How Electrical Testing Uncovers Battery Systems Welding Defects

Key Electrical Tests to Ensure Welding Quality

Electrical testing – both for electric vehicle (EV) batteries and Battery Energy Storage Systems (BESS) – is essential for ensuring safety, reliability, and optimal performance.

In the world of battery manufacturing, where the quality is mandatory to prevent failures and ensure optimal battery performance, electrical testing is a fundamental building block in various applications including electric vehicles, energy storage systems, and portable electronics.

While numerous enhancements have been made to ensure proper electrical connections between the battery systems, manufacturers have recently shifted their attention to improving the quality of welding.

In the battery manufacturing process, welds are utilized at multiple stages for joining purposes. Welding defects that affect electrical circuits are particularly critical because they could prevent a battery system from performing at full capacity, reduce battery efficiency and even compromise battery safety.

This article is focused on the importance of high-quality welds in the battery manufacturing process and the role of electrical testing in identifying welding defects.

Welding defects can cause electrical connections in battery systems to fail

Electrical vehicles (EV) batteries and battery energy storage systems (BESS) are composed of interconnected battery cells and modules. Different materials, configurations, and welding techniques are employed based on the specific design and requirements of the battery system, resulting in a diversity of characteristics. This diversity contributes to significant discrepancies in the integrity of the joints. Additionally, the requirement for high-volume production, which involves a substantial number of welds for electrical connections, increases the overall incidence of welding defects.

Welding defects can lead to a substantial decline in the overall battery performance used in electric vehicles (EV) and battery energy storage systems (BESS), resulting in various complications, including:

Increased resistance: A poorly formed or contaminated weld can increase the electrical resistance, leading to energy loss and potentially causing overheating.
Poor contact: A defective weld may not provide a secure connection between the battery cells or terminals, resulting in intermittent or unreliable electrical contact.
Overheating: Increased resistance and poor contact can lead to overheating, which can damage the battery cells, cause thermal runaway, or even lead to a fire.

To ensure the reliability of the electrical connections, it is essential to inspect welds and conduct electrical testing to identify and address any welding defects.

Electrical testing to ensure battery systems welding quality

The assurance of weld quality in the assembly of a battery system primarily focuses on electrical resistance testing. Accurate measurement of the electrical micro-resistance at the welded electrical connections joints is crucial for ensuring the reliability of the electrical system and preventing any adverse effects on battery efficiency. Ideally, these joints should have very low resistance to allow smooth current flow. An increase in resistance indicates a problem with the weld, suggesting that the battery may not perform optimally.

Other important electrical tests that battery manufacturers utilize to ensure that poor welding is detected early in the production process are:

DC/AC Internal Resistance (IR) Test

Both DC and AC IR testing measure the internal resistance of the battery. Higher internal resistance often indicates poor welding quality, which can lead to reduced charge and discharge efficiency. Detecting high resistance early helps battery manufacturers address welding defects before they affect the battery performance.

Open Circuit Voltage (OCV) Test

The OCV test is another critical assessment. It ensures that the battery delivers the correct voltage as per its design specifications. If the welding quality is poor, it can cause fluctuations in the voltage output, reducing the battery’s ability to maintain stable performance. This test helps ensure that the battery operates within safe and efficient voltage limits.

The specific application of the battery system, whether used in electric vehicles (EV) or battery energy storage systems (BESS), along with the production volumes, require a tailored electrical testing approach to ensure both battery performance and safety.

Challenges in conducting electrical testing within high-volume battery production

The growing demand for electrification compels manufacturers to produce more batteries at a faster rate, leading to a significant volume of welds requiring testing. Ensuring electrical connections functionality and uniform welding quality in high-volume battery manufacturing environments presents considerable testing challenges, including:

Long effort: performing comprehensive weld inspection can be slow and inefficient.
Complexity: the welding processes involve different parameters. Operators need to possess expertise in managing multiple parameters and correlate the testing results.
Inconsistency: variations in operator skill, experience, and fatigue can lead to variabilities.
Imprecision: difficulty of accessing increasingly small welds and measuring extremely small resistance values, on the order of micro-ohms, can be difficult.

Addressing these challenges requires a combination of advanced testing equipment and continuous improvement in end-of-line testing.

Automatic Test Equipment addresses the challenges of Welding Quality testing in high-volume Battery Manufacturing

In most high-volume battery manufacturing environments, electrical testing of welds is typically conducted during the end-of-line test phase. At this stage, the use of automatic test equipment is favored to address challenges related to efficiency, complexity, consistency, and accuracy, thereby ensuring optimal battery performance.

SPEA T100BT automatic battery tester, is designed to meet the rigorous demands of battery manufacturing. With the ability to measure multiple test points simultaneously the tester features dedicated modules that can perform multiple resistance measurements with Kelvin probes, multiplexers, and high-precision instruments. Additionally, the integration of a visual camera and thermal sensors guarantees improved testing with several key benefits, including:

Cost efficiency: the modular testing architecture ensures broader applicability and easy battery systems reconfigurations.
Enhanced Operations: by an integrated flying probe architecture, this automatic tester can perform an extensive array of electrical tests on one platform. Operating around the clock without the need for operators, it identifies all potential weld defects and assists in the welding process development.
Data accuracy: a self-loading test program executes a consistent electrical testing sequence, thereby eliminating any variabilities that may arise from incorrect input.
Repeatability: the advanced linear motion technology combined with sub-micron resolution linear optical encoders and a compact kelvin probe design guarantees fast moving and accurate positioning of the testing probes, detecting any welding defect.
Precision of the electrical measurement: the µΩ-meter instrument developed by SPEA specifically for this tester, it is fully integrated and allows rapid and accurate detection of any variations even as small as a few microohms, resulting in significantly shorter test time and higher precision in defect detection.

Recognizing the importance of preventing failures occurring during welding, the SPEA T100BT automatic battery tester meets the demands for throughput, accuracy, and flexibility, enhancing measurement precision and data management while simultaneously reducing the operational costs associated with electrical testing for battery systems.

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