WO2014100937A1

WO2014100937A1 - Method for monitoring battery gas pressure and adjusting charging parameters

Info

Publication number: WO2014100937A1
Application number: PCT/CN2012/087298
Authority: WO
Inventors: Marlon Galsim; Damir Klikic
Original assignee: Schneider Electric It Corporation
Priority date: 2012-12-24
Filing date: 2012-12-24
Publication date: 2014-07-03

Abstract

Disclosed are methods and apparatus for safely charging a battery and for determining when the battery should be replaced. In one embodiment a method for charging a battery includes monitoring a dimensional parameter of a case of the battery and adjusting a parameter of a battery charging algorithm for the battery responsive to a change in the dimensional parameter of the case of the battery.

Description

METHOD FOR MONITORING BATTERY GAS PRESSURE AND ADJUSTING CHARGING PARAMETERS

BACKGROUND

1. Field of the Disclosure

The present disclosure is directed generally to methods and apparatus for the charging of batteries, in particular to systems and methods of measuring one or more indicators such as pressure within a battery and/or temperature of a battery and adjusting one or more charging parameters for the battery in response to the measured indicator(s).

2. Related Art

The use of uninterruptible power supply (UPS) systems to provide regulated, uninterrupted power for sensitive and/or critical loads, such as computer systems and other data processing systems, is known. A number of different UPS products are available including those identified under the trade name Smart-UPS^® from American Power Conversion Corporation (APC) of West Kingston, Rhode Island. In a typical UPS, a battery is used to provide backup power for a critical load during blackout or brownout conditions. Some examples of UPS systems include flooded cell lead-acid batteries that are used to provide back-up power. It has been observed that in certain environments, flooded cell lead-acid batteries may provide reduced backup time and may experience mechanical or electrochemical degradation, ultimately resulting in battery failure, as the batteries age and/or experience multiple charge and discharge cycles.

One example of a conventional charge profile (also referred to herein as a battery charging algorithm) utilized by some battery chargers for charging flooded cell lead-acid batteries is illustrated in FIG. 1. The charge profile of FIG. 1 includes three regions of operation, as is typically recommended by battery manufacturers for flooded cell lead-acid batteries. In the first region, termed the constant current region (CC region 10), the battery charging current is substantially constant. In the CC region 10, the voltage across the terminals of the battery increases as charge is added to the battery. After the battery voltage reaches a certain level (VBOOST) at time 15, the profile changes to a second region of operation in which the voltage applied across the battery terminals is held constant. This region of operation is termed the constant voltage region (CV region). The CV region is divided in to two parts, namely, a boost region 20 and a float region 30. In the boost region 20, the charging voltage is maintained at a higher level than the open circuit voltage of the battery. After a predetermined amount of time in the boost region 20, terminating at time 25, the voltage applied across the terminals of the battery is reduced to a second level (VFLOAT) and the charge profile enters the float region 30. The charger maintains the battery in a constant voltage charge mode at the VFLOAT voltage level until the battery is needed to provide back-up power.

There is a second type of conventional charging profile (not illustrated), in which the charging profile stays in the CC region until the battery voltage just touches the boost region voltage level, at which point the voltage applied by the charger is reduced to the float region voltage. Charging at the float region voltage may cause limited evaporation of electrolyte, but the charging is slow.

SUMMARY

In accordance with an aspect of the present disclosure there is provided a method of charging a battery. The method comprises monitoring a dimensional parameter of a case of the battery and adjusting a parameter of a battery charging algorithm for the battery responsive to a change in the dimensional parameter of the case of the battery.

In accordance with some embodiments adjusting the parameter of the battery charging algorithm comprises adjusting one of a float region voltage and a charge current limit.

In accordance with some embodiments adjusting the parameter of the battery charging algorithm comprises adjusting the parameter of the battery charging algorithm from a first level to a second level responsive to the dimensional parameter exceeding a first value and further adjusting the parameter of the battery charging algorithm from the second level to a third level responsive to the dimensional parameter exceeding a second value, the second value being greater than the first value.

In accordance with some embodiments the method further comprises adjusting the parameter of the battery charging algorithm to an intermediate level intermediate between the first level and the second level responsive to the dimensional parameter having an intermediate value between the first value and the second value.

In accordance with some embodiments the intermediate level is intermediate between the first level and the second level to a degree proportionate to a degree to which the intermediate value is intermediate between the first value and the second value.

In accordance with some embodiments the method further comprises disabling charging of the battery responsive to the dimensional parameter exceeding a third value.

In accordance with some embodiments the method further comprises providing an estimated remaining life of the battery calculated from the dimensional parameter, a temperature of the battery, and a number of discharge cycles which the battery has undergone.

In accordance with another aspect of the present disclosure there is provided a method of charging a battery. The method comprises monitoring a gas pressure within the case of a battery and adjusting a parameter of a battery charging algorithm for the battery responsive to a change in the gas pressure within the case of the battery, the parameter including one of a float region voltage and a charge current limit.

