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ROVED LEAD ACID BATTERY, PROCESS FOR THE MANUFACTURE REOF, NOVEL PASTE COMPOSITION FOR COATING ELECTRODE REOP AND A PROCESS FOR PREPARATION THEREOF, AND A NOVEL 3 ALLOY AND A PROCESS FOR PREPARATION THEREOF
The present invention relates to an improved maintenance free lead acid battery which has application in electric vehicles and solar photovoltaic applications. The present invention also relates to a novel grid alloy for use in the improved lead acid battery to a novel process for the preparation thereof and novel paste compositions for coating the positive and the negative plates of the battery.
Lead acid batteries are an integral part of solar photovoltaic systems and in vehicles, which are driven electrically. Concerns about the environment and also the increasing depletion of conventional fossil fuels is leading to a growing interest in alternate sources of energy and to improvements in the presently available sources as well. Prototypes of electric vehicles are already being tested across the world with limited degree of success. Similarly, solar power is an economically attractive option provided long life batteries are available. Solar power has very important place in even the rural electrification sector.
Presently available photovoltaic systems of the stand-alone type suffer high energy loss in the collection of Ampere-hours (Ah) by a conventional battery from the photovoltaic modules. In fact only about 60-80% of that of the system, sizing algorithm is collected by the battery.
Experiments and studies show that the charging efficiency of a conventional battery in actual applications is less than 80% on an average whereas the expected efficiency in system sizing is about 90%. Therefore, in actual practice the collection of Ah by the battery from the photovoltaic modules is less than that of the system sizing algorithm. Studies also show that on
an "average, conventional batteries in photovoiraic systems operate only at 40-60% charge during the rainy or winter seasons. This causes hardening of sulphation on the electrodes and therefore, in impairment of efficiency in collection of Ah by the battery.
It is also suspected that a great degree of actual loss of energy occurs due to dust collection on the photovoltaic modules. In system sizing, the energy loss is only about 10 % whereas it is found that dust collection over a period of six to eight weeks results in reduction in the generation of photovoltaic energy by almost 12-18 %.
The collection of energy by a battery depends amongst other factors, on the health of the battery, the photovoltaic module array, cable resistance and on the terminal contract resistance.
Thus, it is necessary to ensure during sizing of photovoltaic systems that the Ah collection does not become less than the real time requirement of the system. Therefore, correction factors need to be developed based on the real time performance of the photovoltaic systems for inclusion in the system sizing algorithm.
BACKGROUND OF THE INVENTION:
Lead acid batteries, as pointed out above are an important element in such electric vehicles as well as in solar photovoltaic cells. The success and commercial feasibility of these technologies depends to a great extent on the availability of high energy density batteries that have a long life cycle and also cost less. It is also necessary to optimise the utility of the battery for such applications by including a built-in protector and life enhancer circuit in such batteries.
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and are not specifically designed for use in solar photovoltaic systems or in electric car/vehicle applications.
Conventional lead acid batteries and presently available maintenance free sealed lead acid batteries are subject to problems in the manufacturing process as well as in operation.
The manufacture of conventional batteries is also subject to constraints in the setting of cut off points for the battery overcharge and over drainage. Different manufactures have different specifications depending also in part on the type of lead acid battery. The incorrect setting of cut off points for over-drainage results in the battery operating at a very high depth of discharge (DOD) usually in the range of 90-100%. This in turn causes permanent damage to the battery due to hardening of the sulphation on the electrodes. Similarly, the incorrect setting of the cut off point for over charging causes a higher loss of water from the electrolyte and renders the battery unservicable.
Conventional lead acid batteries comprise 2 volt cells connected in series in order to increase the battery charge. Each cell contains tubular positive plates and flat pasted negative plates separated in the case of flooded cells by polyvinyl chloride, glass and paper or rubber separators. The separator is present to insulate adjacent positive and negative plates while providing a low resistance path for the flow of ions. Free electrolyte is provided around the plates contained in hard plastic or rubber container. Therefore, installation of conventional batteries requires acid proof rooms. The approximate specific energy available is 20 Wh/kg and the energy density is 38 Wh/lit. Conventional batteries require up to twelve
hours for 100 % charging and their cyclic life is 500 cycles at
80 % D.O.D.
