Battery ignition system is used in automobiles to produce spark in spark plug for combustion of fuel in IC engine. Here the main source of spark generation is the battery. It is mainly used in light commercial vehicles.
Main parts
The main parts of the battery ignition system are
1. Battery
2. Ignition switch
3. Ballast resistor
4. Ignition coil
5. Contact breaker
6. Capacitor
7. Distributor
8. Spark plug
The figure shows the line diagram of the battery ignition system for a 4-cylinder gasoline engine. It mainly consists of a 6 or 12 volt battery, ammeter, ignition switch, autotransformer (step-up transformer), contact circuit breaker, capacitor, distributor rotor, distributor contact points, spark plugs, etc.
spark plugPlease note that the figure shows the ignition system for 4 cylinder gasoline engine, here there are 4 spark plugs and the circuit breaker cam has 4 corners. (If it is for a 6-cylinder engine, it will have 6 spark plugs and the circuit breaker cam will be a perfect hexagon).
battery ignition systemThe ignition system is divided into 2 circuits:
(i) Primary Circuit: Consists of 6 or 12 V battery, ammeter, ignition switch, primary winding, has 200-300 turns of 20 SWG (Sharps Wire Gauge) wire, contact circuit breaker, capacitor.
(ii) Secondary Circuit: It consists of secondary winding. The secondary winding consists of about 21,000 turns of 40 gauge wire (S WG). The lower end is connected to the lower end of the primary winding and the upper end of the secondary winding is connected to the center of the distributor rotor. The distributor rotors rotate and make contact with the contact points and are connected to the spark plugs that are installed in the cylinder heads (engine ground).
(iii) Working: When the ignition key is closed and the engine is running, as soon as the contact breaker closes, a low voltage current will flow through the primary winding. It should also be noted that the contact cup cam opens and closes the circuit 4 times (for 4 cylinders) in one revolution. When the circuit breaker opens the contact, the magnetic field begins to collapse. Because of this collapsing magnetic field, current will be induced in the secondary winding. And because of more turns (@ 21,000 turns) of the secondary, the voltage goes to 28,000-30,000 volts.
This high voltage current is taken to the center of the distributor rotor. The distributor rotor rotates and delivers this high voltage current to the appropriate hard plug depending on the ignition order of the engine. When the high voltage current passes the spark plug gap, it produces the spark and the charge is ignited – combustion begins – the combustion products expand and produce energy.
(a) The function of the capacitor is to reduce the arc at the contact circuit breaker (CB) points. Additionally, when the circuit breaker opens, the magnetic field in the primary winding begins to collapse. When the magnetic field collapses, the capacitor becomes fully charged and then starts discharging and helps in building up voltage in the secondary winding.
(b) The circuit breaker cam and distributor rotor are mounted on the same shaft. In 2-stroke cycle engines, they are started at the same engine speed. And in 4-stroke cycle engines they are activated at half the engine speed.
Benefits
(a) Low initial cost.
(b) Better spark at low speeds and better starting than magnetic system.
(c) Reliable system.
(d) No problems due to adjustment of ignition timings.
(e) Simpler than the magneto system.
Disadvantages
(a) The battery requires periodic maintenance.
(b) In case of battery malfunction, the engine cannot be started.
