When two dissimilar conducting materials (electrodes) are immersed in a solution capable of conducting electricity (an electrolyte) one will become positively charged and the other negatively. The ends of the electrodes protruding above the electrolyte are known as the positive and negative terminals and the whole unit is called a cell. Connecting the terminals with a wire will cause an electrical current to flow through the wire from the positive to the negative terminal. The potential difference or electrical pressure between the terminals is dependent upon the materials of the electrodes and the electrolyte and is measured in volts.
In a torch battery the electrodes comprise the positive carbon rod in the centre of the cell and the negative zinc container with a jelly electrolyte of ammonium chloride. The potential of the cell is approximately 1.5 volts. During use the zinc is slowly dissolved in the production of the current, and when it or the ammonium chloride is exhausted, the flow of current ceases and the cell must be discarded. Such cells are termed primary or non-rechargeable.
The lead acid cell belongs to the group termed secondary or re-chargeable. Here the electrodes are a lead dioxide positive, a sponge lead negative and a dilute sulphuric acid electrolyte. During discharge current flows and positive and negative electrodes convert to lead sulphate and absorb sulphate ions from the solution reducing the electrolyte to water. Unlike the torch cell, the lead-acid cell is reversible and may be restored to its original condition by passing electricity through the cell in the opposite direction from which it was removed. This reverses the reactions in the cell, converting the lead sulphate in the plates back into their original active materials and returning the sulphate ions to the electrolyte. Lead acid cells have a potential of approximately 2 volts irrespective of size. Larger cells will have a higher capacity and deliver the same current for longer or higher current for the same period than smaller cells. Cells may be connected in series (i.e. the negative of one cell to the positive of the next) to give higher voltages. Thus three cells connected in series will give a "battery' of cells having
Having problems with the site?
Please fill in the simple form below and click send, we really appreciate it!