Electrical Characteristics of Lead Acid Battery

Electrical Characteristics of Lead Acid Battery Points : Electrical Characteristics of Lead Acid Battery, As we know that batteries are group of cells connected together in series, parallel or series parallel to provide different voltage, current capacities and other features. The characteristics must always be considered. For example there may be number of batteries having desired voltage for an application, some of these may not have a low enough internal resistance to provide the needed voltage regulation at high current output, other may have insufficient total energy content in ampere hours etc. All these factors affect performance and choice of the type of cell used. We also are going to study in following section different characteristics of battery cells. Remember, however that when a battery is used all characteristics must be considered. 1. Voltage The normal no load voltage of a fully charged cell is approximately 2,2 volts and this value is not fix but depends upon (a) length of time since it was last charged, (b) specific gravity. Voltage increases with increase in specific gravity and vice versa. Just having nominal no load voltage of the right value is not sufficient. It must also have low enough internal resistance to deliver the desired, current without an excessive drop in terminal voltage. It must have sufficient capacity to maintain minimum terminal voltage for the period of time.

The ability of a cell to maintain the voltage close to nominal no load. Voltage under load is related to Its physical size, the larger the size larger is electrode surface and more electrolytes is contact with them and therefore lowers the internal resistance, Hence, good voltage regulation under relatively heavy load Is obtained by using larger size of cell. Voltage aIso depends on the state’ of charge of the cell and It falls as the cell discharge.

2. Capacity This is the total energy that can be obtained from a cell under normal operating conditions. Capacity rating is normally given in ampere hour. The capacity of a given battery, varies with rate and on — off pattern in which discharge takes place. The capacity depends upon the following.

(a) Rate of discharge
The ampere-hour capacity of cell depends on rate of discharge. It decreases with increases in rate of discharge. Rapid of discharge weakens the electrolyte as well greater fall in terminal voltage due to internal resistance.
(b) Temperature:. At high temperature the Ah (Ampere hour) capacity of cell increases because of the following:

(i) Chemical reaction within the cell takes place more vigorously.
(ii) Resistance of the electrolyte decreases.

(c) Density of electrolyte
Ah capacity of cell increases as the density of electrolyte increases. Quantity of active material: