CONSTRUCTIONAL FEATURES OF LEAD-ACID STORAGE BATTERIES AND CELLS
An electrochemical source of current (voltaic cell) that possesses the capacity of accumulating and storing energy and supplying it as electric energy is termed an accumulator or storage cell. Lead-acid storage cells may be of various design, but they all consist of electrodes in the form of plates immersed in an acid electrolyte consisting of sulfuric acid diluted with water. The plates are marked with the signs plus and minus. The electrolyte and plates are placed in an acid-proof jar and to keep plates of different polarity from coming in contact with each other separators are inserted between them.
The plates of lead-acid cells are of diverse design, however, they all consist of some form of grid made of lead and the active material. This grid serves as a support for the active material, and is also necessary for conducting the electric current, and as a means for distributing the current evenly over the active material. If the current is not distributed uniformly, an uneven change will take place in the volume of the active material during the charge and discharge, the result being that the active material will loosen and fall out and the plates warp.
Light type grids are used in starting storage batteries, designed mainly for short discharges. In stationary and traction type batteries which are designed for long-term service, and in which the discharges are followed by idle intervals or are of long duration, heavier grids are used.
a) Starting battery plate
b) Deep Cycle battery plate
The grids are cast of an alloy of lead with antimony. They are usually made with transverse ribs that cross the plate at a right angle or diagonally. Grids for the positive and negative plates are often of the same design, but the grids serving for the negative plates are made lighter, in as much they are not as essential to uniform conduction of the current and are less subject to corrosion than the grids of the positive plates.
The active material takes part in the oxidationreduction processes that will cause a flow of electric current to be set up in the cell when the circuit is closed.
After pasting the grids with the active material the plates are dried and subjected to an electrochemical treatment called forming. As a result of such treatment the positive-plate active material acquires a deep chocolate-brown colour and is converted to lead peroxide, PbO2; on the negative plate of gray-colour sponge lead, Pb, is formed.
The plate thus formed resembles a sponge; it has a large surface in contact with the electrolyte and is well saturated by it, this increasing the ampere-hour capacity of the cell.
Depending on the maker’s technology the plates may be fully pre-charged or partially or completely discharged. Cells made of such plates are called dry-charged or dry-discharged respectively.
To obtain cells of the necessary amperehour capacity and convenient size the positive and negative plates are assembled into groups. The negative group usually contains one plate more than the positive group. This is done so that the positive plates will be interleaved between the negative plates and not be able to buckle when the cell is put in operation.
The plates of each group are joined together by a connector strap or bar provided with a pin or lug called the terminal post or post. In an assembled cell the plates should be located as close as possible to each other; this is because it is necessary to decrease the internal resistance of the cell as well as its dimensions.
The ampere-hour capacity of a battery
The ampere-hour capacity of a battery or a cell is the quantity of electricity delivered by it during a discharge which is continued up 'to the moment the final cell discharge voltage of 1.75 V is reached (lead-acid battery cells).
The capacity depends upon the kind and amount of active material employed and also on its coefficient of utilization.
Self-discharge of cells
The self-discharge of cells is due to the deleterious reactions taking place at the positive and negative plates. Self-discharge takes place in lead-acid batteries and cells. The self-discharge of lead cells at plus temperatures (up to +30°C), in the course of one day, reaches one per cent of the nominal ampere-hour capacity. Within the temperature range from 0 to -30°C the self-discharge of lead-acid cells proceeds very slowly. Therefore, cells that are not in use (on automobiles, etc.) should he stored at temperatures not exceeding 0°C. Towards the end of their service life the self-discharge of lead cells increases because of the deleterious action of the antimony which gets into the electrolyte as the positive plate grid corrodes.
Why Buy Deep Cycle Battery
Starting batteries build to deliver high current over short period of time which called cranking amps. This achieved by installing larger amount of THIN plates in to the battery cell, the more plates the larger the surface area for chemical reaction, therefore higher cranking current (CCA) is easier achieved. Hi current needed for starter motor to crank the engine, as soon as job done battery recharged back to its 100% capacity and remains there. Problem comes when starting battery used for deep cycle application. Every time battery gets discharged and recharged small amount of active material falls of the plates. With thin plates all active material will be lost quickly and battery will not recharge to its full capacity anymore. It is safe to discharge starting battery to 5%-10%, but when it comes to 50%-80% depth of discharge the starting battery is not a good option at all, that’s where you will need proper deep cycle battery.
Deep Cycle Battery designed to withstand 50% - 80% depth of discharge. This achieved by installing much thicker plates in to the battery cell, so it takes much longer for deep cycle battery to loose all active material of the plates. Deep cycle battery provides less cranking current; instead it gives steady current for long period of time.
Deep Cycle Battery Cycle Life
Battery life time directly depends on quality of the battery, battery age before its put in to service, charging and discharging rates and depth of discharge
Good quality deep cycle battery in perfect working condition, receiving proper care and maintenance with steady discharge and recharge rates and good quality charger should sustain about