A Lead Acid Battery cell is formed by inserting two parallel lead plates ( electrodes), one
coated with lead dioxide (PbO2), in a container with Sulfuric acid (H2So4).
The cell has 2 Volts nominal voltage. Installing six such, series connected, cells in a container
forms the popular 12V Lead Acid Battery.
Chemistry Lead Acid Battery :
Connecting resistive load between the lead electrodes, causes current to flow from the positive
(Pbo2) electrode to the negative (Pb) electrode, thus discharging the battery.
Battery charging is accomplished by connecting the electrodes to a voltage source (charger)
with the proper polarity.
The following chemical reactions take place during the charge - discharge cycle:
During the discharge process, the reactions cause both electrodes to be coated with Lead
Sulfate (PbSO4) crystals. Charging restores the situation.
Discharge
Electrochemical formula: PbO2 + Pb + 2H2SO4 PbSO4 + 2H2O + 2e¯
More insight is deduced by considering each electrode separately:
Discharge
At the negative electrode: Pb + SO4 PbSO4 + 2e¯
Discharge
At positive electrode: PbO2 + SO4 + 4H + 2e¯ PbSO4 + 2H2O
Charge
The electrolyte is a mixture of Sulfuric Acid and water. Specific gravity of Electrolyte
measures the content of Sulfuric Acid in the solution. It is typically in the range of 1.200 to
1.300. Whereas water has Specific Gravity of 1, and pure Sulfuric Acid has Specific Gravity
of 1.835. State of charge and other major battery characteristics are strongly related to the
specific gravity of sulfuric acid.
At charging, electrolysis of water produced oxygen and hydrogen as byproducts . In such
process, the external voltage source induces electrical current in the cell according to Ohms
law. The electrolyte due to its low resistance increases dramatically the current in the cell.
This current dissociates water molecules into (OH) ¯ and H ions.
The reaction at the Positive Electrode: 2H2O O2 + 4H + 4e¯
The reaction at the Negative Electrode: 2H2O + 2e¯ H2 + 2(OH) ¯
Thus, during charging, water is decomposed into its constituents. The oxygen gas, generated
at the positive plate and the hydrogen gas, generated at the negative plate.
Lead Acid Battery Technology:
Flooded batteries and Sealed Lead Acid batteries form the two basic lead acid battery types,
they differ mainly by the way water is restored to the battery.
In Flooded batteries the oxygen and hydrogen gases generated at the plates, are vented to the
air through the top of the battery. Water should therefore be added during maintenance in
order to replace the missing quantity, and sustain the charge storage ability.
In Sealed Lead Acid (SLA) Batteries, generally Valve Regulated Lead Acid (VRLA) Batteries,
pressure relief valves do not allow gases to leave the battery. The oxygen generated at the
positive plate diffuses to the negative plate, where it is recombined with hydrogen to form
water. Thus, water refilling is not required and no maintenance is required.
The valves will however allow gas relief, when internal pressure exceeds allowed value, as
may be the case at battery overcharging.
Lead Acid Battery Applications
Flooded batteries, also called wet batteries, are used for energy storage purpose mainly for
stationery, long duration (several hours) long life systems, for Utilities, Telecom and Industrial
applications.
Sealed lead acid batteries (SLA), often called Maintenance Free Batteries, are favored for
standby application and UPS applications. Their unique features in normal operation, such as
maintenance free, hermetically sealed, non spillable, non gassing and vibration resistance
characteristics, makes them an ideal choice to serve as standard UPS Batteries, as well as in
numerous other applications in additional fields, such as communication, security,
transportation, emergency lightning, aviation and more.
coated with lead dioxide (PbO2), in a container with Sulfuric acid (H2So4).
The cell has 2 Volts nominal voltage. Installing six such, series connected, cells in a container
forms the popular 12V Lead Acid Battery.
Chemistry Lead Acid Battery :
Connecting resistive load between the lead electrodes, causes current to flow from the positive
(Pbo2) electrode to the negative (Pb) electrode, thus discharging the battery.
Battery charging is accomplished by connecting the electrodes to a voltage source (charger)
with the proper polarity.
The following chemical reactions take place during the charge - discharge cycle:
During the discharge process, the reactions cause both electrodes to be coated with Lead
Sulfate (PbSO4) crystals. Charging restores the situation.
Discharge
Electrochemical formula: PbO2 + Pb + 2H2SO4 PbSO4 + 2H2O + 2e¯
More insight is deduced by considering each electrode separately:
Discharge
At the negative electrode: Pb + SO4 PbSO4 + 2e¯
Discharge
At positive electrode: PbO2 + SO4 + 4H + 2e¯ PbSO4 + 2H2O
Charge
The electrolyte is a mixture of Sulfuric Acid and water. Specific gravity of Electrolyte
measures the content of Sulfuric Acid in the solution. It is typically in the range of 1.200 to
1.300. Whereas water has Specific Gravity of 1, and pure Sulfuric Acid has Specific Gravity
of 1.835. State of charge and other major battery characteristics are strongly related to the
specific gravity of sulfuric acid.
At charging, electrolysis of water produced oxygen and hydrogen as byproducts . In such
process, the external voltage source induces electrical current in the cell according to Ohms
law. The electrolyte due to its low resistance increases dramatically the current in the cell.
This current dissociates water molecules into (OH) ¯ and H ions.
The reaction at the Positive Electrode: 2H2O O2 + 4H + 4e¯
The reaction at the Negative Electrode: 2H2O + 2e¯ H2 + 2(OH) ¯
Thus, during charging, water is decomposed into its constituents. The oxygen gas, generated
at the positive plate and the hydrogen gas, generated at the negative plate.
Lead Acid Battery Technology:
Flooded batteries and Sealed Lead Acid batteries form the two basic lead acid battery types,
they differ mainly by the way water is restored to the battery.
In Flooded batteries the oxygen and hydrogen gases generated at the plates, are vented to the
air through the top of the battery. Water should therefore be added during maintenance in
order to replace the missing quantity, and sustain the charge storage ability.
In Sealed Lead Acid (SLA) Batteries, generally Valve Regulated Lead Acid (VRLA) Batteries,
pressure relief valves do not allow gases to leave the battery. The oxygen generated at the
positive plate diffuses to the negative plate, where it is recombined with hydrogen to form
water. Thus, water refilling is not required and no maintenance is required.
The valves will however allow gas relief, when internal pressure exceeds allowed value, as
may be the case at battery overcharging.
Lead Acid Battery Applications
Flooded batteries, also called wet batteries, are used for energy storage purpose mainly for
stationery, long duration (several hours) long life systems, for Utilities, Telecom and Industrial
applications.
Sealed lead acid batteries (SLA), often called Maintenance Free Batteries, are favored for
standby application and UPS applications. Their unique features in normal operation, such as
maintenance free, hermetically sealed, non spillable, non gassing and vibration resistance
characteristics, makes them an ideal choice to serve as standard UPS Batteries, as well as in
numerous other applications in additional fields, such as communication, security,
transportation, emergency lightning, aviation and more.
| Lead Acid Battery |
| Rechargeable Lead Acid Battery Basics |
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| Batteries UPS Batteries Lead Acid Batteries |
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