In the sealed recombinant cells, the electrolyte is nrovirled in highly porous and relatively thick glass mats interleaves) between the positive and the negative plates.
Conventional valve regulated lead acid batteries . are normally constructed in 2V and 12V blocks. Both the negative anc the positive plates are flat pasted plates and the electrolyte is immobilised by using glass fibre separators. The approximate specific energy is about 30 Wh/kg and the energy density is about 80Wh/lit. These batteries take up to 12-16 hours for 100 Vt charging and their cyclic life is 250 cycles at 80 % D.O.D.
The manufacture of conventional lead acid batteries involves an open tank formation process which is undesirable due to the generation of heavy fumes of corrosive sulphuric acid and large quantities of effluent. The process is also extremely time consuming, as on an average, a usable plate is product only in about 72 hours.
The choice of lead alloy for the use in the manufacture of the positive and the negative plates is important to determine the operating characteristics as well as the life of the battery jnder the intended battery operating conditions. The choice of illoy can determine the water loss rate during recharge.
It is also important to reduce the level of electrochemical ::orrosion to which the positive grid is subject depending on the application. The corrosion can assume serious levels resulting Ln the loss of the capacity of the grid to conduct energy from :he plate to the external circuit. The formation of low-density Lead compounds also results in the loss of contact between the ,rid and the impressed active material due to the stretching of :he grid.
Existing processes for the manufacture of lead acid batteries involve the use of antimony and arsenic in the lead alloy during the grid casting step and results in the generation of poisonous gases. Another serious environmental hazard in prior art methods is the presence of air borne lead dust and acid fumes since the lead powders are mixed in a dry condition. Additionally, curing of the plates takes a long time and causes abnormally high degree of air borne lead pollution due to the huge quantities of plates being handled. The final formation of the plates takes place in open tanks resulting in heavy acid fumes and air borne lead. The final washing of the plates results in generation of large amount of effluent.
The manufacture of lead acid batteries generally utilises a positive paste comprising of lead oxide, de-ionised water and sulphuric acid with a paste density of 4.2 to 4.4 gms/cc. If desired red lead may also be added for better formation.
The negative paste comprises of lead oxide, de-ionised water, sulphuric acid and conventional expanders like barium sulphate, carbon black and lignin, and has a paste density of 4.4 to 4.6 gms/cc. For both pastes, the lead oxide contains normally about 20-30% free lead and is obtained by the Barton Pot/Ball mill process.
Prior art processes involve an essential curing step necessary to obtain the final product. Additionally, the temperature has to be maintained between 40°C to 64°C in the preparation of the paste mix so as to obtain the desired sulphates. It is also necessary to limit crystallization of lead to below 2% in order to obtain plates that are capable of meeting industry standards of safety and utility. The pasted plates have to be cured for atleast 72 hours to minimise the free lead content and must be done under controlled conditions of temperature and humidity. It is also essential to ensure that
the "density of the paste remains within specified limits to limit shedding.
The preparation of the iste mix involves a time consuming .step of first thoroughly mixing the weighed dry lead oxide and expanders and subsequent addition of water with mixing. Thereafter, the required amount of acid of a specific gravity is added and the paste applied to the grid to obtain the pasted plates. The mixing of the lead oxide, water and sulpjiuric acid to form the paste results in evolution of large quantities of heat. In any paste formula, the lead oxide forms the bulk of the material from which the active material is later formed by electrochemical action. The sulphates formed by the action of the acid on the oxide tend to increase the mechanical strength of the dry plates. The expanders are added to the negative plate paste in order to prevent the contraction and solidification of the spongy lead of the finished negative plate. The residual metallic lead in the oxide reduces to less than 10-20 % during paste mixing and to less than 2 % during curing under controlled temperature and humidity conditions.
