Battery Ignition System/ Coil Ignition System Construction and Essential Components

Car_ignition_system battery

🔗Difference between battery ignition system and magneto ignition system

Battery ignition is the most common type of ignition system. Since ignition coil plays a major role in this system, it is also called Coil Ignition System. They are used in cars, light trucks and in some two-wheelers. The above figure shows a battery ignition system for four-cylinder petrol engine.

Construction of Battery ignition system and essential components

The battery ignition system consists of battery, ignition switch, ballast resistor, ignition coil, contact breaker, capacitor, distributor and spark plug as its main component. Various component of the coil ignition system and their function is listed below.


The electrical energy needed for the ignition is accumulated in a battery. This battery is getting charged by using dynamo driven by the engine. The battery must be strong enough withstand with strains which it continuously subjected to. The battery supplies low tension current usually at 6 or 12 volts. Mainly there are two types of batteries are used in SI engines. The first one is the lead acid battery which is used in light-duty vehicle while the second type, alkaline batteries, are used in heavy-duty vehicles.

The lead-acid battery consists of number of cell connected in series. Each of the cell having a nominal potential 2V when fully charged. The following diagram shows the six 2Volt cell connected in series to produce a 12Volt battery.
battery cell arrangement

🔗Advantages of 12V Ignition System over 6V Battery Ignition

Ignition switch

Ignition switch/ starter switch is the part which used to turn on or off the entire ignition system. Battery connected to ignition coil through the ignition switch. In a motor vehicle, it is a key switch that requires a proper key to unlock the function. They are usually combined with the switch to all electrical system and accessories including starter switch to run the starter motor.

Ballast resistor


Ballast resistor connected in series with primary winding it is used to regulate primary current. Ballast resistor acts as a protector while engine running at low speed for a long time. Ballast resistor in the ignition system is a self-variable resistor. The Ballast coil is made of iron wire, and its resistance increases rapidly when it reaches a certain temperature. So it is made of wire such size of that if the primary current flow continuously, it gets heated to certain temperature. When temperature increase above certain range, the resistance ballast increase and the current passed through the primary coil reduces. This keeps the current down to a safe value. It prevents injury of spark coil by overheating.

For cold starting of an engine the ballast resister bypassed to allow more current flow in the primary circuit.

Ignition coil

ignition coil cross section

The ignition coil is induction coils act as the voltage transformer. This is where the 12V of battery is step up to high voltage (10,000V) enough to induce the spark in electrodes of the spark plug. The secondary wing consists of thousand turns of thin wire, the primary winding consists of a few numbers of turns of wire which wound outside the secondary coil.

Contact breaker

One end of the primary coil is connected to the contact breaker. Contact breaker is a mechanical device for breaking the primary circuit. It is a type of electrical switch. The breaker points are held together by spring, and it is forced apart by the cams connect to the engine. When contact breaker interrupts current flow through primary windings, the collapsing current induces a large voltage in a secondary wing. The contact breaker help to fire spark plug accurately at high speed.

The construction and functions of the ignition capacitor are the same as the normal electrical capacitor. When contact breaker open or primary circuit breaks, the current tends to flow and produce a spark at contact breaker. It may damage the contact breaker point. Ignition capacitor prevents this by absorbing and storing this energy.



The function of distributor to distribute the high ignition surge to the individual spark plug at the correct time and sequence according to the engine firing order. The mechanical distributor is an enclosed rotating shaft which mechanically timed the ignition. The working of the distributor is made to synchronize with the contact breaker. Brush type and Gap type are the two type of distributor.

Spark plug


This is where the actual spark occurs. The spark plug has two electrodes separated by a proper gap. When distributor pass a high voltage to the spark plug, the high potential across the electrodes generate a spark. This spark ignites the air-fuel mixture inside the combustion chamber.

🔗Working of Battery ignition system, advantages and disadvantages

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