Abstract:
A Kelvin connector for coupling to a post of a battery includes a first contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to a surface of the post. The connector also includes a second contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to the surface of the post. An electrical insulator between the first contact and the second contact urges the surface of the first contact and the surface of the second contact against the surface of the post and thereby forms a Kelvin connection to the post.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention generally relates to storage batteries. More specifically, the present invention relates to a Kelvin connector for engaging a battery post.  
           [0002]    Storage batteries, such as lead acid storage batteries of the type used in the automotive industry, have existed for many years. However, understanding the nature of such storage batteries, how such storage batteries operate and how to accurately test such batteries has been an ongoing endeavor and has proved quite difficult. Storage batteries consist of a plurality of individual storage cells electrically connected in series. Typically, each cell has a voltage potential of about 2.1 volts. By connecting the cells in series, the voltage of the individual cells are added in a cumulative manner. For example, in a typical automotive storage battery, six storage cells are used to provide a total voltage when the battery is fully charged up to 12.6 volts.  
           [0003]    Several techniques have been used to test the condition of storage batteries. These techniques include a voltage test to determine if the battery voltage is below a certain threshold, and a load test that involves discharging a battery using a known load. A more recent technique involves measuring the conductance of the storage batteries. This technique typically involves the use of Kelvin connections for the testing equipment. A Kelvin connection is a four point connection technique that allows current to be injected into a battery through a first pair of connectors attached to the battery posts, while a second pair of connectors is attached to the battery posts in order to measure the voltage across the posts. Typically, a pair of pivoting jaw-type battery clamps are respectively clamped to the battery posts and are designed to continue the circuit that includes the Kelvin connection. The jaws of each clamp are electrically isolated from each other. Pivoting jaw-type clamps provide tenuous mechanical and electrical connections to the battery contacts and could easily inadvertently fall off. Thus, pivoting jaw-type battery clamps are usually suitable only for temporarily connecting test equipment to battery contacts. Pivoting jaw-type clamps are not suitable for use with test modules that are integrated with the storage batteries and require relatively permanent connections to the battery posts.  
         SUMMARY OF THE INVENTION  
         [0004]    A Kelvin connector for coupling to a post of a battery includes a first contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to a surface of the post. The connector also includes a second contact having a surface which at least partially conforms to and is adapted to engage and electrically connect to the surface of the post. An electrical insulator between the first contact and the second contact urges the surface of the first contact and the surface of the second contact against the surface of the post and thereby forms a Kelvin connection to the post. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    FIGS.  1  to  3  illustrate simplified block diagrams of Kelvin connector s in accordance with embodiments of the present invention.  
         [0006]    FIGS.  4  to  6  illustrate simplified block diagrams of a method of forming a Kelvin connector in accordance with an embodiment of the present invention.  
         [0007]    [0007]FIGS. 7 and 8 illustrate simplified block diagrams of batteries with integrated testers employing Kelvin connector s in accordance with embodiments of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0008]    [0008]FIG. 1 illustrates a top plan view of a Kelvin connector  100  in accordance with an embodiment of the present invention. The same reference numerals are used in the various figures to represent the same or similar elements. Kelvin connector  100  is designed to engage a battery post  101 , and to electrically couple two external electrical conductors (not shown), such as conductors of a Kelvin connection, to the battery post  101 . Kelvin connector  100  is designed for use on a smooth wall battery post, although it could easily be adapted for use with other kinds of posts, such as, for example, a threaded battery post.  
         [0009]    As can be seen in FIG. 1, Kelvin connector  100  includes a pair of substantially identical opposing electrical contacts  102  mechanically connected together but electrically insulated from one another by means of and an insulator  104  that has a central opening  105 . Each contact  102  includes an insulator support portion  106  and a post grasping portion  108 . Each insulator support portion  106  of contacts  102  is embedded within the insulator  104 . Each post grasping portion  108  extends inwardly from the insulator support portion  106  into the central opening  105  of insulator  104  and engages battery post  101 . A pair of connection bars  110  that extend outwardly from contacts  102  and insulator  104  facilitate the connection of external circuitry to contacts  102 . Connection bars  110  include connection grooves  112  that hold ends of external electrical conductors. The ends of external electrical conductors may be soldered to connection bars  110 .  
         [0010]    In general, each electrical contact  102  may be formed from any electrically conductive sheet metal. Preferably, electrical contacts  102  are formed from copper and solder plated before formation of Kelvin connector  100 . Insulator  104  may be made of any suitable electrically insulative material such as plastic or composite material.  
