Electricity: battery or capacitor charging or discharging – Battery or cell discharging – With charging
Reexamination Certificate
2000-10-19
2001-11-06
Wong, Peter S. (Department: 2838)
Electricity: battery or capacitor charging or discharging
Battery or cell discharging
With charging
Reexamination Certificate
active
06313609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to batteries and, more particularly, to determining the remaining capacity of a battery.
2. Related Art
Sudden cardiac arrest has been attributed to over 350,000 deaths each year in the United States, making it one of the country's leading medical emergencies. Worldwide, sudden cardiac arrest has been attributed to a much larger number of deaths each year. One of the most common and life threatening consequences of a heart attack is the development of a cardiac arrhythmia, commonly referred to as ventricular fibrillation. When in ventricular fibrillation, the heart muscle is unable to pump a sufficient volume of blood to the body and brain. The lack of blood and oxygen to the brain may result in brain damage, paralysis or death to the victim.
The probability of surviving a heart attack or other serious heart arrhythmia depends on the speed with which effective medical treatment is provided. If prompt cardiopulmonary resuscitation is followed by defibrillation within approximately four minutes of the onset of symptoms, the probability of survival can approach or exceed fifty percent. Prompt defibrillation within the first critical minutes is, therefore, considered one of the most important components of emergency medical treatment for preventing death from sudden cardiac arrest.
Cardiac defibrillation is an electric shock that is applied to the victim to arrest the chaotic cardiac contractions that occur during ventricular fibrillation, and to restore a normal cardiac rhythm. To administer such an electrical shock to the heart, defibrillator pads are placed on the victim's chest, and an electrical impulse of the proper magnitude and shape is administered to the victim through the pads. While defibrillators have been known for years, they have typically been complicated, making them suitable for use by trained personnel only.
Recently, portable and transportable automatic and semi-automatic external defibrillators (generally, AEDs) for use by first responders have been developed. A portable defibrillator allows proper medical care to be given to a victim earlier than preceding defibrillators, increasing the likelihood of survival. Portable AEDs may be brought to or stored in an accessible location at a business, home, aircraft or the like, available for use by first responders. With recent advances in technology, even a minimally trained individual can operate conventional portable defibrillators to aid a victim in the critical first few minutes subsequent to the onset of sudden cardiac arrest.
Portable defibrillators require a portable energy source to operate in the anticipated mobile environments. Typically, AEDs utilize battery packs as the portable energy source. Several manufacturers have provided battery packs for use in portable defibrillators, such as a sealed lead acid (SLA) battery, a nickel cadmium (NiCd) battery, a lithium ion (Li) battery, and the like.
AEDs can remain unused in their storage area for hours, days or even weeks without having been tested or otherwise maintained, and months or even years without actually being used. During such extended periods of time, the installed battery may discharge significantly and have insufficient energy to charge the AED during use. Thus, to ensure reliable AED operations, it is important that the condition of the installed battery be determined during use. The user can then determine when to replace the battery.
A conventional technique for measuring remaining battery capacity is commonly referred to as a battery fuel gauge. With this technique, a battery monitoring circuit measures the current output from the battery during use, and, in the case of rechargeable batteries, the current input to the battery during charging cycles. The battery monitoring circuit determines the remaining capacity of the battery based on a tally of the cumulative input and output currents.
A drawback to this approach is that this approach requires the use of an expensive, low-power analog and digital circuit designed to monitor the battery continually to calculate self-discharge quantities during the storage of the device. Another significant drawback is that the requisite current sensor is lossy, reducing the efficiency of the device. Furthermore, due to risks commonly associated with such a technique, a supplemental measurement technique is often implemented concurrently. In addition, the test device must be re-calibrated periodically to adjust for changes in the battery capacity over the cycle life of a rechargeable battery.
SUMMARY OF THE INVENTION
The present invention is a system and associated methodology for quickly and accurately determining a remaining capacity of a battery. The present invention measures battery terminal voltage during each application of one or more constant power loads to the battery, and compares either the measured voltage, or an internal impedance calculated from the measured voltage, with a pre-characterization of the relationship between battery capacity and battery voltage or impedance for the given battery and test conditions. This relationship may be obtained from data provided by the battery manufacturer, derived empirically or otherwise determined. This relationship may be represented by data stored in memory or by a mathematical function implemented in hardware, software, firmware or a combination thereof.
There are a number of advantages associated with the present invention. For example, the approach of the present invention does not require the use of a current sensor, thereby avoiding the associated losses. In addition, the present invention is considerably less expensive and easier to implement than conventional approaches since no circuit is required to be added to the battery to monitor self discharges, nor does the present invention need to be re-calibrated over the life of the battery. A particular benefit is provided when the present invention is implemented in devices also having a constant power source. One such device is an AED in which a constant power capacitor charger is implemented. In such devices, the existing charger controller can be utilized to draw constant power while terminal voltage is measured.
A number of aspects of the invention are summarized below, along with different embodiments that may be implemented for each of the summarized aspects. It should be understood that the summarized embodiments are not necessarily inclusive or exclusive of each other and may be combined in any manner in connection with the same or different aspects that are non-conflicting and otherwise possible. These disclosed aspects of the invention, which are directed primarily to systems and methodologies for determining the capacity of a battery, are exemplary aspects only and are also to be considered non-limiting.
In one aspect of the invention, a battery capacity tester for determining a remaining capacity of a battery is disclosed. The tester applies one or more constant power loads to the battery and determines the battery capacity associated with a selected one of either a measured battery voltage or calculated battery impedance based on a pre-characterized relationship between battery capacity and the selected voltage or impedance.
In one embodiment, one predetermined constant power load is applied. In this embodiment, the tester determines the remaining battery capacity based on the pre-characterized relationship between battery voltage and battery capacity for similar batteries under similar test conditions. In one embodiment, the battery capacity tester includes a constant power source that applies the predetermined constant power load. A battery characterizer measures the battery voltage during the constant power draw, and determines the remaining battery capacity based on the pre-characterized relationship between battery voltage and capacity, wherein the pre-characterized relationship corresponds to batteries having similar characteristics under similar test conditions. Such similar
Tibbits Pia
Wong Peter S.
LandOfFree
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