Working of Lead Acid BatteryThe storage battery or secondary battery is such battery where electrical energy can be stored as chemical energy and this chemical energy is then converted to electrical energy as when required. The conversion of electrical energy into chemical energy by applying external electrical source is known as charging of battery . Whereas conversion of chemical energy into electrical energy for supplying the external load is known as discharging of secondary battery . During charging of battery , current is passed through it which causes some chemical changes inside the battery . This chemical changes absorb energy during their formation. When the battery is connected to the external load, the chemical changes take place in reverse direction, during which the absorbed energy is released as electrical energy and supplied to the load. Now we will try to understand principle working of lead acid battery and for that we will first discuss about lead acid battery which is very commonly used as storage battery or secondary battery . Materials used for Lead Acid Storage Battery CellsThe main active materials required to construct a lead-acid battery are 1. Lead peroxide (PbO2).2. Sponge lead (Pb) and3. Dilute sulfuric acid (H2SO4).Lead Peroxide (PbO2)The positive plate is made of lead peroxide. This is dark brown, hard and brittle substance. Sponge Lead (Pb)The negative plate is made of pure lead in soft sponge condition. Dilute Sulfuric Acid (H2SO4)Dilute sulfuric acid used for lead acid battery has ration of water : acid = 3:1.The lead acid storage battery is formed by dipping lead peroxide plate and sponge lead plate in dilute sulfuric acid. A load is connected externally between these plates. In diluted sulfuric acid the molecules of the acid split into positive hydrogen ions ( H+) and negative sulfate ions (SO4 − −). The hydrogen ions when reach at PbO2 plate, they receive electrons from it and become hydrogen atom which again attack PbO2 and form PbO and H2O (water). This PbO reacts with H2

SO4 and forms PbSO4 and H2O (water). SO4 − − ions are moving freely in the solution so some of them will reach to pure Pb plate where they give their extra electrons and become radical SO4. As the radical SO4 cannot exist alone it will attack Pb and will form PbSO4. As H+ ions take electrons from PbO2 plate and SO4 − − ions give electrons to Pb plate, there would be an inequality of electrons between these two plates. Hence there would be a flow of current through the external load between these plates for balancing this inequality of electrons. This process is called discharging of lead acid battery . The lead sulfate (PbSO4) is whitish in color. During discharging, 1. Both of the plates are covered with PbSO4.2. Specific gravity of sulfuric acid solution falls due to formation of water during reaction at PbO2

plate.

3. As a result, the rate of reaction falls which implies the potential difference between the plates decreases during discharging process.

Now we will disconnect the load and connect PbSO4 covered PbO2 plate with positive terminal of an external DC source and PbO2 covered Pb plate with negative terminal of that DC source. During discharging, the density of sulfuric acid falls but there still sulfuric acid exists in the solution. This sulfuric acid also remains as H+ and SO4 − − ions in the solution. Hydrogen ions (cation) being positively charged, move to the electrode (cathode) connected with negative terminal of the DC source. Here each H+ ion takes one electron from that and becomes hydrogen atom. These hydrogen atoms then attack PbSO4 and form lead and sulfuric acid.

SO4 − − ions (anions) move towards the electrode (anode) connected with positive terminal of DC source where they will give up their extra electrons and become radical SO4. This radical SO4 cannot exist alone hence reacts with PbSO4 of anode and forms lead peroxide ( PbO2) and sulfuric acid (H2SO4).

Hence by charging the lead acid storage battery cell, 1. Lead sulfate anode gets converted into lead peroxide.2. Lead sulfate of cathode is converted to pure lead.3. Terminal; potential of the cell increases.4. Specific gravity of sulfuric acid increases.

onstruction of Lead Acid Battery« Previous

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There are mainly two parts in a lead acid battery. The container and plates.

Lead Acid Battery ContainerAs this battery container mainly contains sulfuric acid hence the materials used for making a lead acid battery container must be resistant to sulfuric acid. The material container should also be free from those impurities which deterious to the sulfuric acid. Especially iron and manganese are intolerable. The glass, lead lined wood, ebonite, hard rubber of bituminous compound, ceramic materials and molded plastics are having the above mentioned properties, hence the container of lead acid battery is made of either of those materials. The container is tightly sealed with top cover.

