Magneto Ignition System: 11 Important Facts

Have you wondered what happens to petrol when it reaches the fuel tank? Well the answer is simple, the fuel is ignited to produce a certain amount of thermal energy which then gets converted into mechanical energy (rotary motion of wheels). 

There are two ways by which fuel can be ignited- with the help of electric spark or by applying high pressure. Now the question arises, how to create a spark inside the engine? This is the situation where magneto ignition system comes into play.

In spark ignition engines (petrol engines), a spark is required to ignite the fuel. The source of electricity to create a spark may vary according to engine requirements. Read this article further to get a deep insight on how does a magneto work.

What is magneto ignition system?

Spark ignition engines create a spark to ignite air-fuel mixture. This spark is created with the help of an ignition engine.

An ignition system that uses a rotating magnet (magneto) for generating electricity is known as magneto ignition system. This electricity is used to power spark plugs.

Magneto ignition system diagram

How does magneto work
Image: Magneto ignition system
Image source

Parts of magneto ignition system

Magneto ignition system uses following parts-

Many parts are employed which work in harmony to give desired output. The basic parts of magneto are discussed below-

  • Magneto
    Magneto refers to a group of rotating magnets used for producing high voltage. The rotational speed of engine (rpm) is directly proportional to the voltage produced by rotating magnets. Based on the rotation of parts, magneto is of three types-  

    -Armature rotating type
    -Magnet rotating type
    -Polar inductor type
  • Distributor
    As the name suggests, distributor invites ignition surges and then distributes it among individual spark plugs. Distributor has a rotor in the center and metallic electrode on the periphery.
  • Primary and secondary winding
    Primary winding act as the input that is draws the power from source and secondary winding having more number of turns acts as output. Secondary winding is connected to distributor.
  • Cam
    Cam facilitates the motion of magnet. It is connected to the poles of magnet.
  • Circuit breaker
    Cam motion is designed in such a way that it breaks the circuit at certain intervals. When the circuit is breaks, the capacitor starts charging by primary current.
  • Capacitor
    A capacitor is an assembly of two metallic plates placed at a small distance from each other.  Capacitor stores charge.
  • Spark plug
    Spark plug is used for igniting air-fuel mixture inside the engine cylinder. Spark plug has two metallic electrodes separated by a small distance.

How does a magneto work?

Magneto system employs a rotating magnet as the source of electricity, rest of the working is similar to the battery ignition system. Working of magneto ignition system is explained briefly below-

As the engine rotates magnet inside the coil, an EMF is generated and so a current starts flowing through the coils. As the poles of magnet start moving away from the coil, the magnetic flux begins to decrease. At this point, the cam breaks the circuit (cam-type contact breaker).

As the contact breaker breaks the circuit, the flow of current disrupts. As a result, capacitor starts charging and voltage on the secondary winding increases rapidly. The voltage increases up to such an extent that it is able to jump small gaps. When this happens, spark is created and fuel-air mixture is ignited.

Types of magneto ignition systems

Based on the engine rotation, magneto ignition system can be of following type-

  • Magnet rotating type- In this type, magnet rotates and armature is kept fixed. As a result there is a relative motion between magnet and the windings. In modern days, this type of magneto ignition system is commonly used.
  • Polar inductor type- In this type, both the coil and magnet is kept fixed. The moving part here is a soft iron core having projections at fixed intervals.
  • Armature rotating type- In this type, magnet is fixed and the armature rotates.

Dual magneto ignition system

Usually a single magnet is used in small engines like in that of two wheelers. Big engines like that of aircrafts need an extra magnet for safety. In dual magneto ignition system, two magnets are used instead of one. This increases the safety factor of the engine.

Dual magneto ignition system is used in aircraft engines where each engine cylinder has two spark plugs and each spark plug is fired by its individual magneto. In case where failure of one magneto takes place, other magneto keeps the engine running with a slight decrease in efficiency.

High tension magneto| Low tension magneto

There are two types of magneto- high tension and low tension magneto. Their working principle being same in ignition system. Both of these magnetos have a minute difference between them.

High tension magneto produces pulses of high voltage that are sufficient enough to jump across the length between two electrodes of spark plug. This type of magneto works when the circuit breaks, only then the voltage rises up to desired level. The main disadvantage of this type of magneto is that it deals with very high voltage.

Low tension magneto produces a low voltage that is distributed in the transformer coil which is again connected to spark plug. Using a low tension magneto eliminates the need of dealing with high voltages. This type of magneto is generally used in spark ignitors and not in spark plugs.

