Meaning
Quality assurance tests measure the electrical potential of cells at rest to identify internal self discharge issues or manufacturing defects before they enter the pack assembly line. The open-circuit voltage screening is a standard procedure in battery manufacturing that occurs after the cells have been formed and aged for several days. By comparing the measured voltage to a known baseline, technicians can find units that are losing energy faster than expected.
This process is essential for ensuring that every cell in a series string will stay in balance during its operation. Cells that fail this test are discarded or downgraded to less demanding applications to maintain the reliability of the finished product.
Measurement Precision
Sensors used for this task must be able to detect changes as small as a few microvolts to be effective. During the open-circuit voltage screening, the cells are kept in a temperature controlled environment to ensure that thermal fluctuations do not skew the results. A very stable environment allows for shorter aging times while still providing the data needed to make a quality decision.
If the equipment is not calibrated correctly, a defective cell might be missed, leading to a failure in the field months later. The data from these measurements is stored in a database to help improve the production process over time.
Discharge Detection
Internal short circuits or impurities in the chemical slurry can cause a cell to slowly bleed energy even when no load is connected. The open-circuit voltage screening is the only way to catch these “soft shorts” before the cells are buried inside a sealed pack. A cell that shows a larger than average drop in potential over a forty eight hour period is a high risk for future failure.
This early detection saves the cost of assembling a complete battery pack only to find that one component is dragging down the performance of the entire system. It also protects the end user from potential safety events.
Batch Sorting
Automated systems group the cells into narrow voltage bins to ensure that the initial state of charge is identical across the production run. This part of the open-circuit voltage screening simplifies the balancing task for the battery management system and extends the life of the pack. When cells from different bins are mixed, the management software has to work much harder to keep them at the same level, which wastes energy and generates heat.
Precision sorting is a hallmark of high quality battery manufacturers who supply the electric vehicle industry. This rigorous attention to detail ensures that the delivered energy remains consistent from the first day of use to the last.
