Abstract:
An overmolded in-line photovoltaic current regulating and heat sink device includes one or more diode elements connected at one or more leads to coils of electrically conductive material. The coils serve a dual purpose; they act as heat sinks to draw heat away from the diode and conduct it to the outside environment; and they act as inductor coils to regulate current through the device. These coils can either be of air core or ferromagnetic core construction. On the opposite end of the diode leads, the coils are connected to either a wire lead protruding from the device or a terminal housed in a connector. The entire assembly is encapsulated in a thermoplastic, thermoset, or combination thereof that maintains intimate thermal contact with the diode and coils. The device may include one or more fuse elements in place of, or in addition to, the one or more diode elements.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    The present invention relates to photovoltaic cell protection, in particular, the protection of photovoltaic cells, strings, or arrays from overheating caused by shading or other light obstruction. Such protection is achieved through the use of blocking or bypass diode elements. 
         [0003]    2. Description of the Related Art 
         [0004]    Historically, blocking and bypass diodes were housed primarily in junction boxes and combiner boxes, or integrated directly into photovoltaic modules. The in-line diode device allows installers and manufacturers to remove the diodes from the combiner boxes and junction boxes and, in some cases, eliminate combiner boxes all together. This development is known and being used in the industry. 
         [0005]    Photovoltaic assemblies often include fuses, which serve to protect photovoltaic cells, strings, or arrays from excessive currents that may cause damage to the components of the circuits through which the currents pass. In-line fuse devices may be similar in physical structure to in-line diode devices. 
         [0006]    Existing in-line diodes and in-line fuses are bulky and lack effective instruments for dissipating the heat generated when the diode or fuse is passing current. The typical method for dissipating heat is by use of a heat sink constructed of heat pipes, metallic blocks, or cylinders with fins. These designs are both costly and large, and are not practical for use in an in-line diode or in-line fuse system. 
         [0007]    The use of inductor coils to regulate current is known and employed in many industries. Inductors can be air cored or can contain a core of magnetic material (typically ferrite) to increase the inductance of the coil. The current conducting material is wound around the core and a magnetic field is created by the current passing through the conductor. This magnetic field stores energy and effectively resists changes in current through the device. 
         [0008]    However, none of those prior devices is adapted to regulate current in the device while optimizing heat transfer from the device without employing a large, costly, or otherwise impractical design. Accordingly, there exists a need for such a device. 
         [0009]    In particular, there exists a need for a system that provides an in-line diode or an in-line fuse, wherein coils within the device both regulate current, and act as heat sinks, dissipating heat along the length of the coils to the adjacent material and consequently to the outside environment. 
       SUMMARY OF THE INVENTION 
       [0010]    Accordingly, it is a principal object of the present invention to provide a device configured to provide photovoltaic cell protection by way of an in-line diode or in-line fuse. 
         [0011]    It is another principal object of the present invention to provide a device comprising an in-line diode or in-line fuse, wherein the device is configured to regulate the current passed through the device. 
         [0012]    It is still another principal object of the present invention to provide a device comprising an in-line diode or in-line fuse, wherein the device is configured to dissipate heat generated by the diode or fuse. 
         [0013]    A key feature of the invention is the use of current conducting material that conducts heat from a diode element or fuse element to an encapsulating material and consequently to the outside environment. The current conducting material may be wound into a coil so that it simultaneously acts as an inductor, having the inherent ability to regulate current passing through it. The invention, however, does not require that the current conducting material be wound into a coil, nor does it require that the current conducting material exhibit inductive properties. Whereupon this specification discloses a coil or coils, it should be understood that alternate configurations of current conducting material may be used to achieve heat conducting characteristics similar to those exhibited by a coil or coils. 
         [0014]    One or more diode or fuse elements are fixed to one end of the coil via soldering, welding, brazing, crimping, or other joining means that will ensure sound thermal and electrical contact. The other lead(s) from the diode or fuse element(s) may be joined to the end of another coil on the other side of the device, or in the case where only one coil is employed, to a wire protruding from the device or to an electrical terminal housed in a connector body. The free end(s) of the coil(s) are similarly joined to a wire protruding from the device or to a terminal. The protruding wires or terminals are connected to the wiring system of a photovoltaic array. 
