GB2198876A - Electric Storage Cells - Google Patents

Abstract

An electric storage cell comprises a rectangular container (2) which accommodates a plurality of plates (6) and is substantially full of electrolyte. The container is sealed by a lid (4) above which is an open topped rectangular reservoir (20) which is closed by a loosely fitting lid (24). The interior of the reservoir (20) communicates with atmosphere and with the interior of the container via an apertured sleeve (16) which is screwed into a hole in the lid (4) and which has an external flange at its upper end which engages the floor of the reservoir (20) thereby connecting it to the battery lid. <IMAGE>

Description

ELECTRIC STORAGE CELLS The present invention relates to electric storage cells, particularly of lead acid type, and is primarily concerned with such cells of so-called motive power or traction type.

Conventional lead acid motive power cells comprise a rectangular container closed by a lid and are flooded with sulphuric acid electrolyte. When such cells are charged a considerable volume of gas is evolved and this results in an apparent temporary expansion of the electrolyte volume. For this reason, it is usual to provide a gap, typically of about 50mm, between the normal electrolyte level and the underside of the lid to provide a space into which electrolyte displaced by evolved gas may be accommodated. Without such an expansion space electrolyte would tend to leak from the container to the atmosphere through the vent commonly provided in the lid when the cell is overcharged.

Motive power cells are frequently required to deliver very substantial electric currents and at such times they tend to be "electrolyte limited", that is to say the maximum current which the cell can deliver is limited by the volume of electrolyte available. It would therefore be desirable to be able to fill the usual gap between the electrolyte level and the lid with electrolyte for the purpose of increasing the maximum current output of the cell, but, as mentioned above, this would run the risk of electrolyte being expelled from the cell when it is charged. A further possibility would be simply to make the container taller without increasing the size of the plates.

Quite apart from the fact that this would result in the cell requiring additional space, it would also require a lengthening of the relatively massive terminal pillars which connect the plates to the external terminals of the cell. These pillars are made of lead or lead alloy in the case of a lead acid battery and lengthening them would add substantially to both the weight and cost of the cell.

It is therefore an object of the present invention to provide an electric storage cell which overcomes the disadvantages referred to above and which in particular exhibits a decreased tendency to electrolyte limitation than a known cell of the same dimensions. It is a further object of the invention to provide such a cell having a construction which readily permits the conversion of a cell having a conventional construction to be in accordance with the present invention.

According to the present invention an electric storage cell, particular a motive power cell of lead acid type, comprises a container which accommodates a plurality of plates and is substantially full of liquid electrolyte and an electrolyte reservoir whose interior is situated above that of the container and communicates with that of the container and with the atmosphere. In the preferred embodiment the container is closed by a lid through which the interior of the container communicates with that of the reservoir.

Thus the cell of the present invention is substantially full of electrolyte and does not have the usual gap between the electrolyte level and the underside of the lid. The interior of the container communicates with an electrolyte reservoir or expansion box into which electrolyte displaced by gas evolved on overcharge may flow and from which the displaced electrolyte will subsequently flow back into the cell once the evolution of gas has terminated. In -normal operation, the cell may be full of electrolyte and the reservoir may contain no electrolyte, but it will be appreciated that the volume of electrolyte may be such that the reservoir always contains at least a certain proportion of it.The provision of the electrolyte reservoir also facilitates the topping up of the electrolyte since additional electrolyte or distilled water can simply be added to the reservoir and need not be poured in through a small filling orifice as is conventionally provided in the lid of motive power cells.

So-called "chicken feeders" are superficially similar to the con-struction of the present invention and one example of such a "chicken feeder" is disclosed in British Patent No. 320026. This prior patent discloses a cell with a central filling aperture through which the neck of an inverted electrolyte filling bottle extends. The neck of the filling bottle extends down to a level just below the level of electrolyte in the cell. A groove or slot is provided in the neck of the filling bottle or a bush in the filling aperture which acts as a venting path for the escape of gas evolved on overcharge of the cell.

Electrolyte is progressively lost by gassing and when the electrolyte level falls below the neck of the filling bottle air enters the bottle and the electrolyte is topped up. In the cell disclosed in this prior patent there is a gap between the underside -of the lid and the electrolyte level and, more importantly, the interior of the electrolyte filling bottle communicates only with the interior of the cell and not with the atmosphere. Thus when gas is evolved the electrolyte expands into the space below the lid and not into the filling bottle and the gas displaced from the said space is vented to atmosphere.

In the preferred embodiment of the present invention the lid affords an internally threaded aperture, e.g. within an upstanding boss, and the reservoir affords an aperture in its lower surface and is connected to the lid by means of an apertured externally threaded plug which passes through the aperture in the reservoir and engages the thread in the lid.The threaded aperture may constitute the aperture which is conventionally provided for the accommodation of a vented filling plus and thus a conventional motive power cell may be readily converted to be in accordance with the present invention by removing the vented filling plug and attaching an electrolyte reservoir or expansion box to the lid by means which connect the interiors of the reservoir and the container.

It is preferred that the size and external shape of the reservoir are substantially the same as those of the lid when viewed in plan and that the reservoir substantially covers the lid. This means that when a plurality of such cells are assembled to form a motive power battery the electrolyte reservoirs constitute a substantially continuous upper surface of the battery.

The cell will of course include two spacer terminals on its lid and it is preferred that the reservoir affords a space adjacent each terminal which may accommodate a terminal connector connecting that terminal to a further cell. It will be appreciated that in this preferred construction the reservoir effectively shields the cell terminals and the connectors connecting those terminals to a further cell or to electrical equipment whereby the insulating connector shrouds which are commonly fitted to protect the cell against short-circuiting need not be provided.

