Abstract:
A passive battery discharge apparatus located within a cap. The cap extends over battery contacts to be discharged. The discharge apparatus includes a conductive material with specified volumetric resistivity properties that is formed into a pad. The cap is positioned over the contacts so that the pad touches and spans between the contacts to be discharged. A spring insures good contact between the pad and the battery contacts. A metal heat sink provides added thermal control. The discharge apparatus provides an economical solution to safely transport batteries that are beyond their useful service life by avoiding circuit components in favor of conductive elastomers or conductive foams.

Description:
BACKGROUND 
     1. Technical Field 
     This disclosure relates to a low cost passive battery discharge device. 
     2. Description of the Related Art 
     Two main types of batteries include rechargeable batteries and primary, non-rechargeable batteries. Rechargeable batteries may need to be completely discharged for reconditioning, or for State-of-Charge synchronization purposes. For these applications, battery chargers may include active discharge circuits which monitor the rate of discharge. A stand alone battery discharge device is shown in U.S. Pat. No. 5,107,196, where a resistor and LED provide illumination until the battery has reached a desired discharge state. 
     Primary batteries often have a requirement to be fully discharged before disposal. Current discharge devices use a fixed resistor or active circuit connected across the battery terminals to discharge the battery. This approach requires the use of relatively expensive connector to mate with the battery, or complicated independent switch mechanisms, U.S. Pat. No. 5,651,821 provides a carousel where batteries rotate through while in contact with a discharge circuit. At the end of the rotation, batteries are ejected to make room for new ones. This system suffers from several drawbacks, because it requires the battery to be retained within the carousel for an indeterminate period of time, and there is no assurance that the ejected batteries are fully discharged. When discharging a single battery, the entire multi-battery carousel must be present, which may be unreasonable in field operations. 
     U.S. Pat. No. 7,190,147 discloses a circuit and a switch which is isolated from the battery terminals by an insulator. A tab extending outside the container is pulled to remove the insulator, thereby allowing the switch to complete the discharge circuit. 
     Therefore, a need exists for a low cost, passive battery discharge device which can be issued as a single unit, and remain with the battery indefinitely. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a passive battery discharge device which can remain with the battery to insure safe and complete discharge. 
     It is another object of the invention to provide a simply designed discharge device that will guarantee operation under a variety of environmental operating conditions. 
     It is a further object to provide a low cost discharge device by avoiding switches and circuit componentry since the device is utilized at the end of a batteries useful life. 
     These and other related objects according to the invention are provided in a discharge apparatus for use in a portable power system including a battery having an outer casing with an equipment flange adjacent to the battery contacts and a removable engagement plate which secures to the equipment flange and extends over the battery contacts. A passive battery discharge apparatus is disposed within the cap&#39;s receiving zone. The cap is part of a discharge cover which is adapted to secure to the engagement flange. A conductive sponge-like material is disposed within the cap. The conductive material is physically configured as a direct contact spanning pad that is adapted to resiliently press on to the battery contacts. The conductive material is electrically configured as a non-switched compressible element that is adapted to passively and safely discharge the battery. A spring and disc-shaped heat sink are employed to exert a biasing force on the pad-shaped conductive material toward the battery contacts. Conductive elastomers, conductive foam and combinations thereof are utilized, 
     In an alternate embodiment according to the invention, there is provided an apparatus for passively discharging a battery including a discharge dome adapted to enclose battery contacts to be discharged. A conductive pad is disposed within said discharge dome and is adapted for directly contacting each contact and spanning across said contacts. The conductive pad forms a passive discharge device that is devoid of switches, wires and resistors. The conductive pad is made from a material selected from a conductive elastomer, a conductive foam, and combinations thereof 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The advantages, nature, and various additional features of the invention will appear more fully upon consideration of the illustrative embodiments now to be described in detail in connection with accompanying drawings. In the drawings wherein like reference numerals denote similar components throughout the views: 
         FIG. 1A  is a perspective view of a portable electronic device according to the prior art. 
         FIG. 1B  is a perspective view of a battery according to the prior art. 
         FIG. 2  is a side elevational view of a battery and passive discharge apparatus according to an embodiment of the invention. 
         FIG. 3  is a cross-sectional view, taken along the line III-III from  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
     The present invention provides a passive device including a conductive material having a spongy consistency that is held under a biasing force against the battery connector terminals to discharge the battery. The device eliminates the need for expensive battery connectors, since the spongy conductive material can be pressed into the terminal hub, and conform to any shape or configuration that the terminals may be in. In a preferred embodiment, the material is a conductive elastomer or conductive foam. Because of its low cost, individual devices can be issued for permanent connection to a primary battery. In other words, the device can travel with the battery to a proper disposal facility, discharging the battery and protecting against accidental arcing along tie way. A locking feature can be incorporated in the device to prevent tampering or accidental removal. The discharge device can incorporate a window, label or flag to identify a date of decommissioning, a date after which the battery can be destroyed/recycled or other informational or safety/hazard or recycling code. 
