Abstract:
Apparatus and method of incorporating a resistive interface between an anode rod and a water heater tank connector. The resistive interface can include a conductive polymer material or coating.

Description:
BACKGROUND 
     Corrosion is an electrochemical process involving an anode (a piece of metal that readily gives up electrons), an electrolyte (a liquid that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the metal, electrons are liberated. When the electrons flow through the electrolyte to the cathode, the metal of the anode disappears, swept away by the electrical flow or converted into metal cations in a form such as rust. 
     A cathodic protection system is implemented in water heaters to prevent corrosion of the water heater tank. The cathodic protection system includes an anode rod, which is electrically connected to the metal water heater tank. The anode rod is comprised of a metal, such as aluminum, magnesium, zinc, or alloys, that is more active than the metal tank of the water heater. The water heater tank is generally comprised of glass coated steel. 
     When water is introduced into the water heater tank, a galvanic circuit is created between the metal tank (and/or connectors) and the anode rod. As a result, electrical current flows from the anode, through the water, to the cathode, thus, the anode rod begins to corrode. If the water supply has a high mineral content, the current flow will increase, resulting in a corresponding increase in the consumption of the anode rod. 
     The addition of a resistor in the galvanic circuit can reduce the consumption time of the anode. Current resistored anodes have utilized electronic component type resistors that are costly, relatively difficult to assemble, and the assembly is fragile. A fragile resistor connection can result in a loss of ground connection that disables the anode and results in accelerated corrosion failure of the water heater tank. 
     Occasionally, certain natural waters that are heated in the presence of a magnesium or aluminum anode can generate smelly water with a sulphur aroma that is undesirable. The addition of a resistor in the galvanic circuit can reduce the anodic current to address the smelly water issue while not detrimentally impeding the necessary current flow that is important for proper water heater tank passivation protection. 
     SUMMARY 
     One embodiment of the invention includes a connector assembly comprising a metal conduit adapted to receive an anode rod and an interface comprising a conductive polymer layer on at least a portion of the metal conduit. 
     In another embodiment, the invention includes a connector assembly comprising a first cap in electrical communication with an anode rod and a conductive polymer layer on at least a portion of the first cap. 
     In yet another embodiment, the invention includes a connector assembly comprising a first cap in electrical communication with an anode rod and a second cap including a conductive polymer layer, the second cap adapted to receive the first cap. 
     In another embodiment, the invention includes a method of providing a resistive interface between an anode rod and a water heater tank. The method includes the acts of applying a layer of a conductive polymer to at least a portion of a metal conduit, connecting the metal conduit to the anode rod, connecting a nipple to the metal conduit, and securing the nipple to the water heater tank. 
     In yet another embodiment, the invention includes a water heater comprising a tank, an inlet to add water to the tank, an outlet that withdraws water from the tank, a heat source to heat water in the tank, a connector assembly electrically coupled to and supported by the tank, the connector assembly comprising a metal conduit adapted to receive an anode rod, and a conductive polymer layer on at least a portion of the metal conduit, and an anode rod electrically coupled to and supported by the connector assembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial broken-away perspective view of a water heater. 
         FIG. 2  is a cross-sectional view of a portion of another construction of a water heater tank. 
         FIG. 3  is a cross-sectional view of a portion of another construction of a water heater tank. 
         FIG. 4  is an enlarged cross-sectional view of a connector assembly of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limited. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected,” “supported,” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting, supporting, and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. 
       FIG. 1  illustrates a water heater  10  including a permanently enclosed water tank  14 , a shell  18  surrounding the water tank  14 , and foam insulation  22  filling the annular space between the water tank  14  and the shell  18 . A water inlet line or dip tube  26  and a water outlet line  30  enter the top of the water tank  14 . The water inlet line  26  has an inlet opening  34  for adding cold water near the bottom of the water tank  14 . The water outlet line  30  has an outlet opening  38  for withdrawing hot water from near the top of the water tank  14 . The water heater  10  also includes a resistance heating element  42  that extends through a wall of the water tank  14  and an anode rod  46 ,  136 . While an electric water heater is shown, the invention can be used with other water heater types, such as a gas water heater, and with other water heater designs. 
       FIG. 2  illustrates a portion of an enlarged cross-sectional view of the water tank  14 , the water inlet line  26 , and the water outlet line  30 . The water outlet line  30  includes an anode rod assembly  50  according to one embodiment of the invention. The water tank  14  includes an opening  54  through which the anode rod assembly  50  is positioned. The water tank  14  includes a spud  58  secured to the top of the water tank  14  and is aligned with the opening  54 . The spud  58  is internally threaded and generally comprised of steel. 
