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  Automated battery cell shunt bypassThe Patent Description & Claims data below is from USPTO Patent Application 20060012334. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATION [0001] The present application claims the benefits, under 35 U.S.C. .sctn.119(e), of U.S. Provisional Application Ser. No. 60/572,289 filed May 17, 2004 entitled "Design of a Large Battery Pack" to Donnelly et al., which is incorporated herein by this reference. FIELD [0002] The present invention relates generally to a method for automatically electrically removing individual battery cells which are malfunctioning from a battery pack of cells electrically connected in series. BACKGROUND [0003] Batteries, in particular large lead-acid batteries, are typically fabricated first by arranging a series of positive and negative plates separated by a separator material in a stack. Positive and negative bus bars are typically welded to positive and negative tabs that extend from the tops of the positive and negative plates respectively. The positive and negative terminals of the battery are typically fabricated as part of the bus bar assembly. The separator material is impregnated with an appropriate electrolyte and the top of the battery case is installed. Atypical cell is illustrated in FIG. 1, which is well-known prior art. [0004] When a large number of cells are used in a series-connected battery pack configuration (the cell voltages add, the battery pack current is the same as the individual cell currents), one cell that begins to degrade or fail can seriously impact or terminate the operation of the entire battery pack. It is therefore desirable to have a means where a malfunctioning cell in a series-connected battery pack can be automatically removed from the battery pack. [0005] In a battery pack, degraded or failed plate pairs in a malfunctioning cell can be open-circuited by utilizing a fuse mechanism to remove one of more electrode pairs in the affected cell from service. The open-circuit approach typically applies to electrode pairs that are in parallel in a cell. This leaves a smaller number of plate pairs in the cell. This is particularly effective if the failing electrode pair has a soft short and is draining the other electrode pairs in the cell. The short causes local heating which makes the electrode hotter and a thermal fuse opens-circuits the failing electrode pair. The disadvantage of this approach is the additional cost and complexity of having a fuse mechanism on each plate pair, and a reduction in the maximum current available from the battery pack since all cells must be derated to the performance parameters of the cell with the shorted plate pair or pairs. This approach can also cause in imbalance in the state-of-charge ("SOC") between cells which can lead to loss of cell lifetimes. [0006] Another approach is to use a battery management system where the battery pack performance is reduced to the level of the degraded or failing cell. This approach limits the maximum available pack current as well as the available storage capacity and output voltage of the pack to match the capability of the malfunctioning cell. [0007] A third approach is to short-circuit a malfunctioning cell to eliminate the cell from the battery pack by shunting pack current around the malfunctioning cell. This approach has the advantage of not reducing the maximum available battery pack current. In a large battery pack which may be comprised of several hundred cells in series, there will be a small reduction in battery pack voltage and ampere-hour capacity when one or a few cells are bypassed. [0008] Thus there is a need for a low cost method to automatically shunt out malfunctioning cells in a large series connected battery pack to avoid seriously impacting or terminating the operation of the entire battery pack. SUMMARY [0009] These and other needs are addressed by the various embodiments and configurations of the present invention which are directed generally to a method for automatically electrically removing individual battery cells which are malfunctioning from a series string of cells. [0010] In a first embodiment of the present invention, a battery pack is provided that includes: [0011] (a) a plurality of battery cells electrically connected in series, the plurality of battery cells including a selected battery cell, and [0012] (b) a shorting mechanism operable, upon the occurrence of a selected event, to automatically remove electrically the selected battery cell from the electrically connected battery cells. [0013] The selected event is commonly at least one of the following: [0014] (i) an internal resistance of the battery cell being in excess of a first selected operating threshold; [0015] (ii) an internal pressure of the battery cell being in excess of a second selected operating threshold; [0016] (iii) an internal temperature of the battery cell being in excess of a third selected operating threshold; [0017] (iv) a voltage of the battery cell during energy removal being in excess of a fourth selected operating threshold; and [0018] (v) a voltage of the battery cell during charging being less than a fifth selected operating threshold. [0019] By removing individual battery cells from the battery pack in the event that the internal resistance or other internal operating characteristic of the battery cell changes beyond specified limits adversely impacting the operation of the battery, the present invention can reduce the risk of battery fires, increase the effective lifetime of the battery pack, and provide a higher effective battery pack energy output over time. The shorting mechanism commonly does not reduce the maximum battery peak current. Depending on the number of cells in the battery pack, there may be a small reduction in battery pack voltage and battery pack ampere-hour capacity. The reduced voltage and storage capacity will commonly not significantly impact battery pack performance. [0020] There are number architectures for implementing the present invention. [0021] In a first configuration, the shorting mechanism includes a piston having a position that changes in response to the internal pressure, a shorting bar, and a shorting bar deployment member. When the internal pressure rises above a selected operating threshold, the position of the piston causes the shorting bar deployment member to position the shorting bar in contact with positive and negative bus bars of the selected battery cell, thereby shorting out the cell and forming a shunt bypass of the selected battery cell. [0022] In a second configuration, the shorting mechanism includes a thermally expansive material having a length that increases in direct response to the internal temperature, a shorting bar, and a shorting bar deployment member. When the internal temperature rises above a selected operating threshold, the length of the thermally expansive material causes the shorting bar deployment member to position the shorting bar in contact with positive and negative bus bars of the selected battery cell, thereby shorting out the cell and forming a shunt bypass of the selected battery cell. [0023] In a third configuration, the shorting mechanism includes a shorting bar, a sensor that senses the occurrence of a selected event, a controller in communication with the sensor, and a shorting bar deployment member. When the controller determines from sensor input that the selected event has occurred, the controller causes the shorting bar deployment member to position the shorting bar in contact with positive and negative bus bars of the selected battery cell, thereby shorting out the cell and forming a shunt bypass of the selected battery cell. [0024] The first and second configurations are particularly desirable. They can be low cost, robust, are self-actuating and have a high degree of reliability. [0025] These and other advantages will be apparent from the disclosure of the invention(s) contained herein. [0026] The above-described embodiments and configurations are neither complete nor exhaustive. As will be appreciated, other embodiments of the invention are possible utilizing, alone or in combination, one or more of the features set forth above or described in detail below. [0027] The following definitions are used herein: Continue reading... Full patent description for Automated battery cell shunt bypass Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Automated battery cell shunt bypass patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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