Basics of Cell Electro-Chemistry
Electrochemistry
DischargeFully discharged: two identical lead sulfate plates
In the discharged state both the positive and negative plates become lead(II) sulfate (PbSO
4), and the electrolyte loses much of its dissolved sulfuric acid and becomes primarily water. The discharge process is driven by the conduction of electrons from the negative plate back into the cell at the positive plate in the external circuit.Negative plate reaction:
Pb(s) + HSO−4(aq) → PbSO4(s) + H+(aq) + 2e−
Positive plate reaction:
PbO2(s) + HSO−4(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l)
The total reaction can be written as
Pb(s) + PbO2(s) + 2H 2SO 4(aq) → 2PbSO 4(s) + 2H 2O(l)
ChargingOvercharging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water, which is lost to the cell. Periodic maintenance of lead-acid batteries requires inspection of the electrolyte level and replacement of any water that has been lost.
Due to the freezing-point depression of the electrolyte, as the battery discharges and the concentration of sulfuric acid decreases, the electrolyte is more likely to freeze during winter weather when discharged.
Ion motionDuring discharge, H+
produced at the negative plates moves into the electrolyte solution and then is consumed into the positive plates, while HSO−
4 is consumed at both plates. The reverse occurs during charge. This motion can be by electrically driven proton flow or Grotthuss mechanism, or by diffusion through the medium, or by flow of a liquid electrolyte medium. Since the density is greater when the sulfuric acid concentration is higher, the liquid will tend to circulate by convection. Therefore a liquid-medium cell tends to rapidly discharge and rapidly charge more efficiently than an otherwise similar gel cell.
Measuring the charge lev
http://batteryworld.co.ke/battery-acid-water/
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Deep Discharge
From sciencedirect.com Irreversible Changes of Active Material Caused by Deep Discharge Deep discharge of batteries often leads to mechanical stresses in the plates, which leads to shedding, poor conductivity, and a diminished lifetime of the system.…More » -
Electrolyte Temperature
Electrolyte : Here is a copy of info from: http://www.trojanbattery.com/tech-support/faq/ 9. Can a flooded battery freeze? The only way that a battery can freeze is if it is left in a state of partial or complete discharge. As the state of charge in a…More » -
Hydrometers
Update: May 28th 2020 Received the Durite 472. It's larger than I thought but usuable. The liquid in the thermometer is red as is the surround so it's difficult to read the temp.Spoke to a guy at tech 01255 555200 for over half an hour ~ details should…More » -
Specific Gravity
A lead acid battery will have a ration of sulfuric acid and water as the electrolyte. The process of charging forces any sulfate from the battery plates back to the electrolyte which increases it's specific gravity. The specific gravity of pure water is…More »
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