Batteries Lecture Notes PDF

Batteries Prepared by: Engr. Ronieto N. Mendoza  BATTERIES Battery is a group of cells that generate energy from an internal chemical reaction. The cell itself consists of two different conducting materials as the electrodes that are immersed in an electrolyte. The electr...

Batteries Prepared by: Engr. Ronieto N. Mendoza  BATTERIES Battery is a group of cells that generate energy from an internal chemical reaction. The cell itself consists of two different conducting materials as the electrodes that are immersed in an electrolyte. The electrolyte of a cell may be liquid or a paste. If the electrolyte is a liquid, the cell is often called a wet cell. If the electrolyte is in a paste form, the cell is referred to as a dry cell.  TWO TPES OF BATTERIES PRIMARY are those which cannot be recharged or returned to good condition after their voltage output drops too low. E.G. DRY CELLS used in flashlights and transistor radios are the examples of the primary cells.  TWO TPES OF BATTERIES PRIMARY  TWO TPES OF BATTERIES SECONDARY are those which are rechargeable. During recharging, the chemicals which provide electric energy are restored to their original condition. E.G. SEALED RECHARGEABLE CELLS is done by passing direct current through a cell in a direction opposite to the direction of the current which the cell delivers to a circuit.  TWO TPES OF BATTERIES SECONDARY  TWO TPES OF BATTERIES SECONDARY A cell is recharged by connecting it to a battery charger on “like-to-like” polarity. Some battery chargers have a voltmeter and an ammeter which indicate the charging voltage and current. The most common example of a secondary cell is an automobile storage battery. TYPES OF BATTERIES  THE VOLTAIC CELL The voltaic chemical cell is a combination of materials used to convert chemical energy into electric energy. The chemical cell consists of two electrodes made of different kinds of metals or metallic compounds, and an electrolyte, which is a solution capable of conducting an electric current. THE VOLTAIC CELL SERIES AND PARALLEL CELL ❑ When cells are connected in series, the total voltage across the battery of cells is equal to the sum of the voltage of each of the individual cells. ❑ When cells are placed in series, the positive terminal of one cell is connected to the negative terminal of the other cell. ❑ The current flowing through such a battery of series cells is the same as for one cell because the same current flows through all the series cells. The total voltage output of a battery of three parallel cells is the same as that for a single cell, but the available current is three times that of one cell. The parallel connection has the same effect of increasing the size of the electrodes and electrolyte in a single cell, which increases the current capacity. Identical cells in parallel all supply equal parts of the current to the load. KINDS OF BATTERIES  LEAD-ACID BATTERY The lead-acid battery consists of a number of lead-acid cells. Each cell has two groups of lead plates: one set is the positive terminal and the other is the negative terminal. All positive plates are connected together with a connecting strap. All negative plates are similarly connected together.  LEAD-ACID BATTERY Between the plates are sheets of insulting material called separators. It prevents the positive and negative plates from touching each other and producing a short circuit, which destroy the cell. The term lead-acid battery refers to the lead plates and the sulfuric acid which are the principal components of the battery. LEAD-ACID BATTERY LEAD-ACID BATTERY  CARBON-ZINC CELL ❑ This is one of the oldest and most widely used commercial types of dry cell. ❑ The carbon, in the form of a rod that is placed in the center of the cell, is the positive terminal. ❑ The case of this cell is made of zinc, which is the negative electrode. CARBON-ZINC CELL  ALKALINE CELL ❑ The secondary alkaline cell is called because it has an alkaline electrolyte of potassium hydroxide. ❑ One battery type that goes by the name alkaline battery has a negative electrode of zinc and a positive electrode of manganese dioxide. It generates 1.5 V.  ALKALINE CELL ❑ The primary alkaline cell is similar in construction to the rechargeable type and has the same operating voltage. ❑ This cell has extended life over a carbon-zinc cell of the same size. ALKALINE CELL  NICKEL-CADMIUM CELL ❑ In the secondary nickel-cadmium dry cell, the electrolyte is potassium hydroxide, the negative electrode is nickel hydroxide, and the positive electrode is cadmium oxide. ❑ The nickel-cadmium battery is the only dry cell battery that is true storage battery with the reversible chemical reaction, allowing recharging many times. ❑ It is a rugged device which gives dependable service under extreme conditions of shock, vibration, and temperature. ❑ Therefore, it is ideally suited for use in powering portable communication equipment such as a two-way radio. NICKEL-CADMIUM CELL  MERCURY There are two different types of mercury cells. One is a flat cell that is shaped like a button, while the other is a cylindrical cell that looks like a standard flashlight cell. Mercury cells and batteries have a good shelf life and are very rugged. Because they produce a constant output voltage under different load conditions, they are used in many different products, including electric watches, hearing aids, test instruments, and alarm systems. BATTERY CHARACTERISTICS  INTERNAL RESISTANCE ❑ A battery is a dc voltage generator. All generators have internal resistance, R. ❑ In a chemical cell, the resistance of the electrolyte between electrodes is responsible for most of the cell’s internal resistance. ❑ Specific gravity of any liquid is a ratio comparing its weight with the height of an equal volume of water.  INTERNAL RESISTANCE ❑ Pure sulfuric acid has a specific gravity if 1.835 since it weighs 1.835 times as much as water per unit volume. ❑ Specific gravity is measured with a hydrometer of the syringe type, which has a compressible rubber bulb at the top, a glass barrel, and a rubber hose at the bottom of the barrel. ❑ A hydrometer reading of 1210 to 1300 indicates full charge; about 1250 is half-charge; and 1150 to 1200 is complete discharge. INTERNAL RESISTANCE INTERNAL RESISTANCE INTERNAL RESISTANCE  CAPACITY ❑ The capacity of a battery is rated in ampere-hours (Ah). ❑ The capacity of a storage battery determines how long it will operate at a given discharge rate. ❑ A cell of a lead-acid automobile battery, when fully charged, has an initial voltage of about 2.1 V at no load, but discharges rapidly. ❑ The battery is “dead” after about 2h of discharging under load condition. ❑ However, under normal use, this battery type is constantly recharged by the alternator in the automobile.  SHELL LIFE ❑ The shell life of a cell is that period of time during which the cell can be stored without losing more than approximately 10 percent of its original capacity. ❑ The capacity of a cell is its ability to deliver a given amount of current to the circuit in which it is used. SIZE OF BATTERIES BATTERY TESTER