The top cover has three holes, one at each end for the posts and one in the middle for vent plug and through which the electrolyte is poured and gases escape out. At inside bottom floor of lead acid battery container, there are two ribs to hold the positive lead acid battery plates and another two ribs to hold the negative plates. The ribs or prisms serve as supports for the plates

and at the same time protect them from short-circuits that would otherwise occur as a result of fall of the active material from the plates on to the bottom of the container. The container is most basic part of construction of lead acid battery .

Lead Acid Battery PlatesThere are, in general, two methods of producing the active materials of the cell and attaching them to lead plates. These are known after the names of their inventors.

1) Plante plates of formed lead acid battery plates.

2) Faure plates or pasted lead acid battery plates.

Plante PlatePlante ProcessIn this process two sheets of lead are taken and immersed in dilute H2SO4. When an current is passed into this lead acid cell from an external supply, then due to electrolysis, hydrogen and oxygen are evolved. At anode, oxygen attacks lead converting it into PbO2 whereas cathode is unaffected because hydrogen can form no compound with Pb.

If the cell is now discharged then peroxide-coated plate becomes cathode, so hydrogen forms on it and combines with the oxygen of PbO2 to form water thus,

PB2 + 2H2 → Pb + 2H2O

At the same time, oxygen goes to anode which is lead and reacts to form PbO2. Hence the anode becomes covered with a thin film of PbO2.By continuous reversal of the current or by charging and discharging the thin film of PbO2 will become thicker and thicker and the cell polarity will take increasingly longer time to reverse. Two lead plates after being subjected to hundreds of reversals will acquire a skin of lead peroxide thick enough to process sufficiently high capacity. This process of making positive plates is known as formation. The negative lead acid battery plates are made of same process.

Structure of Plante Plate

It is seen that since active material on a Plante plate consists of a thin layer of PbO2 formed on and from the surface of the lead plate, it must be desirable to have a large superficial area in order to get an appreciable volume of it. The superficial area of lead acid battery plate can be increased by grooving or laminating. The figure shows a Plante positive plate which consists of a pure lead grid with finely laminated surfaces. The construction of these plates consists of a large number of thin vertical lamination which are strengthened at intervals by horizontal binding ribs. This results in increase of superficial area by a large extend. The main feature of construction of lead acid battery is to accommodate a large volume of active materials i.e. PbO2 in active plate. Positive plates are usually produced by Plante Process and the plates are known as Plante Plates. The negative lead acid battery plates can also be manufactured by this process but for negative plate this process is impracticable. Faure PlateIn Faure process, the active material is mechanically applied instead of being electrolytically developed out of lead plate itself as in Plante process. The active material which is in the form of red lead (Pb3O4) or litharge (PbO) or the mixture of two in various proportions, is pressed into the interstices of a thin lead grid which also serves as conductor of current. After pasting the grids with active material the plates are dried, hardened and assembled in a weak solution of sulfuric acid of specific gravity 1.1 to 1.2 and are formed by passing an current between them. For forming negative plate these plate are connected as cathodes. The oxygen evolved at the anode converts the lead oxide (Pb3O4) into lead peroxide (PbO2)and hydrogen evolved at cathode

reduces the lead monoxide (PbO) into sponge lead (Pb).

Formation of positive plates involves conversion of lead oxide into lead peroxide. A high lead oxide, such as Pb3O4 is used from economic considerations both in current and time, although in practice a mixture of Pb3O4 is employed. Faure process is much suitable for manufacturing of negative Faure plates rather than positive lead acid battery plates.In order to obtain large capacity in smaller construction of lead acid battery , a large surface must be exposed to the electrolyte, and since the size of a single plate is limited, so to increase capacity of lead acid battery number of negative and positive plates are connected in parallel. The adjoining positive and negative plates are separated by placing an insulated berries or separators between them. The separators are made of either plastic, fiberglass, hard rubber or wood. The number of negative plates in a cell is always more than one of number of positive plates so that end plates at both sides of the group remain negative. This is done so that all positive plates can work equally well from both sides. This assembly of positive and negative plates are immersed in the diluted sulfuric acid in the lead acid battery container. The battery has two terminals - the positive and negative.

