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What Are Motorcycle Ignition Systems and How Do They Work

What Are Motorcycle Ignition Systems and How Do They Work

1. Motorcycle Ignition System

Modern motorcycles are a marvel of engineering. There are several systems working together to ensure a motorcycle runs smoothly. One of the most essential systems is the motorcycle ignition system. The main function of the motorcycle ignition system is to produce a spark to burn the fuel and air mixture within the combustion chamber. Though this system sounds simple, it is actually quite complex and requires several components to function.

Continue reading this article to learn about the different types of ignition systems and how they work.

2. Motorcycle Starting System

The motorcycle starting system is a separate part responsible for starting ignition by powering the ignition system. There are two types of motorcycle starting systems: the kick-starter and the self-starter systems.

2.1 Kick-Starter System

When the kick-starter lever is forced downward by your foot, a gear attached to it slides until it comes in contact with the freewheeling gear. As the kick-starter lever is forced further downward, the force is transferred to the freewheeling gear thanks to the helical spline. The freewheeling gear then activates the clutch hub, which is connected to and transfers power to the engine.

2.2 Self-Starter System

The self-starter system includes a battery-powered motor that starts spinning the engine. Once the engine starts, the battery-powered motor has to be disconnected from the crankshaft to prevent damage due to excessive speed.

The battery-powered motor is disengaged using a one-way clutch.

3. Types of Motorcycle Ignition Systems and How Do They Work

3.1 CDI (Capacitor Discharge Ignition) System

AC-CDI (Alternating Current – Capacitor Discharge Ignition)

The Alternating Current - Capacity Discharge Ignition (AC-CDI) is a capacitive discharge type magnetic motor ignition that utilizes a magnetic motor to produce a current. A spark plug requires 20,000 Volts to produce a spark at the firing end. In an AC-CDI system, the voltage comes from the motorcycle’s stator. A stator is an assembly of stationary coils. The magnets attached to the flywheel rotate around the coil of wires; as they move, they produce alternating currents due to the change in magnetic flux. There are different output terminals on the stator for different purposes, including:

  • To power the ignition system and create a spark
  • To charge the battery
  • To power the lights
  • To provide neutral/ground terminal

Exciter Coil

The exciter coil has thinner wires and denser winding that help produce a high voltage and create an alternating current to power the ignition system.

CDI Unit

The exciter coil’s output terminal is connected to the CDI unit, a component that stores and releases the electric charge when required. Also attached to the stator is the pickup coil, which signals the CDI unit when to release the electric charge stored in the capacitor. The pickup coil has a magnet with a wire coil wrapped around it. Facing the pickup coil every time the flywheel spins is a small extrusion on the outer surface. When the extrusion approaches the coil, it produces a voltage that is transferred back to the CDI unit. This voltage helps close an electric switch on the CDI unit, known as the Silicon Controlled Rectifier (SCR). The stored charge in the capacitor is released through the CDI unit’s output terminal.

The CDI unit is also connected to the ignition coil, which includes a step-up transformer installed to multiply the input voltage 200 times over. The increased output voltage then produces a spark at the spark plug.

The flywheel’s magnets revolving around the stator coil can produce 20 volts AC at 1,000 rpm and 50 volts AC at 3,000 rpm. The output terminal that charges the battery is connected to a voltage regulator, also known as a voltage rectifier. This converts the fluctuating AC voltage to the DC voltage that is used to charge the battery.

There are two electrodes on the spark plug: the firing and the ground electrodes. The distance between these two electrodes is usually between 0.5-0.7 mm, allowing the high voltage to jump from the firing electrode to the ground electrode and create a spark.

3.2 DC-CDI (Direct Current – Capacitor Discharge Ignition)

The Direct Current - Capacitor Discharge Ignition (DC-CDI) system works similarly to the AC-CDI, except the capacitor is charged using a battery. When the electric power from the battery is interrupted, the capacitor discharges the voltage, which travels to the ignition coil. The ignition coil increases the voltage level using a step-up transformer and sends it to the spark plug to produce a spark.

4. TCI (Transistor Controlled Ignition)

The Transistor Controlled Ignition (TCI) system uses a transistor to produce a high-voltage spark when the engine is compressing. It also has a contact breaker that functions as an anchor the moment the spark is created. A transistor has three terminals: a collector, a base, and an emitter. The collector acts as the input voltage terminal and the emitter acts as an output voltage terminal. The base terminal acts as a switch that allows the electrical current to pass from the collector to the emitter. The base terminal is connected to the contact breaker and only draws a small amount of the electrical current when the circuit is closed.

When the ignition switch is on, the contact breaker also closes and allows a small amount of the electrical current to pass through the base, which in turn allows the high current to pass through the emitter. The emitter is connected to an ignition coil that acts as a transformer and increases the voltage. When this high current flows through the primary coil, it creates a constant magnetic field. Due to the engine’s cam, the contact breaker opens and the current flowing through the collector and emitter is cut off as there is no longer a current passing through the base. This will result in a change in the magnetic flux that produces a high voltage in the secondary coil. This high induced voltage produces a high-voltage spark at the spark plug, resulting in the combustion of air/fuel mixture within the engine.

5. What Happens Next?

The intake valve allows the air/fuel mixture to enter the combustion chamber, pushing the piston downwards. The piston then rises and compresses the air/fuel mixture. The spark produced between the firing and ground electrodes of the spark plug ignites the compressed air/fuel mixture and pushes the piston downward. The exhaust valve then opens, the piston rises again, and the burnt gases are forced out of the combustion chamber, resulting in continuous piston movement. The continuous piston movement power the rear wheel.

6. Final Words

A motorcycle ignition system is a core system that powers the engine. For a motorcycle to operate smoothly, the spark plug must provide an adequate voltage of up to 20,000 volts. The TCI system lasts longer as the high current does not damage the breaker points indirectly attached to the ignition coil. It produces the magnetic flux in less time and the spark’s intensity is much higher than the DCI system. Meanwhile, the AC-DCI magneto ignition system is best suited for traveling at medium or high speeds as it requires less maintenance.

Motorcycles last longer if they are well-maintained and worn parts are replaced. An old or faulty spark plug should be replaced to avoid damaging the engine. A well-maintained motorbike should also look good and ensure a comfortable, smooth riding experience. Viking Bags has several aftermarket parts, including sissy bars, crash bars, handlebars, fairings, and comfortable seats. You can also improve the storage capacity of your motorcycle by installing saddlebags and sissy bar bags.

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