Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2001-05-16
2003-10-07
Tso, Edward H. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06630814
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of battery powered electronic devices; and, more particularly, to a method and apparatus for calibrating a rechargeable battery for mobile telephones and other portable electronic devices.
2. Description of the Prior Art
Many types of electronic devices utilize battery power instead of or in addition to A/C power from an outlet. For example, mobile telephones and other mobile terminals, laptop computers, camcorders, etc., usually utilize rechargeable batteries; and a variety of types of rechargeable batteries have been developed for use in such applications including nickel-cadmium batteries, nickel metal hydride batteries and lithium ion batteries.
A user of a portable electronic device often wishes to know the operational time remaining with an installed battery so as to be able to properly plan for future usage of the device, and to generally know when the battery should be recharged. For example, a user of a mobile telephone may wish to know if expected calls can be made or received, that the phone can be properly used when taken on a long trip, etc.
Recognizing the importance of providing users of portable electronic devices with information concerning the remaining operational time of their devices, manufacturers often provide portable electronic devices, such as mobile telephones, with a “fuel gauge” capability by which the remaining capacity of a battery maybe monitored. In general, a fuel gauge calculates the remaining capacity of the battery as follows:
Remaining battery capacity=Total battery capacity−Used battery capacity
A mobile telephone, for example, can measure the total current that is fed into it from the battery, and from this information can calculate how much capacity is withdrawn from the battery (i.e., used battery capacity). If it also knows the total recoverable battery capacity (usually referred to herein simply as the “total battery capacity”), it can easily calculate the remaining battery capacity using the above equation. Once the remaining battery capacity is known, the telephone can predict the remaining “talk” and “standby” times for the telephone and provide this information to the user via a display or the like.
In order to avoid possible confusion, it should be noted that the term “battery” as used herein generally refers to a “battery pack” as is used to power many electronic devices. A battery pack typically includes one or a plurality of individual rechargeable battery cells. The individual battery cell is generally referred to herein as a “battery cell” or, more simply, as a “cell”.
A value indicative of the total capacity of a cell is typically provided by the vendor of the cell, and a value indicative of the total capacity of the battery can be determined from this information. In the case of “dumb batteries”, when the software for an electronic device is originally designed, the total battery capacity value is programmed into the device. With respect to “smart batteries”, the total battery capacity value is provided in a memory storage device associated with the battery; and the device is able to communicate with the battery to obtain the total battery capacity value.
The total cell capacity value provided by the cell vendor, however, is a “nominal value”, i.e., an average minimum capacity value of a fully charged cell for a particular cell type. Because it is an average minimum capacity value, it can differ significantly from the actual total capacity of individual cells of that particular type (a difference of as much as 20% has been observed); and, accordingly, the total capacity value of a battery incorporating the cell or cells can also differ significantly from the actual total capacity of that battery. This difference can have a very significant negative impact on the accuracy of the fuel gauging.
Recognizing the inadequacies of basing a determination of remaining battery capacity on the “nominal value” provided by the vendor of the battery cell, it is known that the battery should be periodically calibrated in order to increase the accuracy of the fuel gauging. The calibration process, in effect, endeavors to accurately determine the actual total capacity of the battery at the specific time that the calibration is performed so that the calibrated value maybe used by the mobile phone or other electronic device to more accurately calculate the remaining battery capacity.
One well-known calibration procedure is based on the ageing of the battery. Specifically, it is well-known that the total capacity of a battery degrades as an effect of ageing; and to calibrate a battery using this procedure, the electronic device monitors the ageing process and adjusts the total battery capacity value as a function of battery ageing for use when calculating the remaining capacity of the battery.
Usually, the ageing of a battery is estimated by the electronic device based upon the number of completed charging cycles. Such an estimate, however, is only a rough estimate (a straight line estimate) and is not very accurate. In actuality, the effect of ageing is different for each individual battery and varies depending on a number of factors including temperature and usage intensity. In general, battery ageing is a very unpredictable process and current battery ageing estimations are not sufficient to provide an accurate measure of remaining battery capacity; and, hence, prevent an accurate estimation of remaining operational time of a device using the battery.
Various other procedures for calibrating a battery for a mobile telephone are known. These procedures are typically required to be initiated by the user of the telephone. In addition, if no dedicated hardware is added to the phone, the calibration procedure can take a very long time; and, since the phone normally cannot be used during the procedure, this can be a great inconvenience to the user. For example, in known calibration procedures, a fully charged battery is usually used. The battery is discharged completely while measuring the current and time; i.e., the capacity withdrawn from the battery, so as to provide a measure of the total capacity of the battery. Inasmuch, however, as mobile telephones may have a standby time of hundreds of hours, such a calibration procedure may require as much as several days.
SUMMARY OF THE INVENTION
The present invention provides a method and apparatus for calibrating a battery used, for example, to power a mobile terminal, such as a mobile telephone, or another electronic device.
A method for calibrating a rechargeable battery for an electronic device according to the present invention comprises the steps of charging the battery by a charging process, determining a total amount of charge accepted by the battery during the charging process, and providing a value of total battery capacity of the battery based, at least in part, on the total amount of charge accepted by the battery.
With the present invention, an accurate calibration of the battery can be carried out in a relatively short period of time during charging of the battery. For example, mobile telephones manufactured by the assignee of the present invention charge batteries using a fast charging algorithm, such that a complete charging cycle typically lasts no more than 1-2 hours. With the present invention, therefore, the battery can also be accurately calibrated in this period of time. In general, it is contemplated that a calibration according to the present invention will be carried out automatically during a typical overnight charging cycle so as to minimize possible inconvenience to the user.
According to a presently preferred embodiment of the invention, the step of determining a total amount of charge accepted by the battery comprises determining the net current fed into the battery during the charging process and the duration of the charging process; from which information, the total amount of charge accepted by the battery can be readily calculated.
The net current
Andersson Rickard
Carlson Jeremy
Demers David
Evers Petrus
Forsberg Charles
Jenkens & Gilchrist P.C.
Telefonaktiebolaget LM Ericsson (publ)
Tso Edward H.
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