Battery ignition system| Difference between battery and magneto ignition system

Battery ignition system serves the same purpose as magneto ignition system. It acts as the source of electricity that is used to produce sparks in spark plug.  

Battery ignition system was commonly used in four wheelers but now it is being used in two wheelers as well. A 6V or 12V battery is used to produce a spark unlike magneto ignition system where magneto was the source of electricity.

Battery takes more space hence it was not suggested to use it in two wheelers where space constraint is more. Nowadays compact battery systems are available that can be used in two wheelers also.

The major difference between a battery and magneto ignition system is the source of electricity. In battery ignition system, as the name suggests, battery is used as the source of electricity whereas magneto ignition systems use magneto for generating electricity.

Electronic ignition systems

Electronic ignition systems use electrical circuits having transistors that are controlled by sensors to produce spark. This type of system can ignite even a lean mixture and provides better economy.

Electronic system is divided into two types- Transistor and distributorless ignition system. Electronic ignition system in general, doesn’t use breaker points like those used in magneto ignition system. Hence, this type of system provides breakerless ignition.

Advantages and disadvantages of magneto ignition system

Not every system is ideal, every system has its own pros and cons. It is a design trade off which decides which type of system needs to be used. Following are the advantages of magneto ignition system-

  • It generates electricity on its own hence no need of battery.
  • It occupies less space.
  • No problem of charging or discharging of battery as it doesn’t use one.
  • High efficiency/reliability due to high voltage spark.

Disadvantages of magneto ignition system are-

  • Costlier than other ignition systems.
  • During start, quality of spark is low due to low engine speed. It gets higher with high engine speed.

Practice questions

How does a magneto ignition system work?

Ans: Magneto ignition system works on the principle of Faraday’s first law of electromagnetic induction.

The relative motion between magnet and transformer coils induce an electromotive force (EMF). Due to this, a varying electric current is produced. As rotation of the magnet progresses and poles start moving farther from the coil, a circuit breaker breaks the circuit and disrupts the flow of current.

Due to this, a high voltage is produced at secondary coil which is then distributed to the spark plugs. The voltage is high enough for it to jump across the length between two electrodes of spark plug.

What are the main advantages and disadvantages of magneto ignition system?

Ans: The magneto ignition system has its own pros and cons. Advantages of magneto ignition system are as follows-

  • No batteries are requires as magneto itself generates electricity.
  • Takes up less space than other ignition systems.
  • No problem of discharge as no batteries are used.

The following are disadvantages of magneto ignition system-

  • Expensive as compared to other ignition systems.
  • The voltage produced is directly proportional to the engine speed. So low voltage is produced at start due to low engine speed.

What are the three types of ignition systems?

Ans: To ignite the air-fuel mixture, an ignition system is required. For industrial applications, three types of ignition systems are commonly used-

  • Battery ignition system
  • Magneto ignition system
  • Electronic ignition system

What is the purpose of magneto in an ignition system?

Ans: Magneto is a rotating magnet whose rotation speed is equal to the engine speed.
      Pulses of high voltage are required to produce a spark in spark plugs. These pulses are produced by a magneto. The spark produced ignites the air-fuel mixture.

Why magneto ignition system is not used however it has higher efficiency and low maintenance?

Ans:  Magneto system works solely on mechanics of engine rotation hence the voltage keeps varying at different speeds. Electronic ignition system is more efficient overall as it can also ignite lean air-fuel mixture. With use of transistors and sensors, the precision of producing sparks improved. Also, mechanical components are ought to wear after certain period of time.

Because of above reasons, magneto systems are not used these days. However, they were best suitable at the time of their invention.

What route is followed by current in magneto ignition system?

Ans: Current in magneto ignition system is induced by varying magnetic flux around the coil.

The induced current flows through primary winding. A circuit breaker breaks the circuit at certain intervals. Current flow disrupts when the circuit is broken. This results in increase of voltage at secondary winding which is connected to spark plug. As the poles reverse, the flow of current reverses.

What is a more efficient ignition system coil and battery or magneto?

Ans: The answer to this question depends on the basis of comparison.

        If we compare on the basis of space and discharge rate, then magneto is more efficient as it takes up less space and has no issue of discharging.

       If we compare on the basis of ignition timing, then battery ignition system is more efficient as it doesn’t have fixed ignition timing. Magneto ignition system is designed mechanically so, it has a fixed ignition timing.

This becomes a problem at low speeds because of low voltage produced. Hence, an ignition system with variable ignition timing is more efficient than one with fixed ignition timing.