Abstract:
A metal-air battery with an air moving device controller to determine when a load is present on the battery and the extent of that load is described. The air moving device controller allows the operation of the air moving device for the battery to be responsive to the load. Advantageously, the controller allows the metal-air battery to limit the intake of oxygen and other gases to that amount needed to drive the load.

Description:
RELATED APPLICATIONS  
       [0001]    The present application is a continuation in part of application Ser. No. 09/216,114, filed Dec. 18, 1998.  
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to a battery for electrical power, and more particularly relates to an air-manager system for a metal-air battery.  
         BACKGROUND OF THE INVENTION  
         [0003]    Metal-air battery cells include an air permeable cathode and an anode separated by an aqueous electrolyte. During discharge of a metal-air battery, such as a zinc-air battery, oxygen from the ambient air is converted at the cathode to hydroxide, zinc is oxidized at the anode by the hydroxide, and water and electrons are released to provide electrical energy. Metal-air batteries have a relatively high energy density because the cathode utilizes oxygen from the ambient air as a reactant in the electrochemical reaction, rather than a heavier material such as a metal or a metallic composition. Metal-air battery cells are often arranged in multiple cell battery packs within a common housing to provide a sufficient power output.  
           [0004]    A steady supply of oxygen to the air cathodes is necessary to operate the metal-air battery. Some prior systems sweep a continuous flow of new ambient air across the air cathodes at a flow rate sufficient to achieve the desired power output. Such an arrangement is shown in U.S. Pat. No. 4,913,983 to Cheiky. Cheiky uses a fan within the battery housing to supply a predetermined flow of ambient air to a pack of metal-air battery cells. Before the battery is turned on, a mechanical air inlet door and an air outlet door are opened and the fan is activated to create the flow of air into, through, and out of the housing. After operation of the battery is complete, the air doors are sealed. The remaining oxygen in the housing slowly discharges the anode until the remaining oxygen is substantially depleted. The residual low power remaining in the cells is disclosed as being sufficient to restart the fan the next time the battery is used.  
           [0005]    To ensure that a sufficient amount of oxygen is swept into the housing during use, Cheiky discloses a fan control means with a microprocessor to vary the speed of the fan according to pre-determined power output requirements. The greater the power requirement for the particular operation, the greater the fan speed and the greater the airflow across the battery cells. Several predetermined fan speeds are disclosed according to several predetermined power levels of the load. The disclosed load is a computer. The fan speed is therefore varied according to the power requirements of the various functions of the computer. Conversely, many other known air manager systems run the fan continuously when a load is applied.  
           [0006]    In addition to the need for a sufficient amount of oxygen, another concern with metal-air batteries is the admission or loss of too much oxygen or other gasses through the housing. For example, one problem with a metal-air battery is that the ambient humidity level can cause the battery to fail. Equilibrium vapor pressure of the metal-air battery results in an equilibrium relative humidity that is typically about 45 percent. If the ambient humidity is greater than the equilibrium humidity within the battery housing, the battery will absorb water from the air through the cathode and fail due to a condition called flooding. Flooding may cause the battery to leak. If the ambient humidity is less than the equilibrium humidity within the battery housing, the metal-air battery will release water vapor from the electrolyte through the air cathode and fail due to drying out. The art, therefore, has recognized that an ambient air humidity level differing from the humidity level within the battery housing will create a net transfer of water into or out of the battery. These problems are particularly of concern when the battery is not in use, because the humidity tends to either seep into or out of the battery housing over an extended period of time.  
           [0007]    Another problem associated with metal-air batteries is the transfer of carbon dioxide or other contaminates from the ambient air into the battery cell. Carbon dioxide tends to neutralize the electrolyte, such as potassium hydroxide. In the past, carbon dioxide absorbing layers have been placed against the exterior cathode surface to trap carbon dioxide. An example of such a system is shown in U.S. Pat. No. 4,054,725.  
           [0008]    Maintaining a battery cell with proper levels of humidity and excluding carbon dioxide has generally required a sealed battery housing. As discussed above, prior art systems such as that disclosed by Cheiky have used a fan of some sort to force ambient air through large openings in the battery housing during use and a sealed air door during non-use. If the air door is not present or not shut during non-use, however, large amounts of ambient air will seep into the housing. This flow of air would cause the humidity and carbon dioxide problems within the housing as discussed above.  
           [0009]    The assignee of the present invention is also the owner of U.S. Pat. No. 5,691,074, entitled “Diffusion Controlled Air Door,” and application Ser. No. 08/556,613, entitled “Diffusion Controlled Air Vent and Recirculation Air Manager for a Metal-Air Battery,” filed Nov. 13, 1995, now U.S. Pat. No. ______. These references disclose several preferred metal-air battery packs for use with the present invention and are incorporated herein by reference. The air inlet and outlet openings in the housing are sized with a length in the direction through the thickness of the housing being greater than a width in the direction perpendicular to the thickness of the housing.  
           [0010]    For example, the references disclose, in one embodiment, a group of metal-air cells isolated from the ambient air except for an inlet and an outlet passageway. These passageways may be, for example, elongate tubes. An air-moving device positioned within the housing forces air through the inlet and outlet passageways to circulate the air across the oxygen electrodes and to refresh the circulating air with ambient air. The passageways are sized to allow sufficient airflow therethrough while the air mover is operating but also to restrict the passage of water vapor therethrough while the passageways are unsealed and the air mover is not operating.  
           [0011]    When the air mover is off and the humidity level within the cell is relatively constant, only a very limited amount of air diffuses through the passageways. The water vapor within the cell protects the oxygen electrodes from exposure to oxygen. The oxygen electrodes are sufficiently isolated from the ambient air by the water vapor such that the cells have a long “shelf life” without sealing the passageways with a mechanical air door. These passageways may be referred to as “diffusion tubes”, “isolating passageways”, or “diffusion limiting passageways” due to their isolating capabilities. The isolating passageways also act to minimize the detrimental impact of humidity on the metal-air cells, especially while the air-moving device is off.  
