HOW THE BATTERY WORKS
CHEMICAL ACTION OF DISCHARGE
When a cell is discharged by completing an external circuit, as in switching on the lights, the sulphuric acid acts on both positive and negative plate active materials to form a new chemical compound called lead sulphate. The sulphate is supplied by the acid solution (electrolyte) Which becomes weaker in concentration as the discharge proceeds. The amount of acid consumed is in direct proportion to the amount of electricity used from the cell. When the acid in the electrolyte is partially used up by combining with the plates, the battery can no longer deliver electricity at a useful voltage and the battery is said to be discharged. This gradual weakening of the electrolyte in proportion to the electricity delivered is a very useful action because is allows us to use a hydrometer to measure how much unused acid remains with the water in the electrolyte and this information enables us to judge about how much electrical energy is left in the cell.
CHEMICAL ACTION OF CHARGE
By passing an electric current through the battery in a direction opposite to that of the discharge, the lead sulphate is decomposed. The sulphate is expelled from the plates and returns to the electrolyte, thereby gradually restoring it to its original strength. This action frees the plate active materials of sulphate and they are restored to their original chemical condition., ready to deliver electricity again. Hydrogen and oxygen gases are given off at the negative and postive pates respectively as the plates reach the fully charged condition. This is the result of the decomposition of water by an excess of charging current not utilized by the plates.
The most valuable characteristic of the lead-acid storage battery is its chemical reversibility. this means that, unlike a dry-cell battery which must be thrown away when it becomes discharged, the storage battery may have and electrical current passed through it in the direction opposite to the direction of discharge and battery’s active chemicals be restored to the “good as new” state.
TO TEST A BATTERY
Insert rubber tip in cell of battery. Hold instrument in vertical position. Squeeze bulb and draw up enough liquid until float moves freely, watching to see that the top does not touch the rubber stopper at the top of the barrel. The mark on the battery tester which is in line with the surface of the liquid indicates the condition of the battery, this:
RED 1.100 – 1.205 – BATTERY CELL IS IN DISCHARGED POSITION
WHITE 1.205 – 1.260 BATTERY CELL NEEDS ATTENTION
GREEN 1.260 – 1.300 BATTERY CELL IS O.K.
Return liquid to same battery cell from which it was taken.
NOTE: A test cannot be made properly unless each battery cell has enough fluid to allow the float to rise freely. You will not get an accurate reading is the water has just recently been added to the cells.