Abstract:
A junction box used for making electrical connections to a photovoltaic panel. The junction box has two chambers including a first chamber and a second chamber and a wall common to and separating both chambers. The wall may be adapted to have an electrical connection therethrough. The two lids are adapted to seal respectively the two chambers. The two lids are on opposite sides of the junction box relative to the photovoltaic panel. The two lids may be attachable using different sealing processes to a different level of hermeticity. The first chamber may be adapted to receive a circuit board for electrical power conversion. The junction box may include supports for mounting a printed circuit board in the first chamber. The second chamber is configured for electrical connection to the photovoltaic panel. A metal heat sink may be bonded inside the first chamber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/641,690 filed Mar. 9, 2015, which is a continuation of U.S. patent application Ser. No. 13/901,706 filed May 24, 2013 (now U.S. Pat. No. 9,006,569, issued on Apr. 14, 2015), which is a continuation of U.S. patent application Ser. No. 12/785,773 filed May 24, 2010 (now U.S. Pat. No. 8,476,524 issued on Jul. 2, 2013), which claims benefit from U.S. patent application 61/180,455 filed May 22, 2009. The disclosures of the above-identified applications are incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a junction box for power sources, and specifically to a junction box for electrically connecting to a photovoltaic panel. 
     2. Description of Related Art 
     A photovoltaic module or photovoltaic panel is a packaged interconnected assembly of photovoltaic cells, also known as solar cells. Since a single photovoltaic module can only produce a limited amount of power, commercial installations include several modules or panels interconnected in serial and in parallel into a photovoltaic array. Electrical connections are made in series to achieve a desired output voltage and/or in parallel to provide a desired amount of current source capability. A photovoltaic installation typically includes the array of photovoltaic modules, an inverter, batteries and interconnection wiring. 
     When part of a photovoltaic module is shaded, the shaded cells do not produce as much current as the unshaded cells. Since photovoltaic cells are connected in series, the same amount of current must flow through every serially connected cell. The unshaded cells force the shaded cells to pass more current. The only way the shaded cells can operate at a higher current is to operate in a region of negative voltage that is to cause a net voltage loss to the system. The current times this negative voltage gives the negative power produced by the shaded cells. The shaded cells dissipate power as heat and cause “hot spots”. Bypass diodes are therefore integrated with the photovoltaic modules to avoid overheating of cells in case of partial shading of the photovoltaic module. 
     Blocking diodes may be placed in series with cells or modules to block reverse leakage current backwards through the modules such as to block reverse flow of current from a battery through the module at night or to block reverse flow down damaged modules from parallel-connected modules during the day. 
     Electronic modules may be integrated with the photovoltaic modules which perform electrical conversion, e.g. direct current (DC) to direct current conversion, electrical inversion, e.g. micro-inverter, or other functions such as monitoring of performance and/or protection against theft. 
     U.S. Pat. No. 7,291,036 discloses a photovoltaic connection system including a connection box with for surface mounted diodes mounted on a printed circuit board inside of the connection box. The connection box optionally includes a metal plate mounted inside the lid of the connection box as a heat sink for dissipating heat from the diodes. 
     The term “cable gland” as used herein refers to a device used for the entry of electrical cables or cords into electrical equipment and is used to firmly secure an electrical cable entering a piece of electrical equipment. 
     The term “in situ” in the context of the present invention refers to bonding or attaching during manufacture, e.g. injection molding, of a part as opposed to attaching after manufacture of the part. 
     BRIEF SUMMARY 
     According to an aspect of the present invention there is provided a junction box used for making electrical connections to a photovoltaic panel. The junction box has two chambers including a first chamber and a second chamber and a wall common to and separating both chambers. The wall may be adapted to have an electrical connection therethrough. The two lids are adapted to seal respectively the two chambers. The two lids are configured to be on opposite sides of the junction box relative to the photovoltaic panel. The two lids may be attachable using different sealing processes. One of the lids may be adapted to seal the first chamber and the other lid may seal the second chamber to a different level of hermeticity from that of the first chamber. The first chamber may be adapted to receive a circuit board for electrical power conversion of the power output of the photovoltaic panel. The junction box may include supports for mounting a printed circuit board in the first chamber. The second chamber is configured for electrical connection to the photovoltaic panel. The second chamber may optionally be configured to include diodes, e.g. bypass and/or blocking diodes. The junction box may have electrical connection terminals mounted inside the second chamber for connecting a circuit to the photovoltaic panel. A metal heat sink may be bonded inside the first chamber. The first chamber is adapted to receive a circuit board for electrical power conversion, and the metal heat sink is adapted to dissipate heat generated by the circuit board. The heat sink is placed inside an injection mold during manufacture of the junction box. The junction box may further include a pad adapted to provide thermal conduction and electrical insulation between the circuit board and the metal heat sink. The metal heat sink may include a dovetail structure adapted to prevent mutual separation of the metal heat sink from the junction box. The dovetail structure may be hollow. 