           [0012]    The efficiency of the isolating passageways in terms of the transfer of air and water into and out of a metal-air cell can be described in terms of an “isolation ratio.” The “isolation ratio” is the rate of the water loss or gain by the cell while its oxygen electrodes are fully exposed to the ambient air as compared to the rate of water loss or gain by a cell while its oxygen electrodes are isolated from the ambient air except through one or more limited openings. For example, given identical metal-air cells having electrolyte solutions of approximately thirty-five percent (35%) KOH in water, an internal relative humidity of approximately fifty percent (50%), ambient air having a relative humidity of approximately ten percent (10%), and no fan-forced circulation, the water loss from a cell having an oxygen electrode fully exposed to the ambient air should be more than 100 times greater than the water loss from a cell having an oxygen electrode that is isolated from the ambient air except through one or more isolating passageways of the type described above. In this example, an isolation ratio of more than 100 to 1 should be obtained.  
           [0013]    In accordance with the above-referenced example from U.S. Pat. No. 5,691,074, the isolating passageways function to limit the amount of oxygen that can reach the oxygen electrodes when the fan is off and the internal humidity level is relatively constant. This isolation minimizes the self-discharge and leakage or drain current of the metal-air cells. Self-discharge can be characterized as a chemical reaction within a metal-air cell that does not provide a usable electric current. Self-discharge diminishes the capacity of the metal-air cell for providing a usable electric current. Self-discharge occurs, for example, when a metal-air cell dries out and the zinc anode of oxidized by the oxygen that seeps into the cell during periods of non-use. Leakage current, which is synonymous with drain current, can be characterized as the electric current that can be supplied to a closed circuit by a metal-air cell when air is not provided to the cell by an air moving device. The isolating passageways as described above may limit the drain current to an amount smaller than the output current by a factor of at least fifty (50) times.  
           [0014]    The use of the open air door battery housings described herein therefore simplifies the design of the battery as a whole and simplifies the use of the battery. In fact, these battery-housing designs allow the metal-air battery to act more like a conventional battery, i.e., the battery is available for the given load without any additional activity such as opening the air doors. The only requirement of these designs is that the fan or other air movement device must be turned on to provide a sufficient flow of oxygen for the cells.  
           [0015]    In sum, the desired metal-air battery would be used in an identical manner to a conventional battery in that all the user needs to do is attach and activate the load. The battery itself would need no separate activation. Further, such a battery would have an energy efficient and quiet air manager system.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention is directed towards a metal-air battery with an air moving device controller to determine when a load is present on the battery and the extent of that load. The air moving device controller allows the operation of the air-moving device for the battery to be responsive to the load. Advantageously, the controller allows the metal-air battery to limit the intake of oxygen and other gases to that amount needed to drive the load.  
           [0017]    One embodiment of the present invention includes a metal-air battery with at least one metal-air cell isolated from ambient air except through at least one passageway. The battery further includes an air moving device operative to move air through the passageway to provide reactant air to the metal-air cell. The passageway is operative, while unsealed and while the air moving device is inactive, to restrict airflow through the passageway. The battery further includes an air moving device controller. The air moving device controller includes means for determining whether a load is on the metal-air battery and the extent of the load such that the operation of the air-moving device is responsive to the air moving device controller.  
           [0018]    The means for determining whether a load is on the metal-air battery and the extent of the load includes a power sensor to monitor the voltage across the metal-air cell. The air moving device controller turns the air-moving device on when the voltage across the metal-air cell, as measured by said power sensor, is less than or equal to a predetermined voltage. The air moving device controller also turns the air moving device on when the voltage across the metal-air cell, as measured by the power sensor, is less than or equal to a first predetermined voltage. The predetermined voltage may be approximately 4.7 volts. The air moving device controller turns the air-moving device off when the voltage across the metal-air cell, as measured by the power sensor, is greater than or equal to a second predetermined voltage. The air moving device controller also turns the air-moving device off when the voltage across the metal-air cell, as measured by the power sensor, is greater than or equal to a second predetermined voltage. The predetermined voltage may be approximately 6.5-7.0 volts.  
           [0019]    The method of the present invention provides for operating a metal-air battery. The method includes the step of: confining at least one metal-air cell within a housing. The metal-air cell includes an air electrode and the housing includes an air movement device and at least one air passageway. The method further includes the steps of sensing the voltage across the air electrode; activating the air movement device when a load is present on the air electrode and the voltage across the air electrode is less than or equal to a predetermined voltage so as to move air through passageway; and deactivating the air movement device when the voltage across the air electrode is greater than or equal to a second predetermined voltage.  
           [0020]    Another embodiment of the present invention provides an apparatus for controlling the operation of a fan for a metal-air battery. The apparatus includes a power sensor operable for monitoring an input port for the presence of a load, connecting the battery to the load in response to detecting the presence of the load at the input port, and providing an output signal representative of the voltage across the input port. The apparatus further includes a fan controller operable for determining whether the output signal is within a predetermined range and activating the fan in response to determining that the output signal is within the predetermined range. The predetermined range may be about 4.7 to about 7.0 Volts.  
           [0021]    The apparatus also may include a switch driveable by the fan controller for connecting the battery to the load. The apparatus also may include an electrostatic charge protection device driveable by the fan controller. The electrostatic charge protection device is operable for dissipating an electrostatic charge across the load in response to detecting that the load has an electrostatic charge build-up. Further, the power sensor also may include a bridge circuit driveable by the load. The bridge circuit is operable for driving the switch for connecting the battery to the load. The power sensor also may include a hysteresis voltage driver driveable by the bridge circuit. The hysteresis voltage driver is operable for preventing the battery from being disconnected from the load.  
