Abstract:
A battery, particularly of the lead acid type, has two terminals ( 4 ), one connected to the positive plates and the other to the negative plates. Each terminal ( 4 ) is located in an aperture in the battery lid ( 2 ) and a seal ( 10 ) located under the lid ( 2 ) surrounds the respective terminal ( 4 ). A space is also defined around each terminal and contains settable material such as epoxy resin cement in a set condition.

Description:
FIELD OF THE INVENTION 
     This invention relates to a battery, particularly but not exclusively of the lead acid type. 
     BACKGROUND OF THE INVENTION 
     In a known battery construction the positive and negative plates respectively are electrically connected together and respectively to positive and negative terminals by means of connecting straps. The plates are positioned in a box-like container, usually of moulded plastics material, and a lid is placed on top of the box, the terminals projecting through respective apertures in the lid. The lid is sealed to the box using a suitable cement or by heat-sealing and the terminals are sealed within the respective apertures to prevent unwanted leakage of fluid e.g. acid, fumes or gases such as hydrogen 
     It is also known to use a settable material such as an epoxy resin to seal the terminals in their respective apertures, but nevertheless leakages can and do occur. 
     SUMMARY OF THE INVENTION 
     It an object of the present invention to provide an improved construction which does not suffer from or suffers less from this disadvantage. 
     In accordance with the invention a battery comprises positive and negative plates, two connecting straps, one connected to the positive plates and the other to the negative plates, the plates and straps being enclosed in a box with a lid, two terminals, each one projecting from a respective connecting strap through a respective aperture in the lid, two zones on the underside of the lid each one surrounding one of the two apertures and facing an upper surface of the respective strap, two compressible seals, each one surrounding a respective aperture and being compressibly located between the respective zone and the facing upper surface of the strap, and two spaces, each one being defined around a respective terminal interiorly of the respective aperture, each space containing settable material in a set condition. 
     Preferably each seal, which may be a sealing ring, is compressed by a predetermined amount and may be retained within a groove which surrounds the respective aperture. The groove may have an overall predetermined depth less than the height of the seal and may be formed either wholly in the zone or wholly in the upper surface of the strap, or partly in the zone and partly in the upper surface of the strap. When the zone is in contact with the upper surface of the strap, the seal is compressed from its natural height to a height equal to the depth of the groove. The amount of compression is thereby predetermined. 
     Preferably retaining means is provided for each terminal to ensure that the upper surface of the respective strap and the respective zone remain in contact and that the compression of the seal is maintained. The retaining means may comprise a screw-threaded collar positioned on an externally screw-threaded portion of the respective terminal, a lower part of the collar contacting a region of the lid above the aforementioned zone. 
     At least one channel may be provided for enabling settable material to be fed to the space around each terminal, especially when the retaining means is maintaining the compression of the seal. The channel may be provided in the retaining means and/or in the lid. 
     The apertures may each be positioned at the base of a respective recess formed in the lid and the retaining means e.g. the collar is positioned wholly within the recess. Settable material may surround the retaining means. 
     Each terminal may have a lower part which is embedded in the material of the respective strap, the lower part comprising a flanged base portion and a narrower neck portion above the base portion. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     One embodiment of the invention will now be described by way of example only with reference to the accompanying drawings of which: 
     FIG. 1 shows a cross-section through part of a lead acid battery in accordance with the invention; 
     FIG. 2 shows a similar view to FIG. 1 but the side view of the terminal, collar and upper part of the strap being shown; and 
     FIG. 3 shows a sectional view on line III—III of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The battery according to the invention comprises a box  1  containing positive and negative plates (not shown) and a lid  2  secured to the box by a suitable bonding agent such as an epoxy resin cement. Alternatively the lid may be secured to the box by heat sealing. 
     The positive and negative plates respectively are connected by means of lead connecting straps  3 . These are formed in a conventional manner by casting so that lugs on the corners of the plates (not shown) and a lower part of a plated terminal  4  are embedded within the respective strap  3 . 