     The anode rod assembly  50  includes an anode rod  46  comprised of a rod or metal wire  62  surrounded by metal  66 , which is more active than the metal that is used to make the water tank  14 . For example, the metal  66  on the anode rod  46  can be aluminum, magnesium, zinc, or an alloy. The anode rod  46  is electrically connected to the water tank  14  with a connector assembly  70 . The anode rod  46  is welded or secured in any other manner to the connector assembly  70 . 
     As illustrated in  FIGS. 2 and 4 , the connector assembly  70  includes a metal conduit  74  that is surrounded or over-molded with a conductive polymer material or a conductive coating  78 . The conductive polymer material or conductive coating  78  can be filled with carbon, for example, and/or any other conductive material and/or components. The metal conduit  74  can include the conductive polymer material or conductive coating  78  on the inner portion, outer portion, top portion, and/or bottom portion of the metal conduit  74 . The connector assembly  78  includes an opening  82  through which hot water from the water tank  14  can flow to the water outlet line  30  and to a destination. The opening  82  is generally located above the anode rod  46 . 
     The connector assembly  70  further includes a nipple  86  that is received in the spud  58  to secure the anode rod assembly  50  in the water tank  14 . The nipple  86  is positioned on or around the conductive polymer material or conductive coating  78 . The nipple  86  includes a circumferential groove  90  to receive a lock ring, which secures the connector assembly  70  to the anode rod  46  and generates a galvanic circuit between the anode rod assembly  50  and the water tank  14 . 
     The conductive polymer material  78  provides a resistance to ground potential in the galvanic circuit between the anode rod  46  and the water tank  14 . The resistance can be in the range of about 5 ohms to about 500 ohms. The resistance also can be in the range of about 30 ohms to about 60 ohms. 
     In one construction, the conductive polymer material or conductive coating  78  can be applied only to an area  94  on the metal conduit  74  where the nipple  86  contacts the metal conduit  74  (e.g., a sleeve on the area  94  on the metal conduit  74  where the lock ring is applied on the nipple  86 ). In this construction, the conductive polymer material  78  provides a resistance to ground in the galvanic circuit between the anode rod  46  and the water tank  14 . The resistance can be in the range of about 5 ohms to about 500 ohms. The resistance also can be in the range of about 30 ohms to about 60 ohms. 
       FIG. 3  illustrates a portion of an enlarged cross-sectional view of a water tank  104 . A water inlet line or dip tube  116  and a water outlet line  120  enter the top of the water tank  104 . The water inlet line  116  has an inlet opening  124  for adding cold water near the bottom of the water tank  104 . The water outlet line  120  has an outlet opening  128  for withdrawing hot water from near the top of the water tank  104 . The water tank  104  also includes a resistance heating element that extends through a wall of the water tank  104  and an anode rod  132 . 
     The water tank  104  includes an anode rod assembly  136 . The anode rod assembly  136  can be utilized at a location on the water tank  104  other than the water outlet line  120  of the water tank  104 . The water tank  104  includes an opening  140  through which the anode rod assembly  136  is positioned. The water tank  104  includes a spud  144  secured to the top of the water tank  104  and is aligned with the opening  140 . The spud  144  is internally threaded and generally comprised of steel. 
     The anode rod assembly  136  includes the anode rod  132  comprised of a metal wire  148  surrounded by metal  152  that is more active than the metal that is used to make the water tank  104 . For example, the metal  152  on the anode rod  132  can be aluminum, magnesium, zinc, or alloys. The anode rod  132  is electrically connected to the water tank  104  with a connector assembly  156 . The connector assembly  156  includes a stainless steel cap  160  that is electrically connected to the metal wire  148 . The connector assembly  156  includes a conductive polymer material or conductive coating  164 , (referred to hereinafter as the conductive cap  164 ) that is applied to, supported by, and/or secured to the stainless steel cap  160 . 
     The connector assembly  156  includes a metallic fitting  168  (e.g., ¾″ NPT fitting) that is received in the spud  144  to secure the anode rod assembly  136  in the water tank  104 . The fitting  168  includes a counterbore  172  that can receive the anode rod  132  (including the stainless steel cap  160  and the conductive cap  164  or a conductive coating applied to the stainless steel cap  160 ). The conductive cap  164  or conductive coating on the stainless steel cap  160  can interface with the fitting  168  and or the counterbore  172 . The fitting  168  has a mechanical groove  176  applied to the external diameter during the assembly process, which secures the connector assembly  156  to the anode rod  132 . 
     The connector assemblies  70  and  156  are more robust than a conductive all plastic threaded connector assembly that secures the anode rod in the water heater tank. A plastic connector is expensive to mold and is more prone to breakage than a metal connector. 
     Various features and advantages of the invention are set forth in the following claims.