In accordance with some embodiments monitoring the gas pressure within the case of the battery comprises monitoring a dimension of the case of the battery.

In accordance with some embodiments adjusting the parameter of the battery charging algorithm comprises adjusting the parameter of the battery charging algorithm from a first level to a second level responsive to an indication of the gas pressure exceeding a first value and further adjusting the parameter of the battery charging algorithm from the second level to a third level responsive to an indication of the gas pressure exceeding a second value, the second value being greater than the first value.

In accordance with some embodiments the method further comprises adjusting the parameter of the battery charging algorithm from the second level to a third level responsive to an indication of the gas pressure exceeding a third value, the third value being greater than the second value.

In accordance with some embodiments the method further comprises monitoring a number of discharge cycles of the battery and providing a prediction of a remaining life for the battery using an algorithm including the gas pressure within the case of the battery and the number of discharge cycles as input parameters.

In accordance with some embodiments the method further comprises measuring a temperature of the battery and including the measured temperature as an input parameter in the algorithm.

In accordance with another aspect of the present disclosure there is provided a battery monitoring apparatus. The apparatus comprises a sensor coupled to a case of the battery and configured to provide an indication of a change in a dimension of the case of the battery and a control system configured to adjust a parameter of a battery charging algorithm for the battery responsive to the indication of the change in the dimension of the case of the battery.

In accordance with some embodiments the control system is configured to effect a first adjustment in the parameter of the battery charging algorithm responsive to an indication of the change in the dimension of the case of the battery exceeding a first value and to effect a second adjustment in the parameter of the battery charging algorithm responsive to an indication of the change in the dimension of the case of the battery exceeding a second value, the second value being greater than the first value.

In accordance with some embodiments the control system is further configured to effect a third adjustment in the parameter of the battery charging algorithm responsive to an indication of the change in the dimension of the case of the battery exceeding a third value, the third value being greater than the second value.

In accordance with some embodiments the sensor is one of a capacitive sensor, a piezoelectric film sensor, and a resistive strain gauge sensor. In accordance with some embodiments the apparatus further comprises a battery temperature sensor.

In accordance with some embodiments the control system is configured to further adjust the parameter of the battery charging algorithm responsive to a signal provided from the temperature sensor.

In accordance with some embodiments the apparatus further comprises a user interface configured to notify a user of an end of a useful life of the battery.

BRIEF DESCRIPTION OF DRAWINGS

Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the disclosure. Where technical features in the figures, detailed description or any claim are followed by references signs, the reference signs have been included for the sole purpose of increasing the intelligibility of the figures, detailed description, and/or claims. Accordingly, neither the reference signs nor their absence are intended to have any limiting effect on the scope of any claim elements. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

FIG. 1 is an illustration of a conventional charge profile for a battery;

FIG 2 is a schematic diagram of one example of a UPS system;

FIG. 3 is an image of batteries which have undergone swelling;

FIG. 4 is an image of a battery which has undergone swelling;

FIG. 5 is a chart of parameters of a battery charging algorithm in accordance with an aspect of the present disclosure;

FIG. 6 is a flowchart of a method in accordance with an aspect of the present disclosure; FIG. 7 is a block diagram of a system in accordance with an aspect of the present disclosure;

FIG. 8A is an isometric view of a capacitive sensor in accordance with an aspect of the present disclosure;

FIG. 8B is an exploded view of the capacitive sensor of FIG. 8A;

FIG. 9 is a perspective view of a battery with a sensor attached in accordance with an aspect of the present disclosure;

FIG. 10 illustrates a battery and sensor disposed in a battery compartment of an apparatus in accordance with an aspect of the present disclosure;

FIG. 11A is an exploded view of an embodiment of a capacitive sensor configured to be coupled to a battery;

FIG. 1 IB is an image of capacitive sensors as illustrated in FIG. 11A attached to two different battery packs; and

FIG. 12 illustrates a battery disposed in a battery compartment and a sensor coupled to an external surface of the battery compartment of an apparatus in accordance with an aspect of the present disclosure.

DETAILED DESCRIPTION

This disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The aspects and embodiments disclosed are capable of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," "having," "containing,"

"involving," and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.

Aspects and embodiments of the present disclosure are generally directed to systems and methods for the charging of batteries and for the adjustment of charging parameters to facilitate safe operation of a battery charger. Aspects and embodiments of the present disclosure also include methods and apparatus for determining a remaining useful life of a battery. As used herein the "remaining useful life" of a battery may be expressed in absolute time, an estimated number of remaining functional discharge and/or charge cycles achievable, and/or an estimate of a remaining amount of power which the battery may either supply while discharging or be supplied with while charging.

