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USAGE BASED LOW BATTERY INDICATION METHOD AND SYSTEM

IP.com Disclosure Number: IPCOM000029317D
Publication Date: 2004-Jun-23
Document File: 7 page(s) / 38K

Publishing Venue

The IP.com Prior Art Database

Abstract

The invention relates to a method for determining the coulomb consumption and remaining coulomb capacity of a battery. The method starts with the coulomb capacity of the battery at the time of manufacture and subtracts off the coulombs that are consumed over the life of the battery. Determination of the coulomb consumption is accomplished by tracking the mode of operation, the duration of the time in that mode, and the temperature of the device at time of operation. From the known temperature-dependent characteristics, a nominal temperature-corrected coulomb consumption is computed. The remaining life of a battery is determined by subtracting the accumulated coulomb consumption from the initial battery.

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USAGE BASED LOW BATTERY INDICATION METHOD AND SYSTEM

Christopher Osterloh, Christopher Nagy, Thierry Chatroux

ITRON, Inc., Waseca, MN

ABSTRACT

The invention relates to a method for determining the coulomb consumption and remaining coulomb capacity of a battery. The method starts with the coulomb capacity of the battery at the time of manufacture and subtracts off the coulombs that are consumed over the life of the battery.  Determination of the coulomb consumption is accomplished by tracking the mode of operation, the duration of the time in that mode, and the temperature of the device at time of operation.  From the known temperature-dependent characteristics, a nominal temperature-corrected coulomb consumption is computed.  The remaining life of a battery is determined by subtracting the accumulated coulomb consumption from the initial battery.

FIELD OF THE INVENTION

            The present invention relates generally to the field of battery-powered monitoring systems, and in particular to the determination of the energy capacity of a battery.

BACKGROUND OF THE INVENTION

Recently, low power transmitters have found application in utility meters and similar devices for the remote or automatic polling of metered energy provided by utilities. Often, the transmitters are battery powered, thus requiring periodic replacement of the batteries.  To maximize their use, it is preferable to replace the battery on an as-needed basis, as opposed to replacing it on a fixed schedule.

The conventional method  to determine whether a battery is ready for replacement is to monitor its open circuit or partial load voltage.  Once the battery voltage drops below a pre-determined threshold potential, it is earmarked for replacement.  However, certain batteries, such as a Li-SOCl­2 battery, are designed to maintain a nearly constant voltage over the operable life of the battery, with a sudden and drastic drop in voltage as the coulomb capacity of the battery is exhausted (see FIG. 1).  Because of the precipitous drop in voltage at the end of the life of the battery, detecting the battery before it becomes inoperative requires frequent polling intervals, as well as prompt replacement once detected.  This requires the increased involvement of maintenance personnel, with attendant costs, both in the detection and the ready replacement of the batteries.

SUMMARY OF THE INVENTION

The present invention relates to a method for determining the energy consumption and remaining energy capacity of a Li-SOCl2 battery or a battery with a similar output characteristic.  With standard nickel cadmium or alkaline batteries, the voltage of the battery decreases steadily as the coulomb capacity of a battery is consumed.  Because the decrease in voltage is gradual over time, there is no concern that the battery will become inoperative between reasonable polling intervals.  However, with Li-SOCl2 batteries, catching the battery before it becomes inoperative requi...