         [0015]    The assembly of diode(s), or fuse(s), and coil(s) is encapsulated in an electrically insulative material, which maintains intimate thermal contact with the diode(s), or fuse(s), and coil(s). Preferably, the encapsulating material is formed of a thermoplastic, thermoset, or combination thereof, which may also be referred to as a plastic or resin. Due to the relatively low thermal conductivity of the encapsulating material (0.12 to 0.63 W/m·K) as compared to typical current conducting materials (23 to 388 W/m·K), the coils need sufficient surface area in contact with the encapsulating material to transfer the required heat to the material without simply transferring the heat directly through the conductor and into the adjacent wire connection or terminal. The coils must be of sufficient length to allow for optimal conduction of heat to the encapsulating material, without being too long so as to cause excessive electrical resistance across the device. The parameters of coil wire diameter, coil wire length, overall coil length, outside coil diameter, number of coil turns and turn pitch are all optimized to ensure maximum heat transfer, minimal electrical resistance and minimum cost. These parameters may vary depending on the current ratings of the diode(s) or fuse(s) employed by the device. 
         [0016]    The outside surface of the encapsulating material may have features, such as fins or fin-shaped embossments, disposed thereon to increase the outside surface area and improve the convective heat transfer properties. Due to the low thermal conductivity of the encapsulating material; the use of long, protruding heat sink fins is impractical and the fin length may be shorter than a typical metallic heat sink. 
         [0017]    A major advantage of this invention is its ability to optimize the transfer of heat to the surrounding environment by efficiently distributing the heat through the device. Another advantage of this invention is its ability to regulate current fluctuations passing through it, ensuring that the diode or fuse element, and any other devices to which this device is connected, experience steady current. 
         [0018]    Briefly described, those and other objects and features of the present invention are accomplished, as embodied and fully described herein, by a device comprising: a circuit element having a first lead and a second lead; a first coil formed of electrically conductive material, the first coil electrically connected to the first lead; and an insulative material, the insulative material encapsulating the circuit element and the first coil, and the insulative material maintaining intimate thermal contact with the circuit element and the first coil, wherein the first coil is configured to draw heat away from the circuit element and into the insulative material. 
         [0019]    The system may include one or more diodes, may include a fuse, or may include a combination of diodes and fuses. The system may include one or more coils having either air cores or ferromagnetic cores. The system may include either wires or terminals to facilitate connection to the wiring system of a photovoltaic array. The system may include insulative material formed of a thermoplastic, thermoset, or combination thereof having features, such as fins or fin-shaped embossments, disposed thereon to aid in the transfer of heat from the device to the surrounding environment. 
         [0020]    With those and other objects, advantages, and features of the invention that may become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the invention, the appended claims and to the several drawings attached herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1  is a perspective view of a current regulating device according to the present invention. 
           [0022]      FIG. 2  is a perspective view of the current regulating device of  FIG. 1 , further depicting connector bodies attached to components of the device. 
           [0023]      FIG. 3  is a perspective view of the current regulating device of  FIG. 2 , further depicting an overmold encapsulating components of the device. 
           [0024]      FIG. 4  is a perspective view of a current regulating device according to an alternative embodiment of the present invention. 
           [0025]      FIG. 5  is a perspective view of a current regulating device according to another alternative embodiment of the present invention. 
           [0026]      FIG. 6  is a side elevation view of a coil according to the present invention. 
           [0027]      FIG. 7  is a front elevation view of a coil according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    Several preferred embodiments of the invention are described for illustrative purposes, it being understood that the invention may be embodied in other forms not specifically shown in the drawings. 
         [0029]    Turning first to  FIG. 1 , shown therein is a device  10  including a diode  20  having a lead  22  at each of its opposite ends. An axial, leaded rectifier diode  20  is preferred. However, any rectifier or semiconductor diode  20  may be employed. Diode ratings can range from 1 A to 15 A and are generally 600V or 1000V. Electrically conductive coils  30  are positioned at each end of the diode  20 . Preferably, the coils  30  are wound or coiled wire manufactured from copper or aluminum or an alloy thereof. The coils include ends  32  that are fixed to the leads  22  of the diode  20  via soldering, welding, brazing, crimping, or other joining means to ensure sound thermal and electrical contact between the coils  30  and the diode  20 . Each coil  30  may be air cored (i.e., have no core or have a core formed with non-ferromagnetic material such as plastic or other insulating material) or have a ferromagnetic core (i.e., a core formed with ferrite or other ferromagnetic material). A ferromagnetic core can serve to increase the inductance of the coil  30 . The ends  34  of the coils  30  that are not connected to the diode  20  are fixed to device terminals  40  via soldering, welding, brazing, crimping, or other joining means to ensure sound thermal and electrical contact between the coils  30  and the terminals  40 . Accordingly, each coil  30  is connected in series between the diode  20  and a terminal  40 . A primary function of the coils  30  is to regulate the current that passes through the device  10 . Another primary function of the coils  30  is to optimize the transfer of heat to the surrounding environment by efficiently distributing the heat through the device  10 . 
