Abstract:
Disclosed is a system and method for controlling the activation of isolated circuitry, and more particularly complete discharge devices for batteries, and similar circuits that are enclosed within sealed housings.

Description:
[0001]    This application claims priority under 35 U.S.C. §119, from U.S. Provisional Application No. 61/291,414 for “SYSTEM AND METHOD FOR ACTIVATING AN ISOLATED DEVICE,” filed on Dec. 31, 2009 by Kyle Karren and Athanasios Gkourlias, which is hereby incorporated by reference in its entirety. 
     
    
       [0002]    The present disclosure is directed to controlling a device/circuit contained within a hermetically sealed unit using a non-mechanical stimuli, and more particularly controlling a complete discharge circuit within a sealed housing, in order to neutralize a battery&#39;s potential using a non-contact external actuation. 
       BACKGROUND &amp; SUMMARY OF DISCLOSURE 
       [0003]    A complete discharge device (CDD) generally consists of a resistive load component and an activation component to complete a resistive short circuit between the terminals of a battery, for the purpose of discharging residual power. The incorporation of a CDD into a lithium battery is primarily intended to expend the residual energy remaining in an otherwise functionally depleted battery, thereby making the lithium non-reactive and inert. Interestingly, a study conducted on various lithium-sulfur dioxide (Li—SO 2 ) batteries by the U.S. Army Communications-Electronics Command (CECOM) shows that Li—SO 2  batteries when discharged through the use of a CDD, to a voltage of less than one volt, per cell, are considered to be non-reactive. This fact is significant because in most regions, non-reactive lithium-sulfur dioxide meets the criteria as non-hazardous waste for disposal purposes, but only when equipped with a CDD. The absence of a CDD often necessitates a disposal process including costly procedures for the handling and disposition of hazardous waste materials. Therefore, the complete discharge of a lithium sulfur dioxide battery, as well as similar batteries, is believed essential to alter the classification of the battery from hazardous to non-hazardous waste. Accordingly, the disclosed embodiments provide for controlling or activating a complete discharge circuit within a sealed housing, for example, by positioning a magnetic field adjacent the sealed battery housing to activate the complete discharge circuitry. 
         [0004]    A Conventional CDD includes various switches in combination with an activation method to short circuit the battery terminals using a power dissipation means, such as a load resistor. Examples of batteries with conventional complete discharge devices are the BA-5590 (Li/SO2) battery, as manufactured by Saft America, Inc. Bagvolet, France and the BA-5390 as manufactured by Ultralife Corporation, Newark, N.Y. For example, spring contacts biased toward each other, and an insulating pull-tab arrangement between them, are used in conjunction with a resistive discharge circuit. It is also believed that other circuit activation means include a rigid plastic rod that is pushed into the battery to activate the discharge operation (e.g., Li/SO2 battery cells formerly manufactured by Hawker Energy Products, Inc., now EnerSys Energy Products Inc., of Warrensburg, Mo.). 
         [0005]    Nonetheless, while suitable for battery energy depletion, the known schemes include inherent shortcomings with the use of an insulating pull-tab, or a rod, both from a manufacturing, as well as a performance and utility standpoint. For instance, if the spring contact loses its bias, the removal of the pull-tab would fail to activate the circuit. Similarly, the tab material must be resistant to deformation or penetration by the contacts, and must be resistant to movement until complete discharge is required. A further potential problem, when using a tab or material between the contacts, is that residual material, oxidation and/or corrosion may accumulate on the contacts thereby prohibiting the activation of the discharge circuit. Finally, and perhaps foremost, an inserted tab is generally invasive within the battery case itself, thereby requiring an aperture for it to pass through; consequently, the cells have limited protection from the ambient environment due to a breach of the enclosure, most notably submersion in a liquid. 
         [0006]    Batteries used in military application, for example, are often required to endure exposure to, or immersion in, salt water to a considerable depth without discharging. Also, military specifications may require that certain types of lithium based batteries be manufactured with a CDD that is manually activated to assure complete discharge once the battery has been taken out of service. It should be noted that it is also desirable, and possibly required, to include a state of charge indicator that can be activated on demand, to determine the remaining charge/capacity (or presence thereof) within in the battery. 
         [0007]    One of the potential alternatives to mechanical actuation of a CDD in a battery relies on the use of light to activate a photo-sensitive switch. However, this has, in many cases, proved to be inadequate due to the probability of mistakenly discharging a battery with inadvertent light reaching the sensor and unintentionally activating the CDD. Moreover, in some cases, the intensity of the ambient light breaches the shutter used to shield the sensor. Obviously, the converse is equally problematic wherein there is insufficient ambient light available when complete battery discharge is desirable. Although a light source may be built into the battery to assist in activating the complete discharge device, the need for a built in light source adds superfluous cost and complexity to a single use, simplistic battery design. 