         [0011]    The opening formed by post grasping portions  108  of the opposing contacts  102  is sized to form a tight fit with the battery post  101 . The opening  105  in insulator  104  is larger in diameter than the opening between grasping portions  108  and battery post  101  so as to have a substantial annular space between insulator  104  and the peripheral surface of battery post  101 . Once Kelvin connector  100  is positioned over battery post  101 , force is applied on connector  100  in a downward direction using, for example, a pipe having a bore that is substantially equal to the diameter of the opening  105  in insulator  104 . Thus, Kelvin connector  100  is forced onto battery post  101  such that electrical contacts  102  are in tightly gripping engagement with battery post  101 , thereby providing good electrical contact between post grasping portions  108  of electrical contacts  102  and battery post  101 . Kelvin connectors, such as  100 , are sized according to battery post diameters. Thus, a Kelvin connector for a positive post usually has a larger diameter than a Kelvin connector for a negative post since the positive battery post is typically larger in diameter than the negative battery post.  
         [0012]    [0012]FIG. 2 illustrates a Kelvin connector  200  in accordance with another embodiment of the present invention. As can be seen in FIG. 2, insulator support portions  106  of electrical contacts  102  include a plurality of grooves  202 , which are included to provide better coupling between insulator  104  and electrical contacts  102 . The remaining elements of Kelvin connector  200  are similar to the elements of Kelvin connector  100  of FIG. 1. As in the case of Kelvin connector  100  (FIG. 1) described above, insulator support portions  106  of Kelvin connector  200  are also embedded within insulator  104 . However, in Kelvin connector  200 , portions of insulator  104  extend through grooves  202 , thereby providing additional mechanical coupling between insulator  104  and electrical contacts  102 . The coupling occurs during the formation of Kelvin connector  200  wherein insulator  104  flows around grooves  202  and subsequently solidifies to form a strong mechanical bond with contacts  102 .  
         [0013]    [0013]FIG. 3 illustrates a Kelvin connector  300  in accordance with another embodiment of the present invention. As can be seen in FIG. 3, post grasping portions  108  of electrical contacts  102  include a plurality of teeth or prongs  302 , which are employed to grip battery post  101  instead of post grasping portions  108  with smooth contours shown in FIGS. 1 and 2. The remaining elements of Kelvin connector  300  are similar to the elements of Kelvin connector s  100  and  200  (FIGS. 1 and 2) and function as described above. Teeth  302  help resist axial removal of connector  300  from post  101  in a manner similar to a “Chinese finger trap”. Teeth  302  also prevent slipping, thereby insuring proper electrical connection between electrical contacts  102  and battery post  101 . Teeth  302  are shown disposed substantially in a common plane, but may extend, together or separately, in any number of different non-planer directions and may be of different shapes.  
         [0014]    [0014]FIGS. 4, 5 and  6  collectively illustrate a method of forming a Kelvin connector in accordance with an embodiment of the present invention. The method includes providing an electrically conductive piece which is illustrated in FIG. 4. Conductive piece  400  includes a pair of opposing electrical contacts  102  coupled together by shorting bars  402 . Each contact  102  includes an insulator support portion  106  and a post grasping portion  108 . Each insulator support portion  106  includes a plurality of grooves  202  and each post grasping portion  108  includes a plurality of teeth  302 . Contacts  102  also include connection bars  110  with connection grooves  112 . Insulator  104  is formed over support portions  106  of electrical contacts  102  such that insulator  104  extends through grooves  202 . In FIG. 5, conductive piece  400  is shown with support portions of contacts  102  embedded within insulator  104  after the insulator-formation process is complete. As can be seen in FIG. 5, insulator  104  is formed such that mechanical coupling between contacts  102  is provided. After formation of insulator  104 , shorting bars  402  are removed from conductive piece  400  to electrically isolate contacts  102  from each other. FIG. 6 shows Kelvin connector  600  formed by the method described above. As can be seen in FIG. 6, contacts  102  remain mechanically coupled together by insulator  104  after removal of shorting bars  402 .  
         [0015]    Embodiments of the present invention, described above, are particularly useful with a storage battery having an integrated battery test module for performing a battery test on electrical cells of the storage battery. As used herein “integrated” can include a separate battery test module which is attached to the battery housing. Integrated battery testers employing Kelvin connector s to couple a Kelvin connection to battery posts in accordance with the present invention are described below in connection with FIGS. 7 and 8.  
