Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
1999-06-30
2002-06-25
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S081000, C702S117000, C702S124000, C702S177000, C702S182000, C702S187000
Reexamination Certificate
active
06411911
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for monitoring and diagnosing the health or status of a battery in an electrical system. More particularly, it is concerned with a method for determining a battery's reserve time by comparing normalized battery voltage and time measurements monitored during a battery discharge to a universal normalized discharge curve.
BACKGROUND OF THE INVENTION
A battery is a device used to store electrical energy. As used herein, the term battery will include both a singular device used to store electrical energy as well as multiple storage devices connected in an array or other configuration to provide additive storage capacity. The process of storing electrical energy or power into a battery is referred to as charging the battery. Conversely, the process of removing or using the stored electrical energy from a battery is referred to as discharging the battery. The total amount of energy that can be stored in a battery, i.e. a battery's total capacity, depends on the type, size, and condition of the battery. The amount of electrical energy stored in a battery is typically referred to as a battery's capacity (Q) and is measured in units of ampere-hours (AH). The unit ampere-hours is indicative of the inverse relationship between a battery's remaining capacity or reserve time and the current being supplied by the battery. Specifically, the greater the current being supplied by the battery, the faster the battery discharges, and thus, the shorter the time the battery can supply such current before completely discharging its stored capacity of electrical energy. Conversely, the smaller the current supplied, the slower the battery discharges, and the longer the battery can supply such current before becoming completely discharged.
As electrical devices and systems have become increasingly prevalent in consumer and industrial applications, there has been a corresponding increase in the use of batteries. The uses of batteries to supply electrical power are as varied as the electrical devices and systems in which they are used. Some electrical systems, such as portable electronic devices, use a battery as their primary source of electrical energy. Other electrical systems or devices receive their primary supple, of electrical power from a power source such as a generator, power plant, or line power supply. Even these devices often utilize a battery, however, as a back-up or secondary supply of electrical power. In such battery-backed systems, if the primary power source fails, the battery can be used to supply electrical power until the primary power supply is reinstated. This scheme of redundant power sources is often utilized in electrical devices or systems in which a temporary loss of power is problematic. Such systems include very complex as well as relatively simple applications. Examples include alarm clocks, where a loss of power could result in the clock losing track of the proper time thus resulting in a false or a late alarm; computers, where an untimely loss of power could result in lost data; and telecommunications systems, where a loss of power could result in a shutdown of communications networks.
Since a battery can only store a limited amount of electrical energy, once that energy has been exhausted the battery will no longer be able to supply electrical power to the electrical system or device. For any electrical device, then, knowing how much battery capacity remains is a convenient feature since a battery's remaining capacity determines the battery's reserve time, i.e., how much longer before the battery supply is exhausted and thus how much longer the electrical device or system may be used. In electrical systems which require an uninterrupted power supply, determining when the batterypower supply will be exhausted may not only be a convenient feature, but such capability may be a critical system design feature. In order to ensure an uninterrupted power supply, the remaining battery capacity or reserve time must be accurately predicted such that either the primary power supply can be restored to service, or another alternative power supply can be connected, before the battery power supply is exhausted.
It should be noted that the total amount of energy that can be stored in a battery, i.e. a battery's total capacity, is not constant. A battery's capacity depends not only on the type and size of the battery, but also on the condition of the battery (i.e., age of the battery and its operating environment during its life). For example, the life of a lead acid battery is greatly affected by the temperature of the environment. Moreover, all batteries slowly begin an aging process which results in a continuing decrease in a battery's available capacity and in other performance characteristics. This deterioration in a battery's performance is typically caused by an increase of internal resistance in the battery caused by water loss, grid corrosion/deterioration, bad cells, or other deleterious means. Often, harsh operating environments, such as environments with high temperatures, can accelerate the deterioration of battery performance over time. As a result of the battery's changing total capacity, the battery should be routinely monitored to determine its capacity or reserve time in order to ensure that the battery will have sufficient capacity to support the electrical system if and when necessary.
In systems that rely on batteries to supply electrical power, either as the primary or secondary power supply, battery performance is counted on and therefore must be reliable. In those electrical devices or systems in which a temporary loss of power is problematic ensuring proper battery performance can be a critical system design feature. In many systems that utilize a battery, the system is specifically designed with the capability to monitor the condition or health of the battery. Some systems incorporate a capacity indicator, or “fuel gauge,” which shows the available battery capacity. By knowing the system's power requirements, this fuel gauge allows one to determine if the battery has sufficient capacity to support the system for a sufficient time before the primary power is reinstated. Moreover, such a fuel gauge can be useful during a battery discharge to determine how much battery capacity remains and thus how much reserve time the battery has left.
Certain methods and apparatus are available for determining the condition of a battery. Typically, these methods involve monitoring certain battery parameters during a battery discharge which are indicative of the battery's performance in order to determine the remaining capacity (Q) and reserve time (t) of the discharging battery. The initial method used for predicting remaining battery life is strictly empirical, wherein extensive testing of the battery is conducted in order to compile a large database of characteristics indicative of the battery's performance throughout the cycle of the battery from a fully charged state to a fully discharged state. By comparing these predetermined test characteristics to the battery's actual characteristics, as measured during use, one can predict what stage of discharge the battery is in and thus how much battery capacity or reserve time remains.
For this empirical method to yield accurate and reliable results, however, the initial testing has to account for a multitude of factors which could affect the battery's performance. This means the testing must be performed under conditions matching the actual use of the battery as closely as possible. Not only does this mean testing has to be performed for each type and size battery individually, but also the testing should include other external variables such as the load on the battery as well as the battery's temperature and environment (all factors which can affect the battery's performance characteristics). The result is that there are innumerable combinations of such factors which would have
Hirsch Marc Daniel
Mathiesen Gregory W.
Ng Patrick Kwok-Yeung
Hoff Marc S.
Locke Liddell & Sapp LLP
Tsai Carol S. W.
Tyco Electronics Logistics AG
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