Improvement of failure detection of production line test results by implementing Delta V criteria

The reliability of automotive batteries is an important factor, especially for the OEM market. To ensure consistent reliability all automotive batteri es are subjected to electrical load tests prior to shipment. These tests ar e performed in accordance with industry accepted standards. It is essential that the energy discharged from the battery during test be minimized to av oid the cost and delay associated with recharge. When defining the ideal hi gh rate discharge test process one must consider these basic requirements. Immediately after formation, and preferably, after post cleaning, batteries are discharged at high current for a few seconds. The voltage under load a t the end of test is determined and compared to nominal values resulting in a pass/fail decision. This paper discusses the effectiveness of the present high rate discharge t est evaluation criteria in terms of it's ability to accurately discriminate between acceptable and unacceptable batteries. Variations in materials and manufacturing processes affect open-circuit voltage (OCV) and constant cur rent voltage (CCV) measurements leading to erroneous pass/fail determinatio ns. The paper will illustrate how these variations can be recognized and st atistically evaluated. A supplemental evaluation criterion is presented which significantly improv es the reliability of test results. This criterion is the gradient DeltaV o f the discharge curve. Evaluation of test data using this criterion yields information that directly correlates to the failure mode of the rejected ba ttery, including irregularities in pasting and assembly. This paper concludes that the implementation of DeltaV criterion significan tly improves the failure detection of batteries subjected to production lin e high-rate discharge tests. Using the DeltaV criterion to evaluate the tes t results is a more accurate determinant of an acceptable battery than the traditional criteria and results in fewer customer returns. (C) 2001 Elsevi er Science B.V. All rights reserved.