         [0008]    In accordance with an aspect of the present disclosure, the use of an external non-mechanical stimuli, such as external fields (e.g., magnetic fields) provides for remote activation for controlling the state of a CDD located within a sealed battery housing. In one example an electro or permanent magnetic field source is directed through a non-ferrous region of a battery housing to activate the operation of an internal circuit, CDD and/or state of charge indicators, for example. Accordingly, the magnetic field is encouraged to permeate the outer housing and thereby mitigate the need to physically pass through the housing to activate a discharge circuit. 
         [0009]    In one embodiment, magnetic field sensors may include non-contact sensing devices based on the Hall-effect principle, whereby a voltage differential is sensed in a conductor as a function of the presence of either a parallel or perpendicular magnetic field, which in turn forward biases a solid state switch. Consequently, magnetic fields are able to pass directly through non-ferrous materials, thereby eliminating the need for direct physical contact to activate a switch connected to the CDD. However, a Hall-effect switch requires power in order to sense the change in field direction, and the actual Hall sensor must be positioned between the poles of the external magnet, which may lead to a unique battery housing form factor. As the Hall-effect switch is an active component, it provides a constant power drain during the entire life cycle of the battery, thereby reducing the power available to operate a device. Accordingly it may not be a suitable alternative in many applications. 
         [0010]    Several disclosed embodiments employ a passive, reed type switch within a sealed housing to complete the discharge circuit when activation is required. The reed switch is a continuity device consisting of a pair of electrical contact points located on at least two metal fingers having the contact end portions separated by a small air gap on the distal end and having the proximal ends hermetically sealed within a tubular glass envelope. At least one of the reed fingers is made from a magnetic/conductive material and is operable when positioned in the proximity of an applied magnetic field, for example, a permanent magnet or an electro-magnet. Such a switching device is passive and therefore does not require or draw power in order to be operational. Conventionally, there are two reed switch configurations: “normally open” and “normally closed” positions. The metal reeds on a normally open (NO) switch stay open when there is no magnet field in proximity of the switch. In the presence of a magnetic field, the contacts of a normally-open reed switch will close thereby making contact. Conversely, a normally-closed (NC) reed switch is closed when it is not near a magnet field; but will open the contacts in the presence of a magnet, thereby breaking contact. 
         [0011]    The aforementioned magnetic field sensors are not considered to be exclusive to a CDD, on the contrary isolated or externally remote activation of an internal control circuit is well suited for devices such as cameras, computers, GPS, cell phones and the like that may be further adaptable for use in hostile environments by sealing the devices in a housing that is only permeable to a magnetic or other field. Therefore, any devices operating in a sealed environment, could be activated (and/or deactivated) by non-mechanical stimuli such as magnetic sources outside the sealed unit, that would trigger or displace magnetically sensitive components sealed within the unit. 
         [0012]    It is desirable to provide a system for activating a device or circuit in a sealed housing that enables activation using an externally applied non-mechanical stimuli, such as magnetic fields, visible light, infra-red, acoustics, pressure, or radio frequencies, for example. It is further contemplated that in accordance with an alternative embodiment, a CDD may include internal battery terminals connected to the external battery terminals, whereby an internal switch provides an electrical connection to the exposed terminals and, upon disposal, the switch is placed in an open state. Additionally, it is conceivable to provide a resistive discharge path in combination with an external terminal disconnection means from the internal battery. 
         [0013]    In accordance with embodiments described herein, there is provided a battery system including a complete discharge device within a sealed housing, comprising: (a) a passive switch component sensitive to a non-mechanical stimuli, said switch component (e.g., reed switch) located within the sealed housing; (b) a magnetic field source (e.g., magnetic coil, permanent magnet), said magnetic field source being physically separated from said switch component by the housing, wherein said continuity component is responsive to a variation in the magnetic field caused by relative motion between the magnetic field source and switch component; and (c) a complete discharge circuit, located inside the housing and operatively controlled by said switch component, such that upon activation by said switch component the complete discharge circuit depletes the energy potential within the battery. 
         [0014]    According to further aspects of embodiments described herein there is provided a system for activating a device, comprising: (a) a passive switch, said switch being responsive to a non-mechanical stimuli (e.g., a change in a local magnetic field); (b) a source of non-mechanical stimuli, the source located at a position separated from said sensor and the device; and (c) a circuit, connected to said passive switch wherein the circuit is controlled by said switch and where said switch is responsive to a variation in the non-mechanical stimuli. 