Some embodiments disclosed herein are specific to lead-acid batteries used in conjunction with UPS systems, however, the methods and charging systems disclosed may be applied to any of a number of battery types, for example, sealed maintenance- free batteries, nickel-cadmium batteries, nickel-metal hydride batteries, and lithium ion batteries. The methods and charging systems disclosed may be applied to any of a number of systems employing batteries, for example, UPS systems, automobiles, and consumer electronic devices.

Referring to FIG. 2, there is illustrated an example of a UPS 201 that may utilize a method of battery charging according to embodiments of the present disclosure. The UPS 201 includes an inverter 200 coupled to a power line 202 of an AC power system. The UPS 201 includes an AC input line coupled to the power line 202 which receives an input voltage 220 (and current) via a transfer relay 204. The UPS 201 further includes a transformer 208, a battery 212, and an inverter relay 218. The inverter 200 includes a plurality of diodes 210 functioning as a rectifier, and a plurality of Field Effect Transistors (FETs) 216. The inverter 200 switches between the battery backup state and the battery charging state of operation based on whether the AC input power can support a connected load. When the transfer relay 204 is closed, the input voltage 220 is coupled through the power line 202 to supply an output voltage 206 to a load (not shown). The input voltage 220 is also provided via the transformer 208 to the inverter 200 when the inverter 200 is in the battery charging state of operation, charging the battery 212. When the input voltage 220 goes out of tolerance the transfer relay 204 opens and the inverter 200 transitions from the charger state to the battery state.

The UPS 201 may also include a controller 203. Using data stored in associated memory, the controller performs one or more instructions that may result in manipulated data, and the controller monitors and controls operation of the UPS 201. The controller 203 may direct embodiments of the battery charging methods described in this disclosure. In some examples, the controller may include one or more processors or other types of controllers. In one example, the controller is a commercially available, general purpose processor. In another example, the controller performs a portion of the functions disclosed herein on a general purpose processor and performs another portion using an application-specific integrated circuit (ASIC) tailored to perform particular operations. Examples in accordance with the present disclosure may perform the operations described herein using many specific combinations of hardware and software and the disclosure is not limited to any particular combination of hardware and software components.

The UPS 201 may also include data storage 205. The data storage stores computer readable and writable information required for the operation of the UPS 201. This information may include, among other data, data subject to manipulation by the controller and instructions that are executable by the controller to manipulate data. The data storage may be a relatively high performance, volatile, random access memory such as a dynamic random access memory (DRAM) or static memory (SRAM) or may be a nonvolatile storage medium such as magnetic disk or flash memory. In one example, the data storage includes both volatile and non-volatile storage. A user of the UPS is able to configure and control the UPS either through a computer coupled to the UPS or using through a user interface of the UPS itself.

Many battery chargers, for example, those included in many UPS devices, provide pre-defined or fixed charging parameters for a battery charging algorithm which are utilized regardless of the age or condition of a battery being charged. A same predefined charging voltage and/or current is applied to a battery during periods of charging throughout the entire life of the battery. These battery chargers do not monitor a battery being charged for symptoms indicative of battery deterioration or potential battery failure. Charging of a battery exhibiting indicators of deterioration with a charging algorithm designed for fresh new batteries, however, may result in reduced battery life, non-serviceable equipment due to battery swelling or bloating, or safety hazards due to rupture of a battery case and resultant leakage of acid and/or battery gas explosion. - Si -

Responsive to indicators of battery deterioration such as number of charge and/or discharge cycles performed, elevated battery temperature, and/or battery gas build-up, it may be desirable to adjust parameters of a battery charging algorithm from those which would be utilized with a fresh new battery. The adjustment of these parameters to parameters more appropriate to a battery exhibiting such indicators of aging or deterioration may, for example, facilitate extension of the life of the battery and/or reduce the potential for catastrophic failure of the battery.

Aspects and embodiments of the present disclosure may facilitate safe battery charging by providing for the early detection of predictive indicators of imminent battery failure. Various aspects and embodiments of a battery charger algorithm in accordance with the present disclosure adjust charging parameters for a battery responsive to predictive indicators of imminent battery failure such as a number of charge and/or discharge cycles experienced, a level of battery gas build-up, and operating temperature. These aspects and embodiments may improve battery service life and provide controlled battery operation up to the end of the useful life of the battery and may provide an indication of when a battery has reached end-of-life.

Aspects and embodiments of the present disclosure may improve battery life cycle, provide for controlled battery end-of-life operation and soft failure, and/or reduce the potential for accidents caused by battery explosion or leakage by monitoring the battery gas pressure and adjusting the battery charging parameters responsive to an indication of battery gas pressure buildup. Aspects and embodiments of the present disclosure may provide automatic control of the battery charging parameters by monitoring battery failure parameters through continuous battery life profiling. Aspects and embodiments of the present disclosure may provide a method to alarm/warn a user of the need to replace the battery. Aspects and embodiments of the present disclosure may provide for accurate measurement of battery gas buildup by monitoring swelling of a battery. As used herein "swelling" of a battery refers to a change in a dimensional parameter of a battery, for example, displacement of a portion of the case of a battery from an original position due to, for example, pressure buildup within the battery case. Some aspects and embodiments of the present disclosure may be sensitive to battery swelling or a change in a dimensional parameter of a battery of less than about 0.5 mm.

