Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-11-17
2003-02-18
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
Reexamination Certificate
active
06520018
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to a method for detecting failed lead acid batteries, and more specifically, to a method for evaluating the structural integrity of battery terminal posts on line or off line in the manufacturing plant of said batteries.
DESCRIPTION OF RELATED ART
In the manufacture of the lead-acid batteries normally used in automobiles, groups of battery plates and separators contained in separate cells are placed in a case. The cells are joined to form intercellular connections there between. Battery posts, which will form the positive and negative terminals of the battery, extend above the upper surface of the open battery case. These battery cases are adapted to receive thereon a battery cover, which has formed therein two lead bushings to be pierced by the battery posts when the cover is fitted onto the top of the case. A liquid-tight seal is then formed between the battery case and battery cover, and the final mechanical assembly is completed by fusing the battery post elements with the battery cover bushing elements to produce the desired positive and negative battery terminal posts. Later on, acid filling, battery forming, and other operations, may be conducted in order to produce a finished battery.
Battery formation consists of the electrochemical processing of a battery plate or electrode between manufacture and first discharge, which transforms the active materials into their usable form.
Often, it is desirable to ascertain whether a battery is defective or whether it is capable of being charged, or what its charge capacity is or what its present state of charge is. Detecting failed batteries has become important in order to assure the online quality of each lead-acid battery during its manufacturing. Known means which are used at present for detecting electrical defects during intermediate stages of production are of two types: firstly, devices for measuring the voltage of the batteries at the end of the forming and charging phase enabling the rejection of the batteries whose end voltage is lower than a predetermined threshold; and secondly, rapid discharge devices requiring the rejection of batteries whose voltage is insufficient after a few seconds of discharge.
Prior to the shipping of completed automotive batteries, it is desirable to “high-rate” test those batteries shorting the positive and negative terminals of those batteries while measuring the current capacity of those batteries. The testing method disclosed by Eberle is an example. This “high-rate” testing procedure is necessary since it is possible that various connections within the battery, such as intercell connections, may be cracked or otherwise be unsatisfactory such that the battery would be prevented from delivering its full capacity, as for example, under starting conditions when used in an automobile. By “high-rate” testing these batteries, deficient welds, connections, internal shorts, incomplete formation and other deficiencies within the battery will be reflected in the battery's inability to deliver “high-rate” discharge. The problem of the “high-rate” testing methods is that they do not reliably detect broken fractured battery terminal posts. In the following paragraphs some patents related to lead-acid battery testing methods will be briefly described.
Reeves et al patented a technique for detecting failed batteries while the battery is attached to one or more electronic devices, and is receiving a float charge. The float voltage minimizes the normal voltage differences between battery cells. This technique employs a ratio comparative analysis of cell voltages of a battery provided across the terminals of the battery. The comparative analysis determines a voltage threshold that identifies whether a battery has a shorted or open cell.
Burkum et al disclosed a testing device to measures the impedance of cells that form a lead acid battery, while the battery is in a float charge condition and connected to an active electrical load. The impedance measurement is made at a frequency selected to be different from those frequencies otherwise present in the charger load circuit. A first application of the testing device monitors developing defects in one or more individual cells or intercellular connections that can prevent the battery from delivering its stored energy to the load. In a second application, the testing device is used to compare the impedance of individual cells and electrical connections to locate faulty components. However, this method tends to require a significant amount of precision circuitry and is expensive.
The battery terminal voltage and the specific gravity of each cell making up a battery are indicators, which have been used to determine battery state of charge. It is standard industry practice to take periodic specific gravity measurements and to conduct visual and other checks. However, specific gravity readings do not entirely indicate a battery ability to supply power. For example, the specific gravity of each cell in a battery may indicate a fully charged ready state, but high impedance in one intercellular connection can prevent the battery from functioning as intended.
In the method described by Win de Bank, a controllably varying charging current is supplied to the battery, and the voltage produced across the battery while that, current is supplied is measured. The dynamic voltage current characteristics are obtained, as a function of the measured voltage and supplied current. This voltage current characteristic is compared to predetermined voltage current characteristics representing batteries of the type being tested in order to determine the operating condition and/or characteristics of the battery under test.
These means are insufficient for detecting small or internal short circuits and even large short circuits, which can be detected by conventional checking methods only after long storage or service periods. Moreover, they are not suitable for detecting properly, in a battery the reverse installation and forming of cells or defects such as twisted plates, lack of electrolyte and defective separators. Dupuis et al proposed a checking method and device enabling the above mentioned defects to be detected a short time after the end of the forming and charging phase, i.e. during finishing operations. This method comprises the steps of: passing a charging current pulse through the battery, measuring an elementary transient voltage at the terminal of each storage cell; and comparing elementary transient voltages with the average transient voltage of the storage cells (total transient voltage divided by the number of the storage cells). The battery is rejected if the absolute value of the difference between the average transient voltage and one of the elementary transient voltages, becomes higher than a predetermined threshold and if the sum of the maximum absolute values of the differences constantly becomes higher than a predetermined threshold.
In view of the known lead-acid battery testing methods, there are no disclosed specific methods to evaluate the physical integrity of battery terminal posts in previous patents. It should be appreciated by those skilled in the art that an improper or defected battery terminal post is substantially detrimental to the overall performance of the electric storage battery. There is also a hazard that the electric storage battery may explode causing damage to persons and/or property. In addition, the electrical connections of the positive and negative battery posts to the positive and negative battery bushings are essential to the safety of the electrical storage battery. If a battery terminal post is not properly fused to the battery bushing, the electrical storage may leak acid and/or acid fumes from the battery bushing. For these reasons, it is very important to have a reliable testing method to evaluate the physical integrity of the battery posts.
To ensure that a reliable electrical contact is maintained, the battery terminal connector must be constructed such that it w
Enertec Mexico, S.r.l. de C.V.
Harrison & Egbert
Miller Rose M.
Williams Hezron
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