         [0015]    According to yet another aspect of the disclosed embodiments, a method for controlling the activation of continuous discharge device in a sealed battery housing, comprising: (a) varying a non-mechanical stimuli (e.g., a magnetic field), using a source located outside the housing and physically separated from the continuous discharge device, the housing being permeable to a magnetic field; (b) detecting the variance of the magnetic field using a passive switch component; and (c) in response to the switch component (e.g., SCR or triac), activating the continuous discharge device. It should be appreciated that instead of an SCR, any solid state or mechanical relay may also be used in order to connect the discharge device In embodiments, a NO/NC reed switch may be used and each lead connected to the activation or deactivation pin, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The embodiments disclosed herein may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the embodiments and are not to be construed as limiting the disclosure or the appended claims. 
           [0017]      FIG. 1  illustrates a reed switch and an exemplary magnetic field source; 
           [0018]      FIG. 2  depicts an overview of a magnetic field acting to initiate a circuit; 
           [0019]      FIG. 3  is a partial cutaway view showing the circuit board to the magnet source orientation, in accordance with the embodiment of  FIG. 2 , 
           [0020]      FIG. 4  is a functional electrical diagram illustrating an embodiment of a complete discharge circuit configuration; 
           [0021]      FIG. 5  is a functional electrical diagram illustrating an internal positive terminal connection/disconnection circuit configuration; 
           [0022]      FIG. 6  is a conceptual illustration of a spring biased sliding magnet; and, 
           [0023]      FIG. 7  is a schematic circuit including a field effect transistor 
       
    
    
       [0024]    The various embodiments described herein are not intended to limit the invention to those embodiments described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0025]    For a general understanding of the embodiments, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical or equivalent elements. It is also noted that the various drawings illustrating the embodiments are not drawn to scale and that certain regions may have been purposely drawn disproportionately so that the features and concepts disclosed herein may be properly illustrated. 
         [0026]    Referring to  FIG. 1 , there is shown an example of a magnetic field source  210  in relation to a sensor or switch  140 . Although various magnetic materials may be employed as the source of the magnetic field, it is believed that commonly available ferromagnetic materials (e.g., iron, nickel, cobalt) have a suitable flux density and coercive force for non-mechanical activation of a switch component. The arrangement of the magnet assembly, depicted in  FIG. 1 , is a thin, possibly flexible strip of ferromagnetic material mounted or affixed to a pliable tab or label  220 . Tab  220  may have pressure sensitive adhesive thereon or similar means permitting it to be removably attached to a housing or similar structure in proximity to the battery. Referring also to  FIG. 2 , the mounting of the magnetic field source (e.g., magnet)  210  on tab  220  facilitates the removal of the magnetic field source  210  as the tab is pulled away from housing  110 , along with magnetic field source  210 , from within retention depression  212 . 
         [0027]    Switch  140  may include a reed type switch that includes a passive mechanical contactor for electrical current. In one embodiment, reed switch  118  comprises two identical flat ferromagnetic reeds,  110  and  112 , sealed in a dry inert-gas atmosphere within a glass capsule or similar, thereby protecting the contacts from contamination. The reeds are affixed in the capsule in a cantilever form so that their free ends overlap and are separated by a small air gap. The reed switch includes a pair of electrical contact points on metal fingers separated by a small air gap on the distal end and having the proximal ends hermetically sealed within a tubular glass envelope. At least one of the reed fingers, or at least a portion thereof, is made from a magnetic/conductive material and is operable or moves when positioned in the proximity of an applied magnetic field, for example, a permanent magnet or an electro-magnet. More specifically, when a magnetic field is generated parallel to the reed switch, the reeds become flux carriers in a magnetic circuit and the overlapping ends  114  of the reeds become opposite magnetic poles, which attract each other. If the magnetic force between the poles is strong enough to overcome the restoring force of the reeds, the reeds are drawn together, thus providing electrical continuity between the contacts. The reed-type switching device is passive and, therefore, does not require or draw power in order to be operational. 
         [0028]    As noted previously, there are two types of reed switches: “normally open” and “normally closed” reed switches. The electrically conductive reeds,  118  and  112  respectively, on a normally closed switch open only when there is a magnetic field near the switch. In the disclosed embodiment, given the presence of a magnetic field, the contacts of a NC reed switch will remain open. Reed switch  140  contains at least a pair of electrically conductive metal reeds, which have contact end portions  114  separated by a small air gap when the switch is open (non-conducting). Typically, the reeds are each hermetically sealed in opposite ends of tubular glass envelope of switch  118 . Notably, the hermetic sealing of a reed switch  140  makes them suitable for use in explosive atmospheres, where electrical arcing from conventional switches may constitute a hazard. However, cost considerations may inevitably eliminate the glass envelope of the reed switch, as they are further located within the sealed battery enclosure thus making the envelope redundant. 
