Construction Of lead Acid Batteries:
1) Anode or positive plates
2) Cathode or negative terminal.
3) Electrolyte
4) Separators
5) Container
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Fig. 1 Construction Of Lead Acid Batteries |
Positive plates :
The positive plates are also called as anode. The material used for this is lead peroxide (PbO2). It is a material of dark brown colour
Negative plates :
Negative plates :
The negative plates are also called as a cathode. The material used for the cathode is lead (Pb) and its colour is gray.
Due to this current, the sulphuric acid H2SO4 is disassociated into positive H2 and negative SO4. The external load current flows from anode to cathode, but the internal current flows from cathode to anode through the electrolyte
Therefore the positive H2 ions move to the anode and the negative So4 ions move to the cathode.
The chemical action during discharge is as follows:
Chemical action :
Both the above expressions show that both the anode and cathode become Pbso4 And water (H2O) is also produced. Due to the formation of POSO4 both the clectrodes become whitish and due to the water formation, the specific gravity of the electrolyte reduces.
Hence the output voltage decreases.
Charging action of the battery:
As we have already explained, when the cell is completely discharged, the anode and cathode both transform into Poso4 (which is whitish in colour).
During the charging process, a positive external voltage is applied to the anode of the battery and
negative voltage is applied at the cathode as shown in Fig. 3.
Due to the externally connected source, the current flow from anode to cathode inside the electrolyte. This current results in the following chemical action
Chemical reaction at the time of charging
These two expressions indicate (see RHS) that "PbO2"is being formed at the anode and "Pb at the cathode. Along with that the sulphuric acid (H2SO4) is being created newly.
As the water is consumed and H2SO4 is created, the specific gravity of H2SO4 increases, energy is absorbed and the voltage on the cell increases and the charging is said to have taken place.
The single reversible equation representing the charging and discharging process is given by.
The positive and negative plates are arranged in groups. Positive plates are placed between negative plates. These positive plates are connected together by a connector strap and positive terminal is brought out.
Electrolyte used :
Electrolyte used :
The electrolyte used is dilute sulphuric acid (H2SO4) with 3 parts of distilled water mixed with one part of H2SO4. The specific gravity is 1.2. The anode and cathode both are immersed in the electrolyte.
Separators :
Separators :
These are thin plates of porous insulated material like rubber. These are placed between main plates to avoid short circuit amongst themselves. The main plates are placed close to reduce the internal resistance
Container: The container is made up of plastic or ceramic. All plates and electrolyte is placed in it. No chemical action should take place on the container.
Charging and Discharging of a Lead - Acid Battery :
Discharging:
The cell is fully charged. When it starts discharging, the current starts flowing from the battery to the external load as shown in Fig. 2
Container: The container is made up of plastic or ceramic. All plates and electrolyte is placed in it. No chemical action should take place on the container.
Charging and Discharging of a Lead - Acid Battery :
Discharging:
The cell is fully charged. When it starts discharging, the current starts flowing from the battery to the external load as shown in Fig. 2
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| Fig. 2 Discharging Of Lead Acid Battery |
Due to this current, the sulphuric acid H2SO4 is disassociated into positive H2 and negative SO4. The external load current flows from anode to cathode, but the internal current flows from cathode to anode through the electrolyte
Therefore the positive H2 ions move to the anode and the negative So4 ions move to the cathode.
The chemical action during discharge is as follows:
Chemical action :
Both the above expressions show that both the anode and cathode become Pbso4 And water (H2O) is also produced. Due to the formation of POSO4 both the clectrodes become whitish and due to the water formation, the specific gravity of the electrolyte reduces.
Hence the output voltage decreases.
Charging action of the battery:
As we have already explained, when the cell is completely discharged, the anode and cathode both transform into Poso4 (which is whitish in colour).
During the charging process, a positive external voltage is applied to the anode of the battery and
negative voltage is applied at the cathode as shown in Fig. 3.
Due to the externally connected source, the current flow from anode to cathode inside the electrolyte. This current results in the following chemical action
Chemical reaction at the time of charging
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| Charging of Battery |
These two expressions indicate (see RHS) that "PbO2"is being formed at the anode and "Pb at the cathode. Along with that the sulphuric acid (H2SO4) is being created newly.
As the water is consumed and H2SO4 is created, the specific gravity of H2SO4 increases, energy is absorbed and the voltage on the cell increases and the charging is said to have taken place.
The single reversible equation representing the charging and discharging process is given by.
