112 Electricity & Electronics Types of Lead-Acid Batteries Th ere are three types of lead-acid batteries in use today: fl ooded, gel, and AGM. Th e term fl ooded means that the battery electrolyte is physically totally liquid. It consists of the water and sulfuric acid. Gel type means that the electrolyte is mixed with a thickening agent to create a gel. Th e third type is absorbent glass mat (AGM), which uses a separator material between the battery plates that is made from a fi berglass-type material. Th e fi berglass-type material absorbs the electrolyte and is sandwiched between the battery plates. Both the gel and AGM designs prevent spillage of electrolyte when the battery is tilted, turned upside down, or vibrated excessively in applications such as ATVs and airplanes. Gel and AGM designs are sealed and maintenance free, meaning the electrolyte never needs to be refi lled. Nickel-Cadmium Cell Th e nickel-cadmium cell is a rechargeable dry cell. Basically, these are nickel- cadmium alkaline batteries with paste rather than liquid for the electrolyte. Th e ability to be recharged is just one of their advantages. Other advantages include long life, high effi ciency, compactness, and lightweight. Th e nickel-cadmium cell produces a high discharge current due to its low internal resistance. Other uses include the powering of small radios, burglar alarm systems, camera fl ashes, and aircraft instruments. One type of nickel-cadmium cell uses positive and negative plates, a separator, alkaline electrolyte, a metal case, and a sealing plate with self-resealing safety vent. It is shown in Figure 7-11. Th e positive plate of this battery is a porous, powdered nickel base plate. It is fi lled with nickel hydroxide. Th e negative plate is a punched plate of thin steel, coated with cadmium-active material. Th e separator is made of a polyamide fi ber. For high temperature uses, it is made of a nonwoven polypropylene fi ber. Th e positive plate, separator, and negative plate are pressed together, wound into a coil, and inserted in the metal case. Th e electrolyte is an alkaline aqueous solution. It is totally absorbed into the plate and separator. Th e metal case is constructed of nickel-plated steel. It is welded on the inside to the negative plate. It becomes the negative pole. Th e sealing plate uses a special liquid sealing agent to form a perfect seal. Th e positive plate is welded on the inside to the sealing plate. It becomes the positive pole. Th e self-resealing safety vent permits the discharge of gas in the event of an abnormal increase of internal pressure. Th is prevents against rupture or other damage. Th e vent is made of a special alkaline and oxidation resistant rubber. Th is ensures that operating pressure and safety features will be retained over a long period of time. Th e electromechanical processes of a nickel-cadmium alkaline cell are outlined below. 2NiOOH + Cd + 2H2O 2Ni(OH)2 + Cd(OH)2 Positive Negative Electrolyte Positive Negative Discharge Charge Oxy-Nickel hydroxide Cadmium Water Nickel hydroxide Cadmium hydroxide In this process, charging and discharging are reversed in a very effi cient manner. Th e electrical energy used during discharge is regained during recharge. During the fi nal charging stage, an oxygen gas is created with the reaction occurring at the positive. S A F E T Y During the charging process of a storage battery, highly explosive hydrogen gas may be present. Do not smoke or light matches near charging batteries. Charge only in well-ventilated areas. Batteries should be fi rst connected to the charger before the power is applied. Otherwise, the sparks made during connection might ignite the hydrogen gas and cause an explosion. C A U T I O N Automotive batteries contain large amounts of lead. Consequently, they should never be disposed of in landfills. Stores that sell automotive batteries are required by law to accept old batteries for recycling. Positive terminal (+) Insulation gasket Sealing plate Insulation plate Case (–) (negative) Insulation plate Self-sealing vent Positive lead Separator Negative plate Separator Positive plate Panasonic Battery Sales Division Figure 7-11. Construction of a nickel-cadmium cell. Copyright Goodheart-Willcox Co., Inc.