Some prior art processes use Lead Antimony alloy or Lead Calcium alloys. Antimony lead alloys are highly susceptible to gassing and corrosion. Also, antimony, selenium and sulphur used in this alloy formation result in the generation :n of toxic fumes and are therefore not desirable. While experiments have been made in reducing the antimony content in such alloys, the grids prepared thereby are subject to severe cracking. This is believed to be due to shrinkage during solidification and cooling of the grids during manufacture.
Apart from antimony-lead alloys, prior art processes also disclose use of wrought lead calcium alloys and cast lead calcium alloys in the manufacture o.f grids. While cast lead calcium, alloy grid provides more flexibility, it is not
desirable since there are problems in compositional stability. Also, these alloys require modifications to be carried out in the grid casting equipment. Another problem faced is that the presence of calcium results in the formation of irreversible calcium based plaque around the positive grid and therefore reduces the electrical conductivity. For this reason, calcium lead alloys are not desirable for the manufacture of batteries intended for cyclic and long life applications.
From the above problems, it is clear that there is a dire need for improved maintenance free lead acid batteries in the areas of grid alloy and design, paste composition, cell construction and in the battery managemen system: .
US Patent 3,862,861 discloses an early design of a recombinant cell wherein a lead based grid of more than 99.9 % purity by weight is pasted and assembled into cells which are tightly contained by a cell container. US Patent 4,166,155 relates to use of different alloys in the positive and the negative plates to ensure a maintenance- free lead acid battery. In this patent/ the tensile strength of the positive grid is increased by the addition of antimony and cadmium while limiting the gas evolution associated with constant voltage overcharge.
US patent 4,964,878 relates to improvements in the construction in the battery by arranging the bipolar positive and negative grids in the same grid or substrate separated by glass mat separators.
However, none of the above patents display all the essential properties required for a long life maintenance free lead acid battery.
It is therefore, an object of the invention to provide a long life maintenance free lead acid battery with improved specific energy and specific power.
It is another object of the invention to provide a lead. cn-x
It is yet another object of the invention to provide a battery manufacturing process with improvements in manufacture time of the plates, lesser harmful impact on the environment, elimination or reduction in curing time for the plates, avoidance of lead dusting, and no maintenance .except cleaning and charging.
It is another object of the invention to provide a novel alloy for the manufacture of the positive and the negative plates.
It is yet another object of the invention to provide a novel process for the manufacture of a novel, alloy for use in the manufacture of the positive or negative plates.
It is a further object of the invention to provide a novel paste composition in which the plates are to be embedded and a process for the preparation of the same.
It is a further object of the invention to provide: a novel paste wherein undesirable crystal structure is eliminated, lower active material density and higher percent porosity than conventional pastes is present.
It is yet another object of the invention to provide a process for the preparation of the paste wherein the curing process is reduced or eliminated and paste-mixing tin; is reduced.
Another object of the invention is to provide a usable plate with a substantial reduction in the time required for the manufacturing process.
It is another object of the invention to provide a battery management system which significantly enhances battery life and reliability and reduces or eliminates the effect of high ambient temperature, unpredictable charging current and duration.
actual application.
SUMMARY OF THE INVENTION:
The present invention relates to a lead acid battery comprising one or more cells located in a housing, each cell comprising lead alloy pasted positive and negative plates arranged in an alternating manner in series, separators made of conventional material interleaven between said positive and said negative plates, said separators overlapping beyond the edges of said plates and provided with a Hi" fold at the bottom to avoid edge shorts between the separators and,the plates, cell positive and cell negative terminals weldably connected to the lid bushes, each said positive and negative plate being immersed in electrolyte, each lead terminal pillar being provided with inserts of good conducting material, vent plugs and design valves being provided on the containers and covers eliminates acid fumes, and if desired electronic Ah auditor circuit.