Lead Acid BatteryLead Acid battery is one of the oldest types of rechargeable battery invented by Gaston Planté in 1859. Lead Acid batteries are also the most used batteries in the world, They are used in a wide range of places and in almost every equipment because of their high surge current or power to weight ratio despite having low energy to weight ratio as compared to other types of batteries.

Active Materials of a Lead Acid Cell:The active materials of a lead acid cell which takes parts on chemical reaction actively while charging or discharging of a lead acid cell or battery are:

Lead Peroxide: Lead Peroxide is the combination of lead and oxygen with molecular formula ( PbO2 ). It is made up of one atom of Lead and two atoms of oxygen. The lead oxide is a dark chocolate brown colored. It is brittle and hard in nature and acts as the positive active material in a Lead Acid cell.

Sponge Lead: Sponge lead is the pure form of lead or ( Pb ) in it’s soft , porous sponge form. It acts as the negative active material in a Lead Acid cell.

Dilute Sulfuric Acid: Dilute Sulfuric acid ( H2SO4 ) is the electrolyte in a Lead Acid cell. The sulfuric acid is diluted by adding three parts of water to one part of sulfuric acid to form the electrolyte.

Construction / Parts of a Lead Acid battery:A Lead Acid cell is constructed by immersing the two plates of lead plated with Lead Peroxide and Sponge Lead into the electrolyte Dilute Sulfuric Acid of specific gravity of about 1.21. The Lead Peroxide and Sponge Lead has very little mechanical strength. So, for better mechanical strength both of the active materials are plated into plates of pure lead which are immersed into the electrolyte. All of which are assembled into a suitable plastic or rubber Jar. The Lead plate covered with Lead Peroxide acts as the anode of the cell and the plate covered with sponge lead acts as the cathode. The parts of a lead acid cell or battery using which a Lead Acid cell or battery is constructed are:

1. Container: The container is the outer part of a lead acid battery which hold down all the components of a lead acid battery together. The container of a lead acid battery should be resistant to sulfuric acid and should not deform or become porous or contain impurities which might deteriorate the electrolyte.  The Containers of lead acid batteries are made up of materials like Glass, Lead lined wood, ebonite,  hard

rubber, ceramic materials, molded plastics etc.

The container is sealed from above with a cover and contains apartments inside it which acts as the container of each cells of the lead acid battery , each apartment in a container contains connecting bar which is basically a lead alloy used for linking the cells together in a battery. The container also contains vent plugs or filter caps, which are made up of polystyrene or rubber, usually screwed at the top of cover of each cell It acts the free exit for gasses but prevents the escaping of electrolyte , the vent plugs can also be used to refill the battery with electrolyte when the electrolyte decrease due to gassing.

2.  Electrolyte:  It is the dilute sulfuric acid which is poured into the compartments of the container.

3. Plates: A plate is basically a form of grid made up of lead which hold with it the active material Lead Peroxide or Sponge Lead. The grid supports the active materials and also acts as the conductor of electric current. The grid is made by the cast of an alloy of lead and

antimony. 

There are two plates in a lead acid cell, One Anode plate and another Cathode plate. The plate serving as the anode is made onto a heavier grid because the anode is more subjected to corrosion as compared to cathode.

4. Separator: Separator are the thin sheets of porous non-conductive materials placed between the two plates in a lead acid cell so as to prevent contact between the two plates and thus prevent the internal short circuiting in the cells. The separator is porous enough to allow the circulation and diffusion of electrolytes between the plates. The separator is made up of cedar-wood, glass wool mat, micro-porous rubber or micro-porous plastic.

Formation of Plates:As discussed above the plates of a lead acid cell are constructed by supporting the active material of the plate by the lead grid. The plates thus should be formed by special process  so that the grid strongly grips the active materials into it and is fairly strong and good enough to be used as a plate. There are mainly two ways by which the plates of a lead acid can be formed they are:

a. Formed Plate or Plante Process:

To form a plate with Plante process two sheets of lead plates are immersed into dilute sulfuric acid. Now when a current is passed through the lead sheets immersed in the electrolyte  from external source, Due to the electrolysis Hydrogen and Oxygen are evolved.  Now, At the anode the oxygen reacts with lead sheet to form a layer of Lead Peroxide (PbO2) around the lead sheet but at the cathode the hydrogen cannot react with lead.

