Handbook On Lead Acid Cell For Railway Signaling

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LEAD ACID CELL 1.

Introduction Two different types of lead acid cells are manufactured by the industry and depending on the application, these are normally referred to as mobile or stationary. These are also called Accumulators or storage cells. This document includes instructions, which are applicable for the installation and maintenance of stationary secondary lead acid cells or batteries.

2.

Parts of Lead Acid Cell Parts of Lead acid cell are shown in figure below. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Level indicator Vent plug Terminal ports Cover Separator guard Positive plate Separator Negative plate Container Plate rest

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 Level indicator and Vent plug. For all capacities of lead acid cell vent/float plug shall be of threads M27x3 pitch is provided. The dimension of vent cum float guide plug are shown in figure below: Green mark Transparent Indicator Red mark

Plug Threads (M27x3 Pitch)

Float at green mark level

Float at red mark level

Figure - 2

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Plastic Skirting of suitable colour fire retardant

Microporous body

Body Plug 8 windows of size 25x10 approx Suitable anti splash arrangement for eelctrolyte so that gasses can pass Threads M 27x3 pitch

Figure – 3

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6 or 8 holes 0 2 for releasing gas

Figure - 4

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 Plates The plates, which are actual electrodes, are:  Spongy Lead  Lead Peroxide • •

The plates will usually be plante or faure types. In the plante type the plates are solid type and of wed construction. Where as, in faure type a plate grid of antimony alloy is used with the lead peroxide or spongy lead in a powdered from secured inside a bay made of this grid.  Separators • The separators act as insulating pieces between the different plates. • separators are made of either specially treated wood, perforated rubber, celluloid or rubber fabric made porous by thick cotton threads or glass wool. • The common separator is wood, since it is the cheapest of all separators.  Container • The container is made of vulcanised rubber, pitch celluloid or glass.

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• Celluloid or glass containers are normally used for light duty work and celluloid container for portable work.  Plate rest • The plate rest or bottom blocks are raised ribs either fitted in the bottom of the jar or made in the jar itself so that the plates do not touch the bottom and the tope portion is kept at the correct level. • These also form a receptacle to collect the sludge formed during its period of active life. 

Terminal ports • All the positive plates are welded to one bar and all the negative plates to another common bar. • There is always one more negative plate then the positive to provide equal working area, on all sides of the positive plates. • The outside plates are, therefore, always negative plates. • The terminal posts are upward extensions of connecting bars. This forms the terminal post and passes through the cover to enable external connections to be made.  Cover • The covers are generally of vulcanized rubber or pitch.

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• A hole is provided for pouring the electrolyte and this can be closed by a screwed cap. • The cap is provided with minute holes for gases to escape. • This is also known as ‘Vent Cap’ Brief description and working A lead acid battery consists of positive and negative electrodes immersed in an electrolyte kept in sealed container. The material of the positive electrode is lead dioxide (PbO2) and that the negative electrode is spongy lead (Pb). These electrode are electrically insulated from each other using separators. The electrolyte is a suitable mixture of sulfuric acid and distilled water. When the battery is fully charged, the negative electrode remains as Lead, the positive electrode as lead dioxide and the concentration of sulfuric acid solution (specific gravity is between 12001220). As the battery discharges, the positive and negative electrodes convert chemically in to lead sulfate. The chemical reaction consumes the acid and finally releases water in the electrolyte solution, thereby reducing the specific gravity.  Capacity V/S Discharge rate

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The capacity of the battery is the amount of electricity that can be obtained from it. It can be rated in two ways. • •

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Ampere-hour rating Watt-hour rating.

The ampere-hour rating is always given with the specified discharge rate, that is. a) 100 AH at 10 A rate b) 150 AH at 15 A rate.

• • •

In(a)the maximum discharge current should not exceed 10 Amps, and the period of discharge at this rate is 10 hours. Similarly, for (b) maximum rate is 15 Amps and period is 10 hours. This is also sometimes expressed as ‘hour rate’ for example 100 Amps. @ 5 hours rate worked, mean that the maximum discharge current is 20 Amps. and the period of discharge is 5 hours. The capacity always reduces with increase in discharge rate so that the actual ampere-hour capacity obtained is usually 80 to 90% of the rated value.  Efficiency of a secondary cell • The efficiency of a secondary cell is defined as the ratio of output of a cell to the input required to restore the initial state of