The present invention also provides a novel process for the manufacture of a lead acid battery comprising one or more cells located in a housing, each cell comprising lead alloy pasted positive and negative plates are arranged in an alternating manner in series,, separators made of conventional material interleaven between said positive and said negative plates, said separators overlapping beyond the edges of said plates and provided with a "u" fold at the bottom to avoid edge shorts between the separators and the plates, cell positive and cell negative terminals weldably connected to the lid bushes, each said positive and negative plate being immersed in electrolyte, each lead terminal pillar being provided with inserts of good conducting material, vent plugs and design valves being provided on the containers and covers eliminates acid fumes, and if
dasired an electronic Ah auditor circuit, said process comprising,
a) grid casting of almost substantially pure lead at a temperature of 450-480°C to obtain lead plates;
b) preparing a paste composition by mixing stable lith-. rge powder in wet condition with of Dynel fibres, dry sodium sulphate. Teflon suspension solution of 1.5 S.G., sulphuric acid, and applying said paste composition on said positive plates,
c) preparing a paste composition by mixing stable litharge po"wder in wet condition with of Dynel fibres, dry sodium sulphate, nickel sulphate. Teflon suspension solution of 1.5 S.G., sulphuric acid, and applying said paste composition on said negative plates;
d) assembling the positive and the negative plates in stacks such that a positive plate in one stack is connected to a negative plate in the same relative position in an adjacent stack;
e) positioning a conventional separator between each said positive and each said negative stack, said separator overlapping beyond the edges of the respective plates;
f) applying compressive force on the plate stacks by fixing a
cover weldably connected to the battery container;
g) electrically connecting said negative plates and separately
connecting the positive stacks in the terminal stacks to each
other and to an external negative and an external positive
terminal of the said battery;
h) providing electrolyte solution between the plates.
The invention also provides a novel paste composition for coating the electrode plates,of a lead acid battery and a process for the preparation thereof.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
FIG.l is a comparative graph of the formation capacity of prior art processes vis-a-vis the inventive process for th" same quantity of active material.
FTG.2 is a representation of the battery assembly.
FIG.3 is a representation of the grid casting.
DETAILED DESCRIPTION OF THE INVENTION:
In one embodiment of the invention, there is provided a lead acid battery comprising one or more cells containing positive and negative plates with" separators between them, said cells being arranged in series..
In another embodiment, the invention relates to a lead acid battery wherein the positive and the negative plates are coated with a novel paste.
In another embodiment, the invention relates to maintenance free lead acid battery provided with an" electronic Ah auditor ci rcuit.
In yet another embodiment, the invention relates to a novel cost effective process for the manufacture of lead acid batteries.
In a further embodiment of the invention, the process for the manufacture of the battery of the invention does away with totally or at least substantially the process of curing of the positive plates and the negative plates.
In another embodiment, the process of the invention does not involve the step of washing the formed plates before assemble and involves less curing time compared to conventional processes.
In a further embodiment of the invention, the alloy used in the manufacture of the grid assembly contains no antimony and arsenic and is almost sub"^tantially pure lead.
n
)attery comprising one or more cells located in a housing, each :e]l cdrnp"rlsing lead alloy pasted positive and negative plates irranged in an alternating manner in series, separators made of :onventional material interleaven between said positive, and said legative plates, said separators overlapping beyond the edges of laid plates and provided with a MJ" fold at the bottom to avoic idge ^hortsybetween the separators and the plates, cell positive md cell negative terminals weldably connected to the lid bushes, sach said positive and negative plate being immersed in electrolyte, each lead terminal pillar being provided with nserts of good conducting material, vent plugs and design valves leing provided on the container to minimise acid fumes, and if lesired electronic Ah auditor circuit.
