Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to lead-acid batteries.
A problem exists with lead-acid batteries in that they
tend to discharge if stored for prolonged periods with the
battery elements immersed in the sulphuric acid electrolyte
of the battery. One known solution to this problem with "wet"
batteries is to produce dry, charged lead-acid batteries. This
; involves forming the plates of the battery, removing the formation
electrolyte and then washing and drying the plates before
assembling and sealing the battery. The battery can then be
stored substantially without discharge and in addition transport
of the battery is facilitated since, of course, the extra weight `
of the electrolyte is avoided. When required for service
activation of the battery is effected by adding sulphuric acid
of a suitable specific gravity.
- ~Iowever, dry, charged lead-acid batteries also suffer
from a problem in that washing and drying the formed plates
is a relatively difficult and expensive operation, but never-
theless must be performed rigorously and completely if the
performance of the battery is not to deteriorate during storage. `
Moreover, with a dry, charged battery after addition of the
activation electrolyte, it is necessary to allow the battery
to stand to allow the acid to saturate the plates before the
battery is ready for service.
With a view to overcoming the above-mentioned
, disadvantages of wet and dry, charyed lead-acid batteries, much
recent work has centred on the development of so-called drain,
charged batteries. These are similar to dry, charged batteries
in that they require activation with electrolyte before they
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can be put into service but, unli~e dry, charged batteries, they
are stored with part of the forming electrolyte being retained
by the plates. There is therefore no requirement for initial
washing and drying of the plates, although it is of course
necessary to remove sufficient of the forming electrolyte,
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normally by merely draining the battery, to prevent adjacent
;~ plates being electrically connected through the electrolyte
during storage. Moreover, drain, charged batteries can be
stored for long periods substantially without discharge and
` 10 can be put into service immediately upon addition of the required
activation electrolyte.
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In each of the three types of battery described above,
formation of the plates involves immersing grids supporting
the required lead-acid battery paste in sulphuric acid and
passing an electric current through the plates. Moreover, with
dryanddrain charged batteries, the acid used for the formation
process has to date always been considerably weaker than the
sulphuric acid electrolyte employed in the finished battery.
Thus, the initial specific gravity of the forming acid has
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normally been between 1.00 and 1.15 and although there is an
increase in the acid strength during forming, the specific
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gravity of the acid at the end of the forming process has always
been less than 1.23. The reason for using a relatively weak
forming acid has been to decrease the forming time since at
high specific gravities of the sulphuric acid formation electro-
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lyte conversion of the battery paste into the required active
material of the plates is resisted.
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It has, however, been found that, when conventional
strength forming acid is used to produce drain, charged batteries
there is a tendency for the retained acid in the positive plates
to become depleted during storage by reaction with the negative
plate active material. This can result in the pH of the retained
electrolyte in the positive plate rising towards a neu,ral
value and under these conditions there is a tendency for the
positive plate grid to corrode by reaction with the positive plate
active material. Alth~ugh this problem can be avoided by
employing a separate rinse step with a high specific gravity
acid after draining of the forming acid, the rinse step adds an
extra operation to the battery production cycle and also requires
additional acid. It is therefore an object of the present
invention to provide an improve~ solution to the above-mentioned
problem with conventional drain, charged batteries.
Accordingly, the invention resides in one aspect in a
lead-acid battery capable of activation by the addition of
electrolyte thereto and including at least one pack of formed
positive and negative battery plates having insulating separators
interposed between adjacent plates, part of the sulphuric acid
used to form the plates being retained by the battery and having
a specific gravity between 1.26 and 1.35, the amount of said
-~ retained acid being such that each positive plate contains 0.1
c.c. of the acid/gm of active material but being insufficient to
electrically connect the plates during storage, and means sealing
the batteryagainst ingress of air but allowing escape of gases
generated in the battery during storage.
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In a further aspect, the invention resides in a method
of producing a lead-acid battery capable of activation by the
addition of electroly~e thereto, the method comprising the steps
of: (a) starting with a battery container accommodating at least
one pack of battery plate grids having insulating separators
interposed between adjacent grids, one set of grids in the pack
carrying the lead-acid battery paste required to produce negative
plate active material and the remaining grids carrying the paste
required to produce positive plate active material; (b)
immersing the grids in the container in sulphur acid having a
specific gravity between 1.21 and 1.30 and passing a direct
current between the grids to effect a forming operation on the
grids and thereby convert the paste on the grids to the active
. material of the plates, the specific gravity of said acid rising
during the passage of said current to a value between 1.26 and
1.35 at the end of the forming operation; (c) when the forming
operation is complete, draining sufficient of said forming acid
from the container to ensure each positive plate contains 0.1 c.c.
of the acid/gm of active material but prevent the retained acid
.:~ 20 electrically connecting the formed plates during storage; and
(d) sealing the container with means which prevents ingress of
air into the container but allows escape of gases generated in
: the container during storage.
