Abstract:
A method and apparatus which extends the useful life of a lead-acid type battery by applying conductive cooling directly to the bottom surface of the battery to maintain the battery at a constant temperature of about 25° C. regardless of the ambient temperature surrounding the battery.

Description:
[0001]    This is a divisional application of co-pending, commonly-owned U.S. patent application Ser. No. 09/567,528, filed May 9, 2000 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to extending the life of back-up batteries used in an outdoor equipment cabinet and, more particularly, to a novel battery cooling system which maintains the temperature of back-up batteries at an ideal level despite temperature extremes imposed by ambient conditions.  
           [0004]    2. Description of the Related Art  
           [0005]    Many forms of electronic equipment, of necessity, must be located in an outdoor environment. Such equipment in typical form may be telecommunications and cable television equipment including active electronic and optical systems and passive cross-connect and splicing fields. It is essential that such equipment be protected from a wide range of ambient temperatures and inclement climatic conditions such as rain, snow, sleet, high winds and sand storms as well as other in situ environmental issues like seismic vibration, etc. To this end, cabinet enclosures have been developed to house such electronic equipment in a highly weather tight manner.  
           [0006]    The type of electronic equipment that is typically housed in an outdoor cabinet, particularly in active systems, is known to generate considerable amounts of heat in operation. Further, in many environments the ambient air can become very warm and heat up the air internal to the cabinet. Many active systems enclosed in outdoor equipment cabinets employ battery back-up means to ensure reliable performance. Often the batteries are of a lead-acid construction which is known to be adversely affected by temperature extremes in terms of battery life. In fact, a standard lead-acid battery performs optimally at a temperature of about 25° C., as opposed to more elevated temperatures which can reach as high as 65° C. in some outdoor environments. At 25° C. battery life is about 10 years. However, for every 10° C. increase battery life is cut in half. Temperature fluctuations also are detrimental to battery life.  
           [0007]    Systems are known for cooling batteries for outdoor equipment cabinets exposed to relatively high ambient temperatures. For example, Han et al., U.S. Pat. No. 5,934,079, teach a cabinet wherein back-up batteries are disposed underneath a heat sink through which air circulates at a regulated temperature utilizing forced convection heat transfer. Other known convection systems includes the CHAMPION THERMOSAFE cooling system, a thermoelectric device having a very low coefficient of performance. A Zome Work COOL CELL cooling system uses a water thermosyphon. Another company buries the batteries underground but this also has many drawbacks including the need for additional equipment.  
           [0008]    Another drawback to existing systems is that they may be stand alone units instead of being integrated with the equipment cabinet.  
           [0009]    It is important to develop a system which does not expose batteries to high temperatures or substantial temperature variations if long life for the battery is an objective. For commercial purposes, such a system must be reliable, efficient and reasonably priced.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is an object of the present invention to provide a battery cooling system for back-up batteries used for outdoor equipment cabinets wherein the batteries are consistently maintained at a predetermined constant temperature (or within a very small temperature range), and preferably a temperature on the order of 25° C. Another advantage of the present invention is to provide such a battery cooling system which is incorporated in an outdoor equipment cabinet of known design without major redesign of the cabinet. Still further, an aim of the present invention is to provide such a system which is readily manufacturable and cost-effective to produce. Another object of the present invention is to extend battery life. Yet another advantage of the present invention is that it is highly reliable.  
           [0011]    The present invention improves over the prior art by providing an apparatus for extending the useful life of a lead-acid type battery by applying conductive cooling directly to the bottom surface of the battery to maintain a constant temperature of about 25° C. regardless of the ambient temperature surrounding the battery.  
           [0012]    A more complete understanding of the present invention and other objects, aspects, aims and advantages thereof will be gained from a consideration of the following description of the preferred embodiments read in conjunction with the accompanying drawings provided herein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic elevation view of an outdoor equipment cabinet employing a back-up battery cooling and heating system.  
         [0014]    [0014]FIG. 2 is an isometric view of an equipment cabinet illustrating one variation of the placement of a compressor and back-up batteries.  
         [0015]    [0015]FIG. 3 is an isometric view of an equipment cabinet illustrating another variation of the placement of a compressor and batteries of the present invention.  
         [0016]    [0016]FIG. 4 is an isometric view of the compressor and related apparatus of the present invention.  
         [0017]    [0017]FIG. 5 is a plan view of a cold plate.  
         [0018]    [0018]FIG. 6 is a plan view of a heating pad.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    While the present invention is open to various modifications and alternative constructions, the preferred embodiments shown in the drawings will be described herein in detail. It is understood, however, that there is no intention to limit the invention to the particular forms disclosed. On the contrary, the intention is to cover all modifications, equivalent structures and methods and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.  
         [0020]    Referring now to the drawing, FIG. 1 illustrates in schematic form an outdoor equipment cabinet designated generally by the reference numeral  10  which is designed to enclose active communications equipment such as banks of printed circuit boards. The cabinet is divided into an equipment chamber  12  and a battery chamber  14 . A bank of back-up batteries  16 , typically of the lead-acid type, are disposed in the separate battery chamber  14 . In accordance with the invention, a flat cold plate  20  is disposed beneath the batteries but in direct contact therewith. The cold plate  20 , sometimes also referred to as an evaporator, is connected by suitable conduits  22  and  24  to a compressor  30  which is designed to circulate a refrigerant through the cold plate  20  to achieve a predetermined temperature.  
