Lead–acid battery-How does a lead acid cell work
LEAD ACID
CELL
Describe
components of Lead Acid Cell and provides following data :
(a) What
ought to be relative density of acid at initial charging ?
(b) what's
it once the battery is sufficiently discharged and once it's time for charging?
(c) What
ought to be relative density once it's totally charged?
(d) what's
going to be the voltage per cell once discharged?
(e) what's
going to be the voltage once totally charged?
Ans.
components of lead acid battery
1.
Container: The instrumentality is
formed of India rubber
or
hydrocarbon compound that accommodates plates, separators, solution, etc., in
it. There ar ribs at the lowest of the cell that create sediment chamber or mud
house. The plates rest on these ribs or bridges. The active materials from the
plates falls down and collects in it. A partition wall is provided between the
2 cells therefore their electrolytes don't get mixed.
2. Plate
: +ve and -ve plates. These ar of 2
sorts(a) Plante type, (b) Faure sort. Plante sort plates ar shaped from pure
lead by perennial charge and discharge. just in case of Faure sort, plates ar
created by paste method. Active material is passed in lead created grids within
the variety of pastes of minium lead, on the +ve plates and paste of PbO on-ve
plates. These plates ar immersed in dilute H,SO Electrolysis takes place once
current passes. minium lead.04 is alter to steer peroxide PbO, forming the
positive plate and negative
litharge PbO
is cut back to spongy lead.
3.
Separators: These ar made of
specially treated wood, perforated rubber or celluloid and ar accustomed
insulate the active plates from each other. Separators ought to be specified
acid electre ought to be ready to labor under these setup
4. Cell
Cover: These ar obtained by
moulding rubber and ar accustomed cowl the cell, there vent-plugs within the
cell protect simple escape foro shaped within the cell throughout charge.
5. Plate
Connectors: {they ar|they're} made
from pure lead Positive and negative plates are welded severally with it
forming positive cluster and negative cluster post terminals. As upward
extension from every connecting bar forms the terminal pole.
6. Cell
Connectors : Cells ar connected serial
to make battery. Plates within the cells ar therefore organized that the
negative terminal of 1 cell is closed to positive terminal of succeeding cell
ans therefore on. The adjustment terminal posts ar then welded.
7.
protection Compound : it's made of hydrocarbon compound Associate in Nursingd
is employed to make an acid tight joint between the duvet and containers, so
acid might not initiate whereas cell is in use.
8.
Electrolyte: For lead acid cell the solution used in dilute resolution of
vitriol. These typically consists of 3 components of water to at least one a
part of vitriol and so includes a relative density of 1250 some.
Data:
(a) the
particular gravity of initial charge of the cell is 1250.
(b) Dead
battery
The specific
gravity once totally charged is from one 260 to 1280 The voltage of cell once
discharged is 1.9 potential unit on load.
(c) The
voltage once totally charged is a pair of.1 potential unit on load.
Describe the inner construction of a lead acid battery (or it is
Secondary cell) and justify chemical change that takes place in it
(a) on charge (b) discharge?
Ans. an
entire galvanic battery may be a combination of od cell consists of negative
and positive plates. The plates are soldered to at least one terminal called
tive terminal and every one the positive plates and soldered to positive
terminal. they're therefore assembled that every of the citive plates is
interlinked between 2 negative plates. because the negative and positive plates
ar unbroken about to one another, there's invariably Associate in Nursing
increasing tendency for brief circuit that is avoided by keeping wood, ebonite,
glass or rubber separators in between every positive and negative plate.
Internal
short may additionally occur because of accumulation of active material at the
lowest of the cell. To avoid this, a substantial house is allowed. This whole
assembly of a cell is sometimes place during a instrumentality made from India
rubber composition.
Chemical
Action throughout Discharge of a Storage Cell:
Consider a electric cell that is totally charged; at that instant the anode is lead peroxide (PO2) and also the cathode is lead. The lead ions of the negative plate have a bigger tendency to travel into the solution and there's a powerful tendency for the H ions to gather on the positive plate. for each charged Pb++ particle getting in the answer 2 electrons ar left behind on the plate.
Thus, once
the cell is discharged each the plates ar modified to PbSO, and also the
solution is diluted. The actions throughout discharge also are portrayed by
Fig. 8.17. Thus, throughout discharge
(i) each
anode and cathode become lead salt
(ii) because of formation of water, relative density of the acid decreases.
(iii)
Voltage of the cell decreases.
(iv) The cell offers out energy.
Chemical Action throughout Charge of a Storage Cell: it's been seen that in discharge each the plates area unit modified to steer sulfate. On charging the cell the positive offer terminal is
connected to the anode of the cells, so the present within the solution is passing from anode to cathode within the solution. The sulfate particle can so move to the anode whereas the atomic number 1 ions can drift to the cathode. The atomic number 1 ions at the cathode can on incoming react with lead sulfate within the ionic type and therefore the sulfate ions can react with the lead sulfate ions that enter into the answer per the reactions given as : At the Anode
Hence, throughout charging:
(i) The
anode become semi-sweet chocolate brown in color (PbO,)
and cathode
becomes gray silver lead.
