Page 79 - Electrician - TT (Volume 1)
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ELECTRICIAN - CITS



                                        Comparison : Lead acid cell and Edison cell
                     (The relative strong and weak points of the two cells have been summarized below)

            S.No       Particulars          Lead-acid cel                        Edison Cell
            1     Positive plate       PbO, Lead Peroxide       Nickel hydroxide Ni(OH)  or Nickel Oxide (NiO )
                                                                                     4
                                                                                                        2
            2     Negative plate       Sponge Lead              Iron

            3     Electrolyte          Diluted H2SO4            KOH

            4     Average emf          2.1 V/Cell               1.2 V/Cell

            5     Internal Resistance  Comparatively low        Comparatively higher resistance
            6     Efficiency : amp-hour  90-95%                 Nearly 80%
                  watt-hour            72-80%                   About 60%

            7     Cost                 Comparatively less than   Almost twice that of Pb-acid cell (Easy
                                       alkaline cell            maintenance)

            8     Life                 Gives nearly 1250        Five years atleast
                                       charges and discharges
            9     Strength             Needs much care and      Robust, mechanically strong, can withstand
                                       maintenance. Sulphation   vibration, light, unlimited rates of charge and
                                       occurs often due to      discharge. Can be left discharged, free from
                                       incomplete charge or     corrosive liquids and fumes.
                                       discharge

           Applications
           Due to their high mechanical strength, lightness and free from acid fumes they have been found to be very
           satisfactory for the following applications
           •  Traction purpose

           •  Mine locomotives
           •  Submarines
           •  Industrial trucks
           •  Aero planes

           Similarity of operation NI-FE &NI-CD
           •  The electrolyte is same for nickel-iron and nickel-cadmium cell .ie potassium hydroxide(KOH)
           •  When the cell is discharged the positive plate is converted in to Ni(OH)2
           The specific gravity of electrolyte is remain unchanged during charge or discharge
           Nickel cadmium cell

           Nickel cadmium cell is similar to nickel iron nickel hydroxide Ni(OH)2 for the positive electrode. Cadmium Cd as
           the negative electrode. Potassium hydroxide (KOH)electrolyte
           NI-CD Cell operation
           •  It consist of cadmium anode and a metal grid containing a paste of   NiOH2  acting as a cathode.

           •  The electrolyte is KOH (potassium hydroxide)
           Working (discharging)
           •  When the Ni-Cad battery operates, at the anode cadmium is oxidized to    Cd2+  ions and insoluble    Cd(OH)2
              is formed.
           •  It produces about 1.4V


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