The present invention also provides a novel process for the lanufacture of a lead acid battery comprising" one or more "cells ocated in a housing, each cell comprising lead alloy pasted ositive and negative plates are arranged in an alternating anner in series, separators made of conventional material nterleaven between said positive and said negative plates, said eparators overlapping beyond the edges of said plates and rovided with a "u" fold at the bottom to avoid edge shorts etween the separators and the plates, cell positive and cell egative terminals weldably connected to the lid bushes, each aid positive and negative plate being immersed in electrolyte, ach lead terminal pillar being provided with inserts of good onducting material, vent plugs and design valves being provided n the container to minimise acid fumes, and if desired an
lectronic Ah auditor circuit,] said process comprising,
) grid casting of almost substantially pure lead at a
temperature of 450-480 % C to obtain lead plates; ) preparing a paste composition by mixing stable litharge
powder in wet condition with of Dynel fibres, dry sodium.
sulphate, Teflon suspension solution of 1.5 .S.G., sulphuric acid, , and "applying said paste composition on said positive plates,
c) preparing a paste composition by mixing stable litharge powder in wet condition with of Dynel fibres, dry sodium sulphate, nickel sulphate, Teflon suspension solution of 1.5 S.G., sulphuric acid, and applying said paste composition on said negative plates;
d) assembling the positive and the negative plates in stacks such that a positive plate in one stack is connected to a negative plate in the same relative position in an adjacent stack;
e) positioning a conventional separator between each said
positive and each said negative stack, said separator
ox"^erlapping beyond the edges of the respective plates; .
f) applying compressive force on the plate stacks by fixing a cover weldably connected to the battery container;
g) electrically connecting said negative plates and separately connecting the positive stacks in the terminal stacks to each other and to an external negative and an external positive terminal of the said battery;
h) providing electrolyte solution between the plates.
The present invention also relates to a novel alloy for use in the manufacture of the grid assemble and a process for the preparation thereof. In an embodiment of the invention, the lead alloy contains almost above 98 % lead purity along with tin and silver.
In a further embodiment of the invention, the process of preparation of the grid involves cooling of the prepared grid by cold water spraying, cool air blowing or cold water quenching to achieve hardness.
In yet another embodiment, the invc-ntion relates to a novel paste for coating the positive and the negative plates.
In a further embodiment, the invention relates to a novel paste composition containing litharge with free lead content below 1 % as the primary material allowing for consistent paste mix from batch to batch and with high porosity and higl-performance.
Accordingly, the invention also provides a novel past? composition for coating the positive plate of a lead acid battery comprising litharge, Dynel fibre, dry sodium sulpha.te, Teflo] suspension solution of 1.5 S. G., lignin, carbon black, bariui sulphate, DI water and sulphuric acid.
The paste composition for the negative plate of a, lead acii battery also comprises nickel sulphate in addition to the abov mentioned ingredients.
The battery grid is made from lead alloy with above 98 ^ purity and without any hazardous elements such as antimony o arsenic. Tin and silver may be added. The grid casting is done o an automatic, grid casting machine with pre-set controls for alio melting temperature, casting speed, mould temperature, coolar circulation and other process parameters. Such automatic grid casting machines are known in the art and the values for the casting process depend on the desired grid size. The temperature control is normally set to about 450-480°C to ensure the avoidance of any harmful lead fumes.
The paste is mixed separately for the negative and the positive plates in a Sigma mixer according to the desired composition. The desired paste density is normally 4.0+/- 0.2 gms/cc and the mixing temperature is between 20 to 40°C.
The plates are subj-ct to pasting on an automatic pasting machine with controlled pre-set values and having close tolerance. The plates are then subsequently pickled in acid and dried before assembly.
The cured plates are assembled in to the cells and formed in a closed chamber under controlled conditions. Essentially, the dried plates are wrapped with glass fibre separators and stacked into groups with the negative and the positive plates being positioned alternately. In the case of a monobloc construction, only the end cells are burned together in a group-burning machine. Each stack is compressed at 5 psi.
