Patent Application
20110293987
This invention relates to the field of batteries and more particularly to a system for providing a low-impedance connection to a lead battery terminal.
Battery packs such as flooded lead-acid, absorbed-glass-matt (AGM) and lead-acid often have lead plates that extend out of the battery pack as a lead terminal, so that there is no internal connection between the lead plates and a second metal such as copper.
Since lead-acid varieties of battery packs have very low internal impedance, such batteries are capable of producing very high output currents for, at least, short durations but often continuously. Many lead-acid based battery pack applications include very high current draws through the lead terminals. Because lead has a relatively high resistance, high current flowing through the lead creates several problems. The relatively high resistance coupled with the high current results in a relatively high voltage drop across the terminals and hence since power is the square of the current times the voltage, the power that needs to be dissipated by the terminals is often excessive, leading to reduced power delivered for the intended purposes and heat generation. In that lead has a relatively low melting point, there have been situations in which the battery terminals have melted during peak current draw from certain batteries.
What is needed is a system that will reduce the power loss of the battery terminals thereby increasing power delivery to the intended application and reducing heat generation at the battery terminals.
In one embodiment, a battery terminal interface is disclosed including a battery terminal interface shield made of a conductive metal having a lower impedance than an impedance of lead. The battery terminal interface shield has an inner surface and an outer surface. The inner surface contacts substantially all of an outer surface of a battery terminal and the outer surface contacts a cable connector, thereby distributing electrical current to/from the cable connector to substantially the entire outer surface of the battery terminal.
In another embodiment, a battery terminal interface is disclosed including a battery with battery terminals made of lead that having an outer surface. A cable connector is provided for connecting the battery terminals to a device that is powered by the battery. Battery terminal interface shields that are made of a conductive metal having a lower impedance than the impedance of lead are fitted on the battery terminals. Each of the battery terminal interface shields fit over one of the battery terminals, the inner surface of the battery terminal interface shields contacting substantially all of the outer surface of the battery terminals and an outer surface of the battery terminal interface shield electrically and physically connected to one of the cable connectors.
In another embodiment, a battery terminal interface is disclosed including a battery having two battery terminals made of lead. Each of the battery terminals have a horizontal planar top surface, three substantially vertical planar sides that meet at substantially right angles and one curved vertical side. There are two cable connectors for connecting the battery terminals to a device that is powered by the battery and two battery terminal interface shields made of a conductive metal having a lower impedance than the impedance of lead. Each of the battery terminal interface shields have a horizontal planar top inside surface, three substantially vertical planar inside walls that meet at substantially right angles and one curved vertical inside wall. Each of the battery terminal interface shields fit over one of the battery terminals such that for each battery terminal interface shield, the horizontal planar top inside surface electrically contacts the horizontal planar top surface of one of the battery terminals, the three substantially vertical planar inside walls electrically contact the three substantially vertical planar sides of the one of the battery terminals and the curved vertical inside wall electrically contacts the curved vertical side of the one of the battery terminals. Each of the cable connectors electrically contact one of the battery terminals such that electric current to/from each of the cable connectors is distributed to the horizontal planar top surface, the three substantially vertical planar sides and the curved vertical inside wall and the curved vertical side of one of the battery terminals.
The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which:
Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Throughout the following detailed description, the same reference numerals refer to the same elements in all figures.
Referring to
In high current applications such as starter motor cranking, where the battery 30 is called upon to deliver, for example, hundreds of amperes of current to a starter motor, any resistance of the battery terminals 32/34 reduces power that is needed, for example, in turning the starting motor. For example, in a 12V battery with an the overall terminal resistance of each terminals 32/34 of 0.01 ohms, a 200 amps current draw required to run a starting motor results in a 2 volt drop over each terminal 32/34 as calculated by V=IR or, V=200 A*0.01Ω. Since power is equal to the current times the voltage drop, the power dissipated by each terminal 32/34 is 400 Watts (P=V*1 or 2V*200 A)−800 Watts total when both terminals are included. The 400 watts per terminal is dissipated as heat instead of being used to turn the starting motor. Also, since each terminal drops 2 volts, for a 12V battery, the 2 volt drop per terminal results in only 8V delivered to the starting motor.
If the heat is not adequately removed from the lead battery terminals, the heat has the potential of melting the lead battery terminals.
A 10% decrease in the impedance of the battery terminal interface will result in a 10% decrease in the power dissipated by each of the battery terminals 32/34. In the above scenario, the voltage drop over each terminal is calculated as 200 A*0.09Ω (10% less resistance) or 1.8V and the power dissipated by each terminal 32/34 is 360 Watts (200 A*1.8V)−720 Watts when both terminals are included. Hence, even a small decrease in battery terminal impedance results in a significant decrease in power dissipated over the battery terminals 32/34, a significant reduction in heat generated during high current peaks and an increase in power and voltage delivered to the application.