           [0022]    A further embodiment of the present invention provides an apparatus for controlling the operation of a fan for a metal-air battery. The apparatus includes means for detecting voltage across the metal-air battery. The means for detecting voltage includes means for monitoring an input port for the presence of a load, means for connecting the battery to the load in response to detecting the presence of the load at the input port, and means for providing an output signal representative of the voltage across the input port. The apparatus further includes means for regulating the voltage of the metal-air battery. The means for regulating the voltage includes means for determining whether the output signal is within a predetermined range and means for activating the fan in response to determining that the output signal is within the predetermined range.  
           [0023]    A further embodiment of the invention provides means for determining whether a load is on the metal-air battery and the extent of the load includes a power sensor to monitor the load current and the voltage across the metal-air cell. The air moving device controller turns the air moving device on when both the current through a current sensing element, such as a resistor, is greater than a predetermined current value and the voltage across the metal-air cell, as measured by said power sensor, is less than or equal to a predetermined voltage. The air moving device controller first determines whether the current passing through the current sensing element is greater than a first predetermined current value to activate the air-moving device. Typically, the current is approximately between 350 and 500 milliamperes. Next, the air moving device controller monitors the load to ensure that the current it is above a second predetermined current level. The current induced by the load must be greater than the second predetermined level to sustain operation of the air moving device controller. Typically, the second predetermined level is approximately in the range of 75-300 milliamperes.  
           [0024]    Once the air moving device controller determines that sufficient current is present to sustain the operation of the air moving device controller, the air moving device controller monitors the voltage across the metal-air cell. When the voltage across the metal-air cell, as measured by the power sensor, is less than or equal to a first predetermined voltage, the air moving device controller turns the air-moving device on. The predetermined voltage may be approximately 4.7 volts. The air moving device controller also turns the air-moving device off when the voltage across the metal-air cell, as measured by the power sensor, is greater than or equal to a second predetermined voltage. The predetermined voltage may be approximately 7.0 volts.  
           [0025]    Thus, it is an object of the present invention to provide an improved air manager system for a metal-air battery.  
           [0026]    It is another object of the present invention to provide a self-regulating air manager system for a metal-air battery.  
           [0027]    It is a further object of the present invention to provide an air manager system for a metal-air battery without mechanical air doors.  
           [0028]    It is a still further object of the present invention to provide an air manger system for a metal-air battery with an automatic fan.  
           [0029]    It is a still further object of the present invention to provide for an efficient air manager system for a metal-air battery.  
           [0030]    It is a still further object of the present invention to provide for an air manager system for a metal-air battery with a long shelf life.  
           [0031]    It is a still further object of the present invention to provide a quiet air manager system for a metal-air battery.  
           [0032]    It is a still further object of the present invention to provide a charge prevention function to protect the camcorder battery during charging operations.  
           [0033]    Other objects, features, and advantages of the present invention will become apparent upon reviewing the following description of preferred embodiments of the invention, when taken in conjunction with the drawings and the appended claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0034]    [0034]FIG. 1 is a cut-away diagrammatic top view of the battery housing embodying the present invention, showing the position of the cells, the fan, and the air openings, in combination with the direction of the flow of air with respect to the housing.  
         [0035]    [0035]FIG. 2 is a vertical cross sectional view taken along line  2 - 2  of FIG. 1.  
         [0036]    [0036]FIG. 3 is a diagrammatic pictorial view of a ventilation opening.  
         [0037]    [0037]FIG. 4 is a schematic view of the power sensor circuit.  
         [0038]    [0038]FIG. 5 is a flow chart showing the operation of the fan based upon the detected voltage.  
         [0039]    [0039]FIG. 6 is a comparison chart showing the power consumption of an air manager system in a six (6) volt battery with several fan options.  
         [0040]    [0040]FIG. 7 is a plan view of a camcorder battery of an alternative embodiment of the present invention.  
         [0041]    [0041]FIG. 8 is a side cross-sectional view of the camcorder battery of the FIG. 7.  
         [0042]    [0042]FIG. 9 is a schematic diagram showing the voltage control circuit of the alternative embodiment.  
         [0043]    [0043]FIG. 10 is a schematic view of the power sensor circuit of the alternative embodiment.  
         [0044]    [0044]FIG. 11 is a flow chart showing the operation of the fan based on the detected current and detected voltage.  
     
    
     DETAILED DESCRIPTION  
       [0045]    Referring now in more detail to the drawings, in which like numerals refer to like parts throughout the several views, FIGS.  1 - 4  show a metal-air battery  10  embodying the present invention. The metal-air battery  10  may be similar to that disclosed in commonly owned U.S. Pat. No. 5,641,588 to Sieniinski, et al., commonly owned U.S. Pat. No. 5,356,729 to Pedicini, et al., commonly owned U.S. Pat. No. 5,691,074 to Pedicini, and commonly owned application Ser. No. 08/556,613, which are incorporated herein by reference, or other known metal-air battery configurations.  
         [0046]    The metal-air battery  10  includes a plurality of metal-air cells  15  enclosed within a housing  20 . The housing  20  isolates the cells  15  from the outside air with the exception of a plurality of diffusion tubes or ventilation openings  25 . In the embodiment shown in FIGS. 1 and 2, a single air inlet opening  30  and a single air outlet opening  35  are utilized. The number of openings  25  is not as important as the aggregate size of the openings  25  in connection with the shape of each opening  25 . Alternatively, a single opening  25  may be utilized to provide air to the cells  15 . The openings  25  would function as both an inlet and an outlet with reciprocating airflow therethrough. Further, multiple passageways or openings  25  can be utilized in the aggregate such that the openings  25  function in unison as inlets, and thereafter function in unison as outlets, in an alternating fashion.  
         [0047]    The housing  20  itself may be any type of conventional, substantially air-tight structure. The number of cells  15  within the housing  20  depends upon the nature of the load intended for the battery  10 . The present invention is not dependent upon the configuration of the cells  15  within the housing  20  or the number of cells  15  within the housing  20 . FIGS. 1 and 2 therefore show a cutaway view of a metal-air battery housing  20  showing only the essential elements of the present invention, i.e., a housing  20 , one or more cells  15 , and the air openings  25 . Although only two cells  15  are shown in FIGS. 1 and 2, it is understood that the number and configuration of the cells  15  depends upon the power requirements for the battery  10 .  