Some embodiments of systems disclosed herein can constantly monitor gas pressure within a battery and automatically adjust parameters of a charging algorithm of a battery charger for the battery in response to changes in the battery gas pressure.

Some embodiments of systems disclosed herein can combine the continuous monitoring of battery gas pressure, temperature, and the number of battery charge and/or discharge cycles to determine safe battery charging parameters and adjust a battery charging algorithm accordingly.

In accordance with some embodiments accurate measurement of battery gas pressure buildup may be achieved using a low cost capacitive pressure sensor.

Some embodiments of systems disclosed herein can generate a battery life span profile and provide advanced warning of battery failure symptoms.

Some embodiments of systems disclosed herein can provide accurate predictions of imminent battery failure and warn a user of the need to replace a battery before the battery becomes a safety hazard.

Some embodiments of systems disclosed herein can provide adequate battery charging when the battery is nearing end of life by adjusting charging parameters to reduce the rate of the battery swelling, thereby extending the operating life of the battery without the risk of explosion.

Excessive charging of a battery, such as a lead-acid battery including a sulfuric acid electrolyte, electrolyzes some of the electrolyte, producing a hydrogen and oxygen gas mixture. This phenomenon is referred to herein as "gassing." The accumulation of hydrogen and oxygen gas inside the battery increases pressure inside the battery casing. The pressure buildup can deform the battery casing. FIGS. 3 and 4 illustrate batteries which have cases which have undergone swelling due to the pressure buildup within the battery. Battery swelling is a safety hazard since excessive battery pressure build-up may cause the battery casing to explode, releasing a flammable mixture of hydrogen and oxygen gas as well as toxic electrolyte such as sulfuric acid. Further, an explosion of a battery casing can turn mechanical parts of a battery into projectiles that can cause injuries. Gas pressure buildup within a battery can be determined by using a pressure sensor. Such a sensor may be included within the battery casing. Alternatively, a sensor may be attached to an external wall of the battery casing or to a wall of a compartment in which the battery is housed to monitor changes in the dimensions of the wall of the battery casing associated with battery swelling. Such sensors, which can accurately determine the gas pressure buildup, include, for example, capacitive plate sensors, piezoelectric film sensors, and resistive strain gauge sensors.

FIG. 5 is graph of how parameters of a battery charging algorithm may be modified responsive to indicia of battery pressure buildup sensed by a battery pressure sensor in accordance with aspects of the present disclosure. During an initial time period where no significant amount of battery swelling has occurred, the battery charger algorithm may utilize a charging current limit (corresponding to the battery current in the CC region of FIG. 1) set at an initial level 525 and a charging float level voltage (corresponding to VFLOAT in FIG. 1) set at an initial level 505. Responsive to the battery exhibiting a first amount of swelling reaching or exceeding a first value A, which in some embodiments may be a displacement of a wall of the battery from an initial value prior to swelling by about 0.5 mm for a conventional lead-acid battery, the charging current limit and/or charging float level voltage may undergo a first adjustment to provide a less aggressive charging algorithm. As the battery swells from a swelling level having the first value A to a swelling level having the second value B, the charging current limit may be adjusted from the first level 530 (which may be substantially the same or the same as the initial level 525) to a second level 535, and the charging float level voltage may also be decreased from the first level 510 (which may be substantially the same or the same as the initial level 505) to a second level 515. In some embodiments, second swelling value B may correspond to about 1.0 mm of swelling (for example, a displacement of a wall of the battery of about 1.0 mm from an initial value prior to swelling) for a conventional lead-acid battery. In some embodiments, the second value B may corresponds to an amount of swelling at which it is expected that the battery can still operate adequately to supply a desired runtime to an applied load. The charging current limit and/or charging float level voltage may be adjusted downward linearly to intermediate levels between the levels indicated with respect to an increase in observed battery swelling as illustrated, however, these parameters may alternatively be adjusted in a step wise fashion or in a geometrical or exponential relationship with respect to the increase in observed battery swelling.

After the observed battery swelling reaches or exceeds the second value B, the charger controller will make a second adjustment to the charging floating voltage and/or charging current limit and operate the battery charger using a charging algorithm designed to provide controlled end of life operation of the battery. In the controlled end of life charging algorithm, the battery charging current may be set to a third level, for example, a low level 535 to provide adequate charging while reducing the rate of the battery swelling. Similarly, responsive to the observed battery swelling reaching or exceeding the second value B, the charging floating voltage may be decreased with increasing battery swelling from the second level 515 to the third level 520. This operation can extend the operating life of the battery without the risk of explosion.

