Page 78 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

• It is observed that no water is formed in the reaction. So that the specific gravity remain unchanged during
charging and discharging.
• So that the cell is not damaged if kept long time in a fully discharged state
Characteristics

• Emf fully charged state ----- 1.4 V
• Reaches to 1.2 V on discharge

• Emf fully discharged state ----- 1.15 V
• Mechanical strength is good since they are made of steel.
• The cell can withstand heavy charge and discharge currents.

• Internal resistance is large and efficiency is lower than lead acid battery.
• With increase in temperature of the cell the capacity increases.
Comparison between charge & discharge states

During discharge
• The negative plate turns in to ferrous hydroxide

• The positive plate turns in to lower hydroxide of nickel
• The specific gravity of electrolyte remains constant
• The per cell voltage falls from 1.4 V to 1.15

During charging
• The negative plate turns in to iron
• The positive plate turns in to l nickel hydroxide

• The specific gravity of electrolyte remains constant
• The per cell voltage increases from 1.15 to 1.4 V

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