Battery: definition, functions, Types, History, components, diagram,

 BATTERY:

A battery in automobiles, is an electrochemical device which produce electricity (current) through chemical action inside it. The battery does not store electricity a electrons. The battery stores energy in the chemical form. The electrical energy is produced in the battery by the chemical reaction that occurs between two dissimilar plates that are immersed in a electrolyte solution. 

The automotive batteries are rechargeable, therefore, they can also convert a electrical current into chemical energy and stores that energy until it is needed.

The amount of electrical energy that a battery can produce depends upon the size, weight,  active area of plates, and the amount of sulphuric acid in the electrolyte. The greatest requirement of electrical energy from the battery occurs when it supplies current for operating the starter in When the engine is started, the vehicle's charging system (generator) supplies current to recharge the battery and to run the electrical systems. However, under some conditions (such as engine tuning at idle speed), generator output is below its maximum rating. It may be noted that if there are many electrical components operated during this time (i.e. blower, wipers, headlights, radio etc.) to supply the additional current.

When the ignition switch is turned off, the battery supplies current for opereres. It is computer memory, audio memory etc. The requirement is usually less than 30 milliamperes. It say be noted that when the charging system fails, the battery must supply all the current necessary turn the vehicle.

TYPES OF BATTERY

1. Lead-acid battery
2. Alkaline-battery-    (i) Nickel-iron type   (ii) Nickle-cadmium type  (iii) Silver -Zinc type 
3. Non-conventional-  (i ) Zinc-air battery    (ii) Sodium- Sulphur type   (iii) Lithium - Chlorine type
4.  Dry charge battery

HISTORY-

• Early cars did not have batteries, as their electrical systems were limited. A bell was used instead of an electric horn, headlights were gas-powered, and the engine was started with a crank. Car batteries became widely used around 1920 as cars became equipped with electric starter motors. The sealed battery, which did not require refilling, was invented in 1971.
• The first starting and charging systems were designed to be 6-volt and positive-ground systems, with the vehicle's chassis directly connected to the positive battery terminal. Today, almost all road vehicles have a negative ground system. The negative battery terminal is connected to the car's chassis.
• The Hudson Motor Car Company was the first to use a standardized battery in 1918 when they started using Battery Council International batteries. BCI is the organization that sets the dimensional standards for batteries.
• Cars used 6 V electrical systems and batteries until the mid-1950s. The changeover from 6 to 12 V happened when bigger engines with higher compression ratios required more electrical power to start. Smaller cars, which required less power to start stayed with 6 V longer.
• In the 1990s a 42V electrical system standard was proposed. It was intended to allow more powerful electrically driven accessories, and lighter automobile wiring harnesses. The availability of higher-efficiency motors, new wiring techniques, and digital controls, and a focus on hybrid vehicle systems that use high-voltage starter/generators have largely eliminated the push for switching the main automotive voltages.

CONSTRUCTION OF BATTERY

 

The lead-acid battery, consists of the following components: 

1. Case The battery case is made of polypropylene, hard rubber, or plastic based material. It must be capable of withstanding extreme hot and cold temperatures, vibrations and also must be resistant to the absorption of acid.

2.Cover The top of the battery is covered with a one-piece plastic cover bonded to the container with sealing compound. The cover may have threaded or tapered holes over each cell for filler caps. one filler cap is provided for each cell. Also, the holes are provided in the cover for terminal posts.

3. Filler caps  The battery filler caps are also made up of synthetic resin. A small hole is made in the cap to permit the escape of oxygen and hydrogen gases while containing the sulphuric acid in the electrolyte. 

4. Battery terminals  The two terminals of the battery are made of lead alloy. The post-shaped terminals are slightly tapered to have easy connections of the battery leads. The positive terminal is slightly larger at the top than the negative terminal so as to avoid the wrong installation of b leads. The battery leads are thick, heavy cables which connect the battery to the vehicles electrical system (positive) and to the ground (negative).

5. Plates  A plate consists of a frame structure called as grid. The grid has horizontal and vertical grid bars that intersect at right angles,  The grids are made of lead-antimony.  which makes it resistant to electrochemical corrosion, and gives strength and rigidity to the grid.

6. Separators The separators are provided between the positive and negative plates in each cell  to keep them electrically apart so as to prevent short circuits between the cells. The separators must be non-conductive and porous while having sufficient mechanical strength and acid resistance.  

In addition to the separator, glass mats are formed on both sides of the positive plate to prevent loss of the active material and oxidation of lead peroxide. The material used to make separators include polyvinylchloride (PVC), micro-porous rubber, special type of wood and fibre glass.

7. Cells The positive and negative plate assembly, together with separators in between is called an element. An element becomes a cell when it is installed in a container filled with electrolyte. 

It may be noted that one cell develops only about 2 to 2.2 volts of electrical potential. For example, a six-volt battery has 3 cells and 15, 17 or 19 plates per cell and a twelve-volt battery has 6 cells and 7, 9, 11 or 13 plates per cell, The negative and positive plates are arranged alternately in each cell. In a cell, all the positive plates are connected to each other and all the negative plates are connected to each other by plate straps.

8. Electrolyte  Each cell element of the battery is filled with electrolyte, generally diluted sulphuric acid of high purity. The electrolyte solution of a fully charged battery consists of 64% water and 36% sulphuric acid by weight. 

The electrolyte is both conductive and reactive in nature. If impure sulphuric acid is added to the battery, the plates, separators, etc. will become corroded. resulting in an increase in self-discharging and shortened battery life. It is therefore, vital that only pure sulphuric acid and water purified by ion exchange process should be used.

Sulphuric acid (chemical formula H₂SO) is a highly corrosive and poisonous acid. The melting point is 10° C. This acid is widely used in chemicals, fertilizers, explosives, oil refining etc. As it has a dehydrating property, paper and other fibres become carbonised and black when they come in contact with the acid.