     The lid  2  is shaped to have two recesses  5 , at the base  6  of each of which is an aperture through which one of the terminals  4  protrudes. Underneath the base  6  is a zone comprising a horizontal surface  7  which contacts an upper horizontal surface  8  of the strap  3 . Formed within the zone at the base of the recess is an annular groove  9  having a generally rectangular cross-section which encircles the aperture. A seal in the form of a generally square cross-sectional elastomeric sealing ring  10  which has a natural height more than the depth of the groove  9  is compressed and retained within the groove  9  by contact with the upper surface  8  of the strap  3 . By making the depth of the groove  9  a predetermined amount less than the natural height of the ring  10 , the amount of compression of the sealing ring is predetermined and controlled. 
     The terminal  4 , machined from a copper alloy such as brass, has a hexagonal flange  11  at its base, and immediately above the flange, a neck portion  12 . Lead from the strap  3  enters and fills the neck portion  12  during casting so that the terminal  4  is securely located. The terminal  4  is generally cylindrical, part of the outer surface being formed with a screw thread  13 . Extending part of the way inside and from the top of the terminal  22  is an internally screw-threaded bore  14  for receiving a cable end (not shown). 
     An internally threaded collar  15  of moulded plastics material such as ABS is located on the terminal  4 . The lower part  16  of the collar has a smooth outer surface and is wider than the remainder. The under surface  17  of the collar contacts the upper surface  18  of the base  6  of the recess  5  encircling the terminal aperture and by tightening the collar  15  the zone  7  of the base correctly engages the upper surface  8  of the strap  3  and the seal  10  is compressed by the required amount. Short radially extending channels  25  are provided on the underside  17  of the collar  16  enabling settable epoxy resin to be poured into the recess  5  and flow into the space below the collar  16  surrounding the terminal  4  above the upper surface of the strap  3  to form a ring  26 , which is allowed to set. Channels (not shown) may alternatively or additionally be formed in the upper surface  18  of the base  6 . 
     The collar  15  has a central part  19  immediately above the lower part  16  which is formed with vertical ribs  20  to enable the collar  15  to be gripped firmly and tightened or loosened as required. Above the central part  19  is an upper portion  21  having an undercut shoulder  23  encircling the collar. This retains a separate cap  27  which has a top part  28  and a cylindrical part  24  which covers the top of the collar, the cylindrical part having an inwardly-projecting lip  29  which engages the undercut shoulder  23  In a snap-fit arrangement. The top part  28  covers the recess  5 , which is part filled with epoxy resin, but has a central aperture through which the top  22  of the terminal projects slightly. 
     When assembling the battery seals  10  are each placed in a respective groove  9 , one for each terminal  4 . The edges of the lid are covered in a suitable bonding agent e.g. epoxy resin and the lid lowered on to the box with each terminal projecting through its respective aperture in the base of a recess. A collar  16  is placed on to each terminal and screwed down tightly, causing the seal  10  to be compressed and the undersurface zone  7  of the base to firmly contact the upper surface of the strap. Epoxy resin is then poured into the recess. Some flows down the side of the collar, through the grooves  25  on its under surface and to fill the space between the inner side of the aperture and the outer side of the terminal. This is shown at  26  in the drawings. 
     The ring of resin so formed adheres to the lower part of the terminal, to the strap and to the lid to provide a secondary seal i.e. a safeguard if the elastomeric seal  10  falls. The adhesion of the resin to the lead (of the strap and terminal) and the ABS (of the lid) forms an effective barrier against acid transport, hence limiting corrosion. 
     Enough resin is poured into the recess to reach a height approximately level with the top of the collar. When the resin is set, the collar is effectively locked in position on the terminal. The cap  27  is then placed on the collar to cover the recess  5 . 
     This construction provides for reduced terminal corrosion and higher sealing integrity, thus leading to longer battery life.