         [0016]    [0016]FIG. 7 is a top plan view of battery with an integrated tester with which the present invention is useful. As illustrated in FIG. 7, the integrated system  700  includes a battery  702  with posts  704  and  706  and a test module  708  mounted to the battery housing. A four point or Kelvin connection technique is used to couple battery test module  708  to battery  702 . Kelvin connections  710  and  712  are used to couple to battery posts  704  and  706 , respectively, of battery  702 . Kelvin connection  710  includes two individual connections  710 A and  710 B. Similarly, Kelvin connection  712  includes two individual connections,  712 A and  712 B. Post grasping devices  714  and  716  firmly grip battery posts  704  and  706  and couple them to electrical connections  710  and  712 . Post grasping devices  714  and  716  are Kelvin connector s (such as  100 ,  200 ,  300  and  600 ) of the present invention, described above. Battery test module  708  includes an optional input  718  and optional outputs  720  and  722 . Input  718  can be, for example, a push button or other input which can be actuated by an operator. Output  720  can be, for example, an LED or other type of visual indicator which provides a pass/fail indication of a battery test. Output  720  can also be in the form of a series of outputs which can comprise LEDs. In other aspects, output  722  can be used to send data, using any appropriate technique, to a remote computer or monitoring system. Output  722  can be used to provide a quantitative output of a battery test.  
         [0017]    [0017]FIG. 8 is a simplified circuit diagram of test module  708 . Module  708  is shown coupled to battery  702 . Module  708  operates in accordance with one embodiment of the present invention and determines the conductance (G BAT ) of battery  702  and the voltage potential (V BAT ) between posts  704  and  706 . Module  708  includes current source  800 , differential amplifier  802 , analog-to-digital converter  804  and microprocessor  806 . Amplifier  802  is capacitively coupled to battery  702  through capacitors C 1 , and C 2 . Amplifier  802  has an output connected to an input of analog-to-digital converter  804 . Microprocessor  806  is connected to system clock  808 , memory  810 , visual output  812  and analog-to-digital converter  804 . Microprocessor  806  is also capable of receiving an input from input device  816 . Further, an input/output (I/O) port  817  is provided.  
         [0018]    In operation, current source  800  is controlled by microprocessor  806  and provides a current in the direction shown by the arrow in FIG. 8. In one embodiment, this is a square wave or a pulse. Differential amplifier  802  is connected to posts  704  and  706  of battery  702  through capacitors C 1  and C 2 , respectively, and provides an output related to the voltage potential difference between posts  704  and  706 . In a preferred embodiment, amplifier  802  has a high input impedance. Circuitry  708  includes differential amplifier  820  having inverting and noninverting inputs connected to posts  704  and  706 , respectively. Amplifier  820  is connected to measure the open circuit potential voltage (V BAT ) of battery  702  between posts  704  and  706 . The output of amplifier  820  is provided to analog-to-digital converter  804  such that the voltage across posts  704  and  706  can be measured by microprocessor  806 .  
         [0019]    As described above, module  708  is connected to battery  702  through a four-point connection technique known as a Kelvin connection. This Kelvin connection allows current I to be injected into battery  702  through a first pair of posts while the voltage V across the posts  704  and  706  is measured by a second pair of connections. Because very little current flows through amplifier  802 , the voltage drop across the inputs to amplifier  802  is substantially identical to the voltage drop across posts  704  and  706  of battery  702 . The output of differential amplifier  802  is converted to a digital format and is provided to microprocessor  806 . Microprocessor  806  operates at a frequency determined by system clock  808  and in accordance with programming instructions stored in memory  810 .  
         [0020]    Microprocessor  806  determines the conductance of battery  702  by applying a current pulse I using current source  800 . The microprocessor determines the change in battery voltage due to the current pulse I using amplifier  802  and analog-to-digital converter  804 . The value of current I generated by current source  800  is known and is stored in memory  810 . In one embodiment, current I is obtained by applying a load to battery  702 . Microprocessor  806  calculates the conductance of battery  702  using the following equation:  
             Conductance   =       G   BAT     =       Δ                 I       Δ                 V                 Equation                 1                               
 
         [0021]    where ΔI is the change in current flowing through battery  702  due to current source  800  and ΔV is the change in battery voltage due to applied current ΔI. A temperature sensor  818  can be thermally coupled to battery  702  and used to compensate battery measurements. Temperature readings can be stored in memory  810  for later retrieval.  
         [0022]    Battery test module  708  may be built into battery  702  or mounted on battery  702  any time after it is built and coupled to battery posts  704  and  706  using Kelvin connector s  714  and  716  of the present invention.  
         [0023]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. Embodiments of the Kelvin connector of the present invention can be used to couple different electrical circuits to battery posts other than the tester circuits described above. In addition, although the electrical contacts of the Kelvin connector are shown as opposing each other in FIGS. 1 through 8, the electrical contacts may be positioned in any orientation without departing from the spirit and scope of the invention.