The group burned element is introduced in to the container and the lid and container surfaces are heated and sealed under a pressure of 5 kg/cm^. In an automatic heat sealing machine in order to form a leak proof joint. The heating plate temperature is maintained at 220 - 200°C depending on the wall thickness.
The cell positive and the negative terminals are welded to the Ud bushes by arc welding technique to ensure that the joints can withstand a pressure of up to 10 psi.
The assembled cells are filled with 30-40% concentrated sulphuric acid with sodium sulphate additive at a temperature of 5-10°C in three stages. In the first stage, about 60% of the acid is filled; in the second stage, about 30% of the acid is filled and in the third stage the remaining 10% is filled. The filling is done under vacuum at a pressure of 10-20 psi preferable.
The cells are thereafter connected in series up to a total capacity of 120 volts and charged in three stages. In the first stage, 0.2 Amps for 10 hours; in the second stage, 0.1 Amps for 20 hours and in the third 0.05 Amps for about 6 hours. The total charging time is normally about 36 hours.
During formation, the ceUs/battery is mounted vertically and fitted with porcelain porous vent plugs in order to minimise the acid fumes. After formation, the excess electrolyte is drained and the cells are cleaned in a conventional manner.
;ubsequently, vent plugs of specific design are fitted in to
iperate at a low pressure.
At the time of filling the electrolyte, the electrolyte is
mmobilised, retained by the plates and the separators and therefore does not result in spillage due to free electrolyte. Even in the event of an overcharge, the presence of a safety valve and porous filter for ".he release of any excess gas.
The setting points of overcharge and over drainage are determined on the basis of the state of the Ah and battery terminal voltage instead of battery terminal voltage alone, as was done in the art. Depending on this, a Ah audit circuit can be incorporated if desired to manage the energy level in the battery.
Tf desired, a built in unit of a Ah audit circuit and a decrystalliser can be incorporated to enhance the life and safety levels in the battery. The decrystalliser generates repeatatale packages of varying amplitude/frequency of electrical stress energy for the electrodes of the battery. The continuous application of this stress energy keeps the electrode free from, hardened sulphates.
In another embodiment of the invention, a novel lead acid battery paste mix is provided comprising essentially of litharge, Dynel fibre, dry sodium sulphate, Teflon suspension solution of 1.5 S. G., lignin, carbon black, barium sulphate, DI water and sulphuric acid. For the negative plate, nickel sulphate is included.
Litharge is weighed and proporti^"^ate quantities of the other ingredients are added depending on whether required for the positive or the negative plate. After dry mixing, a proportionate quantity of DI water is added slowly. Subsequently, the sulphuric acid is added slowly. At this stage, a gradual rise in the temperature can be observed due to the evolution of heat. Coolant circulation is started in the mixer when the temperature reaches
2PC to ensure that the temperature does not exceed 45°C. emperature control can also be done by controlling the rate of the acid addition. Continuous mixing is done till the completion of the acid addition and the temperature falls below 30°C.
Paste density is contr. lied to 4.0 gms/cc before the paste is removed from the mixer. The reactions occurring are believed to be as follows;
PbO + H2O -» Pb(0H)2
Pb{OH)- + H:;SO,i -> PbSO^ + H;-0
The m.ixing of litharge with water addition gives lead hydroxide, which then reacts with the addition of sulphuric acid to form lead sulphate and water.
The finished paste can then be applied to the grid plates since the absence of free lead eliminates the need for hydro setting. The plates are dried to moisture content of less than 2 % before cell assembly.
MAINTENANCE FREE SEALED LEAD ACID BATTERY TECHNOLOGY;
The chemical reactions taking place in a lead acid storage battery is as follows:
When battery cnargmg approacnes une i-xiidx sLaye, cue charging current is consumed solely for electrolytic decomposition of water in the electrolyte, resulting in the generation of oxygen gas from the positive plates and hydrogen gas from the negative plates. The generated gas will escape and decrease the electrolyte level, thereby r"-"uiring regular topping up of water for maintaining the level of the electrolyte. However, in the battery of the Bnvention recombination technology is used to eliminate water loss.
