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Battery Ignition System is used in automobile to produce spark in the spark plug for the combustion of fuel in the I.C. engine. Here the main source for the spark generation is the battery. It is mostly used in light commercial vehicles.
Functions of Each part:
1. Battery:
Working Of Battery Ignition System
Battery Ignition System is used in automobile to produce spark in the spark plug for the combustion of fuel in the I.C. engine. Here the main source for the spark generation is the battery. It is mostly used in light commercial vehicles.
Main parts
- Battery
- Ignition switch
- Ballast resistor
- Ignition coil
- Contact breaker
- Capacitor
- Distributor
- Spark plug
1. Battery:
- It is a device which provides electrical energy for the ignition.
- Generally two types of batteries are used in spark ignition engine, lead acid battery & alkaline battery
- The lead acid battery is used in light duty commercial vehicle whereas alkaline battery is used in heavy duty commercial vehicle
2. Ignition switch:
- It is a switch which is used to ON or OFF ignition system.
- One end of the ignition switch is connected to the battery and the other with the primary winding through a ballast resistor
3. Ballast Resistor:
- It is connected in series with the primary winding. It is present in between the ignition switch and ignition coil. The function of ballast resistor is to prevent the overheating of primary winding of ignition coil.
- The Ballast Resistor is made of iron wire and iron wire has a property that its electrical resistance increases rapidly with small increase in temperature.
- If the current from the primary winding flows continuously, the temperature of the ballast resistor increases and this increases the electrical resistance and reduces flow of electric current through the primary winding.
- The reduction of current by ballast resistor prevents the overheating of the primary winding.
- It is used to generate high voltage which is sufficient to generate spark across the electrodes of spark plug. It acts a step transformer and converts a 6 or 12 V of a battery into very high voltage of about 15000 to 30000 V.
- It Consist of a soft iron core surrounded by two insulated coil, named as primary winding and secondary winding. The primary winding consists of 200-300 turns of 20 gauge wires capable of producing resistance of 1.15 ohm. The secondary winding consists of 21000 turns of 38-40 gauge enameled wire and it is sufficiently insulated to withstand high voltage.
- One end of the primary winding is connected to the battery terminal through ballast resistor and ignition switch. And other end is connected with the contact breaker as well as secondary winding. In the case of secondary winding, its one end id connected to the central high tension terminal of the distributor. And other end is connected with the primary winding
5. Contact Breaker
It is a
mechanical device which is used for making and breaking of the primary circuit
of the ignition coil.
It has two
metal points made up of tungsten and place against each other. These metal
points have circular flat face of about 3mm diameter. Among the two metal
points, one is fixed and other is moveable.
The fixed
contact point is being earthed by mounting it on the base of the contact
breaker assembly. The movable contact point is attached to the spring loaded
pivoted arm which is electrically insulated.
The pivoted
arm generally has a heel or rounded part (cam follower) made up of some plastic
material and attached in the middle of the arm. The heel is rest on the cam
driven by the engine.
Every time
when the cam passes under heel, the contact points are forced apart and the
circuit is broken.
The pivoted
arm is spring loaded and in the case when the points are not separated by the
cams, it is held together by the spring force and closes the primary circuit.
When the points are closed, the current flows through the primary circuit and
it stops if open.
6. Capacitor
- The capacitor used in the ignition system is similar to the electrical capacitor. The capacitor is an electrical device in which two metal plates are separated from each other through insulating materials (air).
- It is connected in parallel with the contact breaker. It prevents the contact points of the contact breaker from being damage.
- If there is no capacitor used in the primary circuit, the high primary voltage caused by the collapse of the magnetic field around the primary winding would cause an arc across the breaker points.
- The arc produced would burn and destroy the points and would also prevent the rapid drop in primary current and magnetic field which is necessary for the generation of high secondary voltage.
7. Distributor
- It is a device used in the Battery Ignition System to distribute the ignition pulses to the individual spark plug in a correct sequence and at the correct instant in time.
- There are two types of distributor
1. Brush type: In the brush type distributor, it contains carbon brush carried by the rotor arm slides over the metallic segments embedded in the distributor cap.
2. Gap type: In this type of distributor the rotor arm pass very close to the segments of the distributor cap but do not touch it.
- It also contains some other auxiliary units too. In lower part of the housing, it has a speed sensitive device or governor whose main function is to advance the spark with increase in the engine speed. Contact breaker assembly is present above this, which can be rotated to adjust the timing of the spark.
- In the upper part of the housing, high tension distributor is located. It also carries the vacuum ignition governor which serves to retard the spark as the load on the engine increases. Each metallic segments of the distributor is connected to each spark plug.
- As the rotor rotates, the contact point opens; this allows the high tension current to pass to the spark plug through the segments to which the spark plug is connected. The sequence in which the spark plug is connected to the distributor cap depends upon the firing order of the engine.
8. Spark Plug
- The spark plug is used to generate sparks to ignite the air-fuel mixture in the combustion chamber.
- Each spark plug is connected to the distributor of the ignition system.
Working Of Battery Ignition System
- In the Battery ignition system as the ignition switch is ON, the current from the battery starts to flow through the ballast register to primary winding (in ignition coil) and contact breaker.
- The current flowing through the primary winding induces magnetic field around it. If the current is more, then the magnetic field is stronger.
- As the contact breaker opens, the current through the primary winding collapse and this immediate collapse in the current induces a voltage of about 300V in the primary winding.
- This induced voltage in the winding, charges the capacitor to more voltage than the battery voltage. As the capacitor charged, the current through the primary winding stops and the current starts to flow to the battery form the capacitor.
- This reverses the direction of current and magnetic field in the primary winding. Due to the collapsing and reversing of the current and magnetic field, a very high voltage of about 15000 to 30000 V induced in the secondary winding.
- The high voltage current induced in the secondary winding is transferred to the distributor through a high tension cable.
- The distributor has a rotor that rotates inside the distributor cap. The distributor cap has metallic segments embedded into it. As the rotor rotates, it presses and opens the contact breaker point. This allows the high tension current to transfer to the spark plugs through the metallic segments.
- As the high tension current reaches the spark Plug, it produces spark in the engine cylinder for the combustion of the air-fuel mixture.
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