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Lead-acid battery: Microscopic model of discharging

21 Aug 2015  | Szabo Levente

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In the first step the first primary element releases electrons to the electrode and as the result of the reaction a secondary element appears. In the next step the secondary element changes places with its primary element neighbour. The new primary element near the electrode area releases new electrons and after the reaction it transforms to a secondary element. Pending this time the secondary element produced in the first step changes places with its primary element neighbour. If the time of a reaction and the time of changing places of two elements are equal, then the result can be represented graphically as a line shown in figure 2.

Figure 2: The time of a reaction and the time of changing places.

The line has a rectangular form. The high level represents the release of the electrons, and the low level represents the pause, in other words the change of places of the elements.

The model of the electrical circuit
In the previous chapters we have concentrated on the microscopic phenomenon of the units in the reaction area and we have avoided detailing the command module and the relays which we consider ideal. We present the electrical schema of the circuits in figure 3.

Figure 3: The battery model.

The capacitors are fully charged with the unit of quantity of electricity (depends on the number of electrons released in one reaction). The C1-C10 capacitors are coupled to the external circuit only for the short time, when they release electrons. Every capacitor separately is commanded by the command module. In the first step C1 is connected and the first electrons are released to the external circuit. The time of this period is equal to the reaction time, when the first primary elements are transformed into the first secondary elements. The next step is the pause, when the first secondary elements change places with the next primary elements. In the next step C2 is connected and these steps continue until the last primary elements release electrons and transform into the last secondary elements. The graph, which represents this process, is shown in figure 4.

Figure 4: Timing of connecting the capacitors in the external circuits.

We consider that the time of connecting the capacitors is equal with the time of changing places of two neighbour elements.

This ideal microscopic model using an electric circuit helps us understand easier the phenomenon that happens on the unit area of the electrode in the reaction zone. In the case of a real model we must consider that the time of the reactions and the replacement of the primary elements with the secondary elements may be different, other elements situated outside of this zone in the electrolyte may have influence on the process, the time of the reaction in the case of different elements may be different, the spatial distribution of the elements may not perpendicular, the electrical field may not be homogenous and other internal and external conditions may have influence on the process.

About the author
Szabo Levente is pursuing studies and research in Lead-acid battery chargers and phenomenon and is pursuing his Ph.D which has a larger theme in Management of Electrical Energy with resonance phenomenon.

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