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Ignition Coil and its working


Ignition coils supply the high voltage required by the ignition system to ignite the spark plugs. Most engines with a distributor ignition system use a single-coil, but a few import applications use two coils. Multiple ignition coils are used in distributorless ignition systems (DIS). Each pair of cylinders in a “wasted spark” system shares a lock. Each cylinder or spark plug in other DIS and coil-on-plug (COP) ignition systems has its coil.

How to test ignition coil and the functions of ignition coil as a high-voltage transformer. It raises the primary voltage of the ignition system from 12 volts to thousands of volts.The actual firing voltage required to create a spark across an electrode gap in a spark plug is determined by the width of the opening.

The electrical resistance in the spark plug and plug wires, the air/fuel mixture, the engine load, and the temperature of the spark plug. As a result, the voltage required varies constantly and can range from 5,000 volts to 25,000 volts or more. Under peak demand, some systems can generate up to 40,000 volts.


Each coil has two sets of windings wrapped around a laminated or segmented iron core. The primary windings, which number in the hundreds, are connected to the coil’s two external low voltage terminals. The positive (+) primary terminal is linked to the ignition switch and battery, while the negative (-) primary terminal is related to the ignition module, which serves as a ground. The secondary windings, which have thousands of turns, are connected at one end to the primary positive terminal and at the other end to the high voltage secondary output terminal in the coil’s centre.

The secondary to primary windings ratio is typically around 80 to one. The higher the percentage, the higher the coil’s potential output voltage. Thus, the balance of performance ignition coils generally is higher than that of standard locks.

Current flows through the primary windings when the ignition module closes the primary coil circuit and provides ground. This generates a powerful magnetic field around the iron core and charges the coil. The magnetic field reaches maximum strength in about 10 to 15 milliseconds Yt5s.

Voltage that required

The ignition module then opens the ground connection of the coil and turns off the primary coil windings. As a result, the magnetic field abruptly collapses. The stored energy in the magnetic field has to go somewhere, so it induces a current in the coil’s secondary windings. This multiplies the voltage up to 100 times or more, depending on the ratio of wire turns until there is enough voltage to fire the spark plug.


Ignition coils are extremely tough and dependable, but they can fail for a variety of reasons. Heat and vibration can cause shorts or openings in the primary or secondary windings by damaging the coil’s windings and insulation. The most common cause of ignition coil failure is voltage overload caused by faulty spark plugs or plug wires. 

If a spark plug or plug wire is open or has too much resistance, the output voltage of the ignition coil can rise to the point where it burns through the coil’s internal insulation, resulting in a short. Many coils’ insulation can be damaged if the output exceeds 35,000 volts. When this happens, the coil’s output voltage may drop, resulting in ignition misfire when the engine is under load, or the ring may stop producing voltage, preventing the engine from starting or running.

If a coil has battery voltage at its positive terminal and is being grounded on and off by the ignition module or circuit but does not produce a spark, the coil is faulty and must be replaced.


When a coil on a distributor ignition system fails, it affects all cylinders. When under load, the engine may not start or may misfire severely. The misfire may also jump from one cylinder to the next. 

A single-coil failure, on the other hand, will only affect one cylinder on an engine with a distributorless ignition system (DIS) or a coil-on-plug (COP) ignition system (or two cylinders if it is a DIS waste spark system where two cylinders that are opposite each other in the firing order share the same coil). This article was all about how to test an ignition coil.

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