What does a CDI box do? What Are The Things You Need To Know?

CDI box

Capacitor Discharge Ignition or CDI is the part that is available in the most of the petrol based engines. Its primary purpose is to ignite the motor and make it work properly. It is the made up of the distinct parts that work together so that the ignition system of the vehicle can operate properly.

In this article, we will be trying to solve the query “What does a CDI box do?” We will try to understand the working of the different parts of the CDI box and try to inculcate how they work together in providing ignition to the engine. Hence we will be studying one of the crucial parts of our petrol automobile engine thoroughly.​

CDI box

​Being the successor of the magneto based system, CDI box is used in most of the small IC engine these days. It consists of a storage capacitor that is charged with a high voltage, and this charge is used to ignite the spark. CDI box is developed to overcome the biggest disadvantage of the IDI systems.

Inductive discharge ignition systems used to have the high inductance coils that make them take a long time in heating up. This made them not suited for the small engines. Hence to overcome this disadvantage CDI box was developed so that the time to ignite can be reduced and working of the engine can be improved. For the racing cars, small automobiles like bikes and scooters and for the rotator engines, which need high speed working of the engine capacitor discharge ignition was developed.

In the present world, it is the most widely used ignition system for motorbikes and some other high-speed automobiles and rotator engines.​

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Parts And Their Contribution In The Working Of CDI Box:

In this section of the article we will be inculcating about the different parts of the CDI box and also try to understand how they work. It is with the help of the working of these parts in an integrated manner that makes it possible for the engine to work with the high-speed. One can take a look at the points stated below and understand their working afterward.

1. Flywheel:

The flywheel is the magnetic part of the CDI box that is like a circular horseshoe magnate that spins around the crank shaft. Having its own North Pole and the South Pole, this part is magnetized during the manufacture of the CDI box. It is a large permanent magnet around the crank shaft.

2. Stator:

It is the plate around which the electrical coils or the wire are placed. These loops are responsible for giving the power to the automobile’s lights, battery charging circuits, and ignition.

3. Charging Coils:

It is one of the electrical coils around the stator that is responsible for providing current to the flywheel, condenser and sparks plug. It works in the following stated ways:

  • It produces a 6 volt of current that is required by the capacitor placed in the CDI box.
  • It supplies a single pulse power to the flywheel based on flywheel’s moment around the magnetic field.
  • For ensuring the smooth spark in the spark plug, the CDI box should be capable of absorbing the plus created by the charging coils in the CDI box.

4. Hall Sensor:

It is used to identify the Hall Effect produced at the flywheel. The hall sensor will sense the moment when the flywheel will change the magnet form the North Pole to the South Pole. When this event occurs, the hall sensor sends a pulse to the CDI box that will further dumb the energy from the charging capacitor into the high voltage transformer.

5. Timing Mark:

It is an arbitrary line that is responsible for the acceleration and the retardation of the CDI timing. It is the line that is shared by the stator and the engine case. It is the alignment point that indicates the time when the piston’s travel becomes equivalent to trigger pint on the flywheel and the stator. It is the indication of the time when the stator plate will more from left to right and hence changing the trigger point of the CDI box.

​Integrated Working Of The CDI Box:

Integrated Working Of The CDI Box:


​This section can be easily understood with the help of the points that have been explained below:

  1. The flywheel turns past to the charged coil making the coil to produce +6V and -6V of charge.
  2. This charge will pass through the rectifier present in the CDI box that is responsible for the taking the positive charge to the capacitor and dumping the negative charge.
  3. Then from the capacitor, the charge is passed to the condenser. This condenser will initiate the triggering point when it is fully charged.
  4. Triggering circuit consisting of a switch with the transistors will be triggered with a pulse is sent to the stator by the hall sensor.
  5. This triggering pulse will allow the stored charge to pass through a high voltage transformer consisting of the primary and secondary windings.
  6. Taking the current from the primary side and moving it to the secondary side the voltage is multiplied by the number of coils present at the secondary windings. It makes the tension to grow a thousand times of its original value.
  7.  This value makes it possible for the transformer to develop an arc through the air and hence lead to the ignition.

​All this happens in the fraction of seconds depending on the conditions of the condenser and the stator coil. With the little problem in the working, these two elements there can be the problem in the timing of the ignition that will naturally lead to poor performance of the engine.


​With the help of the above-stated points and explanation we have tried to inculcate you the solution to the query: “What does CDI box do?” we have told you that the CDI box is responsible for the ignition and hence timely and quick working of the motor or the engine.

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