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charge under specified conditions of temperature, current rate and final voltage. • Generally the efficiency is expressed in three ways: • Ampere-hour efficiency. • Volt efficiency. • Watt-hour efficiency. • Ampere-hour efficiency is the ratio of the ampere hours output to the ampere hours of the recharge. • The ampere-hour loss, which determines ampere hour efficiency during cycle of charge and discharge is principally that due to gassing. • Local action is responsible of certain amount, but unless the test is spread over a long period of time or the battery is in a very unhealthy condition this loss may be disregarded. Since gassing is due to charging current in excess of the utilised in charging the active material, ampere hour efficiency can be increased by controlling the charging current to keep it below the value, which will produce excessive gassing, but such careful control of the charging rate, and especially if the cycle of charge and discharge did not involve bringing the battery to an absolutely fully charged condition, an ampere hour efficiency of nearly 100% can be obtained. • Under commercial service conditions including frequent cycles of charge and discharge involving nearly the full capacity of Lead Acid Cell Ver 2.0

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the battery, an ampere hour efficiency between 85 to 90% may be obtained. 4.

Unpacking and storing

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Carefully unpack the cells received from trade (rough handling could damage them) and check all the components including the vent plugs, vent cum float guide, inter cell connectors, nuts and bolts. Inspect the sides and the bottom of the battery packing case for any wet spots, which indicate broken jars/containers. These might have been broken during handling and transportation. Cracked and broken batteries may be rejected and details may be brought to the notice of the supplier for replacement. The battery must be stored in clean, cool and dry room protected from sun, rain and dust.

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5.

Location and Installation

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Mount the batteries in well-ventilated, clean and dry rooms. For small battery installations, natural ventilation through windows and doors may normally be sufficient. However, for larger battery installation (more than 12 cells). Forced ventilation methods using exhaust fans must be provided. Separate battery room are necessary to avoid the adverse effect of fumes on other interlocking and power equipment as well as to provide free

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access to the maintenance staff (battery rooms are not double locked.). The battery room shall be provided with acid proof flooring and acid proof tiles on walls up to suitable height. Wherever, batteries are kept in field inside the location boxes, suitable openings/holes are necessary for ventilation. Where batteries are housed in location boxes, these housings shall be painted with acid resistant paint. In some applications, where a few cells are required to be kept in offices, equipment rooms, residence etc. they may be housed in wooden boxes proved with enough holes for ventilation. Locate the batteries away from direct Sunrays and heat emitting system. Place the batteries on rugged wooden racks of sufficient height so that it is possible to inspect and maintain them properly. Two or more coats of acid resistant paint of approved type shall protect the racks. The racks shall be level and mounted on approved type of insulators. A typical arrangement is shown in figure below.

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Connector

Connector Insulator

-

+

+

Centre of cells

Connector

SINGLE/DOUBLE ROW SINGLE TIER WOOD ON RACK

Figure - 5

Connector

+

Insulator

-

Connector

Connector

+

Centre of Cells

SINGLE/DOUBLE ROW DOUBLE TIER WOOD ON RACK

Figure - 6

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Lead acid cells of an approved type shall be used and shall conform to specification no. IRS: S 88/93 for low maintenance lead acid cells. The cells shall be installed as per approved drawings. At the time of installation, capacity test shall be done and record shall be maintained. Insulate the cells from the floor and from each other using insulators. Place wooden planks under the batteries wherever the cells are kept on masonry racks and floors, metallic frames and location boxes. Keep the individual batteries properly aligned and leveled to avoid stresses on the connectors/cable. Keeping battery insulator block under the battery is desirable. Ensure proper clearance between adjacent cells for connecting the battery terminal connectors and between adjacent rows from the angle of maintenance. Wooden battery racks must be protected against decay by painting them using acid resistance paint (Type 2 of IS 158-68). On receipt of charged secondary cells, the vent plugs shall be removed and the height of the electrolyte shall be noted, if it is below the prescribed level, the loss may be due to spillage during transit. The level of the electrolyte can be restored by adding battery grade acid of recommended specific gravity. Initial Charging

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Unless, good facilities are available in the Chief Signal/Telecom Inspectors depot for charging secondary lead acid cells and their subsequent handling and transportation to actual site of installation it is advisable to do the initial charging at site. Initial charging of the batteries shall be done as per instructions of the manufacturer and the date of charging shall be suitable painted on the batteries, or on a separate board kept near the batteries. The procedure given below, however, generally applies for initial charging to all makes of lead acid batteries. Ensure that all the cells in the battery set are of the same type and capacity. Charging individual cells separately is not advisable. Battery grade dilute sulfuric acid conforming to IS 266 and distilled or de-mineralized water conforming to IS 1069 shall only be used as electrolyte A glass, porcelain, rubber or any other acid proof container shall only be used for mixing acid and water. Always acid shall be added to water. During mixing, the solution must be stirred constantly so that its temperature does not exceed 50° C. Ratio in which sulfuric acid and distilled water must be mixed is given in the table –1.