Responsive to the battery swelling reaching or exceeding a third value C, for example, a swelling of about 1.5 mm (for example, a displacement of a wall of the battery of about 1.5 mm from an initial value prior to swelling) for a conventional lead-acid battery, the battery charger controller will perform a third adjustment in the charging floating voltage and/or charging current limit. For example, responsive to the battery swelling reaching the third value C, the battery charger controller may rapidly decrease the charging floating voltage from the third level 520 and/or the charging current limit from the third level 540 (which may be substantially the same or the same as the second level 535) with increased battery swelling. The battery charger controller will shutdown the battery charger power (points 545, 550) upon detection of a maximum allowable battery swelling corresponding to fourth level D, and disconnect power from the battery.

FIG. 7 illustrates a battery charging system, indicated generally at 700, in accordance with an aspect of the present disclosure. The system 700 monitors and controls the charging of a battery 710. The system 700 is provided with a source of input power 715, for example, alternating current (AC) electrical power from an electrical outlet. The source of input power is electrically connected to a battery charger power converter 720 which converts the AC input power to direct current (DC) if necessary and regulates the voltage and current applied to the battery 710 during charging.

A voltage and current sensor 775 may be provided external to the battery charger power converter 720 or internal to the battery charger power converter 720. The voltage and current sensor 775 monitors the current and voltage supplied to the battery 710 and in some aspects is also used to detect and record the number of battery charge/discharge cycles of the battery. The data regarding the number of battery charge and/or discharge cycles may be utilized together with an indicator of the battery gas pressure build-up as an input parameter in a battery life calculation algorithm or to calculate a desired level of one or more battery charging algorithm parameters.

The voltage and current sensor 775 also monitors the magnitude of the charging voltage and current and provides an indicator of these parameters to the battery charger controller 750, in some aspects through an analog-digital signal converter (ADC) 760. The charger controller 750 compares the measured battery voltage/current sense data to reference data provided by, for example, the battery charger current/voltage reference generator 725 and adjusts the charging

voltage/current if not within the reference range.

One or more of various sensors, such as a capacitive sensor 810, a piezoelectric film sensor 815, and/or a resistive strain gauge sensor 820 may be arranged to detect swelling of the battery case. For example, the capacitive sensor 810 may include a first plate mechanically coupled to an external wall of the case of the battery and a second plate separated from the first plate by a dielectric material and mechanically coupled to a fixed object external to the battery, for example a wall of a compartment in which the battery is contained. In other embodiments, one plate of a capacitive sensor may be coupled, directly or indirectly, to a portion of a wall of the battery, for example, a central portion of a side wall of the battery casing which displaces upon battery swelling. A second plate of the capacitor may be coupled, directly or indirectly, to a portion of the battery, for example, a region proximate a corner or corners of the battery casing which do not displace significantly upon battery swelling. Swelling of the battery case will compress the capacitive sensor, bringing the first and second plates closer together and increasing the capacitance of the sensor.

A capacitive plate pressure sensor oscillator 780 will generate a signal having a frequency depending on the capacitance of the capacitive plate sensor. For example, in some aspects the increase in the battery gas pressure will result in an increase in the sensor capacitance and the capacitive plate pressure sensor oscillator will generate a lower frequency output responsive to the increase in the capacitance of the capacitive sensor 810.

A frequency counter 765 monitors the signal from the capacitive plate pressure sensor oscillator, measures the frequency of the signal, generates measurement data from the measurement of the frequency of the signal, and provides the measurement data to the battery charger controller 750. The battery charge controller 750 then determines a level of battery gas pressure build-up based on the measurement data.

The battery charge controller 750 provides a signal to the battery life indicator 740, which is a user interface that displays the actual state of the battery, for example, an estimated remaining life of the battery. The battery charge controller 750 will also notify a user for the need to replace the battery when necessary, for example, by providing an audio and/or visual indication of an alarm condition.

Piezoelectric film sensor 815 is an alternative pressure sensor that may be used in place of or in combination with the capacitive sensor 810. The piezoelectric film sensor 815, in combination with the piezoelectric film pressure sensor oscillator 785 generates a low level AC oscillation signal that depends on the deformation of the piezoelectric film sensor 815 caused by pressure or tension applied by the battery case as it swells. This signal may be monitored by the frequency counter 765 which may provide data to the battery charge controller 750 for a determination of a level of battery swelling in a similar manner as the signal from the capacitive plate pressure sensor oscillator. Resistive strain gauge film sensor 820 is an alternative pressure sensor that may be used in place of or in combination with one or both of the capacitive sensor 810 and/or the piezoelectric film sensor 815. The resistive strain gauge film sensor 820 exhibits a variation of resistance that depends on the deformation of the resistive strain gauge film sensor 820 caused by pressure applied by the battery case as it swells. An analog to digital converter 770 may measure the resistance of the resistive strain gauge film sensor 820 and convert the measurement into a digital signal that is supplied to the battery charge controller 750 for a determination of a level of battery swelling.