     According to an aspect of the present invention there is provided a junction box used for making electrical connections to a photovoltaic panel. The junction box has a metal heat sink bonded in situ inside the first chamber. The first chamber is adapted to receive a circuit board for electrical power conversion, and the metal heat sink is adapted to dissipate heat generated by the circuit board. The junction box optionally may have two chambers including a first chamber and a second chamber and a wall common to and separating both chambers. Two lids may be adapted to seal respectively the two chambers. The metal heat sink may include a dovetail structure adapted to prevent mutual separation of the metal heat sink from the junction box. The wall may have an electrical connection therethrough 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the invention are herein described, by way of example only, with reference to the accompanying drawings, wherein: 
         FIGS. 1A and 1B  illustrate isometric views of a junction box, according to an embodiment of the present invention. 
         FIG. 2A  shows details of cross section of the junction box indicated by dotted line XX in  FIG. 1A . 
         FIG. 2B  shows details of cross section YY of the junction box indicated by dotted line in  FIG. 1A . 
         FIGS. 3A and 3B  show isometric views of a heat sink according to another embodiment of the present invention. 
     
    
    
     The foregoing and/or other aspects will become apparent from the following detailed description when considered in conjunction with the accompanying drawing figures. 
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures. 
     By way of introduction, diodes and/or electronic modules within junction boxes attached to the photovoltaic modules dissipate heat. When insulating junction boxes are used, heat must be dissipated mostly through air inside the junction box. When metallic junction boxes are used then heat may be dissipated directly through the junction box. However, the use of a metallic junction boxes may be inconvenient because of regulations which require accessible metallic surfaces to be grounded and extra wiring is required. 
     Before explaining exemplary embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of design and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. 
     Referring now to the drawings,  FIG. 1A  shows an isometric view  10 A of a junction box  12 , according to an embodiment of the present invention. Junction box  12  is shown mounted on the back (or non-photovoltaic side)  4  of a photovoltaic panel  16 . Junction box  12  has cable glands  130  which allow for termination of cables inside of junction box  12 . Junction box  12  has an outer casing  102  and an access into junction box  12  using a lid  106 . 
       FIG. 1B  shows an isometric view of the underside of junction box  12  detached from photovoltaic panel  16 . The isometric view shows glands  130  and two sections A and B of junction box  12 . chamber A is bounded by the dimensions Z×X with chamber A covered by lid  108 . Lid  108  gives access into chamber A of junction box  12 . Chamber B is an open section which is bounded by dimensions X×Y and shows terminals  104 . A bypass diode  110  is connected between terminals  104 . According to a feature of the present invention, lid  106  removed to access chamber B and lid  108  used to access chamber A are on opposite sides of junction box  12 . 
       FIG. 2A  shows details of cross section XX of junction box  12  indicated by dotted line in  FIG. 1A , showing features of the present invention. Cross section XX shows chamber sections A and B of junction box  12  mounted on non-photovoltaic side  4  of photovoltaic panel  16  with clips  216 . The mechanical attachment between junction box  12  and photovoltaic panel  16  using clips  216  is such that junction box  12  is flat on photovoltaic panel  16  and a gasket may be used to seal the open end of chamber B. 
     Chamber A includes circuit board  260 , thermally conductive pad  262 , heat sink  264 , outer casing  102  and lid  108 . Circuit board  260  is preferably mounted on supports adapted to receive circuit board  260 . Thermal pad  262  provides electrical isolation and thermal conductivity between heat sink  264  and circuit board  260 . The component side of circuit board  260  is preferably in contact with thermal pad  262  so that heat created by the components of circuit board  260  is dissipated by heat sink  264  via thermal pad  262 . Radio Frequency Interference (RFI) emission from junction box  12  as a result of the operation of circuit board  260  is reduced by having the side of lid  108  coated in an electrically conductive shielding  108   a . Shielding  108   a  connects electrically to heat sink  264  to form a Faraday cage which suppresses RFI emission from junction box  12 . 
     Lid  108  according to an aspect of the present invention is preferably manufactured by an injection molding process. During the injection molding process of lid  108  a shield  108   a  may be placed in situ and bonded to lid  108  during the injection molding process. Thus, when lid  108  is attached to box chamber A; junction box  12  is electrically isolated by heat sink  264  and shield  108   a . Outer casing  102  and lid  108  additionally provide a non-electrically conductive isolation of heat sink  264  and shield  108   a  between the backside  4  of panel  16  and the exterior of junction box  12 . Lid  108  is optionally permanently and/or hermetically sealed to chamber A. 