Now, if the cell thus produced is discharged the role of anode and cathode is  reversed or the peroxide coated plate becomes cathode thus the hydrogen reacts with the peroxide to form water at the same time the oxygen reacts with the previously unaffected plate to form a layer of lead peroxide around it.  After continuous reversal of the current by charging and discharging the process will take longer and longer time to reverse. Thus producing a thicker and thicker layer of lead peroxide at one plate and a porous lead at another plate with each cycle. Thus producing the plates required.

b. Pasted or Faure Process:

To form the plates with faure process , the active materials are mechanically applied instead of producing them electro-chemically out of the lead plates.To form the plates with Faure process; first of all the red lead (Pb3O4)  or litharge (PbO)  or the mixture of read lead and litharge in various proportions is pressed into a lattice of thin lead. The plates are then allowed to dry and then immersed into a weakly concentrated Sulfuric Acid of specific gravity 1.1 to 1.2 and are formed by passing electric current between them from an external source. The oxygen evolved at anode reacts with the lead oxide to form lead peroxide and the hydrogen at cathode reacts with Litharge to reduce it into sponge lead.

Comparison of Plates produced by Plante and Faure Process:

The formation of plates takes a longer time and a lot of external electrical energy with Plante process, but the life time and the strength of the plate produced by Plante process is better as compared to the plate produced by the Faure process.  The plates produced by faure process is cheaper to build but is more liable to disintegrate and is weaker then the plates produced by the Plante process. Also the plates produced by the plante process have less capacity to weight ratio of about 12 to 21 AH per Kg of plate as compared to 65 to 90 AH per Kg of plate produced by Faure process.

Working Principle of Lead Acid Cell/BatteryIn the electrolytic solution of Sulfuric Acid , the sulfuric acid is dissolved and ions of Hydrogen (2H + ) and Sulfate ( SO4

— ) moves freely. Now when the external current is supplied into the electrodes of Lead Plates immersed into the solution, the Anion Sulfate ( SO4

— ) moves toward the Anode and Cation Hydrogen (2H + ) moves towards the cathode. At cathode the Hydrogen takes electron from the cathode and escapes from the solution as the hydrogen gas. At anode the Sulfate gives it’s electrons to the anode and reacts with water to form more Sulfuric acid and oxygen atoms. The oxygen atoms thus produces reacts with Lead at anode and form Lead Peroxide. Now the Lead Acid cell thus produced is capable of supplying electrical energy to external devices and can be used as a power source. After which the following chemical changes occurs:

Chemical Changes During Discharging: When a lead acid battery is fully charged the anode and cathode of it’s cells are converted into Lead Peroxide ( PbO2) and Sponge Lead ( Pb ) respectively.  During the process of discharge , The current within the cell is moving from cathode to anode , So the Hydrogen ions moves to anode and Sulfate ions moves to the cathode. At Anode, Hydrogen combines with Lead Peroxide and reacts with Sulfuric acid to form Lead Sulfate.  or,PbO2 + H2 + H2SO4 = PbSO4 + 2H2OAnd at the cathode, the Lead and Sulfate combines to form Lead Sulfate. Or,Pb + SO4 = PbSO4

So, during the discharging of lead acid battery the plates of cells are both converted into Lead Sulfate which is whitish in colour, Due to formation of water the specific gravity of the cells decreases and also the EMF of the cell decreases.

Chemical Changes During Charging: Now, When the cell is recharged again , The hydrogen ions moves to cathode and Sulfate Ions moves to anode, At cathode , The lead sulfate reacts with Hydrogen to give Lead and Sulfuric acid, Or,PbSO4 + H2 = Pb + H2SO4And at anode the Sulfate reacts with Lead sulfate along with water to give Lead Peroxide and Sulfuric acid. Or,PbSO4 + 2H2O + SO4 = PbO2 + 2H2SO4

So, during the process of recharging the plates gets reverted back into their original conditions, The specific gravity of the cells increases due to formation of Sulfuric acid and the EMF of cells or battery

increases.

Types of Lead Acid Batteries:Based on their uses and services rendered by them lead acid batteries are classified into following three categories:

1. SLI Batteries: These batteries are used to provide supply power for engine starting , ignition and lighting of vehicles such as Automobiles , Buses etc. Usually these batteries provides 12 V through a six-series connected lead acid cells with capacity of the order of 100AH.

