Fully charged battery
Behold the chemical panorama of a fully charged battery. Its elemental composition unfolds as follows: a positive plate adorned with lead dioxide (PbO2), a negative plate fashioned from lead (Pb), and an aqueous solution blending the acidic prowess of sulfuric acid (H2SO4) with the fluidity of water (H2O).
The chemistry of discharge
The positive plate undergoes a gradual metamorphosis from lead dioxide (PbO2) to lead sulphate (PbSO4) during discharge.
Similarly, the negative plate, crafted from lead (Pb), experiences a slow transformation into lead sulphate (PbSO4) during discharge.
As a normal discharge concludes, the resulting sulphation on the positive and negative plates manifests as very fine lead sulphate (PbSO4) crystals.
On a minor scale, sulphation is an inherent element of the discharge process.
A three-stage charge algorithm adeptly eliminates this sulphation.
It's crucial to emphasize that persistent and detrimental sulphation is abnormal. It arises when lead sulphate assumes a non-retroactive form and remains unremoved from the plates during recharging, a phenomenon observed when the battery languishes in a discharged state for prolonged durations.
Battery chemistry during discharge
As discharge unfolds, the sulphuric acid undergoes disassociation into SO4 and H+ ions. Engaging in a transformative dance, the SO4 molecule unites with both the positive and negative plates, culminating in the creation of lead sulphate (PbSO4). Meanwhile, electrons liberated from the hydrogen molecule within the sulphuric acid contribute the essential charge, propelling the flow of electrical current.
Positive plate chemical reaction during discharge
As discharge progresses, the positive plate undergoes a gradual metamorphosis into PbSO4, facilitated by the breakdown of acid and its amalgamation with the positive plate.
Liberating electrons for current supply, the hydrogen molecule combines with the resulting Pb molecule and the free SO4 molecule, ultimately producing lead sulphate (PbSO4).
The free O2 molecule joins forces with the liberated hydrogen ions (H+), giving rise to the formation of water.
Amidst this intricate process, two free electrons emerge, originating from the hydrogen atoms.
The ongoing transformation sees the solution transitioning into water, a consequence of the dissociation of sulphuric acid.
Negative plate chemical reaction during discharge
As discharge unfolds, the Pb molecule unites with the SO4 molecule, giving rise to the formation of PbSO4, accompanied by the emergence of two positive hydrogen ions (H+) and two liberated electrons.
Simultaneously, the solution undergoes a transformative phase, transitioning into water as sulphuric acid undergoes dissociation.
Normal charging – no lead sulphate on plates
Within each 12V battery, the precise balance among the six individual 2-volt cells is not assured. Consequently, certain cells may register a slight undervoltage (2.3 volts), gradually accumulating sulphation over multiple charge/discharge cycles.
Plates mildly sulphated over time can be restored by equalization
In the quest to eradicate the routine, mild sulphation that arises from discharge, a meticulous equalization routine comes into play. This involves the application of a slight overcharge to ensure that the lowest cell voltage reaches a minimum of 2.5 volts. Executed with a low current, typically capped at 0.5 amps, this equalization stage unfolds over an extended period, often spanning up to 15 hours.
When sulphation is not normal
When a battery is left in a discharged state for an extended duration, the sulphation stemming from a typical discharge continues its relentless progression.
In a deviation from the formation of fine particles, this prolonged state gives rise to the development of hard crystals on both the positive and negative plates.
Plate sulphation, particularly in its heavy form, proves resistant to removal through recharging, ultimately evolving into an irreversible state over time.
Sulphated plates, acting as subpar electrical conductors, impede the normal processes of recharging and equalization.
Imposing high charging currents on a sulphated battery can lead to overheating and inflict damage upon the battery.
A specialized desulphating device becomes imperative to effect the restoration of the battery to a normal and functional condition.
When is a desulphation device required?
As mentioned earlier, sulphation naturally occurs as part of the discharge process, culminating in the transformation of both plates into lead sulphate (PbSO4) at the discharge's conclusion.
In the course of a standard recharge, the chemical reversal transpires, reverting the two plates back to lead and lead dioxide.
However, if the battery remains in a discharged state for an extended period, the sulphation progresses from fine crystals to robust and rigid formations.
When these thick crystals begin to take shape on the plates, the equalization process loses its efficacy, as insufficient current can be channeled through the battery to reverse the sulphation.
The removal of excessively grown PbSO4 crystals necessitates the intervention of a desulphation device, given that a conventional equalization process proves ineffectual in such cases
Heavy sulphation requires a desulphation device
When hard crystals of lead sulphate have taken shape on the plates, the prospect of conventional recharging or equalization becomes unattainable. These crystals, acting as extremely inefficient electrical conductors, restrict the battery's ability to transmit only a minimal amount of current. In such cases, the intervention of a desulphation device becomes imperative. This desulphation mechanism hinges on the induction of mechanical resonance within the crystals.
Summary
The sulphation of both positive and negative plates is a customary outcome during the battery discharge process.
In instances where the recharging process falls short of complete reversal, equalization serves as a remedy to desulphate a battery exhibiting mild sulphation.
It's important to note that equalization isn't a mandatory step after every recharge cycle.
To swiftly convert lead sulphate (PbO4) in the plates back to lead (Pb) and lead dioxide (PbO2), timely battery recharging is crucial.
Minimizing the time lapse between discharge and recharge is imperative to forestall excessive and potentially permanent sulphation.
The extent of sulphation is contingent upon the duration the battery lingers in a discharged state.
When sulphation reaches an excessive threshold, hindering the battery's ability to conduct electric current and accept a charge, a desulphation device becomes indispensable.