Cover - Train Lighting - Indian Railways Institute of Electrical ...

The nominal voltage of a lead acid cell is 2.0 volts. The true open circuit voltage,
however, is dependent on the specific gravity of the electrolyte and varies between 2.02 to
2.05 volts. During discharge the voltage depends on the rate of the discharge current.
4.3 Constructional Features Main components of lead acid cell are :-
a) Positive Plates - Usually tubular construction is adopted. Positive plates are
made up of a number of tubes which contain active materials. Tubes have a
large number of minute pores which allow the electrolyte to pass through
pores freely, while preventing any loss of active material.
b) Negative Plates - Usually consist of a lead grid into which active material is
pressed. The grids are designed to retain the active material in position.
c) Separators - Synthetic separators are used between positive and negative
plates. The separators allow good diffusion of electrolyte.
d) Container - is made of hard rubber with high insulating strength to resist acids.
e) Cell cover - is also made of hard rubber, resistant to acid having vent and level
indicator holes.
An exploded view of a cell is Figure 1.
4.4 Accessories: The following are few accessories of a lead acid cell -
a) Float,
b) Float guide,
c) Vent plug.
a) Float ;
The float stem will have markings to indicate the lowest and highest
electrolyte levels permissible. It should be ensured that the electrolyte level is
maintained in service by adding pure distilled / de-mineralised water to IS:
1069.
b) Float guide :
The float guide is of removable and antisplash type and facilitates unrestricted
vertical movement of float stem. During maintenance it is essential to ensure
that the float assembly is designed to prevent acid splash in service (IS:6848).
Any defective float guides/assemblies should be replaced promptly.
c) Vent plug :
This is of the anti-splash type with more than one exit hole. This will allow
the gases to escape freely but effectively prevent acid particles or spray from
coming out. It should be ensured that the vent plug is tightened fully whenever
the plug is opened during maintenance for checking specific gravity of cell or
after topping up electrolyte level with distilled water.
GENERAL SERVICES : TRAIN LIGHTING 45