2. Vehicle Traction Batteries: These batteries are used to power up the electrically powered vehicles and automobiles. These batteries are  of higher quality as compared to SLI batteries and provides constant EMF for a longer period of time, are more resistant to Vibrations and have longer service life. The EMF of these batteries varies from 12 V to 240 V.

3. Stationary Batteries: These batteries are used for standby power systems. like UPS.

Maintenance and Care of Lead Acid Battery or Accumulator:To prolong the lifetime and also improve the quality of a Lead Acid Battery a regular Maintenance and care should be done while handling and using the battery. Regular maintenance and care of lead acid battery also increase it’s weight to power ratio and weight to energy ratio. Some of the main steps for maintenance and care of lead acid batteries are:

1. While charging the Battery , it should always be charged with rated voltage and ampere with direct and non-fluctuating current with right direction of current.

2. The level of electrolytes should always be maintained to the level as stated in it’s manual. Normally the electrolyte should always be 10 to 15 mm above the plates so as not to expose the plates to the air. With time the electrolyte might get lesser and lesser to regular inspection should be done.

3. A Lead Acid battery should not be left at discharged condition for prolonged period. Leaving the battery discharged for prolonged period might cause the crystallization of lead sulfate at plates which makes the reformation during recharging almost impossible. If the battery is to be stored without use a regular top-up charging  should be done in the interval of every 4- 6weeks.

4. Naked flames should be kept away from battery. The flames might cause explosion or fire due to the discharged gases from the lead acid battery.

5. The batteries should be overcharged on a regular basis so as to remove the whole of the sulfate formed on the plates.

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In industrial or substation applications mainly three types of batteries are used namely:1. Vented / Flooded Lead Acid batteries2. Sealed maintenance  free batteries/Valve Regulated Lead Acid3. Nickel Cadmium (Ni-cd) batteriesFor UPS applications batteries are the most popular and hence are widely used. Hence, in this detailing, mainly emphasize has been put on these type of batteries.

Vented / Flooded Lead Acid Batteries

Vented / Flooded Lead Acid Batteries

There are two types for vented or flooded lead acid batteries namely tubular and Plante. The difference between the two is the construction. For tubular battery normal life is 8-10 years. The Plante battery is both mechanically and electrically more durable. The normal life for Plante batteries is 15-20 years. Because this type of battery generates corrosive fumes when charging and because the sulfuric acid electrolyte does evaporate to some extent, these batteries must be used in a special room, which is well ventilated to the outside and kept away from delicate electronic equipments.

It needs separate room/racks with acid proof tiles for installation. Because of evaporation, it needs regular maintenance to check specific gravity, to add water and acid. These batteries can withstand high temperature, voltage, and deep discharge with minimum damage to itself. A notice should be exhibited in the battery room prohibiting smoking and use of naked flames. These batteries cannot be transported in charged condition and therefore need charging at site.

Typical initial charging of the battery will take about 55 to 90 hours. Nominal cell voltage is 2V/cell. The charger for this battery should be able to provide the first charge at 2.6 to 2.7 V/cell.

Tubular Type Lead acid battery

These types of batteries are typically used for UPS Systems of very high rated capacity, typically engaged for plant application, wherein maintenance and space is not really an issue.

Sealed Maintenance Free batteries (SMF)

VRLA/SMF type Lead acid battery

These are also known as Valve Regulated Lead Acid (VRLA) batteries. These batteries are the most popular for usage with UPS systems for computer or commercial application. Being sealed, these batteries do not emit any fumes and hence can be very well installed next to electronic equipment. These batteries also can be housed in a close enclosure if necessary. These batteries are also maintenance free and avoid any hassles of checking specific gravity, adding water or acid, etc.These batteries have a relatively lesser life of approx. 3-5 years. The life expectancy typically depends on the number of charge/discharge cycle experienced by the batteries and the ambient temperature in which the batteries are used. These batteries are primarily the most popular for commercial applications due to “Install and forget” approach.

The Performance and service life of these batteries can be maximized by observing the following guidelines:

1. Permissible operating temperature range of SMF batteries is 15 deg C to 50 deg C, but using within an

operating range 5 C to 35 C will extend service life. Below – 15 deg C, the battery changes its chemical composition and cannot hold a charge. You will enjoy longer service life, if batteries are operated in ambient temperature range of 20 deg C to 25 deg C (68F to 77F). At lower temperature they have longer life and lower capacity while at higher temperature they have higher capacity and lower life.