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Specific Gravity of the original Acid 1825 1825 1400

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Specific Gravity of the solution required 1400 1190 1190 Table-1

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Distill water

Sulfuric acid

11 5 6

7 1 5

While preparing electrolyte, the solution should be continuously stirred using a glass or wooden rod. The temperature of the same should not be allowed to exceeds the limit, then allow it to cool. Allow it to cool for at least 10 to 12 hours and see that the specific gravity is between 1190 and 1200. Since, specific gravity varies with the temperature a correction must be applied to arrive at the correct value. For temperature > 27° C 0.0007 per ° C For temperature < 27° C -0.0007 per ° C

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Clean all the new cells for the battery set with distilled water and fill all of them with this electrolyte which will ensure uniform specific gravity.

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The level of the electrolyte should be about 12 to 15 mm above the plate. Check either the red mark indicated on the vent float or use a glass tube to see the level. The charger output terminals must be correctly connected to the battery set i.e. + to + and – to -. Ensure that all electrical connections between the charger and the battery are tight and offer good conductivity. Apply charge for 35 hours at the starting current rate given by the empirical formula/ thumb rule, where the starting charging current is taken as 4% of the ampere hours (AH) value of the cells. Starting Current = 0.04 x AH value (For initial charging) Check specific gravity and voltage reading every 8 hours. Apply temperature correction on the specific gravity readings. Stop charging when the specific gravity becomes 1210±5. If the specific gravity of the cell/cells after charging does not improve to its normal value, a small quantity of electrolyte is taken out and replaced by solution of higher specific gravity (1400). A fresh charging cycle must then be given for two hours to ensure mixing. Discharge the battery through a suitable load (lamps) till the specific gravity reduces to between 1180 and 1190 and the voltage of cells to 1.85 V.

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Repeat the cycle of charge and discharge once again and then charge finally for use. Ensure that the battery is charged optimally and no over charging, over gassing or heating takes place. Apply a coat of petroleum jelly or non-oxidizing grease on the battery connectors to avoid corrosion. Close all the vent caps and ensure that the floats are in position. If after charging, the battery are not put up in use for 15 days they should be given as equalizing charge to bring specific gravity of all the cells to 1210±5.

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7.

Maintenance and Inspection

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Maintenance tests and repair work on the cell, which may interfere with safe operation of trains, shall not be started until movements are fully protected. Temporary repairs or adjustments shall be made in such a manner that safety of train operation is not impaired when repairs and or adjustments are made. After the maintenance and repair work (Including temporary repair) are completed tests shall be immediately carried out to ensure that the connected apparatus functions satisfactorily. Battery charger used shall be as per specification no. IRS: S 86/2000 for battery charger self regulating. Float and boost mode shall be adjusted to 2.15 Volt/cell and 2.4 Volt/cell The battery room and location boxes shall be kept well ventilated, free from water, oil or dust surroundings and batteries shall be kept clean. Connecting cables shall be flexible and sufficiently long to prevent strain on the battery terminals. The electrical connection shall always be kept tight. The terminals and connections shall be coated with pure Vaseline or petroleum jelly to prevent corrosion. Grease shall not be used.

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The electrolyte shall be maintained at the correct level by topping up as often as necessary with distilled or demineralised water. Electrolyte lost due to spillage shall be replaced with proper amount of electrolyte of the same specific gravity as that of other cells of the battery. Electrolyte shall not be added in any other circumstances. Each cell shall be tested periodically and its cleaning and charging arranged so that its voltage and specific gravity are within specified limits. Test results and dates of cleaning and charging adjustments shall be recorded on the Battery History Card. A separate card shall be maintained for each battery set. The voltage of individual cell shall not fall below 1.85 Volts.

7.1

Precautions

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Checks / tests on battery and general cleaning normally do not affect the circuit it is feeding. However, care must be taken to ensure that the working circuits do not get affected. For maintenance and repair works (including temporary repairs) which may require disconnecting or recharging or replacement of the battery, disconnection notice must be issued to the ASM on duty and work commenced after

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the same is allowed and necessary precautions have been taken. This will ensure safety in train operation. Always use suitable goggles and rubber gloves and wears an apron while working with battery electrolyte.