In the battery according to the first aspect of the
invention and the battery produced by the method according to
the second aspect of the invention, the strength of the acid
retained by the battery is sufficient to maintain a highly acidic
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environment for the positive plates during storage. Moreover,
the fact that the retained acid is the acid employed in forming
the plates avoids the necessity for an extra rinsing step. In
addition, since the retained forming acid has a specific gravity
between 1.26 and 1.35, activation of the battery san be effected
with the same or a lesser strength sulphuric acid than that
normally employed to activate dry, charged batteries, i.e. having
a specific gravity of 1.26.
Preferably, the specific gravity of the forming acid
at the start of step (b) is between 1.21 and 1.30.
More preferably, the specific gravity of the forming
acid at the start of step (b) is between 1.22 and 1.25.
~ The amount of said retained acid is such that each
; positive plate contains at least 0.1 cc of the acid/gm of active
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material. This ensures maximum protection of the positive plate
grids.
Preferably, step (b) includes a period of standing of
at least 30 minutes without passage of the electric current and
the temperature of the forming acid is allowed to rise to at
least 150~ prior to the standing period. During the period of
standing the lead dioxide of the positive plates is believed to
be converted to a chemically resistant form, and by allowing the
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c~ acid temperature prior to standing to reach at least 150F, the
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standing period can be decreased to 30 minutes.
~`~7' Preferably, the container is sealed substantially
ri immediately after draining of the forming acid so as to minimise
oxidation of the negative plates and consequential loss in initial
`~ battery power.
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1091~62
In the accompanying drawings, which illustrate a
method according to one exarnple of the invention, of producing
. a multi-celllead-acid battery.
Figure 1 is a perspective view of a battery box during
assembly of packs of battery plate grids and separators into --
the box, ~ ~ .
Figure 2 is a part sectional view of a battery box .
illustrating the completion of the intercell connections, and
Figure 3 is a sectional view of a vent plug for
sealing one cell compartment agalnst ingress of air.
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Referring to the drawings, the method shown involves
initially producing lead alloy grids 11 each of which carries
the lead-acid battery paste required to produce a positive or -
negative battery plate after conversion of the paste into the
active material of the plate. The composition of the paste
is entirely conventional and will not therefore be described in
detail, although it is to be appreciated that the paste will
always contain some sulphuric acid. The grids 11 are then
assembled into packs 12 with insulating separators 13 being
interposed between the grids 11 and with each pair of adjacent
grids in a given pack carrying the paste required to produce a
negative battery plate and a positive battery plate respectively.
The packs 12 are then inserted into a battery box 14
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which is moulded from a thermoplastic material preferably poly-
, propylene and is divided into six cell compartments 15 by
,~ parallel, spaced partition walls 16. Each cell compartment 15
-. receives a respective pack 12 and in each of the four packs
received in the central compartments of the box 14, each grid
~ which is to define a positive plate is connected to a conductive
,~ 20 lug 17 and each grid which is to define a negative plate is
connected to a conductive lug 18. Each of the lugs 17, 18
~.~ includes an integral extension which, in use, extends substan-
i~, tially parallel to the partition walls 16 and each of the lugs
17 is further formed with a projecting spigot 17a integral with
~:~ its respective extension. Each of the packs 12 which is
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received in an end compartment of the box 14 has one set of
; grids connected to a lug 17 or 18 and its other set of grids
connected to a terminal post 19.
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109i762
As shown inFigure 2, the partition walls 16 have
' holes 16a stamped therein and arranged so that when the packs
12 are assembled in the box 14, each spigot 17a extends through
a respective hole 16a into engagement with the extension of a
~; lug 18 in an adjacent compartment. Of course, it will be
appreciated that the partition walls 16 have to be flexed to
permit the packs 12 to be positioned in the box 14. ~hen all
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the packs 12 are in position, the required intercell connections
are completed using the resistance welding tool shown at 21 in
Figure 2. The tool 21 includes a pair of electrodes 22, 23
which are engaged in turn with the extensions respectively of
each pair of lugs 17,18 to resistance weld the lugs together.
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During the resistance welding operation, the electrodes 22,23
simultaneously press the extensions of the lugs 17,1~ against
` the respective partition wall 16 and pass current between the
extensions through the spigot 17a so that the spigot melts and
fills the hole 16a in the partition wall.
When the intercell connections are complete, the box
is closed by welding to the box, a battery lid (not shown) which -
is moulded in a thermoplastic material, again preferably poly-
propylene and which has a peripheral edge adapted to engage the
top peripheral edge of the box and ribs adapted at their free
ends to engage the tops of the partition walls. Welding is
` effected by pressing the flat surfaces defined by the top of the
box and said peripheral edge and rib ends of the lid against
opposite surfaces respectively of a heater plate (not shown).,~
so that said flat surfaces are softened. The heater plate is
then removed and the softened portions of the lid and the box are
pressed into engagement so that the lid becomes butt welded
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109~762
to the box 1~.
i When the box has been closed by the lid, each cell
compartmen~ 15 is filled with sulphuric acid of specific gravity
between 1.16 and 1.30, or preferably between 1.21 and 1.30
~; or more preferably between 1.22 and 1.25. Thereafter, the
terminal posts 19 are connected to a d.c. source and an electric
~ current is passed between the posts to effect a forming operation
; on the grids 11 and thereby convert the paste on the grids 11
into the active material of the plates. Since the paste on
the grids is entirely conventional, the passage of current
converts the paste on the grids which are to define negative
battery plates into metallic lead and converts the paste on the
grids which are to define positive plates into lead dioxide.