2. A good rule of thumb when determining battery service life in relation to temperature is that for every 8.3

deg C (15F) average annual temperature above 25 deg C (77F), the life of the battery is reduced by 50%. Therefore warranty of the battery should be ideally reduced to 50% for every 8.3 deg C (15F) increase in operating temperature above 25 deg C (77F).

3. SMF batteries are designed to have a float voltage of 2.3 V/cell. This means that a 12 V battery (with 6

internal cells) has a float voltage of 13.8 Volts. Most of the battery manufacturers recommend float voltage of 2.25 – 2.3 volts per cell. When there are more cells (generally >120) in series, to compensate for higher temperatures, float voltage should be decreased by approx. 3 mV per cell per deg C above 25 deg C. It should be increased by the same amount when operated at a temperature less than 25 deg C to avoid undercharge. The Cutoff voltage is 1.67 V/cell for high rate of discharge (

4. It is recommended that SMF batteries should not be left in totally discharged state more than 72 hrs. The

batteries may get partially or fully damaged due to SULPHATION if charging does not start within 72 Hrs from totally discharged state. Sulphation is the formation of lead sulphate on negative plates which acts as an insulator and has a detrimental effect on charge acceptance.

5. In normal float / equalize use (2.25 to 2.35V/cell), gas generated inside battery is recombined into

negative plates, and return to water content of the electrolyte. Thus electrical capacity is not lost because of this recombination. There is no need to add external water, but due the corrosion of the electrodes battery will eventually lose capacity.

6. At ambient temperature of 30 – 40 deg C, the shelf life of batteries is 5-6 months only. A freshening

charge must be given to the batteries every 6 months, if needed to be stored for longer periods. Batteries should be kept in dry, cool place. At ambient temperature of 20 deg C (68F), the self-discharge rate is 3-4% (approx.) of rated capacity per month. The self-discharge rate varies with ambient temperature.

7. SMF batteries are equipped with a safe, low pressure venting system, which operates at 7 psi to 10 psi

(can vary slightly from manufacturer to manufacturer), automatically releasing excess gas in the event that gas pressure rises to a level above the normal rate ensuring no excessive buildup of gas in the batteries. Resealing is automatic once the pressure is returned to normal.

8. Cyclic life of the battery depends on ambient operating temperature, the discharge rate, the depth of

discharge, and the manner in which the battery is recharged. The most important factor is the depth of discharge. At a given discharge rate and time, the shallower the depth of discharge, the longer is the cyclic life.

9. Failure mode at the end of life includes:

1. Capacity decrease2. Internal short circuit

3. Damage to container/lid4. Terminal corrosion5. Reduced open circuit voltage.

10. The IEEE defines “B” (Bend of useful life) for a UPS battery as being the point when it can no longer

supply 80 percent of its rated capacity in ampere-hours (AH). The relationship between AH capacity and runtime time is not linear, a 20% reduction in capacity results in a much greater reduction in runtime. When battery reaches 80% of its rated capacity , the aging process accelerates and the battery should be replaced. Some UPS/ Battery manufacturers define “B” (Bend of useful life) for a UPS battery when battery capacity reaches 50-60% of its rated capacity.

11. Mixed use of batteries with different capacities, different makes should be avoided as it will cause

accelerated aging of the whole string.

12. If two or more battery groups are to be used, connected in parallel, they must be connected to the UPS

through lengths of wires, cables or busbars that have the same loop line resistance as each other. This makes sure that each parallel bank of batteries presents the same impedance to the UPS as any other of the parallel banks thereby ensuring correct equalization of the source to allow for maximum energy transfer to the UPS load.

13. The normal life SMF battery will support approx. 200 charge/discharge cycles at 25 deg C (77F) and

100% depth of discharge.

14. The term “B” (Bend of useful life) for a UPS battery refers to the fact that these batteries do not

require fluid. But preventive maintenance like checking for cracks and deformation of the container & lid, electrolyte leakage/spills tightening of the connection etc, particularly for higher AH capacity batteries should be done to prevent any damage.

