The short circuit test data is inaccurate? Several overlooked issues with equipment

The external short-circuit test of lithium batteries is a core safety project for lithium battery certifications as per UN38.3, IEC 62133, and GB 38031. Many enterprises and laboratories encounter situations where the equipment operates normally but the test data is abnormal and the curves are distorted, resulting in the rejection of the certification report. Many people initially suspect the samples, but in fact, most of the problems stem from the hidden defects and details of the equipment. This article sorts out common equipment hazards to help you avoid errors and ensure the compliance and traceability of the data.

1. Static resistance is qualified, but dynamic loop resistance drifts

The standard requires that the total resistance of the short-circuit loop be stable ≤ 100 mΩ. Many personnel only test the static resistance before the test and ignore the resistance changes under high current operation.

Thousand-ampere instantaneous current will cause copper bars, contactors, and connection terminals to heat up rapidly, and the combination of contact oxidation and wear will cause the dynamic loop resistance to continuously increase. This directly limits the peak short-circuit current, preventing the battery from reproducing the real thermal runaway phenomenon, resulting in optimistic test results that cannot pass the certification. This is the primary cause of data inaccuracy.

2. Contactor hazard: Data fluctuation + safety risk

The contactor is the core vulnerable component of the short-circuit testing machine. Aging or inferior contactors will produce arcs after being subjected to a large current impact, causing contact sintering, inaccurate contact, and delayed disconnection.

Minor faults result in poor test repeatability and curve fluctuations for samples in the same batch; severe cases cause contact welding, making the circuit unable to be cut off, and the battery continues to short-circuit and heat up, posing a risk of fire and explosion. This fault generally does not have equipment error messages, but is only reflected through data deviations, making the troubleshooting difficult.

3. Insufficient sampling rate, missing transient key information

Battery short-circuit is a millisecond-level failure process, with peak currents, voltage drops, and temperature changes occurring in an extremely short time. Insufficient sampling rate will directly lose peak data, resulting in incomplete curves.

At the same time, high current generates strong electromagnetic interference. Incomplete equipment shielding, poor grounding, and uncalibrated sensors, as well as misaligned temperature measurement points, further increase data noise, making the test results unable to meet the requirements for laboratory traceability and certification audits.

4. Pre-treatment conditions not up to standard, test conditions deviate from the standard

According to UN38.3 and GB 38031, short-circuit tests should be conducted under a 57°C high-temperature condition. Some laboratories adopt a split scheme, where the battery is preheated in a drying oven before being transferred to the short-circuit equipment.

During the transfer process, the battery temperature drops, deviating from the standard conditions, changing the internal resistance and thermal runaway threshold of the battery. Additionally, the uniformity of the cavity temperature field can also cause significant differences in test results for samples in the same batch, becoming a common reason for report rejection.

5. Ignoring regular calibration, errors accumulate gradually

The accuracy of the equipment at the factory is not equivalent to long-term stability. Repeated tests will bring oxidation of fixtures, aging of cables, sensor drift, etc. Without regular calibration, replacement of consumables, and self-check of the circuit, systematic errors will continue to accumulate, eventually leading to batch data non-compliance and hindering the progress of research and development and certification.

Conclusion

The core of the short-circuit test is to restore the real fault and obtain reliable data, rather than just going through the process. Data anomalies are mostly caused by the insufficient dynamic performance of the equipment, hardware defects, non-compliance with conditions, and lack of maintenance. Selecting a short-circuit equipment with a stable low-resistance loop, arc suppression, millisecond-level high-speed sampling, and an integrated constant temperature chamber, along with standardized calibration and maintenance, can ensure the compliance and effectiveness of the test and meet the requirements for global lithium battery safety certifications.