The car ignition system primarily uses DC (Direct Current) from the car's battery to power the ignition coil.
How Car Ignition Works with DC
The ignition system relies on a 12V DC source, typically the car battery. Here's a simplified breakdown:
- Battery Power: The 12V DC from the car battery is the initial power source.
- Ignition Coil: This DC current is fed into the primary winding of the ignition coil. The primary winding has few turns and low resistance, allowing a large DC current to flow.
- Creating High Voltage: The key element is the rapid switching of this DC current. When the current is interrupted (by points in older systems or a transistor in newer systems), the magnetic field in the coil collapses. This collapsing magnetic field induces a very high voltage in the secondary winding of the ignition coil.
- Spark Plug Ignition: This high-voltage pulse is then sent to the spark plugs, creating a spark that ignites the air-fuel mixture in the engine cylinders.
Why DC is Used Initially
- Availability: The car's electrical system is fundamentally a DC system. The battery provides DC power, and the alternator generates DC power (which is rectified from AC).
- Simplicity: Using DC simplifies the initial energizing of the ignition coil.
Important Clarification: The Induced Voltage is a Pulse, Not Sustained AC
While the rapid switching of the DC current creates a pulse of high voltage, this isn't the same as alternating current (AC). AC continuously reverses its polarity, while the high voltage created in the ignition coil is a short-duration pulse in one direction. The change in the magnetic field (which produces the pulse) is caused by switching DC.
In summary, while the effect of the ignition coil might seem similar to a step-up transformer in an AC circuit (because it produces a much higher voltage), the fundamental power source is DC, and the voltage generated is a high-voltage pulse resulting from the interruption of the DC current.
