Electricity: battery or capacitor charging or discharging – Diverse charging or discharging rates for plural batteries
Reexamination Certificate
2001-12-14
2003-02-18
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Diverse charging or discharging rates for plural batteries
C320S160000
Reexamination Certificate
active
06522102
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to battery charging methods and system and more particularly to charging methods and systems for preventing battery overcharge.
2. Cross-references
The present application is related to two copending applications, one patent application, entitled “Battery Charging System,” and the other patent application, entitled “Battery Charging Method and System,” each by inventors Michael Cheiky and Te-Chien Felix Yang, serial numbers to be determined, each filed Dec. 14, 2001, which are included herein by this reference, and which are not admitted to be prior art with respect to the present invention.
3. Background Art
Rechargeable batteries, for storing electrical energy, and battery chargers, for charging batteries and bringing the batteries back to a charged state, after the batteries have been depleted, have been known and are common. Typically, the batteries are charged after full or partial depletion by delivering energy to the batteries and reversing chemical processes within the batteries, by applying a voltage to the batteries, forcing current through the batteries, and, thus, restoring charge. A common charging method is to apply a voltage source to the battery to be charged, which is greater than the battery voltage of the battery, and stop charging when the battery ceases to accept additional current. Such charging methods do not consider the state of charge of the battery at the onset of charging, and almost always result in deleterious effects on the battery, reduces performance and battery life.
A battery charging method that minimizes overcharging, and, thus, increases battery performance and life is needed. The battery charging method should be capable of charging one or more batteries simultaneously, evaluate the state of charge of the batteries, i.e., whether the batteries are substantially charged or substantially fully depleted early during the charging cycle, and charge the batteries accordingly, based upon such state of charge.
Batteries generally consist of two or more galvanic cells. Two electrodes of dissimilar materials are isolated one form the other electronically, but placed in a common ionically conductive electrolyte. Overcharge of the battery can lead to complicated and undesirable side reactions, in particular as they pertain to the decomposition of electrolyte. The latter can lead to gas production, which in turn leads to increased battery internal impedance. The battery with this increased battery internal impedance can quickly stray from optimum operating conditions. Additionally, overcharging promotes the growth of dendrites, which in turn leads to battery shorting. On other hand, present demands upon batteries call increasingly for greater power densities, so that undercharge is also to be avoided in any charging scheme.
Silver-based batteries typically have high energy densities, i.e., high energy to weight and volume ratios, an ability to deliver energy at relatively high current drains, and high reliability, making them excellent candidates for use in next generation technologies, as well as meeting current day energy storage and delivery demands. Thus, there is a need for a battery charging method and system that minimizes the deleterious effects of overcharging.
The charging of silver-based batteries is characterized by two plateaus, reflecting the two active oxidation states of silver. The first plateau occurs as silver is transformed to monovalent silver oxide (Ag
2
O) while the second plateau reflects the formation of divalent silver (AgO). Towards the end of charge, generally at approximately 90% of maximum capacity, the plateau transforms into a steeply rising curve and the battery begins to be overcharged. Consequently, a battery charging method and system that limits the maximum charging voltage and charging current is needed. The battery charging method and system should taper charge the battery, so as not to drive too much energy into the battery too fast, and, thus, prevent damage to the battery. Gassing, which damages the battery, should be minimized.
With the advent of more sophisticated and expensive battery systems, such as silver-based batteries and other high impedance batteries, the need arises for more advanced charging methods and systems, which prevent overcharging and damage to the batteries. This need becomes more important, especially for silver-based batteries and other high impedance batteries, which have high energy densities and require long term reliability. Such batteries may be used in spacecraft and in other applications, requiring no replacement or minimal replacement over extended periods of time. Thus, there is a need for devices and methods to facilitate charging such batteries to their maximum capabilities, with minimum or substantially no deleterious effects, and maximization of life of such batteries. The charging method and system should be inexpensive, easy to manufacture and use, small and light weight, durable, long lasting, reliable, and capable of being used in aerospace and defense applications.
Different battery charging methods and system have heretofore been known. However, none of these battery charging methods and system satisfies these aforementioned needs.
Different charging methods and system, using shunt regulators have been disclosed.
U.S. Pat. No. 5,821,733 (Turnbull) and U.S. Pat. No. 5,747,964 (Turnbull) disclose rechargeable batteries and battery charging systems for multiple series connected battery cells which include a plurality of shunt regulators, adapted to be connected in parallel with each of the cells. The voltage of each cell is monitored during charging. When a cell is fully charged, excess charging current is shunted around the fully charged cell to enable the remaining cells to continue to charge.
Turnbull shows different embodiments of his shunt regulators. In one of Tunrbull's embodiments, Turnbull simply shows shunt regulators, each in parallel with a battery cell. In another embodiment, Turnbull uses shunt regulators and field effect transistors, whose drain and source terminals are connected in parallel across each of the battery cells. Each shunt regulator is under the control of a voltage sensing circuit, which includes a differential amplifier which senses the actual cell voltage of the battery cell and compares it with a reference voltage, elsewhere in the charging circuit. In yet another embodiment, Turnbull uses a plurality of isolation switches to disconnect the battery cells from the charging circuit to prevent the battery circuit from discharging the cells when the battery charger is not being used.
U.S. Pat. No. 5,982,144 (Johnson et al) discloses a rechargeable power supply overcharge protection circuit with shunt circuits that shunt current about a battery or battery cell of a string of battery cells, when it is charged to a maximum charge limit. The shunt circuit includes shunt regulators connected across each battery cell.
U.S. Pat. No. 6,025,696 (Lenhart et al) discloses a battery cell bypass module having a sensor for detecting an operating condition of a battery cell, such as voltage or temperature, and a controller connected across the battery cell of a lithium ion battery, the controller then being operable to change to the conductive mode and thereby shunt current around the battery cell. The controller includes a voltage limiting operational amplifier operable for transmitting a voltage excessive output signal, when the input thereto exceeds a predetermined value, and a transistor having a predetermined gate voltage allowing bypass current flow, the transistor being responsive to the voltage excessive output signal from the voltage limiting operational amplifier to shunt current around the battery cell.
U.S. Pat. No. 4,719,401 (Altmejd) discloses zener diodes, each of which are shunted across each cell in a series connected string of battery cells.
Different charging methods and systems, using plateaus and inflection points have been disclosed.
U.S.
Cheiky Michael
Yang Te-Chien F.
Jacobs Marvin E.
Tso Edward H.
Zinc Matrix Power, Inc.
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