Referring to
The battery terminal interface shield 20 is shaped and sized to fit tightly around the battery terminal 32/34 of, for example, the battery 30. It is anticipated that, in some embodiments, the battery terminal interface shield 20 is made of a material that is resilient and applies force, keeping one or more inside walls of the battery terminal interface shield 20 in contact with as much surface area of the lead battery terminals 32/34 as possible. For example, the battery terminal interface shield 20 has cuts or openings 24 (see
The battery terminal interface shield 20 reduces the impedance between the internal battery plates (anode and cathodes) and a connector 7 and screws 6 that are screwed through the connector 7 and into one of the threaded holes 36/38. Lead has a relatively higher impedance than many other metals such as copper, nickel and brass. Impedance values are typically provided in scientific tables for a given length and area of each material since direct current flows through the entire area of a conductive material. The impedance of lead for a given length and cross sectional area is 2.2×10−7 while for the same length and area, copper is 1.68×10−8, brass is 3.5×10−8 and nickel is 6.99×10−8 (at 20° C.). Using copper as a material for the battery terminal interface shield 20, the impedance of lead is approximately 13 times that of an equivalent area and length of copper. Although, determining the actual impedance of a connection between a small area of the surface and one of the threaded holes 36/38 to the internal plates of the battery pack 30 is complicated due to many different path lengths and cross sectional areas, it can be understood that by distributing the current over a greater area of the battery terminal will reduce the total impedance between the connector 7, cable 33/35 and the internal plates of the battery pack 30. Furthermore, current flow through the battery terminals 32/34 creates heat, the impedance of lead (and copper) increases with heat at approximately 0.39% per degree over 20° C. Therefore, the resistance of lead is around 2.372×10−7 for the same area at 40° C., as opposed to 2.2×10−7 at 20° C.
For example, implementing a copper battery terminal interface shield 20, having 13 times lower impedance than lead, will distribute power through contact points along many surfaces of the lead battery terminals 32/34, thereby increasing the overall cross-sectional area and/or decreasing the overall length of the electrical path between the cable connector 7 and the internal plates of the battery pack 30. The result is a lower impedance between the cable connector 7 and the internal plates of the battery pack 30 which, in turn, reduces power loss through the battery terminals 32/34 and reduces heating of the battery terminals 32/34. The reduced heating also leads to reduced power loss because, as shown above, as the lead battery terminals 32/34 are heated, the impedance of the lead terminals 32/34 increases, further increasing power loss and further increasing heating of the lead battery terminals 32/34. For some applications, the battery terminal interface shield 20 reduces heating enough to prevent melting of some lead battery terminals 32/34.
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The battery terminal interface shield 20 is shaped and sized to fit tightly around the battery terminal 32/34 of, for example, the battery 30 (see
The battery terminal interface shield 20 reduces the impedance between a connector screwed into one of the threaded holes 36/38 and the plates (anode and cathodes) of the internal battery. It is preferred, though other materials also perform well, to use copper as a material for the battery terminal interface shield 20 because the impedance of lead is approximately 13 times that of an equivalent area and length of copper. The battery terminal interface shield 20 distributes the current load over a greater area of the battery terminal, thereby reducing the total impedance between the connector 7 and the internal plates of the battery pack 30. Furthermore, current flow through the battery terminals 32/34 creates heat. The impedance of lead (and copper) increases with heat at approximately 0.39% per degree over 20° C. Therefore, impedance increases as the terminals 32/34 heat, reducing available power output and creating additional heat at the terminals 32/34.
For example, implementing a copper battery terminal interface shield 20, having 13 times lower impedance than lead, will distribute power through contact points along many surfaces of the lead battery terminals 32/34, thereby increasing the overall area and/or decreasing the overall length of the electrical path between the cable/connector and the internal plates of the battery pack 30. The result is a lower impedance between the cable/connector and the internal plates of the battery pack 30 which, in turn, reduces power loss through the battery terminals 32/34 and reduces heating of the battery terminals 32/34. The reduced heating also leads to reduced power loss because, as shown above, as the lead battery terminals 32/34 are heated to, for example, 40° C., the impedance of the lead terminals 32/34 increases, further increasing power loss and further increasing the temperature of the lead battery terminals 32/34. For some applications, the battery terminal interface shield 20 reduces heating enough to prevent melting of some lead battery terminals 32/34.
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Equivalent elements can be substituted for the ones set forth above such that they perform in substantially the same manner in substantially the same way for achieving substantially the same result.
It is believed that the system and method as described and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all of its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.
