Page 82 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Series-parallel connection: Sometimes the requirements of a piece of equipment exceed both voltage and
ampere hour rating of a single cell. In this case a series-parallel grouping of cells must be used (Fig 5).
The number of cells that must be connected in series to have voltage rating is calculated first and then the number
f parallel rows of series connected cells is calculated for required ampere-hour rating.

Battery charging method - Battery charger

Objectives: At the end of this lesson you shall be able to:
• state the necessity of charging a battery
• describe the preparation of electolyte
• describe the use of a hydrometer and high rate discharge tester
• state the precautions to be followed while charging and discharging a battery
• describe the different types of charging methods of secondary cells
• explain the purpose, construction and working principle of battery charger.

Necessity of charging: During discharge, due to chemical reaction, the active electrodes become smaller and
the internal resistance becomes high causing a low output. To reverse the action, send a current (DC) through
the battery or cell in the opposite direction to that of the discharge. This process is called charging. The charging
can be done through a battery charger.
Battery chargers: When the chemical reaction in a rechargeable battery has ended, the battery is said to be
discharged and can no longer produce the rated flow of electric current. This battery can be recharged, however,
by passing direct current from an outside source to flow through it in a direction opposite to that in which it flowed
out of the battery.
When charging a battery, the negative lead of the charger must connect to the negative lead of the battery and
the positive lead of the charger to the positive lead of the battery
A simple variable-voltage DC power supply works well as a battery charger.

Charging current: When charging any battery, it is important to set the charging current to a value recommended
by the manufacturer. This current is set by adjustment of the output voltage on the charger and read by an
ammeter connected in series with the charger and battery (Fig 1). When the battery and charger are at the same
voltage, no current flows. The charger voltage is set to a value higher than that of the battery to produce a current
flow.
Before charging the battery or cell the following points are to be observed to ascertain the condition of the battery.
1 Specific gravity of the electrolyte
2 Voltage of each cell of the battery
3 Ampere hour capacity of each cell.

Electrolyte
The electrolyte used in a cell is dilute sulphuric acid having a specific gravity between 1.21 and 1.3.
Specific gravity
The ratio of the mass of a given volume of liquid to the mass of the same volume of the water at 4°C, is known
as specific gravity of the liquid.

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