     Referring now in specific detail to the drawings in which like reference numerals identify similar or identical elements throughout the several views, and initially to  FIGS. 1A and 1B , there is shown a battery  50  and an engagement plate  10  which collectively form a portable power system according to the prior art. Battery  50  includes an outer casing  52 , one or more equipment flanges (referred to generically as  54 ) and contacts  56 . Engagement plate  10  includes one or more lip portions (referred to generically as  14 ) for securing under one or more equipment flanges. For example, diametrically opposed lip portions  14   a  and  14   b  can be secured under diametrically opposed flange sections  54   a  and  54   b . Engagement plate further includes a contact zone  16  which is disposed over contacts  56  when the engagement plate is in its installed configuration. 
     Engagement plate  10  may form the bottom end of a piece of electronic equipment, for example, a radio  20 . Engagement plate  10  may also be provided as a thin blank which is used during transport of new batteries to keep dirt and moisture away from contacts  56 . As a blank, contact zone  16  is empty. When engagement plate  10  incorporated into an electronic device, contact zone  16  includes mating contacts which will align with contacts  56  on the battery. In the embodiment shown, contacts  56  include two or more concentric rings of individual contacts. In addition to the positive and negative battery terminal, additional contacts may he provided to communicate battery state state of charge, state of health, or other battery usage information to connected equipment. In the concentric embodiment shown, contact zone  16  includes a central axis  16   x , which aligns with contact axis  56   x  of the battery. To install engagement plate  10 , contact zone  16  is aligned with contacts  56 , and engagement plate  10  is then rotated approximately 90 degrees counter-clockwise, in direction  56   y.    
     In certain applications, battery  50  is a non-rechargeable battery, referred to as a primary battery. At the end of its service life, battery  50  will be destroyed or recycled. However, a problem exists, in that the battery still has residual energy. There are several risks in transporting these “dead” batteries. First, service personnel may confuse the dead batteries with live batteries, and mistakenly take one into the field. Second, dead batteries can still arc causing potential fire hazards, or causing damage to delicate electronic equipment that it may come into contact with. Since primary batteries are never recharged, there is no existing charger that can be equipped with a discharge circuit. Providing a separate discharge circuit is impractical, because the cost of a mating connector assembly is prohibitive. 
     As can be seen in  FIG. 2 , there is provided a discharge apparatus  80  according to one embodiment of the invention, Discharge apparatus  80  includes a incharge cover  82  and a cap  88 . Discharge cover  82  includes one or more lip portions for securing under one or more flanges. For example, diametrically opposed lip portions  84   a  and  84   b  connect under diametric opposed equipment flanges  54   a  and  54   b . In one embodiment a locking tab  86  is provided in combination with one lip portion. for example lip portion  84   b . When discharge cover  82  is rotated in direction  56   y , locking tab  86  comes into contact with flange  54   b . A ramp forcus locking tab to ride along the top surface of flange  54   b  until it encounters a recess  54   r . Locking tab  86  then snaps back into its original position, being seated in recess  54   r , and preventing clockwise rotation. This essentially locks discharge cover  80  onto battery  50 . Locking lab  86  can be manufactured with sufficient sufficient so that can be forced along the ramp by mannal pressure. Once locked, tab  86  cannot be unseated manually without destroying part of the cover or the flange. Additional safeguards nuts be employed to insure the discharge cover remains permanently fastened, or to insure that removal is possible only with special tools or keys. References to a discharge apparatus means an apparatus that is designed to harmlessly dissipate power or energy, i.e. an energy discharge apparatus. 
     As can be seen in  FIG. 3 , cap  88  is being installed over contacts  56 . Cap  88  serves as a discharge dome to completely enclose contacts  56 . A passive battery discharge apparatus  92  is disposed within the cap&#39;s internal receiving zone  90 , which consists of ail open proximal end  90   a  and a closed distal end  90   b . The essential component of discharge apparatus  92  is a conductive material  94  having a spongy consistency. Conductive material  94  is physically configured as a direct contact spanning pad. For the concentrically arranged contact in the illustrated embodiment the direct contact spanning pad may be configured in a cylindrical shape. As discharge apparatus  92  is forced down and rotated (in direction  56   y ) about axis  56   x , the spongy material  94  directly contacts, and spans across, all of the individual contacts  56   a ,  56   b  and  56   c . A conductive material may be foamed in situ to Fill or overfill cap  88 . For example, a conductive material may be injected into the cap, and then expand around ribs (such as  90   u  and  90   s ) to bold it in place. By overfilling the cap, an excess of material will be forced on to the contacts when the discharge cover is installed on the battery. 