         [0029]    Again, it is noted that a battery with enclosed electronics is only one example of utilizing a non-mechanical stimuli such as magnetic activation to control an isolated switch. Although described relative to the activation of circuitry within a sealed battery housing, the disclosed embodiments are also applicable to other embodiments where an isolated or embedded switch is to be activated. In the following figures, more detail is provided regarding the battery related embodiments described above. 
         [0030]    Referring again to  FIG. 2 , sealed battery  310  is enclosed within housing  110 , along with various circuit components to completely discharge battery  310  upon user demand. Reed switch  140  provides a non-invasive method to control the internal electronics necessary for discharging the electrical potential of the battery. Accordingly, sealed housing  110  encloses and isolates the complete discharge device or circuits that are held in an inactive status during the life of battery  310 , by an ever present externally applied magnetic field source  210  situated within depression  212  of the battery housing  110 , located in the proximity of internal reed switch  140 . 
         [0031]    In the absence of a magnetic field, NC reed switch  140  closes, thereby providing a voltage to trigger silicon controlled rectifier (SCR)  350 , or a similar semi-conductor device, which is “locked” or forward biased to allow current to pass through load resistor  352  until battery  310  is depleted of substantially all electrical potential. Notably, the magnetic source  210  and reed switch  140  should be in place before the CDD is connected to assure no premature discharge of the battery. 
         [0032]    In the exemplary embodiment depicted in  FIG. 3 , a magnetic field source  210  is operatively affixed within depression  212 , at a position on the outside of sealed housing  110 , in proximity to reed switch  140 . Reed switch  140  (e.g., a normally-open or normally-closed device) may be used as a passive switch to conduct an electrical current that is subsequently used to forward bias a semi-conductor component, such as a thermister, selenium controlled rectifier (SCR), a triac, or insulated gate bipolar transistor (IGBT) for example, for the purpose of activating a complete discharge device. Alternatively, reed switch  140  may be a nominally open switch and on its own operate in the manner of a switch suitable for providing a limited current flow directly through resistor  352 , in response to variation in an externally applied magnetic field. The magnetic field source (magnet or magnetic coil) used to actuate the sensor  140  can be provided by most any object that exhibits the characteristics of a magnetic field. However, in consideration of power conservation an electro-magnet, while providing substantially more magnetic force, could potentially yield an undesirable continual current drain on the battery. The same would be true for a dynamic electronic switch, such as a Hall-effect detector, which necessitates a continual standby circuit drain on the battery or other power source to be operable. In this regard mechanical reed switch  140  provides a significant advantage as a passive switching device, dependent only upon a change in magnetic field for operability. 
         [0033]    As further illustrated in  FIG. 3  housing  110  is designed to be impervious to the surrounding atmosphere, especially salt water, hence the requirement for a non-invasive and passive external control of battery operation. As a further aspect of the embodiment, a second reed switch  142  could conceivably be associated with a circuit designed to indicate the remaining charge in the battery. In this situation, due to the current measurement required to ascertain the remaining battery power, a momentary switch  214  is activated by, for example, sliding magnetic field source  210 , within cavity  212 , over reed switch  142 . Once the battery life is displayed a spring could return magnet  210 , of momentary switch  214 , to a neutral position, allowing reed switch  142  to return to the normally open position. Notably, this switch embodiment is adaptable to either normally closed or open operation, and can be momentary in either configuration. 
         [0034]    Now, referring to  FIG. 4 , the electrical elements of an exemplary complete discharge device are presented, including as at least three functional elements; (i) switching circuit  306 , (ii) complete discharging load connection  304  and (iii) discharge indicator  302 . As previously noted, reed switch  140  essentially provides the trigger current from a voltage divider comprising resistors  146  and  144  to the battery current discharge circuit within section  304 , in this case SCR  350 . Load resistor  352  is used to dissipate the heat generated from the current of the residual battery power (watts), as a function of voltage times the current [P=(I)(E)]. Once triggered, SCR  350  will remain in a conductive state until the current drop across resistor  352  falls below 3 mA. Concurrently, as the residual power is being consumed and dissipated across resistor  352 , LED  345  provides an indication of such dissipation, for example, being illuminated during discharging and turning off once the battery discharge cycle has been completed. 
