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Overcharge protection

Verifies the battery system's overcharge protection terminates charging before damaging overvoltage or thermal overshoot — exercised with the external charger's control limits disabled and the manufacturer's most aggressive charging strategy.
Clause (method) 8.2.14
Clause (pass criteria) 5.2.14
Object system
Status vs. 2020 revised
Observation period 1 h at test environment temperature

Pass criteria

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

Source: GB 38031-2025, clause 5.2.14 (PDF p. 12).

Pre-conditions

  • Object: The test object is a battery system. (8.2.14.1)
  • Ambient temperature: 20 °C ± 10 °C (or higher if specified by manufacturer). (8.2.14.2 a)
  • SOC: Adjust to the middle of the manufacturer-recommended normal operating range (precise adjustment not required as long as the system can operate normally). (8.2.14.2 b)
  • Protection devices: All protection devices that affect functionality and are related to the test results shall be in normal operation. (8.2.14.2 c)
  • Contactors: All relevant main charging contactors shall be closed. (8.2.14.2 c)
  • Insulation baseline: Measure before the test per Appendix B (clause 6.1.5).

Test parameters

Parameter Value Source
Ambient temperature 20 °C ± 10 °C (or higher per manufacturer) 8.2.14.2 a)
SOC at start Middle of normal operating range 8.2.14.2 b)
Charging equipment External, connected to main terminals 8.2.14.3 a)
Charging-control limits Disabled on the external charging equipment 8.2.14.3 a)
Charging strategy Shortest allowed by the manufacturer 8.2.14.3 b)
Termination — auto cutoff Test object automatically terminates the charging current 8.2.14.4 a)
Termination — signal Test object sends a signal to terminate the charging current 8.2.14.4 b)
Termination — temperature overshoot Continue charging until temperature exceeds max operating temperature by 10 °C (if no cutoff per a) 8.2.14.4 c)
Termination — 12 h continuation If charging current does not terminate and temperature is 10 °C below max operating T, continue charging for 12 h 8.2.14.4 d)
Post-test observation 1 h at test environment temperature 8.2.14.5

Procedure

  1. Confirm pre-treatment per 7.2 and measure baseline insulation per Appendix B. (6.1.5)
  2. Adjust SOC to the middle of the normal operating range. (8.2.14.2 b)
  3. Bring ambient to 20 °C ± 10 °C (or higher per manufacturer). (8.2.14.2 a)
  4. Confirm all relevant protection devices are in normal operation and main charging contactors are closed. (8.2.14.2 c)
  5. Connect the external charging equipment to the main terminals of the test object. (8.2.14.3 a)
  6. Disable the charging-control limits on the external charging equipment. (8.2.14.3 a)
  7. Charge the test object using the shortest charging strategy allowed by the manufacturer. (8.2.14.3 b)
  8. Continue charging until any of: a. Test object automatically terminates the charging current. (8.2.14.4 a) b. Test object sends a signal to terminate the charging current. (8.2.14.4 b) c. If neither (a) nor (b), continue until temperature exceeds the maximum operating temperature by 10 °C. (8.2.14.4 c) d. If the charging current does not terminate and the test-object temperature is 10 °C below maximum operating T, continue charging for 12 h. (8.2.14.4 d)
  9. Disconnect external charging and observe at the test environment temperature for 1 hour. (8.2.14.5)
  10. Re-measure insulation per Appendix B; inspect for leakage, housing cracks; confirm no fire/explosion.

After-test observation

Observe the test object for 1 hour at the test environment temperature (22 °C ± 5 °C) after charging is terminated. (8.2.14.5)

What changed from GB 38031-2020

  • Listed in the preface change list as both requirements (5.2.14) and method (8.2.14) revised.

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): Termination conditions (a)/(b) are the success path: the BMS or contactor logic detects overcharge and stops it. (c) is the "thermal runaway approach" path — protection failed, and the test continues until the cells are 10 °C past their thermal limit. (d) is the surprising case: protection failed, but the system stays cool (10 °C below max), so the test runs for 12 hours. This catches systems where overcharge protection is missing or broken, but the cell chemistry's terminal voltage clamp keeps energy input low enough to be thermally benign — still a non-conformance because the spec requires protection to work.

Engineering note (non-normative): "Shortest charging strategy allowed" is the worst case from the BMS's point of view: highest current, fastest voltage ramp. Document the rate. With control limits disabled, the only thing stopping the charger is the system itself; if the test ever terminates on (c), expect to also re-qualify the cell-level safety chain.