The battery charger current/voltage reference generator 725 generates voltage and current limit reference values for the battery charging operation. The magnitude of the reference values depends on the battery health. The battery charger current/voltage reference generator 725 provides battery charging parameters which facilitate maintaining a higher battery capacity, a longer battery runtime, and/or a larger number of remaining discharge cycles than if the battery was charged using battery charging parameters more appropriate for a new battery. The battery charger current/voltage reference generator 725 also provides battery charging parameters to facilitate adjusting the battery charging algorithm to provide for a controlled end of life battery operation and/or soft failure. These parameters may be communicated from the current/voltage reference generator 725 to other components of the system, for example, the battery charger power convertor 720. The battery charger power convertor 720 may adjust the battery charging parameters responsive to the communication from the current/voltage reference generator 725.

The reference battery life profile memory 730 is a memory bank that stores references data or one or more look-up tables which comprise a battery charging parameter matrix. The matrix points to a battery charging voltage and current that is desirably used in a battery charging algorithm for a battery displaying a degree of swelling, age (in terms of absolute age or number of charge/discharge cycles experienced), and/or temperature as measured by one or more of the battery pressure sensors 810, 815, and 820 and/or temperature sensor 795. The battery charger controller compares the measured sensor parameters to the pre-defined and stored parameters and extracts the battery charging parameters (for example, voltage/current settings) associated with the measured sensor parameters for the battery from the reference battery life profile memory 730. The battery charger controller 750 also compares the measured sensor signals to the reference battery life profile in the reference battery life profile memory 730 to determine the state of the battery.

The measured battery life profile memory 735 is a non-volatile memory bank for the storage of the measured sensor signals, generated profiles, and/or remaining battery life estimates.

The temperature sensor 795 monitors the battery temperature and/or the ambient temperature close to the battery. The battery charger controller 750 adjusts the battery charging parameters to compensate for temperature variation.

Temperature is also included in the parameter matrix to determine the state of the battery, for example, a remaining usable life of the battery.

Upon detection of a degree of swelling of the battery 710 and/or a temperature which is outside of an acceptable range, the battery charge controller 750 instructs the shutdown driver 745 to cut power to the battery charger, for example by disabling flow of power through the battery charger power converter 720. The battery charge controller 750 also instructs the battery life indicator and alarm 740 to provide an indication of the unacceptable condition of the battery and/or an indication of an end of life condition of the battery 710.

FIG. 6 illustrates a method of operating a battery charging apparatus in accordance with aspects of the present disclosure. Upon start of the method (act 605), the battery charging system is initialized. Initialization includes the calibration of the battery pressure sensor(s) (act 610). In some embodiments, calibration of a capacitive battery pressure sensor includes programming a typical capacitance versus temperature profile and capacitance values corresponding to various battery swelling thresholds (FIG. 5, swelling values A, B, C, and D) in a memory bank of the battery charge controller 750. The battery charge controller 750 will then compare the preprogrammed capacitance versus temperature profile with the actual measured value of the capacitive sensor 810. The battery charge controller 750 will compensate for any error by adjusting the capacitance values corresponding to various battery swelling thresholds proportional to the percentage of the error.

Upon starting operation with a new battery, the charger will operate in "normal mode" (act 615) with battery charging algorithm parameters set as recommended by the battery manufacturer, which may vary depending on the type of battery, or set as desired by an operator of the system. These parameters may be loaded (act 620) from a memory associated with the battery charger controller, for example, the reference battery life profile 730, or manually input by a user.

The battery charger controller 750 will continuously monitor and measure the battery pressure sensor through the ADC module 770 and/or frequency counter 765 when present (act 625). Measurement data is stored in a non- volatile memory (act 630), for example, in the measured battery life profile 735 for future processing. The battery charger controller 750 will analyze the sensor parameter(s) and generate a sensor signal profile (act 635) which may include, for example, the battery voltage, battery current, the number of charge and/or discharge cycles the battery has undergone, the temperate of the battery or of the atmosphere proximate the battery, and the battery gas pressure. The battery charger controller 750 then performs an analysis of the sensor signal profile by comparing the sensor signal profile (act 640) to the pre-programmed parameter matrix retrieved from the reference battery life profile 730 (act 645).

Responsive to a result of the sensor profile analysis, the battery charger controller 750 will generate an estimate of a remaining life of the battery (act 650) which may be stored in memory, for example, the measured battery life profile storage 735 (act 655). The battery charger controller 750 will also send a signal to the battery life indicator 740 (act 660) so that a user can check the state of the battery, for example, the estimate of the remaining life of the battery.

If the sensor profile analysis indicates an end of life condition of the battery (decision 665) the battery charger controller 750 will shutdown the battery charger power converter (act 675) and alarm the user to replace the battery (act 680).