     As can be seen in  FIG. 2 , there is provided a discharge apparatus  80  according to one embodiment of the invention. Discharge apparatus  80  includes a discharge cover  82  and a cap  88 . Discharge cover  82  includes one or more lip portions for securing under one or more flanges. For example, diametrically opposed lip portions  84   a  and  84   b  connect under diametrically opposed equipment flanges  54   a  and  54   b . In one embodiment a locking tab  86  is provided in combination with one lip portion, for example lip portion  84   b . When discharge cover  82  is rotated in direction  56   c , locking tab  86  comes into contact with flange  54   b . A ramp forces locking tab to ride along the top surface of flange  54   b  until it encounters a recess  54   r.  Locking tab  86  then snaps back into its original position, being seated in recess  54   r , and preventing clockwise rotation. This essentially locks discharge cover  80  onto battery  50 . Locking tab  86  can be manufactured with sufficient rigidity so that it can be forced along the ramp by manual pressure. Once locked, tab  86  cannot be unseated manually without destroying part of the cover or the flange. Additional safeguards may be employed to insure the discharge cover remains permanently fastened, or to insure that removal is possible only with special tools or keys. References to a discharge apparatus means an apparatus that is designed to harmlessly dissipate power or energy, i.e. an energy discharge apparatus. 
     As can be seen in  FIG. 3 , cap  88  is being installed over contacts  56 . Cap  88  serves as a discharge dome to completely enclose contacts  56 . A passive battery discharge apparatus  92  is disposed within the cap&#39;s internal receiving zone  90 , which consists of an open proximal end  90   a  and a closed distal end  90   b . The essential component of discharge apparatus  92  is a conductive material  94  having a spongy consistency. Conductive material  94  is physically configured as a direct contact spanning pad. For the concentrically arranged contact in the illustrated embodiment, the direct contact spanning pad may be configured in a cylindrical shape. As discharge apparatus  92  is forced down and rotated (in direction  56   c ) about axis  56   x , the spongy material  94  directly contacts, and spans across, all of the individual contacts  56   a ,  56   b  and  56   c . A conductive material maybe foamed in situ to fill or overfill cap  88 . For example, a conductive material may be injected into the cap, and then expand around ribs (such as  90   u  and  90   s ) to hold it in place. By overfilling the cap, an excess of material will be forced on to the contacts when the discharge cover is installed on the battery. 
     The spongy consistency of conductive material  94  allows it to resiliently press on all of the individual battery contacts. To provide additional downward force, a resilient member  96  may be provided. For example, a leaf spring or coil spring may be compressingly installed within the discharge dome, to exert a biasing force against the distal end  90   b  of the dome and against the conductive material  94 . Material  94  gets pressed down into the interstices between the contacts as a result of the downward force in combination with the twisting movement. This insures good electrical coupling to all battery contacts. 
     Electrically, the conductive material  94  serves as a non-switched compressible element that is adapted to passively and safely discharge the battery. In a preferred embodiment the conductive material may be a conductive elastomer or conductive foam. As methods of imparting conductivity to an elastomer, the following two methods are conventionally used: In one known method, an electroconductive polymer composition containing a conductive filler such as powder of metal oxide, carbon black or the like in a polymer thereof is used. In the other known method, an ionic-conductive polymer composition such as urethane rubber, acrylonitrile butadiene rubber, epichlorohydrin rubber or the like is used. Such elastomers are available from Sumitomo Rubber Industries, Ltd. Conductive polyurethane foams are also known to be made using a post-treatment wherein a solvent swells the foam and allows conductive chemicals to interpenetrate the polyurethane. After the solvent is removed, the chemicals remain in the polymer. Such foams are available from Inolex Investment Corporation (Wilmington, Del.). 
     Generally, suitable conductive materials will possess electrical properties including a volume resistivity in the range of 10 2  to 10 5  in ohms-cm. Volume resistivity, or volumetric resistivity, is the electrical resistance between opposite faces of a 1 cm cube or material. It is specified in units of resistance (ohms) multiplied by units of length (cm). In non-limiting examples, certain suitable conductive foams will include: 
     STATFREE® Foam, Conductive having a volume resistivity ranging between 10 3  and 10 5  ohms-cm per ASTM-D-3674-81, available from Desco of Canton, Mass. Conductive fillers include carbon black in crosslinked polyethylene. 
     Conductive polymer foams as described in U.S. Published Patent Application 2008/0213565, the entire contents of which is incorporated herein by reference thereto. 
     PLASTAZOTE® LD50CN, Conductive Low Density Polyethylene Foam having a volume resistivity about 10 3  ohms-cm per ASTM-D991-89, available from Zotefoams of the U.K. 