         [0030]      FIG. 2  shows the device  10  with each of the terminals  40  housed in a separate electrically insulative connector body  50 . The terminals  40  are therefore not visible in  FIG. 2 . The terminals  40  may be electrically connected to the wiring system of a photovoltaic array (not shown) via the connector bodies  50 . The respective terminals  40  and connector bodies  50  need not be identical. Rather, each terminal  40  and each connector body  50  may be adapted for the specific use for which it is desired. For example, each connector body  50  may be a male, female, or other type of connector, and each may be adapted to connect to a solar panel, a combiner box, an inverter, or other appropriate assembly. The connector bodies  50  are configured to maintain intimate thermal contact with the terminals  40 . Preferably, the connector bodies  50  are formed of a hard, strong material, such as polycarbonate (PC). The connector bodies  50  may be formed separate from the overmold  60 , or may be formed integrally with the overmold  60 . 
         [0031]      FIG. 3  shows the device  10  with the diode  20  and the coils  30  encapsulated in an electrically insulative overmold  60 . The diode  20  and coils  30  are therefore not visible in  FIG. 3 . The overmold  60  may be formed with a plastic material such as a thermoplastic, thermoset, or combination thereof. A thermoplastic material is preferred, specifically one with a melting temperature below 200° C., such as thermoplastic elastomer (TPE), to ensure that the diode  20  is not damaged during molding. The overmold  60  is configured to ensure intimate thermal contact between the overmold  60 , the diode  20 , and the coils  30 . Heat is transferred from the diode  20  and coils  30  to the overmold  60 . The heat is subsequently transferred from the overmold  60  to the surrounding environment through the outside surface of the overmold  60 . Accordingly, the outside surface of the overmold  60  may include embossments, protrusions, contours, etchings, or other features disposed thereon to increase the outside surface area of the overmold  60 , thus increasing the convective heat transfer properties of the device  10 . For example, the outside surface of the overmold  60  may have fins  62  or fin-shaped embossments disposed thereon. The fins  62 , for example, may be ring-shaped or partial ring-shaped protrusions that are axially spaced along the length of the overmold  60 . Preferably, the material used to form the overmold  60  is such that the thermal conductivity of the overmold  60  is approximately 0.12 to 0.63 W/m·K. Due to the low thermal conductivity of the overmold  60 , the use of long, protruding heat sink fins is impractical. Accordingly, the length of the fins  62  may be shorter than a typical metallic heat sink. The overmold  60  also protects the diode  20  and coils  30  from damage that could result from exposure of the diode  20  or coils  30  to the surrounding environment. 
         [0032]    Preferably, the encapsulating material is a thermoplastic overmold  60  formed by an injection molding process. However, the encapsulating material is not limited to a specific type of material, nor is it limited to a specific manufacturing process. For example, the encapsulating material may be a compound formed by a potting process. 
         [0033]    A primary function of the coils  30  is to regulate the current that passes through the device  10 . An unregulated current spike passed through a diode  20 , for example, may damage the diode  20 , and impair its functionality. The coils  30  act as inductors, thereby reducing current fluctuations within the device  10  and ensuring that the diode  20  and any other devices to which the device  10  is connected experience steady current. 