         [0048]    A circulating fan  40  is provided for convective airflow both in and out of the housing  20  and to circulate and mix the gasses within the housing  20 . The arrows shown in FIG. 1 represents a typical circulation of gasses into, out of, and within the housing  20  to provide the reactant air to the cells  15 . The capacity of the fan  40  also depends upon the size of the housing  20  and the power demands of the battery  10 . The term “fan”  40  as used herein is intended to mean any device to move air, including a pump.  
         [0049]    The fan  40  may be positioned within the housing  20  or adjacent to the housing  20  in communication with one of the openings  25 . If the fan  40  is located within the housing  20 , the ventilation openings  25  are positioned such that the inlet opening  30  and the outlet opening  35  are positioned on opposite sides of the fan  40 . The only requirement for the positioning within the housing  20  of the fan  40  and the openings  25  is that they are in sufficiently close proximity to each other to create a convective air flow into, through, and out of the housing  20 . The fan  40  may be mounted within or adjacent to the housing  20  in any convenient manner. The fan  40  is generally sealed into place by a gasket  41  or other conventional means to ensure that the low pressure and high pressure sides of the fan  40  are isolated from one another.  
         [0050]    As is shown in FIG. 2, the plurality of cells  15  within housing  20  are generally arranged such that a reactant air plenum  50  is positioned under or over the cells  15 . The air plenum  50  defines an air plenum inlet  55 , an air passageway  60 , and an air plenum outlet  65 . The fan  40  is generally positioned between and isolates the air plenum inlet  55  from the air plenum outlet  65  for efficient airflow through the housing  20 . Examples of air plenum designs are shown in the commonly-owned references cited above. As described above, the present invention is not dependent upon any particular air plenum design.  
         [0051]    As is shown in FIG. 3, the ventilation openings  25  are preferably sized such that their length  26 , i.e., the direction through the thickness of the housing  20 , is greater than their width  27 , i.e., the direction perpendicular to the thickness of the housing  20 . By using a large enough ratio between the length  26  and the width  27  for the ventilation openings  25 , it has been found that diffusion of air through the openings  25 , without the assistance of the fan  40 , is substantially eliminated. By “substantially eliminated,” it is meant that the rate of diffusion of oxygen or contaminates through the openings  25  is so slow that humidity transfer or drain current is sufficiently small and has little appreciable impact on the efficiency or lifetime of the battery  10 . In sum, the openings  25  are sufficiently long and narrow to provide a barrier to diffusion of gases therethrough when the fan  40  is turned off.  
         [0052]    This desired ratio between length  26  and width  27  is at least about two to one. These ratios are sufficient to prevent appreciable diffusion through the openings  25  when the fan  40  is turned off while permitting convective airflow therethrough when the fan  40  is turned on. The use of larger ratios between length  26  and width  27  is preferred. Depending upon the nature of the battery  10 , the ratio can be more than 200 to 1. The preferred ratio is about 10 to 1.  
         [0053]    In use, ambient air is drawn into the air inlet  30  by pull of the fan  40  when the fan  40  is turned on. As is shown by the arrows  45  in FIG. 1, the air is then drawn through the fan  40  and into the air plenum  50 . The air enters the air plenum  50  through air plenum inlet  55 , travels though the pathway  60  to provide a reactant airflow for the cells  15 , and exits via the air plenum outlet  65 . The air is then again drawn into the fan  40  where it either mixes when fresh incoming ambient air or is forced out of the housing  20  via air outlet  35 . When the fan  40  is turned off, the rate of diffusion of air through the openings  25  is reduced to acceptable levels such that a mechanical air door is not required.  
         [0054]    As is shown in FIGS. 1 and 4, the invention includes a voltage monitor  100  to determine the voltage across the cell  15  or other electrical characteristics and to control the operation of the fan  40 . The voltage monitor  100  can be positioned at any convenient location within or adjacent to the housing  20 . The preferred voltage monitor  100  is a programmable voltage detection or sensing device such as that sold by Maxim Integrated Products under the mark MAX8211 and MAX8212. Depending upon the desired operation of the fan, the voltage monitor  100  can be an analog circuit for a simple “on/off” switch or can incorporate a microprocessor (not shown) for a more complex algorithm. The voltage monitor  100  of FIGS. 1 and 4 is an analog circuit.  
         [0055]    The voltage monitor  100  determines the voltage across the air electrode  150  of the cell  15 . The air electrode  150  is shown in phantom lines in FIG. 4. Because the zinc potential within the air electrode  150  of each cell  15  is relatively stable, the air electrode  150  is used to sense the residual oxygen in the cell  15 . As the oxygen within the housing  20  is depleted, the voltage across each air electrode  150  diminishes. Likewise, as the flow of oxygen into the housing  20  increases, the voltage across the air electrode  150  increases.  
         [0056]    A preferred air electrode  150  is disclosed in commonly owned U.S. Pat. No. 5,569,551 and commonly owned U.S.  
         [0057]    Pat. No. 5,639,568, which are incorporated herein by reference. U.S. Pat. No. 5,639,568 discloses a split anode for use with a dual air electrode metal-air cell. Although the use of the invention with a zinc-air battery is disclosed, this invention should be understood as being applicable to other types of metal-air battery cells.  
         [0058]    As is shown in FIG. 4, the voltage monitor  100  is connected to the cells  15  in a voltage monitor circuit  105  via a cathode tab  130  and an anode tab  140 . The voltage monitor circuit  105  also includes the fan  40 . All of the cells  15  within the housing  20  are connected in this circuit  105 . The voltage across the cells  15  is continually monitored to ensure that the voltage does not drop below a predetermined voltage V p1 . If the voltage does drop to V p1 , the fan  40  is turned on and then runs continuously until the voltage is increased to a second predetermined voltage V p2 . The fan  40  is then turned off and remains off until the voltage again drops to V p1 . The predetermined voltages V p1  and V p2  are programmable values in the voltage monitor  100 .  