     According to the prior art, the following conductive elastomers are commercially available: 
     CHO-SEAL® and CHO-SIL® Conductive Elastomers having a volume resistivity between about 1 and 10 −4  ohms-cm per MIL-g-83528, available from Chomerics. Conductive fillers include silver (Ag), copper (Cu), nickel (Ni), aluminum (Al), carbon (C), silver-plated copper, nickel coated graphite, silver-plated glass, silver-plated aluminum, and combinations thereof. 
     Silicon rubber conductive elastomers having a volume resistivity between about 5 and 10 ohms-cm, available from Spectrum Control, Inc. of Fairview, Pa. 
     Electrically Conductive RTV Silicones having a volume resistivity between about 0.06 and 0.005 ohms-cm, available from Moreau of Lexington, N.C. Conductive fillers include nickel-graphite, silver-glass, silver-nickel, silver-aluminum, silver-copper, silver and combinations thereof. As currently manufactured these conductive elastomers could be used in applications involving batteries that are almost completely discharged. For general purpose applications according to the invention, suitable conductive elastomers would have to be doped at alternate levels to bring their volume resistivity within the range of 10 2  to 10 5  ohms-cm. 
     The present invention is not limited to the illustrative example and may be employed with other conductive materials, or combinations of other conductive materials. All statements herein reciting principles, material properties, and embodiments of tie invention, as well as specific examples thereof, are intended to encompass all structural, electrical and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future (i.e., any elements developed that perform the same function, regardless of structure). Furthermore, it is intended that such equivalents include both currently known materials as well as materials developed in the future (i.e., any conductive material developed that performs the same function, regardless of chemical composition). 
     As demonstrated above, there is a wide range of material choices. For applications requiring higher discharge rates, the thermal properties may be enhanced by providing a heat sink  98  in contact with conductive material  94 . For example, conductive material  94  may be glued to heat sink  98  with a conductive adhesive. Other connection methods may be employed, like metal fasteners or clips. Heat sink  98  may be fashioned from a highly conductive material like metal, for example, aluminum. Heat sink  98  may provide other advantages by its placement between spring  96  and conductive material  94 . Heat sink  98  allows the biasing force of the spring to be distributed over a large surface area. If a soft conductive material is used, the lower end of the spring may tend to penetrate through, thereby reducing its effectiveness. 
     As can be seen in  FIG. 3 , cap  88  is provided with an upper stop  90   u  and a lower stop  90   s.  The stops may be divided into several short sections, or may constitute armular rings which encircle the entire cap  88 . In one embodiment, cap  88  is produced in two sections, one upper section carrying stop  90   u  and a lower section carrying lower stop  90   s  which is integral with discharge cover  82 . In other words, the cap is split in a region between stops  90   u  and  90   s . Heat sink can be supplied in a coin shape, for example, a disc having the approximate dimensions of a dime, with a thickness of three nickels. In a practical embodiment, the heat sink was configured as a  318  inch diameter disc of ¼ inch thickness. Spring  96  and conductive material  94  are pre-attached to heat sink  98 , collectively forming the passive battery discharge device  92 , in this embodiment. With cap and upper stop  90   u  being removed, device  92  can be installed on to lower stop  90   s . Cap and upper stop  90   u  can then be placed over device  92  and secured with adhesive, ultrasonic welding, or any other suitable means. Cap  88  is concentrically arranged over the battery contact hub, in the illustrated embodiment. Cap  88  and the enclosed passive battery discharge apparatus can be configured for any number of hubs, or any alternate hub configuration. The conductive pad  94  may be sculpted into various shapes or levels, in order to effectively touch all contacts to be discharged. 
     The completed assembly provides a direct contact ( 56   a ,  56   b ,  56   c ) spanning pad  94  which resiliently presses on the contacts ( 56   a ,  56   b ,  56   c ). Additional downward force may be provided by a resilient member  96 . Additional heat sinking may be provided by a metal disc  98 . Accordingly, a non-switched, compressible energy-dissipating element is provided in the form a pad of conductive elastomer or conductive foam with the cap  88  molded as part of the cover. The discharge cover  80  can be locked in place with varying degrees of security. It should be understood that the elements shown in  FIGS. 2 and 3  may be implemented in various forms of hardware, various material choices or combinations thereof. For example, the dome can be alternately shaped, i.e. non-cylindrical, rectangular, or other suitable shapes which can accommodate a resilient member, heat sink and conductive material. The conductive material can be altered to any battery contact configuration, or battery connector configuration. Discharge cover can be designed to mimic the interface of any electrical device, in order to deliver the conductive material so that it can directly span and touch some or all battery power and data contacts. 
     Having described preferred embodiments for (which are intended to be illustrative and not limiting), it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as outlined by the appended claims. Having thus described the invention with the details and particularity required by the patent laws, what is claimed and desired protected by Letters Patent is set forth in the appended claims.