     Chamber B includes terminal  104 , support  214 , bypass diode  110 , lid  106 , bus bar  212  and wall  202 . Wall  202  provides physical separation between chambers A and B. Electrical connectivity between circuit board  260  in chamber A and electrical connector  104  in chamber B is via bus bar  212 . Bus bar  212  is sealed in wall  202  in such a way as to preserve the desired hermeticity of chamber A for example against the ingress of water or humidity. Both electrical connector  104  and bus bar  212  are supported mechanically by support  214 . Support  214  may also provide hermetic sealing and/or electrical isolation between one end of connector  104  which connects to bus bar  212  and the other end of connector  104  which connects to connections provided by photovoltaic panel  16 . Bypass diode  110  connected to connector  104  may be located between support  214  or backside  4  of panel  16  or between support  214  and lid  106 . Lid  106  gives access to chamber B whilst junction box  12  is physically attached photovoltaic panel  16  but electrically isolated from panel  16 . A preferred mechanism of attaching lid  106  to junction box  12  is to use a rubber gasket arrangement such that chamber B is hermetically sealed against for example the ingress of water/humidity through lid  106  into chamber B. 
     According to another embodiment of the present invention, junction box  12  is constructed with a wall  202  that may be a double wall so that chamber A and chamber B are mutually separable and re-attachable. Similarly, bus bar  212  is re-connectable between chamber A and chamber B. In this embodiment, a failure within the electronics of circuit board  260  may be repaired by replacing chamber A with a new circuit board  260  without requiring disconnection of chamber B from photovoltaic panel  16 . Similarly, an electronics upgrade may be easily achieved. 
     Junction box  12  including casing  102 , lids  108 / 106 , heat sink  264 , and thermal pad  262  are preferably adapted to comply with temperature and insulation standard of IEC 61215 (Ed. 2) or other applicable industry standards for use with connection to photovoltaic panels. Junction box  12  and lids  108 / 106  may be manufactured by injection molding of acrylonitrile butadiene styrene (ABS) thermoplastic, Polybutylene terephthalate (PBT), Poly(p-phenylene oxide) (PPO) or a thermoset such as epoxy resin. 
       FIG. 2B  shows details of cross section YY of junction box  12  indicated by dotted line in  FIG. 1A , according to an embodiment of the present invention. Cross section YY is of chamber A mounted on backside  4  of photovoltaic panel  16 . Cross section YY shows outer casing  102 , heat sink  264  with dovetail structure  264   a , thermally conductive pad  262 , circuit board  260  and lid  108  with electrical shield  108   a.    
     The manufacture of box chamber sections A and B of junction box  12  in a preferred embodiment of the present invention is by an injection molding process. During the injection molding process heat sink  264  with or without dovetail structure  264   a  is placed inside box chamber A and is bonded in situ to box chamber A as a result of the injection molding process. 
     Additional strength of the bonding between heat sink  264  and box chamber A may be provided by a dovetail structure  264   a  which may be an integral part of heat sink  264 . A further function of dovetail structure  264   a  ensures that the bonding between heat sink  264  and chamber A remains intact when for example junction box  12  is subjected to thermal stresses as a result of electronic components operating inside chamber A, high ambient heat and sunlight when junction box  12  attached to a photovoltaic panel. Where a fastener, e.g. screw is used to fasten chamber A to heat sink  264 , the lateral dimensions of dovetail structure  264   a  is typically increased in order to accommodate the size of the fastener. A further feature of dovetail structure  264   a  is a hollow structure within dovetail structure  264   a  which allows for a deformation of dovetail structure  264   a . The deformation of dovetail structure  264   a  allows for the different rates of thermal expansion of enclosure  102  and heat sink  264 /dovetail structure  264   a  during the curing/cooling of the bond between heat sink  264  and enclosure  102  of chamber A. 
     Reference is now made to  FIGS. 3A and 3B  which show isometric views of heat sink  264  according to another embodiment of the present invention. Heat sink  264  has four holes  302 . Holes  302  are used to attach heat sink  264  into chamber A of junction box  12  using screws. The attachment of heat sink to chamber A may come as an additional step after the injection molding of junction box  12  or of a junction box  12  which is not injection molded. An additional thermal pad may be placed between heat sink  264  and enclosure  102  to ensure good contact between heat sink  264  and enclosure  102  after heat sink  264  is attached enclosure  102 . The deformable nature of the thermal pad used to accommodate non-uniformity in surfaces of the heat sink  264  and enclosure  102  due to manufacturing tolerances of heat sink  264 /enclosure  102 . Alternatively a thermally conducting glue or potting material may be placed between heat sink  264  and enclosure  102 . 
     The articles “a” “an” as used herein mean “one or more” such as “a heat-sink”, “a circuit board” have the meaning of “one or more” that is “one or more heat-sinks” or “one or more circuit boards”. 
     Although selected embodiments of the present invention have been shown and described, it is to be understood the present invention is not limited to the described embodiments. Instead, it is to be appreciated that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and the equivalents thereof.