         [0059]    The operation of the fan  40  is shown in FIG. 5. The algorithm is an “on/off” type with predetermined values. As is shown in step  201 , the voltage monitor  100  measures the voltage across the air electrode  150 . In step  202 , the voltage monitor  100  determines if the voltage is less than or equal to V p1 . If so, the voltage monitor  100  turns on the fan  40  in step  203 . If not, the voltage monitor  100  determines if the voltage is greater than or equal to V p2  in step  204 . If so, the voltage monitor  100  turns off the fan  40  in step  205 . If not, the voltage monitor  100  returns to step  201 . This algorithm may be modified to add an additional step of first checking if a load is present on the battery  10 . If so, the voltage monitor  100  proceeds to step  201  as shown above. If not the fan  40  will remain in the off state.  
         [0060]    Alternatively, the speed of the fan  40  maybe altered depending upon the drain rate of the battery  10  as a whole or other electrical parameters. In other words, the voltage monitor  100  can be replaced with other types of conventional electrical sensors known to those practicing in the art. For example, a conventional power sensor, i.e., a sense resistor, could be used. This monitor  100  can set the speed of a variable speed fan  40  as a function of current draw. Instead of the algorithm of FIG. 5, the circuit  105  would contain a conventional microprocessor with a look-up table to compare the determined current draw with a voltage input value for the fan  40 . The input voltage and speed of the fan  40  varies with the determined output current drain. The physical arrangement of the components in this embodiment is the same as that described above.  
         [0061]    The operation of the invention is shown in an example using a six (6) volt battery  10 . Such a battery  10  has six (6) metal-air cells  15 , with each cell  15  having an output of about 1.0 volt or slightly higher at about 1 to 4 amps. An up-converter (not shown) also may be used. The housing  20  has openings  25  with a length  26  to width  27  ratio of about four (4) to one (1). The gas flow through the housing when the fan  40  is on is about 15 to about 30 cubic inches per minute for an output current of about 1 amp. When the fan  40  is turned off, the gas flow rate is reduced to about 0 to about 0.03 cubic inches per minute or less, with a leakage current of less than 1 mA. The ratio of output current density with the fan  40  turned on to drain current density with the fan  40  turned off is expected to be at least 100 to 1 in an efficient battery  10 . It is understood that the respective sizes, capacities, densities, flow rates, and other parameters discussed above are dependent upon the overall size and power requirements of the battery  10 .  
         [0062]    The first predetermined voltage V p1  under which the voltage should not fall may be about 1.0 volts per cell  15  or about 5.0 volts for the battery  10  as a whole. The fan  40  is turned on when the voltage monitor  100  determines that the voltage of the battery  10  has reached about 1.0 volts per cell  15  or about 5.0 volts for the battery  10  as a whole. The fan  40  then stays on until the voltage of the battery  10  reaches about 1.1 volts per cell  15 , or about 5.5 volts for the battery  10  a whole. The fan  40  remains off until the voltage again reached about 1.0 volts per cell  15  or about 5.0 volts for the battery  10  as a whole.  
         [0063]    Assuming the drain rates given above, it would take approximately one month for the six (6) volt battery  10  of the present example to fade from about 1.1 volts per cell  15  to about 1.0 volts per cell  15  to trigger the fan  40  during periods of non-use. The shelf life of the battery  10  would be at least several years. The battery  10  would be immediately ready for use without the need for any independent activation of the battery  10  such as by turning on the fan  40  or by opening a mechanical air door. Rather, the battery  40  is ready for use. The activation of a load on the battery  10  will cause the voltage across the cells  15  to drop as the oxygen within the housing  20  is consumed. This voltage drop will activate the fan  40  until the proper amount of oxygen is introduced into the housing  20  and the proper voltage is restored.  
         [0064]    In addition to the present invention being self-regulating, the present invention also provides an energy efficient air manager system. The efficiency of the battery  10  as a whole is increased because the running of the fan  40  is minimized. FIG. 6 compares the energy to load ratio  300  of the present invention in terms of the energy to load ratio  310  of a battery without a fan and with the energy to load ratio  320  of a fan running constantly at various drain rates. As described above, most air manager systems either run the fan continuously or employ a variable speed fan as is described in Cheiky. As is shown in FIG. 6, the present invention provides efficiencies of essentially ninety percent (90%) of an air manager system without a fan.  
         [0065]    For example, the energy to load ratio  300  of the present invention in a six (6) volts battery is about 235 Wh while the energy to load ratio  310  of an air manager system without a fan is about 250 Wh. The energy to load ratio  320  of an air manager system with a fan running continuously is only about 135 Wh. The pulsing fan operation of the present invention is therefore an improvement of almost 100 Wh as compared to a constantly running fan. The improvement is maintained until drain rates reach about 5 watts. At that point, the fan  40  of the present invention is essentially running continuously.  
         [0066]    Although these efficiencies may be possible with the variable speed fan of Cheiky, the present invention uses a simple on/off switch rather than the complex, load specific algorithm disclosed therein. In other words, Cheiky requires a specific algorithm for each different type of load. The present invention, however, is available to provide power to almost any type of electrical device.  
         [0067]    In sum, by pulsing the fan  40  as described herein, several goals are achieved:  
         [0068]    1. The life of the battery  10  is maximized from the standpoint of environmental exposure. In other words, only enough oxygen is admitted into the housing  20  as is needed to maintain the predetermined voltages.  
         [0069]    2. Power consumption of the fan  40  is minimized as a percentage of the power consumed by the battery  10  as a whole. For example, a fifty percent (50%) duty cycle may be all that is required at low drain rates. This decreases the overhead energy consumed by the battery  10  as a whole.  
         [0070]    3. Because the fan  40  runs in a duty cycle, the battery  10  as a whole is quieter than a battery  10  with a continuously running fan  40 .  
