Page 72 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Cell connectors
These are the thick drilled bar made of pure lead. The cells are connected and welded in series to form a battery.

Cell cover
It is made of hard rubber or PVC.

Vent plugs or filler caps
They are made of polystyrene or rubber and are usually screwed in the cover. It prevents the escape of electrolyte
and allows free exit of gas. It can be easily removed for topping up or taking hydrometer reading.
Seperators
These are made of thin sheets of chemically treated porous wood or micro porous rubber or glass wool mat or
perforated PVC. They are used to avoid short in between the positive and negative plates.
Electrolyte
The electrolyte used in a lead acid cell is dilute sulphuric acid (H SO ). The specific gravity of the electrolyte is 1.24
4
2
to 1.28. Specific gravity of electrolyte is measured by using hydrometer. It varies according to the manufacturer’s
specification.
Chemical action

If two cells are connected dipped in dilute sulphuric acid and connected to a DC supply main, current flowing
through the electrolyte splits up into hydrogen and sulphate ions. The hydrogen ions travel towards the negative
plate and it has positive charge.
Chemical action during discharging of storage cell
Consider a cell has fully charged at the instant anode is lead per oxide (pbo2) and the cathode is lead (pb).The
lead ions of the negative plate go into the electrolyte and there is hydrogen ions to collect on the positive plate.
For every positively charged pb ions entering into the solution two electrons are lift behind on the plate. For
++
every positively charged hydrogen atoms deposition on the positive plate on negatively charged sulphate ions is
left in the solution.
When plates are connected through a resistance R the electrons flow from negative plate to anode and that in
case more lead ions go into the electrolyte and more hydrogen ions are attracted by the anode. At the negative
plate sulphuric acid molecules attract the lead ions and lead sulphate is formed.
Negative Plate Pb + H So = pbSo 4
4
2

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CITS : Power - Electrician & Wireman - Lesson 13-19 CITS : Power - Electrician & Wireman - Lesson 13-19