Nickel Cadmium Batteries (Ni-Cd)Ni-cd batteries do emit hydrogen and oxygen gas, products of electrolysis, but there are no corrosive gases as lead acid batteries, so these can be installed near electronic equipment. Water consumption is relatively low and so therefore maintenance is low. Normal service life is 20-25 years. These are most expensive of the various types of batteries previously discussed. Initial cost may be approximately three times that of lead acid battery depending upon their AH capacity.

These batteries do not experience the severe shortening of life when operated at elevated temperatures and perform better at low temperatures than do the lead acid batteries. Nominal cell voltage is 1.2 V/cell. The battery chargers and inverters have to be designed to operate with low end cell cutoff voltages and higher recharging voltages needed for such batteries.

These batteries occasionally demand boost charging and typically find their applications wherein UPSs support critical equipment in hazardous environment such as chemical, fertilizer, cement industry.

Merits/demerits

As spelled earlier, all the above discussed types of batteries have their own merits and demerits. Let us now look at them individually.

A) Vented / flooded Lead acid batteriesMerits

1. Most economical among three types of batteries.2. Life is higher than SMF batteries.3. Robust- not much sensitive to temperature.

Demerits1. Needs periodic maintenance- twice a month.2. Emits corrosive fumes.3. Needs special battery room with acid proof tilling.4. Cannot be transported in charged condition, initial charging takes 55 to 90 hours.5. Needs specially trained persons for handling due highly hazardous sulphuric acid.

B) Sealed maintenance free batteries / Valve Regulated Lead AcidMerits

1. No maintenance as far as water filling, specific gravity check etc is concerned.2. Can be shipped in charged conditions so ready to use.3. User friendly.

Demerits1. Leaving batteries in discharged state for longer life will reduce life significantly or can damage them

permanently.2. Very sensitive to temperature3. Service life lowest among the three types4. Costlier than flooded / vented lead acid battery

C) Nickel Cadmium (Ni-cd) batteriesMerits

1. Moderate maintenance2. Higher service life3. less sensitive to temperature4. Fumes not corrosive so can be installed near electronic equipment

Demerits1. Most expensive among three types2. Cannot be transported in charged conditions.

3. Compatibility with respect to charger and inverter needed to be considered.

Summary of Techno-Commercial Analysis between Ni-Cd & Lead acid BatteriesNo. Description Ni-Cd Lead acid Remarks

1 Reliability Criteria Worst case failure is cell short circuit. Result is reduced performance. The battery will continue to support the system.

Worst case failure is cell open circuit. Result is complete loss of battery, known as ‘sudden death’, resulting in an unpredicted system failure.

This point makes NiCd to be superior in terms of purpose

2 Requirement of Air-Conditioning & additional cost of Electrical Energy

Nil Yes Additional Cost due to Air conditioning equipment and running cost-For VRLA

3 Battery Life as claimed by UK manufacturers (Industrial Batteries)

20 Years 5-7 Years Replacing cost of VRLA after every 5-7 years will involve manufacturing cost escalation during that year. Eg.at 6th year, 12th year and 18th year.

4 Battery Cost Approximately 3 times than VRLA

– –

5 Relative Costs Initial & Life Cycle

Ni-Cd cells have a higher initial cost than lead acid but superior lifetime and characteristics, giving a lower life cycle cost in many applications.

Lead Acid has a low initial cost but a restricted lifetime. In many applications they can have a poor life cycle cost.

–

6 Physical Size Ni-Cd cells are generally larger than VRLA cells.

In terms of Ah, Lead acid (VRLA) is the most compact battery.

7 Water Topping Occasionally Required Not Required

Summary of Comparison between tubular flooded (ordinary Lead-acid) battery with SMF Lead Acid BatteryNo. Tubular Lead Acid battery VRLA Battery

1 Tubular positive Plates:The positive active material is held in a polyester tube. This does not allow the materials to shed during charge-discharge cycling resulting in long cyclic life- minimum 1200 cycles at 80 % depth of discharge.

Flat pasted positive plates:The positive active material is a paste form pasted over a lead alloy grid.  This results in a shorter cyclic life compared to tubular construction.- minimum 500 cycles at 80% depth of discharge

2 Electrolyte:  Stationary batteries of UPS and Power plant back up works on low specific gravity (1.200) electrolyte and larger in volume. This results in less corrosion of grids and longer life. The larger volume keeps the battery comparatively cooler which also adds to life.

