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A battery is a group of cells which produce electrical energy from their internal chemical relation. The battery is a source of steady DC voltage. Where heavy current are necessary the lead-acid cell is used.
The lead-acid cell contains container, plates, cell connecter sealing compound & electrolyte.
1) Container -
The container is made of hard rubber bituminous compounds which accommodate plates, separation, electrolyte etc. In it there are ribs at the bottom of the of the cell chamber or mud house the plates rest on these ribs or bridges.
2) Plates -
Positive and negative these are two types. a) Plate type. b) Frame type Plate type - Plates are formed from pure lead by repeated charge & discharge in case of fare type plates are made by paste process active material is passed in lead made grids in the form of paste of red lead ( Pb3O4) on the positive plates & immured in dilute (H2SO4) electrolysis takes place when current posses red lead (Pb3O4) is oxidized to lead peroxide (Pb3O2) forming the positive plate & negative with age (PbO) is reduce to spongy lead.
3) Separators -
These are made from especially treated wood performed rubber or cell void & used to insulate the active plates from one another separator should be able to pass through these separators.
4) Vent Plug
These are obtained by moldings hard rubber & are used to for easy escape for gas formed in the cell during charge.
5) Cell connectors -
Cells are connected in series to farm battery plates in the cells are so arranged that negative terminal of one cell is to positive terminal of next cell & so on the adjustment terminal posts are then welded.
6) Plate Connectors -
They are made from pure lead positive & negative plates are welded separated with it forming positive group & negative group post terminals.
7) Sealing Compound -
It is made from bitumen compound & is used to form and avoid tight joint between the cover & containers so that may not come out while cell is seal.
8) Electrolyte -
For lead acid cell the electrolyte used is dilute solution of sulphuric acid these usually consists of three parts of sulphuric acid & thus has a specific gravity of 1.250 approximately.
Fig. 3Construction of lead acid cell.
Chemical action -
The newly battery is not charged so it is necessary to charge before using. A secondary cell is charged by passing direct current through it from positive terminal to negative terminal.
On charge, the reversed direction of the ions flowing in the electrolyte results in a reversal of the chemical reactions. Now the lead sulfate on the positive plate reacts with the water & sulfate ions to produce lead peroxide & sulfuric acid. This action reforms the positive electrode & strengthens the electrolyte by adding sulfuric acid. At the same time, charging enables the lead sulfate on the negative plate to react with hydrogen ions, which also sulfuric acid while reforming lead on the negative electrode.
As a result, the charging current can restore the cell to full output with lead peroxide on the positive plates spongy lead on the negative plates & the required concentration of sulfuric acid in the electrolyte. The chemical formula for the lead acid cell is -
= Pb + PbO2 + 2H2SO4 Charge 2PbSO4 +2H2O
On discharge the lead (Pb) & lead peroxide (PbO2 ) electrodes supply Pb ions that combine with the sulfate ions (SO4) to form lead sulfate ( PbSO4) & water ( H2O). On charge, with reverse current through the electrolyte, the chemical action is reversed. Then the Pb ions from the lead sulfate reform the lead peroxide electrode. Also the SO4 ions combine with the H2 ions to produce more sulfuric acid.
Indications of charged & discharged conditions -
A] Full charged condition -
1. The colors of the positive & negative plates become dark brown & grey respectively.
2. The electrolyte becomes saturate & its specific gravity lies between 1.26 & 1.28.
3. The e.m.f. of the cell becomes 2.1 volt.
4. Plates of the cell evolve gases in the form of bubbles.
B] Discharged Condition-
1. The colors of the positive & negative plates become white comparatively due to formation of lead sulphate.
2. The electrolyte becomes dilute & its specific gravity lies between 1.150 & 1.180.
3. The e.m.f. of the cell becomes 1.8 volts. 1] IN TEXT QUESTIONS- a) Fill in the blanks -
1. A cell is an _______ device.
2. _______ , _______ & _______ are two main defects in primary cell.
3. A group of cells is called as ______.
4. ________ cells once discharged cannot be recharged again.
5. A battery is a _______. b) True or False-
1. Primary cell is also known as voltaic cell.
2. Dry cells can be charged.
3. Battery is a source of steady D.C. voltage.
4. Vent Plug used to cover for easy escape for gas.
The battery should be charged as soon as possible after each discharge is completed & the charge should be continued until all the plates are gassing well & the specific gravity & voltage readings remain constant. Necessity of charging - After using battery it discharge. After discharging cannot deliver power that’s why it is necessary to charge the battery for delivering power again. For this purpose 230 A. C. Volt supply is not suitable. You know that for battery charging low voltage D.C. Supply is required. An instrument which converts A. C. Voltage into required low D.C. Voltage is called 1 Known as battery charger.
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