battery mitra

7/29/2019 Battery Mitra

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200Q.9.8. Compare the advantages and disadvantages of Lead-Acid &Alkaline

ANS.Batteries.

-,LEAD-ACIDi) Develops nominal 2 volt per i)

cell, demanding. 12 cellsbattery for the normal 24 voltsupply.Less expensive in initial cost ii)and more efficient. .

.ALKALINEDevelops 1.2 volt per cell,so20 cells are required fornormal 24 volt supply.

Costly bus has the longer lifeof 15 years compared to 5yrsof lead-acid.. Preferred for emergency powersupply being ore suited to longperiods of idle operation onstand-by. It is regarded asmore reliable.Electrolyte is aqueous KOHsolution, evolve gas.continuously during charging.Hydrogen and Oxygen gasesare evolved during changingand vented through non-returnvalues.Gases arehighly explosive and .alkaline in nature.

vii) Evolution of gas causes water. loss during changing, whichshould be tapped up.

viii) Life starts reducing viii) Can be operated continuouslyconsiderably above 25C. at 45C, without loss of life.

ii)

iii) Preferred for regular recycling iii)duty of essential powersupplies operating on charge /discharge basis.

iv) Electrolyte IS dilute H2S04, iv)evolves gas when nearing thetop of the changing.Hydrogen & Oxygen gases are v)evolved due to chemicalbreakdown of water. Cells arerented to allow gases to escape.Gases are highly explosive and vi)acidic in nature.

v)

vi)

vii) Evolution of gas causes waterloss which should be topped upwith distilled water.

ix) Care must be taken not to ix)cause sparks or produce nakedflame, when inspectingbatteries.

Sparking and naked film areprohibited in the battery room.


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201Q.9.9. Give detailed report on Battery Checking, Maintenance And Safety.

What is Voltage Drop Test?ANS.1. Cell tops must be kept clean, dry, vents clear, and free of deposits. Terminalconnections should be tight, free of corrosion and coated with petroleum jetty toprevent corrosion.2. Electrolyte levels should be checked and topped up with distilled water to cover theplates, by about 1/8" higher than the top end of plates.3. Checking of specific gravity or relative density by hydrometer-

For a lead-acid battery, the relative density varies between 1.275-1.285 at 15C for afully charged cell, to about 1.11 when fully discharged. The terminal voltage to bemeasured when supplying load. The terminal voltage of an idle cell is likely to be highgiving false indication of a fully charged cell. The terminal voltage of a fully charged cellis about 2.0 volt on load falling to 1.75V when fully discharged.

For alkaline battery, the relative density does not change, however, as the cell ages,relative density gradually falls. A new cell will have a relative density of 1.190 at 15C,whereas when it falls to 1.145, it indicates chemical deterioration has occurred andelectrolyte should be renewed or battery replaced. The terminal voltage of afully chargedalkaline cell is about 1.2V falling to 1.09V when fully discharged.4. The relative density readings vary with temperature and correction must be made toarrive at a correct value. The figures specified above are for idea electrolyte at 15C.Actual readings should be corrected by adding 0.007 for each 10C rise above 15Cand subtracting 0.007 for each 10C fall below 15C. .5. The end charge is indicated when the terminal voltage of an alkaline cell levels out at1.7volt and for lead acid cell, it is about 2.6 volt.6. Lead acid cells should be charged until gassing freely and charging should continuefor a further period until the charging voltage per cell levels out at 2.6 V.Overcharging causes overheating, distortion of cell plates and consequent dischargingof plate active materials.

Lead acid cells suffer self- discharge due to spontaneous chemical reaction even whennot in use, so they must bemaintained on atrickle charge, a low rate of charging... I

7. Alkaline cells should be charged at the recommended rate until gassing freely and thecharging voltage per cell rises to about 1.7 V. Alkaline cells are able to retain theircharge for a considerable period and do not suffer, self-discharge, except at high temp.Periodically, alkaline batteries should be given' a sort refresher charge by specialarrangement or through shore facility.Lead acid cells best o~erating temp. range is 15-:-25C and maximum recommendedoperating temp. is 45 C. If the temp. goes above, the battery condition deterioratesand battery life decreases for Alkaline cells, the operating range is 15 - 45C. Atlow temp., battery condition does not deteriorate but capacity decreases.


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Safety-

2029. The battery capacity is rated in terms of its discharge current at the 10hour rate. A250 Amp-Hr battery can supply 25 Amp for 10hours.Voltage drop test- The condition of a battery is checked by allowing it to discharge atthe recommended rate for 10 hrs (i.e. for a 150 Amp-Hr battery, @15Amp for 10 Hrs.),the voltage drop should not exceed 12.5% of the nominal system voltage after the testThe voltage variation should bewithin the limits of +10% and -12.5% from fully chargedto completion of full performance on load of the prescribed duty.

1. Wearing of protective clothing e.g. rubber apron, rubber gloves and eye goggles,while checking and topping up of batteries.2. No naked light, flame should be taken into battery room because of hydrogen gas

evolving from cells which can cause inflammable mixture. Insulated spanners andnon-metallic water jugs should be used to prevent sparking and short circuiting ofcells.3. Ventilation fan should be kept on.4. First aid treatment - H2S04 splashes should be washed off with fresh water andpotassium hydroxide should be washed off with boracic powder or boracic acidsolution. .

Q.9.10. a) State how short circuit may develop in a lead-acid battery and how thiscan bedetected.

b) State five causes of why the rated capacity of a lead-acid battery may fall offin service.Ans. a)Causes of short circuit -i) If ametallic or conducting material falls across the positive & negative terminals of a

cell.ii) If the battery container or the electrolyte gets heated up above the maximum

recommended temperature, then the electrolyte resistance (internal resistance of thebattery) decreases as it has negative temp. coefficient of resistance, and the cell platesget shorted causing high current flow and further rise irrtemperature.For every 10C rise in temp,the battery life reduced to half of its remaining life..

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iii) If the separation plates deteriorates and the +ve and -ve plates comes in contact witheach other.

iv) If contaminated water of higher conductivity is added in place of distilled watertopping up.v) .Accumulation of sulphate at the bottom can also short the plates.


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High current flow, heat generation and high temp. of battery container and buckling ofplates arethe indications of short circuit.b)i)Since the discharge action of the battery depends on the surface area of the plates

dipped in electrolyte, the capacity reduces if the electrolyte level falls off and does notimmerse the plates fully..

ii) A fall in relative density ofthe electrolyte reduces the rated capacity of the battery.iii) Corrosion or oxide formation at the battery terminals causes reduction in rated

capacity.IV ) Temperature below lSoC or in theminus range causes fall in rated capacity.v) Due to long use and ageing of the plates, the active material deteriorates or sometimescovered with sulphate deposition.

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204Q.9.11. Draw the Wiring Diagram For Two Sets of. Batteries On A Charge-DischargeBasis Br 4-PoleChange-Over SwitchWhileOne Is BeingCharged TheOther IsOnStand-ByDuty.

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