If the sensor profile analysis indicates that the battery is still in an operational state, the battery charger controller 750 will determine appropriate battery charging parameters for the battery based on a comparison between the sensor data and the reference battery life profile in the reference battery life profile memory 730 (act 670). The determined battery charging parameters are provided by the battery charger controller 750 to the battery charging power converter 720.

FIGS. 8A and 8B illustrate an embodiment of a capacitive pressure sensor 800 which may be utilized with the disclosed battery charging system. Capacitive pressure sensor 800 may be utilized, for example as capacitive pressure sensor 810 illustrated in FIG. 7. Capacitive pressure sensor 800 includes a first capacitive sensor 825 comprising a conductive plate 830 separated by a dielectric 840, for example, a MYLAR(r) polyester film, and a foam spacer 835 from a second conductive plate 845. The spacing between the two plates 830, 845 and the surface area of the conductive plates determines the capacitance of the first capacitive sensor. Capacitive pressure sensor 800 may also include a reference capacitive sensor 850 including conductive plate 845, a third conductive plate 860, a second dielectric layer 840, and a second foam spacer 855. The capacitance of the first capacitive sensor 825 may be compared to the capacitance of the reference capacitive sensor 850 during operation to check for faults of the capacitive pressure sensor 800. A lead wire 865 may provide electrical communication between the capacitive sensor 800 and remainder of the battery charging system, for example, between the capacitive sensor 800 and the capacitive plate pressure sensor oscillator 780.

FIG. 9 illustrates the placement of a battery pressure sensor 900 on a battery 710. The battery pressure sensor 900 may include any one or more of the capacitive sensor 810, piezoelectric film sensor 815, and resistive strain gauge sensor 820. The battery pressure sensor 900 may be coupled or adhered directly to an outer surface of a case of the battery 710 by, for example, an adhesive. A lead wire 945 may provide electrical communication between the sensor 900 and remainder of the battery charging system.

FIG. 10 illustrates how the battery pressure sensor 900 may be compressed by swelling of the battery 710. The side of the battery case to which the sensor 900 is coupled may be placed against a wall 1000 of a battery storage compartment where the battery resides during operation. Swelling of the battery will cause the battery case to expand against the wall 1000, applying a force to the sensor 900 which is communicated to the battery charging system to provide an indication of the amount of swelling of the battery.

In another embodiment, illustrated in FIGS. 11A and 11B, a conductive plate 910 of a capacitive sensor is adhered, for example, with an adhesive to the outer surface of the case of the battery 710 to cover the weak center point where battery swelling is typically observed to be most significant. A non-conductive spacer 920 is also adhered, for example, with an adhesive to the outer surface of the case of the battery 710 about the periphery of the side of the battery case where deformation due to battery gas pressure buildup is typically very minimal. The spacer 920 may be formed of plastic or any other significantly or completely non-conductive material. An outer conductive plate 930 is adhered, for example, with an adhesive to the opposite side of the spacer 920 from the side of the spacer adhered to the case of the battery. The conductive plates 910, 930 form a capacitor whose capacitance may be measured to determine a degree of battery swelling due to the buildup of pressurized gas within the battery case.

In operation, at least a portion, for example, a center portion of the conductive plate 910, will move freely in the direction of the outer conductive plate 930 upon the occurrence of battery swelling. In some embodiments the spacer thickness is selected to produce an initial capacitance of from about 50 picofarads (pF) to about 100 pF, for example, about 80 pF of the capacitive sensor formed from the plates 910, 930 and spacer 920. For example, a 1.5 mm thick plastic spacer may be utilized in some embodiments. In some embodiments, the outer conductive plate 930 includes is a rigid fiber glass printed circuit board or other rigid material to maintain clearance from the conducive plate 910 and provide a reproducible initial capacitance value. As the battery swells the inner conductive plate 910 moves freely but the outer plate 930 will have negligible movement due to the strong structure of the corner of the battery. As the inner conductive plate 910 gets closer to the outer conductive plate the sensor capacitance will increase. Conductive elements, for example, wires, are in electrical communication with each of the conductive plates to provide electrical

communication between the capacitive sensor and the battery charging system. Alternatively or additionally, as illustrated in FIG. 12, a battery pressure sensor 900 may be coupled or adhered to an external side of the wall 1000 of the battery storage compartment. The sensor 900 may include a capacitive sensor similar to that illustrated in FIGS. 11A and 11B but adhered to the external side of the wall 1000 of the battery storage compartment rather than directly to the case of the battery. A first conductive plate similar to conductive plate 910 may be adhered to a portion of the side of the wall 1000 of the battery storage compartment in contact with a portion, for example, a central portion of a side wall of the battery case, which would exhibit a significant degree of displacement responsive to the swelling of the battery due to the buildup of pressurized gas in the battery case. A spacer similar to spacer 920 may be adhered to a portion of the side of the wall 1000 of the battery storage compartment in contact with a portion, for example, a periphery of a side wall of the battery case which would exhibit little if any displacement responsive to the swelling of the battery due to the buildup of pressurized gas in the battery case. A second conductive plate, similar to conductive plate 930 may be adhered to the opposite side of the spacer 920 from the side adhered to the side of the wall 1000 of the battery storage compartment. Swelling of the battery 710 may induce mechanical deformation of the wall 1000 which may be detected by the battery pressure sensor 900 which will provide an indication of the sensed deformation to the battery charging system to provide an indication of the amount of swelling of the battery. In some embodiments, the wall 1000 of the battery storage compartment is formed of a conductive material and is used as the conductive plate 910.