         [0021]    Located beneath the cold plate  20  is a heating pad  32 . Once again, there is direct contact between the heating pad and the cold plate. Direct contact means that heat transfer will occur through conduction and not convection. That is, a cooled cold plate will engender heat flow from the batteries to the cold plate under warm ambient conditions. The same is true under cold ambient conditions. Heat from the heating pad will transfer by conduction to the cold plate and in turn be transferred to the batteries by conduction.  
         [0022]    The main objective here is to efficiently and effectively maintain the batteries at 25° C., plus or minus about 2° C. This will greatly prolong battery life in a reliable and relatively inexpensive manner.  
         [0023]    An insulation pad  34  is located beneath the heating pad and minimizes heat transfer to a concrete pad  35  which is typically used to mount equipment cabinets. The insulation pad may be made of high temperature plastic, one-eighth of an inch thick.  
         [0024]    The cabinet also encloses a heat exchanger  36  in the equipment chamber  12 . The heat exchanger sucks in ambient air  40  by a fan  42  through a set of louvers  44 . The used air is then exhausted through a second opening  46  back to the ambient environment.  
         [0025]    The air heated by the equipment in chamber  12  is moved through the heat exchanger by a second fan  50 . The air enters the heat exchanger through an opening  52  and exits back into the equipment chamber  12  through another opening  54 . The air from the equipment chamber  12  and the ambient air never mix even though heat exchange occurs. Moreover, the equipment chamber  12  is weather sealed so that air, dust, water and the like is kept away from the equipment except when the equipment is serviced. The compressor dissipates heat through an opening  56  in the cabinet.  
         [0026]    Another important advantage of the present invention is that the ambient air  40  passes through the battery chamber  14  before entering the heat exchanger  36 . To the extent the thermal mass (the batteries and cold plate) in the battery chamber is cooled by the cold plate, the ambient air experiences heat exchange in the battery chamber where this air is cooled before it enters the heat exchanger in the equipment chamber. The air entering the heat exchanger in the equipment chamber is at a lower temperature than would normally be the case, and hence, the heat transfer between the equipment air and the ambient air is improved since the temperature gradient between the two is initially greater.  
         [0027]    Referring now to FIG. 2, a cabinet  100  is shown although it is missing side walls and doors. The batteries are mounted behind a panel  102 , just below the compressor  104 . Ambient air louvers  106  are shown at the front of the cabinet. FIG. 3 illustrates a cabinet  110  having the batteries  112  and the compressor  114  both located in the battery chamber  116 .  
         [0028]    Referring now to FIG. 4, the compactness of the compressor and related parts are shown. This compactness means that existing cabinets do not have to be modified in any major way. A compressor system  58  is illustrated, including a compressor  60 , a fan  62 , a condenser  64 , an expansion valve  66 , a filter/dryer  68  and a recuperative heat exchanger  70 . These elements are all compactly packaged in a frame  72 .  
         [0029]    Referring now to FIG. 5, the cold plate is illustrated in more detail. The cold plate  20  is a half inch tall plate of aluminum having a serpentine three-eighths of an inch groove  120  for receiving a copper tube  122 . The copper tube is about one hundred and twenty inches long and is connected to the compressor  30  so that a refrigerant may be circulated between the cold plate (evaporator) and the compressor. In this way the batteries may be maintained at 25° C. A suitable refrigerant is known as  404 A and the compressor has a heat removal capacity of about 500 watts.  
         [0030]    The cold plate is a square in plan view having sides of about 20.5 inches. This size assumes four batteries which are disposed on top of the cold plate. The batteries each measure about 20 inches in length and 4.5 to 5 inches in width. The use of the cold plate insures a large surface area for contact between the batteries and the cold source. Such a large contact enhances conductive heat transfer. Thus the system is very efficient.  
         [0031]    Referring now to FIG. 6, the heating pad  32  comprises silicon rubber covers over heating coils. The heating pad uses resistive wire at 120 volts. The heating pad is operated in cold weather to maintain the batteries at about 25° C. In warmer weather the heating pad is not operated. The system may be AC or DC powered.  
         [0032]    It can now be appreciated that a system constructed according to the invention offers considerable advantages over prior art systems, and in particular, over forced convection cooling systems, by assuring that the temperature of the batteries is maintained at a near constant predetermined temperature due to their direct contact with the cold plate  20 , thereby providing for conductive heat transfer. Preferably, the desired constant temperature is set to about 25° C. which is the recommended temperature for maximizing the life of lead-acid type batteries. That is, rather than exposing the batteries to a wide range of temperatures, even with convection cooling, the present invention maintains an almost constant temperature at the most optimum level in either hot or cold ambient conditions. It has been found that the cold plate should be maintained at about 25° C. below zero for the batteries to be at 25° C. above zero.  
         [0033]    In addition to battery life extension, the method and apparatus described is simple, reliable and relatively inexpensive. The apparatus fits within existing cabinet structures and, thus, does not require a cabinet redesign.  
         [0034]    The specification describes in detail several embodiments of the present invention. Other modifications and variations will, under the doctrine of equivalents, come within the scope of the appended claims. For example, the exact material of the cold plate may change as may the arrangement of the copper tubing in relation to the cold plate. Moreover, the heating pad structure may also be different as may its material. Further, the location of the compressor may change as may the location of the batteries. All of these and other matters are considered equivalent structures. Still other alternatives will also be equivalent as will many new technologies. There is no desire or intention here to limit in any way the application of the doctrine of equivalents.