Electrolyte: VRLA batteries work on high specific gravity electrolyte (1.280 to 1.300) and less volume. The cells get heated up during charging and high rate discharges which affects the service life.

3 Separators: Micro porous poly ethylene separators are used. This permits the ion movement and positive to negative plate separation.

Separators: Adsorptive glass mat separators are used in these batteries with a closer spacing between the positive and negative plates. Chances of cell shorting are therefore more.

4 Charging compatibility: Tubular stationary lead acid batteries can be charged with constant current and constant voltage mode. Flooded electrolyte batteries can withstand more abuses during charging. Water lost in electrolyte during such abusive overcharging

Charging compatibility:  VRLA batteries require constant voltage charging with a specified limit only specifically to avoid overcharging.  If by any chance, the charging conditions are altered, the battery will get heated up which will deteriorate the battery

could be easily made up manually by periodic top-up. Lagging cells could be brought to normal life by an extended equalizing charging without significantly affecting the other cells.

life. Though there is no need to top-up due to the recombination principle, it is not always 100% efficient, so some water loss during use is not avoidable. This results in a further increase in electrolyte specific gravity and life reduction. Equalizing (Extended) charging in VRLA batteries results in some cells getting heated up and life reduction.

5 Containers: We use transparent SAN containers. The electrolyte level is easily seen for topping up needs and ease of maintenance. Low maintenance.

Not applicable: Cannot monitor Electrolyte

6 Need for temperature control: Due to the large electrolyte volume the temperature of the cells generally do not rise abnormally during charging. No need for Air conditioning.

Need for temperature control:  The close packing arrangement and compactness of the stack in the cell assembly rises the temperature sharply during charging. Due to this, VRLA battery manufacturers invariably recommend the need for air conditioned environment for the battery compartments. This adds to the cost of maintenance.

Consturction of lead acid batteryIn this topic we are discussing about the lead acid battery working , and construction . mainly construction

Main parts of lead acid battery

1. Separator.

It is most important part of lead acid battery. Which separate the positive and negative plates from each other and prevents the short circuit? The separators must be porous so that the electrolyte may circulate between the plates . The separators must have higher insulating resistance and mechanical strength. The material used for separators are wood, rubber, glass wood mate, pvc.

2. Electrolyte 

in lead acid battery dilute sulphuric acid (H2SO4)is used as an electrolyte. For this purpose one part concentrated sulphuric acid is mixed with three parts of distilled water.

3. Container.

Container is a box of vulcanized rubber, molded rubber, molded plastic, glass or ceramic , on the base of this box there are supports block on which the positive and negative plates are established. Thus between this supports there are grooves which works like a mud box. The active material separated from the plates get collected in this mud box and it cannot make the contact with the plates thus the internal faults due to the mud are avoided.

4. Cover of cell. 

In lead acid battery it is also made of the same material which is used is used for making container. It is used to cover th complete cell after the installation of the plates in it . it protects the cell from the dust as well as other external impurities.

5. Vent plug.

The vent plug are provide in the cover plate of the cell which are used to fill up the electrolyte in the cell or the inspection of internal condition of the cell the vent plugs  are aslo use for to exhaust the gases generated in the cell to the atmosphere.

6. Connecting bar.

It works like a link and used to connect the two cells in series. Terminal of one cell and negative terminal of another cell.

7 terminal posts

There are the terminals of the battery which are connected to charging circuit as well as the load. For identification the diameter of the positive terminal is design more as compared to the negative terminal. Hence it is the lead acid battery construction, working also discuss below.

 lead acid battery, working

Dilute sulfuric acid used for lead acid battery   has ration of acid: water = 1:3.This lead acid storage battery   is formed by dipping lead peroxide plate and sponge lead plate in dilute sulfuric acid. A load is connected externally between these plates. In diluted sulfuric acid the molecules of the acid split into positive hydrogen ions  and negative sulfate ions  . The hydrogen ions when reach at PbO2 plate, they receive electrons from it and become hydrogen atom which again attack PbO2 and form PbO and H2O (water). This PbO reacts with H2 SO4 and forms PbSO4 and H2O (water).

Hence it is the lead acid battery, construction and working. if you will fined any incorrect in this article pleas comment below in comment box.

For knowing more about lead acid battery working and construction pleas sea this video.