(ii) because
of consumption of water, relative density of sulfuric acid (H,SO) is inflated
(iii)
Voltage of the accumulator rises.
(iv) Energy
is absorbed within the cell.
Give reasons why negative plates inflated by one than the +ve plates.
Ans. it's as
a result of whereas discharging +ve plates area unit active plates thus to
require the good thing about each the perimeters of +ve plate we tend to use
one extra-ve plate than +ve plates.
What area unit the indications of a totally charged battery or
Associate in Nursing
accumulator?
Ans.
Indications of a Fully-charged Accumulator: the very fact that the battery is
totally charged is indicated by many phenomena-visual, physical and electrical.
The visible
indications of a totally charged cell are:
(a) {the
color|the color} of the electrodes : The anode or the positive plate having a
chocolate brown color (the colour of lead peroxide) and therefore the cathode a
slate gray colouration
(b) The
gassing at the electrodes : a totally charged accumulator offers off gas and
atomic number 1 freely as gas bubbles, as these gases now not takes half in
chemical reactions. The battery being charged to capability and no a lot of
electricity will be absorbed within the style of energy and thence chemical
reactions stop.
(C) The
outstanding physical indication is that the state of
the solution
whose relative density depends upon the condition of charge that the battery is
bearing. we've seen that in charging, this relative density rises, from 1250 to
1280; therefore the attainment of 1280 indicates a totally charged condition.
(d) The
electrical indication of the state of charge is that the voltage of the
battery, that rises bit by bit throughout charging from concerning one.8 V to
2.1 V on load, finally remaining constant at a pair of.1 V. once this state is
reached, the accumulator is totally charged.
What precautions ought to be discovered in victimization search
accumulator?
Ans.
Precautions for victimization lead acid cell:
1. The
battery mustn't be left in discharged condition for an extended time.
2. the
extent of the solution should be a pair of cm on top of the highest of the
plates.
3.
Evaporation of solution ought to be salaried by adding water from time to time.
4. Keep the
cell in dry and clean position.
5. The
charge and discharge ought to be at traditional rates.
6. whereas
charging, vent plugs ought to be unbroken loose for passing out of the evolved
gases, if any.
7. The naked
flame, close to the battery, whereas charging, ought to be avoided.
8. whereas
getting ready solution,water mustn't be poured into the acid, however acid
ought to be poured in water visit drop.
In lead acid batteries what do the low and high relative density of solution indicate? provide the higher and lower limits of relative density underneath totally different conditions?
Ans: In lead
acid batteries the low relative density indicates the discharging of the cell.
The high relative density indicates that cell is in charged condition. The
totally charged cell has 1260 to 1280 relative density and totally discharged
cell has 1250 relative density.
Charging of
lead acid battery.
Ans.
Charging rate : the speed at that A battery could also be charged safely
depends upon the speed at that lead sulfate could also be reduced on electrodes
and thence depends upon rating and condition of battery.
Safest rate
of charging for any lead acid battery notwithstanding a size and condition is
that the numbers of ampere needed, that is found by dividing the ampere hour
capability of the battery with charging hours.
Capacity
Capacity
Charging current = ----------------
Hour
Rapid rate
of charge mustn't be used as a result of it'll harm the battery.
Method of
charging From d.c. offer there area unit 2 ways of charging a lead acid
battery.
(i) Constant
current technique
(ii)
Constant voltage technique.
This method
is used where the supply is high voltage d.c. (220 V, 110 V etc.) but the
battery is of low voltage (6 V, 12 V etc.). The e.m.f. of the battery is small
in comparison to the supply voltage so a lamp-load or a variable resistor is
connected in series with the battery. This causes a loss of energy, so, the
method is inefficient.
(ii) Constant Voltage Method: In this method, charging voltage is held constant throughout the charging Charging current in the beginning is high which however reduces as the back e.m.f. of the battery increases. This is the most common method of charging. In this method, the voltage is maintained at a fixed value about 2.3 V per cell, the current decreases as the charging proceeds. A variable resistor is connected in series so, a voltage source of 2.5 to 2.6 V per cell is required. For a 12 V motor car battery, the charging dynamo is of about 15 V. In comparison to constant current method less power is wasted for charging and less time is taken. Figure 8.20 shows the connection for constant potential method of charging batteries.
The
battery is charged till the cells are gassing freely and the specific gravity
of the electrolyte and the terminal voltage of cells remain constant.
The fully charged battery has following
indications:
Specific gravity of electrolyte 1260 to 1280
Voltage of
cell 2.1
Volt
Where specific gravity can be determined by hydrometer and
voltage by cell tester accurately.
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