         [0071]    The present invention therefore can provide a battery  10  with a relatively long shelf life without the need for a mechanical air door or a fan switch. The present invention can function as, for example, a power source of an emergency device than can be automatically activated because there is no need for a separate activation step. More importantly, the present invention provides for an efficient air manager system that minimizes the running of the fan  40  and the energy drain associated with the fan  40 .  
         [0072]    [0072]FIGS. 7 and 8 show a further embodiment of the present invention. These figures show a metal-air battery  500 . The metal-air battery  500  is in the form of, for example, a camcorder battery. The metal-air battery  500  includes six (6) metal-air cells  510 . The metal-air cells  510  are of conventional design and may be similar to the cells  15  described above. Likewise, each metal-air cell  510  has one or more air electrodes  515 . The air electrodes  515  are also of conventional design and may be similar to the air electrodes  150  described above. In this embodiment, the metal-air cells  510  are arranged in three (3) pairs  520  with each pair  520  sharing an air plenum  530 . The air plenums  530  may be of conventional design. The metal-air cell pairs  520  are each separated by a separator layer  540 . The separator layers  540  may be made from a substantially rigid, non-air permeable material or simply may be a plurality of protrusions on the outer casing of the metal-air cells  510 . The metal-air cells  510  each have dimensions of approximately 4 by 7 by 0.6 cm. Likewise, the air plenums  530  may have a width of approximately 0.1 cm. Each cell  510  may have a voltage of about one (1) Volt such that the battery  500  as a whole will have a voltage of about six (6) Volts.  
         [0073]    Positioned over the metal-air cells  510  is an air manager unit  550 . The air manager unit  550  includes a fan  560  and one or more diffusion tubes or ventilation openings  570  extending through the battery housing as described above. The fan  560  may be of any conventional design and may be similar to the fan  40  described above. The needed fan capacity should be varied based on the size of the cells to which air is supplied and the amount of electrical current being supported by the battery. In this embodiment, the fan  560  may have a capacity of about 1-10 liters per minute of standard air, to support a current of up to about 6 amperes. The one or more diffusion tubes  570  may be similar to the ventilation openings  25  described above, i.e., the diffusion of air through the diffusion tubes  570 , without the assistance of the fan  560 , is substantially eliminated such that the rate of diffusion of oxygen or contaminates through the tubes  570  is sufficiently slow and has little appreciable impact on the efficiency or lifetime of the battery  500 .  
         [0074]    Also positioned within or adjacent to the air manager unit  550  is a fan control circuit  580 . The fan control circuit  580  includes a voltage monitor  590  to determine the voltage across the cells  510  or other electrical characteristics and to control the operation of the fan  560 . The voltage monitor  590  may be of conventional design and may be similar to the voltage monitor  100  described above. In this embodiment, the voltage monitor  590  incorporates a camcorder battery circuit  600  as described below for the execution of a more complex function than the “on/off” design of the voltage monitor  100 .  
         [0075]    [0075]FIG. 9 shows an electrical schematic for the preferred embodiment of the camcorder battery circuit  600 . The camcorder battery circuit  600  has two main functions: (1) to monitor the voltage output of the battery  500  and (2) to monitor the voltage output to the internal fan  560  which forces air into the air plenums  530 . The electrical circuit  600  is comprised of three circuit components shown by the dashed lines in FIG. 9: a power sensor  602 ; a switch  604 ; and a fan controller  606 .  
         [0076]    The camcorder battery circuit  600  contains a first comparator  608 , a second comparator  610 , a third comparator  614  and a fourth comparator  616 . The combination of comparators  608 ,  610 ,  614 ,  616  is preferably implemented by a quad, ultra low power, and low offset voltage comparator, such as the model LP339M manufactured by Texas Instruments Corporation, of Dallas, Tex.  
         [0077]    The power sensor  602  includes the first comparator  608  and the second comparator  610 . The resistors R 5 , R 6 , R 8 , R 10 , R 11 , and R 12  form a resistive bridge. The first comparator  608  in combination with the resistive bridge formed by the resistors R 5 , R 6 , R 8 , R 10 , R 11 , and R 12  form a bridge circuit  609 . When there is no load applied across battery output terminals E 3  and E 4 , the output of the comparator  608  is high. The voltages at the inverting terminal and non-inverting terminal of first comparator  608  are unequal and the output of first comparator  608  is high.  
         [0078]    When a load is applied across the output battery terminals E 3  and E 4 , current flows through the resistor R 12 . The voltage that appears at the inverting input of the first comparator  608  will be greater than voltage at the non-inverting input such that the output voltage of first comparator  608  will be at ground. When the output of first comparator  608  is at ground, a current path is established through the resistors R 15  and R 16  and the first comparator  608  from the terminal E, to the terminal E 2 . The resulting voltage drop across R 16  provides a large forward bias voltage across the emitter-base junction of transistor Q 2 , thereby allowing current to pass therethrough. The combination of the transistor Q 2  and the resistors R 15  and R 16  form a voltage switch  612 . The bias voltage is chosen such that the transistor Q 2  operates in saturation mode whenever the output of the first comparator  608  is at ground. This ensures that the voltage drop across the transistor Q 2  is minimal when the transistor Q 2  is conducting. Preferably, the transistor Q 2  is a small signal pnp transistor, such as the model MMBT3906 manufactured by the Motorola Corporation, of Schaumburg, Ill.  
         [0079]    Each function (e.g., record, rewind, play, view, etc,) of the camcorder typically will have different operating current levels. Each of these different operating currents produces a corresponding voltage level across the current sensing resistor R 12 . Some of these voltage levels may be below the initial reference voltage at the non-inverting input of the first comparator  608 . To protect the circuit  600  from disconnecting the load from the battery  500 , the current-sensing circuit  602  lowers the voltage at the non-inverting input of the first comparator  608  by establishing a hysteresis voltage driver. Second comparator  610  and resistor R 9  form the hysteresis voltage driver. The output of the first comparator  608  is connected to the non-inverting input of the second comparator  610 . When the output of the first comparator  608  is high, the non-inverting input of the second comparator  610  is also high. The inverting input of the second comparator  610  is connected to the positive voltage across the resistor R 6 . Because the voltage across the resistor R 6  is less than an input voltage applied across input ports E 1  and E 2 , the output of the second comparator  610  is high. Therefore, when no load is applied to the output ports E 3  and E 4 , no current flows through the resistor R 9 .  