7.2

General Cleaning

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Check each cell of the battery set once every fifteen days. Ensure that all connections are tight. Remove dust or dirt from the battery top and connections. Wipe the battery using a wet cloth piece and allow it to dry. At least once in three months, neutralize the acid on the battery covers and terminals with either ammonia or sodium bicarbonate solution in water before cleaning. Keep terminals and metal parts free of corrosion.

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7.3

Electrolyte

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Distilled water (IS 1069) should be used to top up the cells at regular intervals to maintain the recommended electrolyte level. The level goes down on account of evaporation, the electrolyte level should never drop below the top of the plates. Do not let it spill out to avoid electrolyte loss and corrosion. Add distilled water only when the battery is charging or gassing.

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Electrolyte lost due to spillage should be replaced with proper amount of electrolyte of the same specific gravity as that of other cells of the battery. Under no other circumstances should electrolyte be added.

7.4

Voltage and Specific Gravity.

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The specific gravity and the terminal voltage of batteries should be checked. Measurements must be taken after switching OFF the charger of at least one hour. It is a good practice to switch off the charger of at least one or two battery sets for 4 hours or based on the battery set condition during inspection and maintenance trips to the station. This helps in not only accessing the condition of the battery but also provides a discharge cycle. Keep accurate records of the battery voltages and sp. gravity as these are extremely important. They provide a detail history of the performance of each cell. Variations observed from normal values pin point the degradation in battery condition which can be promptly corrected. In case, in a particular battery set, the specific gravity of individual cells are observed to be varying considerably, the electrolyte must be exchanged / balanced between cells with higher value of specific gravity for those having lower value. This will also ensure uniform gravity in all of them. Balancing of electrolyte has to be

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done for individual cell after taking out from the set. Records must include in the following proforma.

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Param eter

1

2

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10

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remarks Work done and

Date

SECONDARY BATTERY HISTORY CARD No. of Cells: Installation date: Capacity (AH): Circuit reference: Battery Set no.: Charging current: Battery set voltage: Charger make: Battery make : Charger capacity: Cell no.

Signature

Form - S&T/BCP ______Railway______Division Station_________ Signal and Telecommunication Department

Specific gravity Cell voltage Specific gravity 1220 Cell volts

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When the charge in the battery set has gone down considerably, recharging must be done at a current equal to 10% of the AH value until the specific gravity of the cell came to 1210±5.

7.5

Cable and connections

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Connectors and connecting cable should be flexible and sufficiently long to prevent strain on the battery terminals. The connecting cables should have lead coated eyelets/lugs for connections. Electrical connection should always be kept tight. Loose connections get heated up leading to failure. Terminals and connections should be coated with pure Vaseline or petroleum jelly or non oxidizing grease to prevent corrosion. If corrosion occurred, it should be removed by wiping clean with a solution of washing soda and water (or dilute ammonia) taking care that the solution does not enter the cells. Grease shall not be used.

7.6

Equalizing charge

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The battery, which is continuously used in “Float Service” should be given equlising charge to compensate for low/ uneven specific gravity of cells. Equilsing charge is given to cells once in a three months at fixed current (normally 1/10th of AH capacity). The charging should be continued

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till the voltage and specific gravity in all cell have remains constant for three consecutive half hourly readings. 7.7

Miscellaneous

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The vent plugs should be kept in position and tight. If a vent plug is lost, it should be replaced early to prevent spillage of electrolyte. Defective cells should be disconnected and replaced. Batteries showing irregularities, which can not be corrected, should be taken out of service and report made to proper authority. Only approved hydrometer and voltmeter should be used for recording observations. It is recommended that :  Voltmeter should be of an accuracy class not inferior to 1.0 in accordance with IS:1248-68. The resistance of the voltmeter must be at least 1000 Ohms per Volt.

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7.8

Periodicity

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The periodicity of maintenance, will generally be as given below, except otherwise modified by the concerned Railway. Maintainer ESM/WTM JE/SE SSE

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Trouble shooting

Sr.

Cause

1. 1.1

Battery does not charge. Disconnection in the charging circuit. Blowing OFF of charger fuse AC or DC side Loose connections or high resistance at terminals

1.2 1.3 1.4 1.5 2. 2.1

2.2 2.3 2.4

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Remedy

Check the circuit and rectify. Check the fuse and rectify Check the connection, clean and tighten them. Defective charger not Replace the feeding current charger Wrong connections Check the connections and rectify Battery takes more time to charge Loose connection or higher Open the resistance at terminals connections and clean and the reconnect Charger not able to feed Replace the enough charging current charger Excessive discharge Charge the battery separately Wrong connection Check the connection and rectify. The charger out put Voltage