In a sealed recombination cell, the stoichiometry of active material ratio is designed to ensure that the positive plate is fully charged and the negative plate is partially charged. The oxygen evolving from the positive plates diffuses through the separator voids, to react with the negative plate lead, to form lead oxide. The lead oxide in turn reacts with sulphuric acid to form lead sulphate and water, thereby completely eliminating water loss.
REPRESENTATION OF REC
a) oxygen is produced at the positive plate during end of the
charge
b) oxygen diffuses through the separator to the negative plate
c) oxygen combines with lead on the negative plate to produce
lead oxide
d) Lead oxide on the negative plate reacts with sulphuric acid
to form lead sulphate and water.
All these reactions occur in a closed loop, the net result being that the water consumed in oxygen evaluation is regenerated and the state of the charge of the positive plate and negative plate does not change including the electrolyte.
BATTERY DESIGN AND CONSTRUCTION:
The positive and the negative plates are made of pasted type flat plates with above 98 % purity lead alloy casted grid over which the paste is applied and is intended to deliver the rated capacity with minimum self-discharge and to maintain capacity performance for long life. The separator is preferably made of a glass fibre mat with a porosity of over 95 % and excellent oxidation resistance. The function of the separator is to prevent short circuit, active material shedding and to retain the electrolyte.
The electrolyte is normally sulphuric acid and its functions involve chemical reactions and as an ion transfer media. The :ontainers and covers are preferably made of polypropylene and iccommodate both the negative and the positive plates wrapped ?ith the separator in order to retain sufficient mechanical strength to withstand internal pressure.
The safety valve cap shaped and made of synthetic rubber, nd prevents the ingress of air and releases gas if cell internal ressure rises and reseals automatically.
The terminals are made of brass inserts cast into a lead alloy and are intended to enhance the high rate discharge characteristic with good charge acceptance.
PRODUCT FEATURES;
Durable polypropylene containers and covers are heat sealed and the terminal seals are air tight, thereby ensuring no electrolyte spillage and acid fumes. The batteries can be installed in any position.
The glass fibre separator completely absorbs and immobilises the electrolyte. No gelling agent is added. The battery is maintenance free, and there is no necessity to check the specific gravity or to add water throughout the service life of the battery.
The low-pressure safety valve is designed to release excess
pressure and reseal automatically. The heavy duty plates are thick grids pasted with the novel paste of the invention and ensure good performance and long life. Due to the high purity and the sealed design the self-discharge is low (approximately 1 % per week) thereby allowing a long shelf life for a period of 6-12 months depending on storage temperature.
The plate design and construction give low internal resistance, thereby resulting in a high rate performance and charge acceptance. The materials and construction allow the product to have a long life performance, even after repeated discharges.
xne paste nas excellent: aanesion to tne grla plate.
The necessity for open tank formation of the plates is done
away with due to the low paste densities and high porosity. Dried plates can be assembled and then formed, thereby
eliminating air borne lead, and effluents. The step of curing of the plates is done away with totally or
at least substantially. The mixing of lead powders in a dry condition during paste
formation is not required. Stable lead powder is mixed in a
wet condition thereby eliminating airborne lead. Harmful substances such as antimony and arsenic are not used
to improve the mechanical strength of the plates, without
the loss of such strength.
The manufacture of the battery is environmentally safe. Due to the negative plate absorbing any gas produced by the
positive plate resulting from overcharge, and returning to
the electrolyte, the need to replonish water during the
entire use period of the battery is done away with. The cyclic life of the battery is enhanced due to the
components and the novel construction. The use of litharge having a long shelf life ensures a
greater batch consistency for the battery as opposed to lead
oxide.
The formation of undesirable crystal structures during plate manufacturing is eliminated.