In one construction the reservoir is of rectangular shape in plan with a central trough extending across its lower surface through the base of which trough' the reservoir communicates with the container. It will be appreciated that the formation of the base of the reservoir with such a trough inherently results in two spaces being provided above the lid into which the two terminals may extend.

Furthermore, the trough will direct electrolyte displaced from the cell to a position from which it can readily flow back into the cell.

The reservoir may communicate with the atmosphere through a relatively small aperture but it is preferred that it does so through a relatively large aperture.

In the preferred embodiment the reservoir is provided with a lid or cover which extends over its entire plan area and does not form a gas-tight seal with the reservoir.

Further features and details will be apparent from the following description of one specific embodiment which is given by way of example only with reference to the accompanying drawings, in which: Figure 1 is a partly exploded and partly cut away perspective view of a lead acid motive power cell in accordance with the present invention; Figure 2 is a sectional elevation of the lid of the electrolyte reservoir; Figure 3 is a scrap vertical sectional view showing the connection of the electrolyte reservoir to the lid of the cell; Figure 4 is a scrap diagrammatic elevation showing the interconnection of two cells in accordance with the invention.

The cell comprises a rectangular container 2 which is sealed by a lid 4 and contains a plurality of positive and negative plates 6 which are separated by sheets of separator material 8 and are connected by respective plate straps 10 which in turn are connected to respective terminal pillars 12 extending through the lid.

Upstanding from the centre of the lid is an internally threaded boss 14 which conventionally receives a vented filling plug. In this case the boss 14 accommodates an apertured externally threaded ring or sleeve 16 at whose upper end is a radially extending flange 18 which engages the margin of a hole formed in the base of an electrolyte reservoir or expansion box 20 and thereby secures the reservoir to the lid of the cell. The joint between the base of the reservoir and the upper surface of the boss 14 is sealed by a circular sealing ring 22 which is T-shaped in crosssection.

The reservoir 20 comprises an open-topped, rectangular box which is closed by a loosely fitting lid 24. The box has four side walls 26 and in its floor there is a central trough 28, in the centre of the bottom of which is a hole through which the ring 16 passes. On each side of the trough 28 the base of the box is somewhat raised and is inclined downwardly and inwardly towards the trough. As best seen in Figure 2, the lid 24 comprises four triangular, substantially planar, downwardly and inwardly extending surfaces 30 which terminate at a central upstanding cruciform boss 32 by which the lid may be handled by the user.

Extending round the edge of the lid is a depending double flange 34 defining a gap which loosely accommodates the side walls 26 of the box.

As best seen in Figure 4, the provision of the trough 28 results in the base of the expansion box defining together with the cell lid two spaces which accommodate a respective one of the cell terminals.

Two external intercell connectors 36 and 38 are shown in Figure 1 and Figure 4 shows the accommodation of one of these intercell connectors 38 in a space defined by the lids and reservoirs of two adjacent cells. In use, the cell is normally full to the top with sulphuric acid electrolyte and the reservoir 20 is empty. When the cell is charged and substantial volumes of gas are evolved electrolyte is displaced from the cell into the reservoir 20 and the air displaced from the reservoir 20 escaped to atmosphere by virtue of the poor fit between the lid 24 and the box. When all the evolved gas has escaped to atmosphere the electrolyte in the reservoir is returned to the cell through the apertured plug 16.It will be appreciated that it is also possible for the volume of electrolyte to be such that a proportion of it is always present in the reservoir and that the electrolyte may be topped up very simply by adding distilled water to the reservoir after removing the lid 24. By virtue of the fact that the reservoir precisely overlies the lid of the cell the lids of adjacent cells assembled into a battery abut and thus provide a substantially continuous surface for the battery.

In the embodiment described above the cell container is substantially full of electrolyte whilst the plates terminate short, e.g.50mm short, of the lid and the volumetric energy density of the cell is higher than that of a conventional cell of the same dimensions by virtue of the elimination or reduction of the acid limitation. In an alternative embodiment, which is not illustrated, the plates extend substantially all the way to the lid, that is to say into the space which in a conventional cell constitutes the empty gas or expansion space. Such a cell is still acid limited but the volumetric energy density is increased by virtue of the provision of the additional plate area

Claims (8)

1. CLAIMS 1. An electric storage cell comprising a container which accommodates a plurality of plates and is substantially full of electrolyte and an electrolyte reservoir whose interior is situated above that of the container and communicates with that of the container and with the atmosphere.
2. 2. A cell as claimed in Claim 1 in which the container is closed by a lid through which the interior of the container communicates with that of the reservoir.
3. 3. A cell as claimed in Claim 2 in which the lid affords an internally threaded aperture and the reservoir affords an aperture in its lower surface and is connected to the lid by means of an apertured externally threaded plug which passes through the aperture in the reservoir and engages the thread in the lid.
4. 4. A cell as claimed in Claim 2 or Claim 3 in which the size and external shape of the reservoir are substantially the same as those of the lid when viewed in plan and the reservoir substantially covers the lid.
5. 5. A cell as claimed in any one of Claims 2 to 4 which includes two space terminals on the lid, the reservoir affording a space adjacent each terminal which may accommodate a terminal connector connecting that terminal to a further cell.
6. 6. A cell as claimed in any one of Claims 2 to 5 in which the reservoir is of rectangular shape in plan with a central trough extending across its lower surface, through the base of which trough the reservoir communicates with the container.
7. 7. A cell as claimed in any one of the preceding Claims in which the reservoir is provided with a lid or cover which does not form a gas-tight seal with the reservoir.
8. 8. A lead acid motive power cell substantially as specifically herein described with reference to the accompanying drawings.