         [0080]    When the output of the first comparator  608  is at ground, the voltage level at the non-inverting input of the second comparator  610  will be greater than the voltage level at the inverting input of the second comparator  610 . Therefore, the output of the second comparator  610  is at ground, which causes current to flow through the resistor R 9 . This places the resistor R 9  in parallel with the resistors R 8  and R 10 , which produces a hysteresis effect. The resulting combination of the resistor R 9  in parallel with the resistors R 8  and R 10  reduces the resistance of the bridge circuit, which causes a downward shift in the voltage level at the non-inverting input of the first comparator  608 . The input voltage level at the non-inverting input of the first comparator  608  is now at a level below the minimum voltage, which corresponds to the minimum current required to operate the camcorder in a given mode. Reducing the voltage at the non-inverting input ensures that the load will not be disconnected from the battery  500  due to changes in the voltage during the operation of the camcorder.  
         [0081]    The switch  604  comprises the component transistor Q 1 . Typically, the transistor Q 1  is a dual TMOS Power metal-oxide semiconductor field effect transistor (MOSFET), such the model MMDF3NO3HD manufactured by the Motorola Corporation, of Schaumburg, Ill. The input signal of a gate of a transistor  620  is supplied by the output of the transistor Q 3 , which in turn is driven, by transistor Q 2 . Preferably, the transistor Q 3  is a small signal pnp transistor, such as the model MMBT3906 manufactured by the Motorola Corporation, of Schaumburg, Ill.  
         [0082]    When the transistor  620  is in the “OFF”, or non-conducting state, current flows through a body drain diode, which is inherent to transistor  620 . The output voltage at terminals E 3  and E 4  is then approximately equal to a voltage drop across the drain diode, V drain . When the transistor Q 2  is conducting, the emitter of Q 3  will be at a voltage VCC, which is essentially equal to the battery voltage V batt . Current will flow through the base-emitter junction of Q 3  due to the base being tied to ground through R 17 . This allows Q 3  to conduct current to the collect node, which is connected to the gate of the transistor  620 . This allows the gate of transistor  620  to be positively biased at nearly the battery voltage V batt  (the voltages V Q2  and V Q3  across the transistors Q 2  and Q 3 , respectively, are negligible). The positive bias at the gate of the transistor  620  creates a channel so that current flows from the drain to the source of the MOSFET transistor  620  and the body drain diode is removed from the circuit. The entire load current is conducted through the transistor  620  with negligible losses. The source of the transistor  620  is connected to the output terminal E 3 . Thus, when the transistor  620  is conducting, a voltage nearly equal to the battery voltage appears across the output terminals E 3  and E 4  of the battery  500 .  
         [0083]    The transistor  620  in combination with transistor Q 3  and R 18  acts as a charge prevention circuit. In the event that a power source capable of causing current to flow in a direction opposite to that of the load current, is attached to the output battery terminals E 3  and E 4 , the circuit keeps transistor  620  in the “OFF” state thereby preventing current from passing through transistor  620 . Resistor R 18  provides a bleed path for the gate charge on transistor  620  and the leakage current of Q 3  so that transistor  620  is not turned on when a power source having a positive polarity is applied across terminal E 3  and E 4 .  
         [0084]    Referring again to the transistor Q 2 , the output of the transistor Q 2  also is connected to the fan controller  606 . The output voltage VCC from the power sensor  602  powers the fan controller  606 . A voltage reference element, CR 1  establishes a constant voltage at a node  628 . Preferably, CR 1 , is an integrated circuit, micropower voltage reference element, such as the model LM385BD-1.2 manufactured by the Motorola Corporation. In the preferred embodiment, the voltage established by CR 1  is about 1.24 volts. Those skilled in the art will appreciate that other voltage reference elements that have different voltage values may be used as long as the specified voltage is less than the voltage VCC established by the transistor Q 2 .  
         [0085]    The Resistor R 1  supplies enough bias current to meet the requirements of CR 1  and one input of each of the third and fourth comparators  614  and  616 . Therefore the resistor R 1  and CR 1  establish a known, fixed voltage reference. The resistors R 2 , R 7 , R 3 , and R 4  form a voltage divider circuit connected to the third and fourth comparators  614  and  616 . These comparators  614  and  616  are wired in a window comparator configuration. In this configuration, if the output of either comparator is negative, the output of both comparators is negative. More specifically, if the voltage at the node  624 , which is connected to the non-inverting input of the third comparator  614  is greater than the reference voltage established by CR 1 , the output of the third comparator  614  will be positive, which corresponds to an open circuit.  
         [0086]    The output of the third and fourth comparators  614  and  616  are connected to the gate of the transistor  621  in the transistor Q 1 . When either the output of the third comparator  614  or the fourth comparator  616  is positive, the gate voltage of the transistor  621  is positively biased which results in a low-channel resistance being formed between the source to the drain. The drain of the transistor  621  is connected to the negative terminal of the fan  560 . Therefore, whenever the gate of the transistor  621  is positively biased, the transistor  621  will conduct. This causes a voltage across the terminals E 5  and E 6  that activates the fan  560 .  
         [0087]    Generally, when the output voltage VCC is within a predetermined voltage range, the output of the comparators  614 ,  616  will be positive and voltage will be supplied to the fan  560  through the transistor  621 . This range is set by the values chosen for the resistors R 2 , R 3 , R 4 , and R 7 . In the preferred embodiment, the predetermined voltage range is 4.7-6.5 volts, and the values of the resistors R 2 , R 3 , R 4 , and R 7  are 383 KΩ, 51 KΩ, 133 KΩ, and 133 KΩ, respectively. However, those skilled in the art will appreciate that other predetermined voltage ranges that are within the voltage limits of the battery  500  may be used by selecting different values of the resistors R 2 , R 3 , R 4 , and R 7  without affecting the scope of the invention.  