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2.6 3. 3.1

Cause

Remedy

may be less than 2.5 Volt per cell. Number of cells use may be more than the charger capacity. Battery does not last for long Low electrolyte level

charger output voltage. Adjust number of cells as per 2.15 volt per cell

3.2

Uneven specific gravity and voltage of the cells

3.3 3.4 3.5

Not properly or full charge Leakage in some cells Reverse polarity on some cells

3.6

Inadequate number of cells or load current is more. Low specific gravity

3.7 3.8 3.9

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Charger output voltage or charging current may not be adequate Batter charger may not be adequate for charging battery of given AH

Maintain the level properly Equalize the specific gravity of each cell with the electrolyte Recharge again Replace them Remove the reverse polarity cell from the set. Installed the cells as per the load Add the solution of higher specific gravity. Adjust the output voltage and charging current. Replace the charger with adequate capacity

Battery over heats during charge or discharge

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Sr.

Cause

Remedy

4.1 4.2

Charging current very high, especially at the finish. Charger voltage high.

4.3

Charged for longer period.

4.4

Over discharged or excessive load current Poor ventilation or temperature is high

Make proper charging current Check the voltage and adjust properly. Discharge the battery with suitable load. Adjust the load current Make proper ventilation

4.5 4.6

Internal short circuit

4.7

More sediment material in the cell, old/worn out cells Low level of electrolyte

4.8 5. 5.1 5.2

Low electrolyte level Broke/cracked container of cell Distilled water not recouped regular.

5.3

Excessive charging

5.4

Excessive heat

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Replace the battery Replace the cell Add the distilled water as per requirement Replace the cell. Add the distilled water as per requirement Adjust the charger current Provide March’2005

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Cause

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Remedy

ventilation Vent caps missing Provide new vent caps Voltage and specific gravity of cells unequal Internal short circuit or Replaced the cell. leakage Leakage of electrolyte Replaced the cell through crack cell, sealing compound and covers Dirty terminals of cell top Clean the terminals. Used with low electrolyte Use proper level electrolyte Sedimentation high inside Replace the the battery battery

6.6

Plates worn out

6.7

Impure electrolyte

7.

Specific gravity is higher then normal during float charging due to float voltage is high.

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Replace the battery Replace the electrolyte and recharge the battery. Adjust float voltage.

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Spare parts The following spare parts and consumables will be necessary.             

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Acid resistance paint IS158-68 Sulfuric acid IS-266 Distilled water IS-1069 Ammonia Sodium bicarbonate (washing soda) Petroleum jelly or Vaseline or non-oxidizing grease Cloth for cleaning Nuts and bolts Connectors and cables Cotton waste grade A Vent cum float guide plugs Floats Rubber gloves.

Tools and measuring equipment Following tools and measuring equipment will be necessary:  For measuring voltage, DC voltmeter ranges 0 volts to 200 volts  DC ammeter ranges 0 amps to 50 amps  Syringe type hydrometer  Crocodile clips  Wires or cables of adequate current capacity

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 Battery charger with controls for charging current  Spanner set  Battery shunt meter  Thermometer °C range 0-80°C  Glass tube (20 to 30 cms long)  Glass or PVC or porcelain or rubber container  Glass rod (30 to 40 cms long )  Nylon brush with tough bristles. 11.

Do’s and Don’ts

11.1

Do’s

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Ensure that the positive and negative wires are connected to positive and negative terminals respectively, while connecting the charger to the batteries. If the batteries not in use, keep the battery in full charge condition by given an equalizing charge atleast once every month. Ensure that the float indicator is available and in working order. Electrolyte is highly corrosive and should be handled carefully to avoid injury to person or damage to clothing or equipment. If the electrolyte is accidentally spilled, it should be flushed with plenty of water immediately, after treating with washing soda solution.

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After the failure of power supply battery should be charged on boost mode i.e. load plus three ampere, preventing the battery from buckling of battery due to rising temperature and evaporation of distilled water. Ensure that charger float and boost voltages has been adjusted to 2.15 Volt per cell and 2.4 Volt per cell respectively. Ensure that charger is suitable for charging the AH capacity of battery used.

11.2

Don’ts

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Do not allow over charging, excessive gassing and heating Do not allow the batteries to get fully discharge. Do not allow open flame smoking near the batteries to eliminate danger from explosion or fire. Extreme care must be exercised to avoid a spark or flash when changing connections or working on or near the battery. Battery lead should first be disconnected at a point remote from the battery set. Metal jugs should not be used for carrying water required for topping up. Do not miss handle the cells, specially during transportation. Do not hold the cells by the electrode terminals.

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