         [0034]    Another primary function of the coils  30  is to optimize the transfer of heat to the surrounding environment by efficiently distributing the heat through the device  10 . Accordingly, the coils  30  draw heat from the diode  20  through the leads  22  of the diode, which maintain sound thermal contact with the coils  30 . Heat drawn by the coils  30  is transferred to the overmold  60  and consequently to the outside environment. The device  10  is configured such that enough heat is dissipated into the surrounding environment so as to ensure that the terminals  40  do not exceed the required safe temperatures as per the relevant industry standards. Examples of industry standards include UL1703, UL1741, UL6703, UL4248, NEC 2011, CEC Part 1 2009, and similar relevant IEC standards, all of which are incorporated herein by reference. The total heat dissipated by the device  10  is dependent on the current rating of the diode  20  employed by the device  10 . Heat (measured in Watts) is generated by the diode  20  and is equal to I 2 ×R (current squared times resistance). The heat is dissipated to the surrounding environment by free convection, wherein heat (in Watts) is equal to k×A×ΔT (convection constant times surface area times temperature difference between ambient air and device surface). Because the standards will dictate the maximum surface temperature and ambient temperature, it follows that increasing the surface area of the device  10  is the only means of increasing the heat dissipation. Therefore, a higher amperage diode  20  requires a larger device  10  to dissipate the heat generated by the diode  20 . 
         [0035]    The coils  30 , therefore, are specifically configured to optimize heat transfer within the device  10 . Due to the relatively low conductivity of the overmold  60  (approximately 0.12 to 0.63 W/m·K) as compared to typical current conducting materials (approximately 23 to 388 W/m·K), each coil  30  requires sufficient surface area in contact with the overmold  60  to transfer the required heat from the diode  30  to the overmold  60 , rather than transfer the heat from the diode  30  directly through the coil  30  and into the adjacent terminal  40 . The coils  30  must be of sufficient length to allow for optimal conduction of heat to the overmold  60 , without being too long so as to cause excessive electrical resistance across the device. For each coil  30 , the parameters of coil wire diameter, coil wire length, overall coil length, outside coil diameter, number of coil turns, and turn pitch, for example, can be optimized to ensure maximum heat transfer, minimal electrical resistance, and minimum cost. The parameters may vary depending on the power rating of the diode  20  employed in the device. Optimal heat transfer is a balance between minimizing the temperature of the terminals  40  and ensuring the overmold  60  does not exceed industry standard allowable temperatures. Generally, overall coil length, outside coil diameter, and number of coil turns will increase with increasing diode current ratings. The higher the diode current rating, the longer the total coil wire length must be. The parameters are then adjusted to package this total length of wire into a coil  30  that will fit into the design. 
         [0036]    In an alternative embodiment of the invention, shown in  FIG. 4 , the device  10  may include a fuse  70  instead of a diode  20 . Any type of axial fuse  70  may be utilized. Fuse current can range from 1 A (or less) to 30 A maximum. In the case in which the device  10  includes a fuse  70 , the fuse  70  is incorporated into the device  10  in the same manner as the diode  20  discussed herein. Although, in photovoltaic applications, a device  10  having a fuse  70  may serve a different function than a device  10  having a diode  20 , the function of the coils  30  is the same, regardless of whether the device includes a fuse  70  or a diode  20 . In a device  10  having a fuse  70 , the primary functions of the coils  30  are to regulate the current that passes through the device  10 , and to optimize heat transfer from the device  10  to the surrounding environment. In an embodiment of the device  10  comprising a fuse  70 , the total heat dissipated by the device  10  is dependent on the current rating of the fuse  70 . Therefore, a higher amperage fuse  70  requires a larger device  10  to dissipate the heat generated. The ability of the coils  30  to regulate current through the fuse  70  is particularly advantageous as this ability prevents the fuse  70  from unnecessarily interrupting a circuit as a result of a current spike introduced to the device  10 . 
         [0037]    In another alternative embodiment, shown in  FIG. 5 , the device  10  may include wires  80  instead of terminals  40 . The wires  80  are electrically connected to the ends  34  of the coils  30 . Portions of the wires  80  protrude from the device  10 , and those protruding portions may be connected to the wiring system of a photovoltaic array. In an embodiment of the device comprising wires  80 , each coil  30  transfers the required heat from the diode  30  or fuse  70  to the overmold  60 , rather than transferring the heat from the diode  30  or fuse  70  directly through the coil  30  and into the adjacent wire  80 . The use of wires  80  in place of terminals  40  may provide a low cost option for large installations employing the invention. 
