A DC ignition coil works by using the principle of electromagnetic induction to step up a low DC voltage into a high-voltage pulse required to ignite a spark plug.
The Core Principle
At its heart, an ignition coil is a type of transformer that operates on DC voltage. The fundamental principle, as highlighted in the reference, is that when an electric current flows through an electrical conductor such as a coil of wire, it creates a magnetic field around the coil. An ignition coil uses this magnetic field and its subsequent collapse to generate a much higher voltage.
Components of a DC Ignition Coil
A typical DC ignition coil consists of several key components:
- Core: Usually made of laminated iron or ferrite material, it concentrates and strengthens the magnetic field.
- Primary Winding: This coil is made of relatively thick wire with fewer turns. It connects to the vehicle's low-voltage (typically 12V) electrical system.
- Secondary Winding: This coil is made of very thin wire with many more turns than the primary winding. One end is connected to the primary winding, and the other connects to the high-voltage output terminal for the spark plug.
- Casing: Protects the internal components and is often filled with insulating epoxy or oil.
The Working Process Explained
The process of generating a high-voltage spark involves a rapid sequence of events:
-
Building the Magnetic Field:
- Low-voltage DC current flows from the battery (or power source) through the primary winding of the coil.
- As per the principle, this current flow creates a magnetic field around the primary winding and within the core. The field strength builds as the current flows.
-
Collapsing the Magnetic Field:
- At the precise moment the spark is needed (timed by the vehicle's ignition system, like points or an electronic module), the current flow to the primary winding is suddenly interrupted or switched off.
- Without the current sustaining it, the magnetic field rapidly collapses.
-
Inducing High Voltage:
- The quickly collapsing magnetic field passes through both the primary and secondary windings.
- According to Faraday's law of induction, a changing magnetic field through a coil induces a voltage across it.
- Because the secondary winding has significantly more turns than the primary winding (often ratios of 50:1 or more), the voltage induced in the secondary winding is proportionally much higher than the voltage in the primary winding.
-
Spark Discharge:
- The induced high voltage in the secondary winding (often tens of thousands of volts) is directed to the spark plug.
- When this high voltage exceeds the dielectric strength of the air gap at the spark plug tip, it causes an electrical arc – the spark – which ignites the fuel-air mixture in the engine cylinder.
Primary vs. Secondary Winding
Understanding the difference between the two windings is crucial:
| Feature | Primary Winding | Secondary Winding |
|---|---|---|
| Wire | Thick wire | Thin wire |
| Turns | Fewer turns | Many turns |
| Voltage | Low voltage (e.g., 12V DC) | Very high voltage (e.g., 20kV+) |
| Current | Higher current | Very low current |
| Function | Creates magnetic field | Steps up voltage for spark |
Practical Insight
The speed at which the magnetic field collapses is critical. The faster the collapse, the higher the induced voltage pulse in the secondary coil. This rapid switching is typically handled by mechanical breaker points in older systems or by a transistor in modern electronic ignition systems.
In summary, a DC ignition coil leverages the electromagnetic principle of generating a magnetic field with current flow. By rapidly interrupting this current, it causes a swift collapse of the magnetic field, inducing a very high voltage in the secondary coil due to the significant difference in the number of turns between the primary and secondary windings, ultimately creating the spark needed for combustion.
