removing the power module from the cabinet. The maintenance manual specifies that the heatsink should be cleaned every 6 months. However, the design does not allow for cleaning without module removal.

Observation: The design makes routine maintenance difficult. This may explain why the maintenance was not performed. The operator may have avoided the task because it was too time-consuming.

5.2 Cooling Fan Filter

The cooling fan does not have a filter. Dust and debris enter the cabinet directly. In a highway environment with high dust and pollen levels, the fan and heatsink become blocked quickly.

Observation: A filter would reduce the frequency of cleaning. The absence of a filter increases maintenance requirements.

5.3 Thermal Interface Material Specification

The TIM used in the module is a standard silicone pad. The pad has a rated operating temperature of 150°C and a thermal conductivity of 1.5 W/mK. The specification is acceptable for clean conditions but degrades faster under high-temperature cycling.

Observation: A higher-performance TIM (e.g., phase-change material or graphite sheet) would be more resistant to degradation. The current TIM is a cost-optimized choice, not a reliability-optimized choice.

6. Root Cause Analysis

Primary Root Cause: Thermal runaway due to IGBT junction temperature exceeding maximum rating.

Contributing Factors:

7. Corrective Action Recommendations

7.1 Immediate Actions (0-30 Days)

7.2 Short-Term Actions (30-90 Days)

7.3 Long-Term Actions (90-180 Days)

8. Supplier Notification

The module supplier has been notified of the findings. The supplier has acknowledged the design limitations identified in this report. The supplier has agreed to:

1. Provide replacement IGBT modules at cost for the failed unit.

2. Provide upgraded TIM for all units in the fleet at a discounted price.

3. Work with the operator to redesign the heatsink access for easier maintenance.

4. Include a cooling fan filter in future module shipments.

9. Financial Impact

10. Conclusion

The failure of the DC fast charging module was caused by a combination of thermal factors:

1. Dust blockage reduced cooling capacity.

2. Thermal interface material degradation increased thermal resistance.

3. Maintenance was overdue.

4. The design made maintenance difficult.

5. The absence of a fan filter increased dust ingress.

The failure was not caused by a manufacturing defect in the IGBT or capacitor. It was caused by a combination of design limitations and maintenance gaps. The corrective actions in this report address both.

The operator has implemented the immediate actions and is proceeding with the short-term actions.

Report Prepared By:

Li Chen, Lead Electrical Engineer
September 11, 2026

Reviewed By:

Wang Wei, Engineering Manager
September 11, 2026

This report is confidential and intended for internal use only. Distribution to third parties is prohibited without the written consent of the Engineering Department.

A 120kW DC fast charger failed at a highway station in Jiangsu. The unit was 14 months old. The investigation found a de

120kW DC fast charger. 14 months old. Thermal runaway at a highway station. Field investigation revealed a design issue affecting the entire production series.

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