TERMINAL OBJECTIVE

1.0 DESCRIBE the operating characteristics of a lead-acid battery to include methods of voltage production, state of charge, and hazards associated with storage batteries.

ENABLING OBJECTIVES

1.1 DEFINE the following terms as they relate to batteries and voltaic cells: a. Voltaic cell

b. Battery c. Electrode d. Electrolyte e.Specific gravity f. Ampere-Hour

1.2 STATE the purpose of a battery.

1.3 DESCRIBE the operation of a simple voltaic cell.

1.4 STATE the chemical equation for the reaction that occurs when a lead-acid battery is being charged or discharged.

1.5 EXPLAIN the relationship between specific gravity and state of charge of a lead-acid battery.

1.6 DESCRIBE the relationship between total battery voltage and cell voltage for a series-connected battery.

1.7 STATE the advantage of connecting a battery in parallel with respect to current-carrying capability.

1.8 STATE the difference between primary and secondary cells with respect to recharge capability.

1.9 STATE the advantage of each of the following types of batteries: a. Carbon-zinc cell

b. Alkaline cell

c. Nickel-cadmium cell

d. Edison cell

e. Mercury cell

1.10 EXPLAIN the adverse effects of a shorted cell.

1.11 EXPLAIN how gas generation is minimized for a lead-acid battery.

1.12 EXPLAIN how heat is generated in a lead-acid battery.

BATTERY TERMINOLOGY

Batteries are used for a wide variety of services throughout technology today. To begin to study battery operation and characteristics, a few terms that are used with batteries must be understood.

EO 1.1DEFINE the following terms as they relate to batteries and voltaic cells:

a. Voltaic cell b. Battery c. Electrode d. Electrolyte e. Specific gravity f. Ampere-Hour

Voltaic Cell

The term voltaic cell is defined as a combination of materials used to convert chemical energy into electrical energy. A voltaic or chemical cell consists of two electrodes made of different types of metals or metallic compounds placed in an electrolyte solution.

Battery

A battery is a group of two or more connected voltaic cells.

Electrode

An electrode is a metallic compound, or metal, which has an abundance of electrons (negative electrode) or an abundance of positive charges (positive electrode).

Electrolyte

An electrolyte is a solution which is capable of conducting an electric current. The electrolyte of a cell may be a liquid or a paste. If the electrolyte is a paste, the cell is referred to as a dry cell; if the electrolyte is a solution, it is called a wet cell.

Specific Gravity

Specific gravity is defined as the ratio comparing the weight of any liquid to the weight of an equal volume of water. The specific gravity of pure water is 1.000. Lead-acid batteries use an electrolyte which contains sulfuric acid. Pure sulfuric acid has a specific gravity of 1.835, since it weighs 1.835 times as much as pure water per unit volume.

Since the electrolyte of a lead-acid battery consists of a mixture of water and sulfuric acid, the specific gravity of the electrolyte will fall between 1.000 and 1.835. Normally, the electrolyte for a battery is mixed such that the specific gravity is less than 1.350.

Specific gravity is measured with a hydrometer. A simple hydrometer consists of a glass float inside a glass tube, as shown in Figure 1. The hydrometer float is weighted at one end and sealed at both ends. A scale calibrated in specific gravity is positioned lengthwise along the body of the float. The float is placed inside the glass tube, and the fluid to be tested is drawn into the tube. As the fluid is drawn into the tube, the hydrometer float will sink to a certain level in the fluid. The extent to which the hydrometer float protrudes above the level of the fluid depends on the specific gravity of the fluid. The reading on the float scale at the surface of the fluid is the specific gravity of the fluid.