         [0038]    In yet another alternative embodiment, the device  10  may include only one coil  30  electrically connected to the diode  20 . In this embodiment, the lead  22  of the diode  20  not connected to the coil  30  may be connected directly to a terminal  40 , or to a wire  80  protruding from the device  10 . A device  10  having two coils  30  will generally transfer more heat than a device  10  having one coil  30 . However, a device  10  having only one coil  30  may provide sufficient heat transfer in lower amperage applications of the invention. 
         [0039]    In yet another alternative embodiment, the device  10  may include a plurality of diodes  20 , which form a diode component. The diode component is positioned between, and thermally and electrically connected to the coil  30  or coils  30 . When a plurality of diodes  20  is used, the diodes  20  may be connected in series, or parallel, or both. When diodes  20  are connected in series to form a diode component, the voltage ratings of the diodes  20  are added to determine the voltage rating of the diode component. When diodes  20  are connected in parallel to form a diode component, the current ratings of the diodes  20  are added to determine the current rating of the diode component. The use of multiple diodes  20  may allow for the use of diode components having voltage or current ratings that are not readily available in single diode versions. 
         [0040]    In yet another alternative embodiment, the current conducting material that electrically connects the leads  22  of the diode  20  or fuse  70  to the terminals  40  or wires  80  need not be wound into a coil  30 , but may take on other configurations. An exemplary configuration includes a first strip electrically connecting the leads  22  of the diode  20  or fuse  70  to the terminals  40  or wires  80 , the first strip having one or more second strips, perpendicular to the first strip, protruding along the length of the first strip. Other configurations may include, for example, a tube or pipe, or a zigzag pattern. 
         [0041]    Turning to  FIGS. 6 and 7 ,  FIG. 6  shows a side view of the coil  30 .  FIG. 7  shows the coil  30  with its central longitudinal axis A extending perpendicular to the page. These figures are provided for exemplary purposes only and are not drawn to scale. Furthermore, the parameter values discussed with respect to  FIGS. 6 and 7  are provided as examples and are not intended to limit the scope of the invention.  FIGS. 6 and 7  show a coil  30  having n turns, where n is equal to five. Additional parameters of the coil  30  include coil length L C , outside coil diameter D C , outside coil radius R C , coil wire diameter D W , coil pitch P, coil end length L E , coil lead length L L , and coil lead thickness T L , wherein the coil pitch P is the distance between corresponding points of two adjacent turns, the coil end length L E  is the length of unturned conductive material at an end  32 ,  34  of the coil  30 , and the coil lead length L L  is the length of unturned conductive material at an end  32 ,  34  of the coil  30 , in which the current conducting material has been flattened to a thickness T L  to facilitate attachment of the diode  20  or the fuse  70  to the coil  32 . Another parameter, coil wire length L W  (not labeled in figures), is the total length of wire used to form the coil  30 . The ends  32 ,  34  of the coil  30  lie along an axis A, wherein A defines a central longitudinal axis of the coil  30 . The ends  32 ,  34  of the coil  30  need not be identical. Rather, each end  32 ,  34  may be adapted for the specific use for which it is desired. In an exemplary embodiment of the invention, the coil  30  is configured such that n=5, L C =20 mm, D C =10 mm, R C =5 mm, D W =2 mm, P=4 mm, L E =8 mm, L L =7 mm, and T L =1 mm. 
         [0042]    The quantity of heat transferred by the device  10  is determined by the equation 
         [0000]      q=k A ΔT,
 
         [0000]    wherein k is the heat transfer coefficient in W/m 2 K, A is the outside surface area of the device, and ΔT is the difference between the ambient air temperature and the device surface temperature. For natural convection in air, k can range from 5 W/m 2 K to 100 W/m 2 K. In an exemplary embodiment employing a thermoplastic elastomeric material for encapsulation, this design has been shown empirically to have a k value of approximately 25 W/m 2 K. Assuming an ambient temperature of 40° C. and a maximum surface temperature of 70° C., we calculate a total heat transfer of 5.3 W for a mid-range power version with an outside surface area of 7,067 mm 2 . A high power version with a surface area of 16,557 mm 2  is capable of dissipating 12.4 W of heat. 
         [0043]    Although certain presently preferred embodiments of the disclosed invention have been specifically described herein, it will be apparent to those skilled in the art to which the invention pertains that variations and modifications of the various embodiments shown and described herein may be made without departing from the spirit and scope of the invention. Accordingly, it is intended that the invention be limited only to the extent required by the appended claims and the applicable rules of law.