We Claim,
1. A lead acid battery comprising one or more cells located in a housing, each cell comprising pasted lead alloy positive and negative plates arranged in an alternating manner in series, separators made of conventional material interleaven between said positive and said negative plates, said separators overlapping beyond the edges of said plates characterized in tliat the said positive and negative plates are in the form of a grid and said separator are provided with a U fold at the bottom to avoid edge shorts between the separators and the plates, cell positive and cell negative terminals weldably connected to the lid bushes, each said positive and negative plate being immersed in an electrolyte, each lead terminal pillar being provided with inserts of good conducting material, vent plugs and design valves being provided on the container and cover eliminates acid fumes, and if desired an electronic auditor circuit.
A lead aid battery as claimed in claim 1, wherein the said grid is made of a lead alloy preferably containing Tin and Silver and free of Antimony and Arsenic.
A lead battery comprising one or more cells located in a housing, each cell comprising pasted lead alloy positive and negative plates arranged in an alternating manner in series, separators made of conventional material interleaven between said positive and said negative plates said separators overlapping beyond the edges of said plates and provide with a U fold at the bottom to avoid edge shorts between the separators and the plates, cell positive and cell negative terminals weldably connected to the lid bushes, each said positive and negative plate being immersed in an electrolyte, each lead terminal pillar being provided with inserts of good conducting material, vent plugs and design valves being provided on the container and cover eliminates acid fumes, and if desired an electronic auditor circuit, characterized in that the said positive and negative plates are in the form of a grid, said process comprising.
electrolyte, each lead terminal pillar being provided with inserts of good conducting material, vent plugs and design valves being provided on the container to minimise acid * fumes, and if desired an electronic Ah auditor circuit, said process comprising,
a) grid casting of almost substantially pure lead at a temperature of; 450-480 % C to obtain lead plates;
b) preparing a paste composition by mixing stable litharge powder in wet condition with Dynel fibres, dry sodium sulphate, Teflon suspension solution of 1.5 S.G., sulphuric . acid, and applying said paste composition on said positive plates,
c) preparing a paste composition by mixing stable litharge powder in wet condition with Dynel fibres, dry sodium sulphate, nickel sulphate, Teflon suspension solution of 1.5 S.G., sulphuric acid, and applying said paste composition on said negative plates;
d) assembling the positive and the negative plates in stacks such that a positive plate in one stack is connected to a negative plate in the same relative position in an adjacent stack;
e) positioning a ,conventional separator between each said positive and each said negative stack, said separator overlapping beyond the edges of the respective plates;
f) applying compressive force on the plate stacks by fixing a cover weldably connected to the battery container;
g) electrically connecting said negative plates and separately connecting the positive stacks in the terminal stacks to each other and to an external negative and an external positive terminal of the said battery;
h) providing electrolyte solution between the plates.
A process as claimed in claim 3, where in the step of during of the formed, electrodes is substantially eliminated.
A process as claimed in claim 3, wherein the grid formation takes place by the jar formation method.
6. A novel paste composition for coating the electrodes of a lead acid battery, comprising litharge and of Dynel fibres, dry sodium sulphate, Teflon suspension solution of 1,5 S.G., sulphuric acid, D,I. water.
7. A paste composition as claimed in claim 6 wherein, nickel sulphate is also present in the mixture.
8. A paste composition as claimed in claim. 6, wherein the electrode is a positive electrode of said lead acid battery.
9. A paste composition as claimed in claim 7, wherein the electrode is a negative electrode of said battery.
10. A process for the preparation of the novel paste composition of claim 6, wherein the said ingredients are thoroughly intermixed.
11. A lead acid battery comprising one or more cells substantially as described herein before and with reference to the accompanying drawings.
12. A (novel process for the manufacture of a lead acid battery comprising one or more cells substantially as described herein before and with reference to the accompanying drawings. .
A novel paste composition for coating the electrodes lead acid battery substantially as described herein before.
A process for the preparation of the novel, paste composition for coating the electrodes of a lead acid battery substantially as described herein before. |