Storage battery is a device for converting chemical energy into electrical energy. There are several types of battery, but lead- acid battery is most common for I.C. engines, used for tractors and automobiles.
Components of Storage Battery:
A battery consists of:
a. Plates
b. Separators
c. Electrolyte
d. Container and
e. Terminal wire
a. Plates:
Plates are of two types:
(i) Positive and
(ii) Negative.
All the positive and negative plates are rectangular in shape. All the positive plates are connected together to form a positive group and all the negative plates are joined together to form a negative group. Positive plates are made of lead and antimony and negative plates are made of spongy lead.
b. Separators:
Separators are used to act as insulators between the plates to prevent them from touching each other for avoiding short circuiting. Usually separators are of wood, rubber and cellulose fibre.
c. Electrolyte:
Electrolyte is the chemical solution used in a battery for chemical reaction. Usually this consists of about 35% sulphuric acid and 65% distilled water by weight with a specific gravity of 1.280 in fully charged condition. The specific gravity is measured by hydrometer. The electrolyte level should be 12 to 14 mm above the top edge of the plate.
d. Container:
Container is usually made of hard rubber. The tops are covered with rubber material and sealed with a water proof compound. There are few openings on the top for refilling the cell with electrolyte and for testing purpose.
e. Terminal Wires:
Terminal wires are two in number, one connects the positive terminal and other connects the negative terminal with the electric circuit.
The battery on tractor engine consists of three or six cells, each developing about 2.2 volts.
Chemical Action in Lead-Acid Battery:
Chemical reaction in the battery is as follows:
PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
During action, the active materials in the plates are changed to lead sulphate.
Capacity of the Battery:
The quantity of electricity that a fully charged battery can deliver while being discharged at a constant rate (current) until its terminal voltage falls to a definite value is called the capacity of the battery. It is measured as ampere hours (A.H.).
Battery Leakage (Self Discharge):
Battery leakage is considered excessive if the battery loses more than 1% of its capacity during 24 hours. To avoid this loss, battery cells should be regularly cleaned.
Care and Maintenance of Battery:
i. Specific gravity of the electrolyte should be checked at suitable interval. If the specific gravity is below 1.225, it should be charged.
ii. Level of the electrolyte should be checked in the battery. The level should be about 12 to 14 mm above the battery plates. If it is not so, distilled water should be added in the battery.
iii. The top of the battery should be kept clean and dry.
iv. Over-tightening the clamps and terminals should be avoided.
v. Battery terminals should be cleaned frequently.
vi. Over-charging of battery should be avoided.
Causes of Ignition Failure in Battery System:
i. Breaker points not properly set
ii. Discharged battery or defective dynamo
iii. Defective condenser
iv. Spark plugs broken
v. Timing setting not properly done
vi. Distributor bearing or shaft worn or shaft bent and
vii. Spark plugs of wrong heat range used.
Magneto Ignition System:
A magneto is used to generate an electric current for producing spark in I.C. engine. A high tension magneto generates very high voltage, needed for spark plug.
The electrical principle involved in magneto ignition is similar to battery ignition, the chief difference being that the primary current is produced by magneto and not by battery. Magneto may be considered as combination of a generator for producing low voltage current and an ignition coil for producing high voltage current.
Main Components of Magneto Ignition System:
The main components of magneto ignition system are:
(i) Frame
(ii) Permanent magnet
(iii) Armature
(iv) Soft iron field
(v) Rotor
(vi) Primary and secondary winding
(vii) Breaker points and
(viii) Condenser.
The armature consists of an iron core on which there are two sets of winding:
a. Primary, and
b. Secondary
The armature is driven by the engine. As the armature rotates, primary windings cut the lines of force of the magnetic field and an induced current flow in the primary circuit. As the primary current reaches its maximum value in each direction, the primary circuit is suddenly opened by a contact breaker and the current collapses. This action induces a very high voltage in the secondary winding which causes a momentary spark to jump at the spark plug gap. A distributor is provided which carries current to the spark plug through high tension wires.
The condenser is used to eliminate the arching at the breaker points and intensifying the current in the secondary circuit. For multi-cylinder engines, a distributor and a rotor are required to distribute the current to the different spark plugs. Some high speed engines have magneto built into the flywheel.