Potassium hydroxide solution is strongly alkaline and the physical and chemical properties of potassium hydroxide closely resemble those of caustic soda (sodium hydroxide). It is corrosive, so care is essential when topping up batteries or handling the electrolyte. In the event of skin or eye contact, the remedy is wash with plenty of clean water (for 15 min) to dilute and remove the solution quickly. Speed is vital to prevent burn damage and water, which is the best flushing agent, must be readily available. Neutralizing compounds, usually weak acids, cannot be located easily, although they should be available in the battery compartment.
The electrolyte slowly attacks glass and various other materials. Containers are therefore of welded sheet steel which is then nickel plated or molded in high-impact polystyrene steel casings are preferred when batteries are subjected to shock and vibration. Hardwood crates are used to keep the cells separate from each other and from the support beneath. Separation is necessary because the positive plate assembly is connected to the steel casing.
6. Battery charging
A direct current supply for charging is obtained from A.C mains, through the transformer and rectifier in the battery charger. The positive of the charge supply is connected to the positive of the cell, and negative to negative terminal. Flow of current from the charging sources reverses the discharge action.
The circuit for changing from D.C mains includes a resistance connected in series, to reduce the current flow from the higher main voltage. Feedback from the battery on charge is prevented, at mains failure by a relay (which de-energizes) and spring arranged to automatically disconnect the battery. The contacts are spring operated; gravity opening is not acceptable for marine installations.
Main A.C voltage is reduced by transformer to a suitable value and then rectified to give direct current for charging. The supply current may be taken from the 230 volt section and changed to say 30 volts for charging 24 batteries. Smoothing is not essential for battery charging but would be incorporated for power supplies to low pressure D.C systems with standby batteries.
7. Capacity of Battery
Battery capacity refers to the total amount of energy stored within the battery. It is measured in ampere-hour (Ah). The capacity is always given at a specified rate of discharge (10-hour rate in U.K, 8-hour rate in the U.S.A). However to be on the safer side, 20 hour rate (calculated at 20 C) are also acceptable. Capacity of the battery mainly depends on the five major factors: rate of discharge, temperature, density of electrolyte, quantity of active material and history of the battery.