         [0088]    When the output voltage, VCC exceed 6.5 volts, the voltage at the inverting input of fourth comparator  616  will exceed the reference voltage established at the node  628 . The output of fourth comparator  616  will become negative, thereby cutting off the voltage to the fan  560 . Similarly, when VCC is less than the 4.7 volts, the voltage at the non-inverting input of the third comparator  614  will be less than the reference voltage at the node  628 . The output of the third comparator  614  will go negative thereby cutting power off to the fan  560 .  
         [0089]    The resistor R 13 , is a step-down resistor that reduces the voltage, which appears across terminals E 5  and E 6  to match the voltage requirements of the fan  560 . TP 1  and TP 2  form a socket in which an additional resistor can be added to output voltage across terminals E 5  and E 6 .  
         [0090]    Finally, diode CR 2  is a Zener diode that protects the transistor Q 1  from large electrostatic discharge (ESD). Preferably, CR 2  is a Zener diode; such as the model number BZX84C27 manufactured by Vishay/LiteOn Corporation.  
         [0091]    As is shown in FIG. 10, the fan control circuit  580  includes each of the elements described in shown in FIG. 4. Specifically, the voltage monitor  590  is connected to the cells  510  via a cathode tab  512  and an anode tab  514  and to the fan  560 . All of the cells  510  within the battery  500  are connected in this circuit  580 . The voltage across the cells  510  is continually monitored to ensure that the voltage does not drop below a predetermined voltage V p1 . If the voltage does drop to or below V p1 , the voltage monitor  590  first determines if a sufficient load is on, the battery  500 .  
         [0092]    Specifically, the voltage monitor  590  determines if the external current flow on the battery  500  is greater than the minimum camcorder current. In this embodiment, the minimum camcorder current is about 500 milliamperes to enable the operation of the camcorder and at least 100 milliamperes to sustain the operation of the camcorder. This first step is possible because this minimum camcorder current is reduced as compared to other known designs. If the voltage drops to or below V p1 , the fan  560  is turned on and then runs continuously until the voltage is increased to or above a second predetermined voltage V p2 . The fan  560  is then turned off and remains off until the voltage again drops to or below V p1 . As described above with respect to FIG. 9, the predetermined voltages V p1  and V p2  are programmable values in the voltage monitor  590 . In the present embodiment, V p1  and V p2 , V p1  may be about 4.7 Volts and V p2  may be about 7.0 Volts.  
         [0093]    The camcorder battery circuit  600  of the voltage monitor  590  also may use hysteresis to prevent erratic operation of the fan  560  as operating modes of the camcorder are changed. In other words, a sudden but short increase in the electrical load on the battery  500  when, for example, the user presses the Play, Record, or Rewind buttons, will not necessarily activate or deactivate the fan  560  immediately.  
         [0094]    Other features of the camcorder battery circuit  600  include the use of charge prevention. Charge prevention is accomplished by having a minimal voltage drop at the battery tabs  512 ,  514  during normal battery discharge. In other words, the battery voltage at the tabs  512 ,  514  will be approximately 50-100 mV less than the internal raw battery  500  voltage. The camcorder battery circuit  600  also incorporates electrostatic discharge protection on the battery tabs  512 ,  514  to prevent damage to the circuitry within the battery  500 .  
         [0095]    The algorithm  700  in FIG. 11 shows an alternative embodiment of the operation of the fan  40 . The algorithm  700  is an “on/off” type with predetermined values. As is shown in step  702 , the hysteresis is OFF, which corresponds to the output of the hysteresis voltage driver  611  being open circuit. In step  704 , the power sensor  602  determines whether the current through the current sensing resistor R 12  is greater than an upper threshold current I H . Typically, the threshold current I H  is in the range of approximately 350-500 milliamperes. If so, the hysteresis is ON in step  706 , which corresponds to the output of the hysteresis voltage driver  611  being low. This prevents the load from becoming disconnected during the operation of the camcorder.  
         [0096]    The power sensor  602  next determines whether the load current through resistor R 12  is less than a lower threshold current, I L  in step  708 . Typically, the lower threshold voltage I L  is in the range of approximately 75-300 milliamperes. If the load current is greater than the lower threshold current, the “NO” branch is followed to step  710  in which the fan controller  606  determines whether the load voltage is greater than V p1 . If so, the fan controller  606  turns the fan  40  off in step  714 . If not, the algorithm proceeds to  712 , in which the fan controller  606  determines if the load voltage is greater than V p2 . If the load voltage is greater than V p2 , the fan controller  606  turns off the fan  40  in step  714 . Step  714  is followed by step  718  in which the fan controller  606  determines whether the hysteresis is ON. If so, the algorithm loops back to step  708 . If not, the algorithm loops back to step  704 .  
         [0097]    Returning to step  712 , if the load voltage is less than V p2 , the voltage monitor  100  turns the fan on at step  716 . The algorithm branches back to step  708  to continue monitoring the load current and voltage.  
         [0098]    Returning to step  708 , if the load current is less than the lower threshold current, I L , then the “YES” branch is followed to step  720 , in which the hysteresis function is OFF. The fan monitor  606  then turns the fan  40  off in step  714 . The algorithm proceeds to step  718 , in which the determination is made whether the hysteresis is ON. If the hysteresis function is ON, the algorithm loops back to step  708 . If not, the algorithm loops back to step  704 .  
         [0099]    Returning to step  704 , if the power sensor  602  determines that the current through resistor R 12  is less than the upper threshold current I H , The algorithm proceeds to step  720 , in which the power sensor  602  switches the hysteresis OFF. In response, the fan controller  606  turns the fan off at step  714 .  
         [0100]    It should be understood that the foregoing relates only to preferred embodiments of the present invention, and that numerous changes may be made therein without departing from the spirit and scope of the invention as defined by the following claims.