         [0035]    It will be appreciated by those skilled in the art that an electrical “latch” is preferred as the control for the CDD to assure complete or adequate discharge of the battery, wherein once discharge is initiated, regardless of any subsequent replacing of the magnetic field source  130 , discharge continues to completion. Therefore, it is noted that when SCR  350  is turned on by a positive gate current it will remain in the latched and forward conductive state, independent of the gate current initially passed from reed switch  140 , as long as the anode to cathode current remains above a specific holding level. For example, an industry standard SCR, such as C106 from Motorola and others, will conduct up to a maximum current of 4 amps (DC) and will subsequently turn off only when the current reaches a minimum holding level of 3 mA., which would be indicative of a fully discharged battery. Additionally, a visual discharge indicator, such as light emitting diode (LED)  345  is illuminated as long as current is being dissipated across load resistor  345  whereas at the time battery  310  is completely discharged LED  345 , will be off. 
         [0036]    An alternative embodiment for the use of a magnetically activated reed switch  140 , within battery case  110 , is shown in the functional schematic of  FIG. 5 . Referring to  FIG. 5 , an internal connection, caused by switch  140  and SCR  350  results in the external terminal  158  to substantially be one and the same as the internal terminal  530  of battery cell  310 . Alternatively, the same circuit within housing  110  could cause at least one of the battery terminals to be electrically isolated and disconnected from the external terminal  158  to prevent accidental discharge via a short circuit between the external terminals when not in service. Accordingly,  FIG. 5  illustrates a general schematic including a battery terminal switching circuit whereby the DC power to positive terminal  530  is switchable from (i) an open external terminal for storage transporting and disposal to (ii) terminal  158  having positive power applied from internal terminal  530 , when in use. As is evident in  FIG. 5 , SCR  350  provides the basis for positive external terminal  158  to be electrically connected and/or disconnected from the primary cell(s) of battery  310 . When external magnet  210  is removed from battery case  110 , reed switch  140  detects a change in the magnetic field and gates SCR  350  which, in turn, is forward biased to allow the terminal  158  to be electrically in connection to the positive terminal  530  of battery  310 . 
         [0037]      FIG. 6  is yet another example of a system for magnetically motivating a passive internal switching device that is sealed within a housing. Like the mechanically biased reeds of the earlier embodiments, actuator  630  is also a magnet and is physically connected to a spring-biased slider switch  650  to activate an associated circuit. The position of actuator  630  is determined by the magnetic attraction of actuator  630  to the magnetic field source  620  and the opposing force of the attached spring  640 . When the magnetic field source  610  is moved a sufficient distance away from the actuator  630 , the force of the spring  640  overcomes the magnetic field force and actuator  630  changes position to an off state. Magnetic field source  220  is mounted outside of housing  110  and is moveable. In this embodiment, actuator  630  comprises a simple magnet whereby the alignment of the poles with magnetic source  220  poles causes actuator  630  and thereby a contactor in switch  650  to move towards the closed direction. On the other hand, opposing pole alignment (e.g. N→S and S→N), in combination with spring  640  may be used to cause switch  650  to be held in a normally closed position. 
         [0038]    Referring next to  FIG. 7 , depicted therein is a circuit that may be used in accordance with the embodiments disclosed herein. Although the circuit symbols and labels depict particular characteristics of the components, it should be appreciated that such information is for purposes of describing the circuit, and that alternative characteristics or components may be used or substituted to accomplish a similar function. For example, the value of the SCR load resistor  706  could vary depending upon the battery and the desired rate of the discharge. In operation selenium controlled rectifier (SCR)  716  will forward conduct once the magnetic field is removed from normally closed reed or similar switch  704 , which then opens, thereby placing the load resistor  706  directly across the terminals of battery  702 , in order to bleed off any residual energy. Accordingly, light emitting diode  720  will be on as long as there is a voltage drop across load resistor  706 . Concurrently, the disconnect circuit relies on comparator  708  to sense the opening of switch  704  in order to gate MOSFET  714 , which in turn disconnects the internal ground return from the external negative terminal. 
         [0039]    Although the various embodiments described herein are directed to the activation of a device or circuit in a sealed housing using a non-mechanical stimuli, for example, in response to a change in an externally applied magnetic field, it is understood that aspects of the disclosed embodiments may also be suitable for use with alternative energy types or fields. 
         [0040]    While various examples and embodiments have been shown and described, it will be appreciated by those skilled in the art that the spirit and scope of the disclosure are not limited to the specific description and drawings herein, but extend to various equivalents thereof as well as other modifications and changes.