During the forming operation, the temperature and specific
gravity of the sulphuric acid within the compartments 15 rises,
the magnitude of the current passed between the terminals 19
preferably being arranged so that the temperature of the acid
increases to a value in excess of 150F but normally not greater
~ than 210F.
; 20 As the forming operation progresses, the charge on
the partly formed plates increases and when the charge reaches
` at least 50% and preferably at least 90~ of the required final
charge on the plates, the passage of the electric current
between the terminals 19 is ceased. In fact, the charge on
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the plates can be allowed to rise as high as, or bevond, the
required final charge before the passage of current is ceased.
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` When the passage of the electric current has been
terminated the battery plates are allowed to stand in the hot
sulphuric acid for a period of at least thirty minutes. ~ormally
the period of standing is between forty-five minutes and three
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^~ hours, the time depending upon the temperature of the acid at the
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~ end of the forming operation. During standing, the positive
!~;' plates undergo a chemical reaction whi~h is believed to partially
sulphate the active material of the positive plates such that
on subsequent charging the sulphate material is converted to a
chemically resistant form of lead dioxide. In this way the
ability of the positive plates to withstand long periods of
storage, without deterioration of the active material, is
improved.
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During standing some discharge of the plates inevitably -
occurs and so, after standing, an electric current, preferably
of the same magnitude as previously, is passed between the
terminals 19 to either complete formation of the plates or
return the charge on the plates to the required final value.
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;'-; During forming the acid in the box bubbles vigorously
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as the gases generated by the forming reactions escape through
the apertures which are necessarily provided in the lid to allow
` filling and venting of the battery in service. This can lead
not only to an acid laden mist being expelled through the
apertures but also, in extreme conditions, in the acid solution
bubbling out of the apertures. It is therefore desirable to
provide above eachaperture, means for collecting any expelled
i~ acid and returning it to the box.
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On completion of the formation operation or the
formation and recharging operation, the box is inverted to allow
the forming acid to drain from the box, through the filling and
venting apertures, the specific gravity of the acid having risen
by this stage to between 1.26 and 1.35 depending, of course,
on the initial concentration of the forming acid. Aftex drainage,
some of the forming acid is necessarily retained in the box,
mainly being absorbed in the active material of the plates. In
some cases, however, some of the retained acid can be free in
the bottom of the box provided it is of insufficient depth to
electrically connect the plates when the battery is stored in
its normal upright position. Preferably, the draining operation
is arranged so that each positive plate retains at least 0.1 cc
. of the forming acid per gram of positive plate active material,
and conveniently so that the amounts of retained acid per gram -
: of each separator and negative plate active materialare at
least 0.6 and o og cc respectively.
After drainage of the forming acid, and without -
performing an acid rinsing step, the filling and venting apertures
aresealed against ingress of air using vent plugs of the kind
shown in Figure 3. Each vent plug includes a hollow, generally
cup-shaped body 31 which tapers inwardly towards its base 32
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and which is formed with an external, circumferential flange
33 at its open end 34. The taper on the body 31 is such that
in use when inserted into an aperture in the battery lid, the
; tapering wall sealingly engages the lid, while the flange 33
provides an abutment to prevent the body 31 being pushed through
the aperture.
Moulded integrally with the base 32 is
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~ a centrally disposed, tapering spigot 35 which is provided to
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facilitate removal of the vent plug when it is required to
activate the battery.
Integral with the base 32 is a flap 36 which
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` normally seals an opening 37 in the base, but which is capable
of flexure into the interior of the body 31 to allow fluid to
flow through the opening 37. The flap is however, held by
abutment with the wall of the opening 37 against flexure towards
the exterior of the body 31, and hence defines a valve member
which permits the flow of fluid into the body 31 but resists ~ -
fluid flow in the opposite direction. Thus, when the vent plug
r~ is inserted into an aperture in the battery lid, the flap 36
substantially prevents the ingress OL air and/or moisture into
;~ the battery casing, but any yases generated within the battery
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; casing can escape through the opening 37 when they are of
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sufficient pressure to overcome the inherent resilience of the
` flap 36. Typically, the vent plug is arranged so that the
flap 36 can flex to permit gas escape through the opening 37
; when the gas pressure within the battery casing is between
0.3 and 1.0 psig.
After insertion of the vent plugs, the battery can be
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stored for long periods substantially without discharge or
deterior,lation of the plates, the high specific gravity of the
retained forming acid ensuring that envlronment of the positive
plates remains strongly acidic. When rec~uired for service,
the battery can be activated by adding the normal strength
acid (SG1.26) used for activation of dry, charged batteries,
whereupon it is ready for immediate use.
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