Having thus described several aspects of at least one embodiment of this disclosure, it is to be appreciated various alterations, modifications, and

improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure. Accordingly, the foregoing description and drawings are by way of example only.

What is claimed is:

Claims

1. A method of charging a battery comprising:

monitoring a dimensional parameter of a case of the battery; and

adjusting a parameter of a battery charging algorithm for the battery responsive to a change in the dimensional parameter of the case of the battery.

2. The method of claim 1 , wherein adjusting the parameter of the battery charging algorithm comprises adjusting one of a float region voltage and a charge current limit.

3. The method of claim 2, wherein adjusting the parameter of the battery charging algorithm comprises adjusting the parameter of the battery charging algorithm from a first level to a second level responsive to the dimensional parameter exceeding a first value and further adjusting the parameter of the battery charging algorithm from the second level to a third level responsive to the dimensional parameter exceeding a second value, the second value being greater than the first value.

4. The method of claim 3, further comprising adjusting the parameter of the battery charging algorithm to an intermediate level intermediate between the first level and the second level responsive to the dimensional parameter having an intermediate value between the first value and the second value.

5. The method of claim 4, wherein the intermediate level is intermediate between the first level and the second level to a degree proportionate to a degree to which the intermediate value is intermediate between the first value and the second value.

6. The method of claim 3, further comprising disabling charging of the battery responsive to the dimensional parameter exceeding a third value.

7. The method of claim 1, further comprising providing an estimated remaining life of the battery calculated from the dimensional parameter, a temperature of the battery, and a number of discharge cycles which the battery has undergone.

8. A method of charging a battery comprising:

monitoring a gas pressure within the case of a battery; and

adjusting a parameter of a battery charging algorithm for the battery responsive to a change in the gas pressure within the case of the battery, the parameter including one of a float region voltage and a charge current limit.

9. The method of claim 8, wherein monitoring the gas pressure within the case of the battery comprises monitoring a dimension of the case of the battery.

10. The method of claim 8, wherein adjusting the parameter of the battery charging algorithm comprises adjusting the parameter of the battery charging algorithm from a first level to a second level responsive to an indication of the gas pressure exceeding a first value and further adjusting the parameter of the battery charging algorithm from the second level to a third level responsive to an indication of the gas pressure exceeding a second value, the second value being greater than the first value.

11. The method of claim 10, further comprising adjusting the parameter of the battery charging algorithm from the second level to a third level responsive to an indication of the gas pressure exceeding a third value, the third value being greater than the second value.

12. The method of claim 8, further comprising monitoring a number of discharge cycles of the battery and providing a prediction of a remaining life for the battery using an algorithm including the gas pressure within the case of the battery and the number of discharge cycles as input parameters.

13. The method of claim 12, further comprising measuring a temperature of the battery and including the measured temperature as an input parameter in the algorithm.

14. A battery monitoring apparatus comprising:

a sensor coupled to a case of the battery and configured to provide an indication of a change in a dimension of the case of the battery; and

a control system configured to adjust a parameter of a battery charging algorithm for the battery responsive to the indication of the change in the dimension of the case of the battery.

15. The apparatus of claim 14, wherein the control system is configured to effect a first adjustment in the parameter of the battery charging algorithm responsive to an indication of the change in the dimension of the case of the battery exceeding a first value and to effect a second adjustment in the parameter of the battery charging algorithm responsive to an indication of the change in the dimension of the case of the battery exceeding a second value, the second value being greater than the first value.

16. The apparatus of claim 15,wherein the control system is further configured to effect a third adjustment in the parameter of the battery charging algorithm responsive to an indication of the change in the dimension of the case of the battery exceeding a third value, the third value being greater than the second value.

17. The apparatus of claim 14, wherein the sensor is one of a capacitive sensor, a piezoelectric film sensor, and a resistive strain gauge sensor.

18. The apparatus of claim 14, further comprising a battery temperature sensor.

19. The apparatus of claim 18, wherein the control system is configured to further adjust the parameter of the battery charging algorithm responsive to a signal provided from the temperature sensor.

20. The apparatus of claim 14, further comprising a user interface configured to notify a user of an end of a useful life of the battery.