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Damp heat cycling

Verifies the battery pack or system survives repeated cycles of high humidity and elevated temperature without losing electrical safety. Stress targets sealing integrity, insulation aging, and condensation handling.
Clause (method) 8.2.5
Clause (pass criteria) 5.2.5
Object pack / system
Status vs. 2020 revised
Observation period 2 h at test environment temperature

Pass criteria

After the damp heat cycling test, the battery pack or system shall show no leakage, no housing crack, no fire, and no explosion. The insulation resistance within 30 minutes after testing shall not be less than 100 Ω/V (DC), or 500 Ω/V if an AC circuit is present.

The 30-minute window is specific to this test (5.2.5); other STD tests do not impose a measurement deadline. Surface condensation falls off quickly, so the requirement effectively measures the wet-state insulation, not a dried-out post-test value.

Source: GB 38031-2025, clause 5.2.5 (PDF p. 12).

Pre-conditions

  • Pre-treatment: Standard, per clause 7.2.
  • SOC: Highest working SOC per clause 6.1.10.
  • Insulation baseline: Measure before the test per Appendix B (clause 6.1.5).

Test parameters

Parameter Value Source
Test method Per GB/T 2423.4 Test Db 8.2.5.2
Maximum temperature 60 °C (or higher if required by manufacturer) 8.2.5.2
Cycle profile Per Figure 8 (temperature + relative humidity curves) 8.2.5.2
Number of cycles 5 8.2.5.2
Post-test observation 2 h at test environment temperature 8.2.5.3
Insulation measurement deadline Within 30 min after testing 5.2.5

Procedure

  1. Confirm pre-treatment per 7.2 and measure baseline insulation per Appendix B. (6.1.5)
  2. Adjust SOC to the highest working value. (6.1.10)
  3. Place the test object in a damp heat chamber configured per GB/T 2423.4 Test Db, with maximum temperature 60 °C (or higher if specified by the manufacturer). (8.2.5.2)
  4. Run the test profile (temperature and humidity) per Figure 8 for 5 cycles. (8.2.5.2)
  5. After the 5th cycle completes, remove the test object and observe at the test environment temperature for 2 hours. (8.2.5.3)
  6. Re-measure insulation resistance per Appendix B within 30 minutes after testing. Inspect for leakage and housing cracks. Confirm no fire or explosion occurred. (5.2.5)

After-test observation

Observe the test object for 2 hours at the test environment temperature (22 °C ± 5 °C) after the 5th cycle. (8.2.5.3)

The post-test insulation measurement must be completed within 30 minutes of test end (5.2.5) — sequence the observation, inspection, and insulation measurement so the meter reading lands inside that window.

What changed from GB 38031-2020

  • Listed in the preface change list as both requirements (5.2.5) and method (8.2.5) revised.
  • The 30-minute insulation measurement deadline is part of the 2025 requirements text in 5.2.5.

Migration impact: Already-type-approved vehicle models must comply from 2027-08-01. New type approvals from 2026-07-01. See Re-certification timeline.

Engineering notes (non-normative)

The notes below are practical interpretation, not part of the standard.

Engineering note (non-normative): The 30-minute insulation deadline is the operational pinch point. Plan the chamber-extraction → visual inspection → terminal connection → Appendix B measurement sequence so the meter reading is recorded inside the window — not just initiated. With a soaked DUT, condensation drains quickly; even a 45-minute delay will read substantially higher and is non-conforming on procedure even if the value passes.

Engineering note (non-normative): "Maximum temperature 60 °C or higher per manufacturer" lets an OEM volunteer a stricter test. If the manufacturer-declared upper operating temperature exceeds 60 °C, type-approval reviewers will typically expect the test to track the manufacturer value, not the floor.