IGNITION PRIMARY CIRCUIT

The function of the ignition primary circuit is to deliver current to the coil primary winding, allow collapsing of the coil primary and dissipation of all the excess voltage. A failure within the primary circuit can be the cause of a failure in the ignition secondary. Always perform a thorough check on the ignition primary before condemning any secondary components. Without a correct voltage source and proper switching, the secondary will not function correctly.

A typical ignition primary circuit consist of the following components : battery, ignition switch, ballast resistor, loom resistor ( some models ), ignition coil, a sensor to switch the primary on and off ( breaker points, pickup coil, hall effect sensor ), a condenser ( points ignition ), a noise suppressor, and a module which houses a switching transistor ( electronic ignition ), that controls the primary circuit to ground.

Battery : The available battery voltage determines the amount of energy in the ignition primary circuit .An undercharged battery lessens the available voltage in the ignition primary which in turn reduces the secondary output.

Ignition Switch : Power for the entire ignition system is via the ignition switch.Excessive resistance in the switch could cause a low primary circuit voltage and this in turn affects the efficiency of the entire ignition system.

Primary Resistor ( ballast or loom resistor ) : These resistors reduce the current within the primary circuit to prevent breaker point arcing and in some systems to protect other components within the ignition system. Because battery voltage is reduced when the starter is cranking the resistors are usually bypassed when the starter is engaged.

Ignition Coil : The ignition coil acts as a transformer. Current flowing through the coil primary windings creates a magnetic field which surround the secondary windings. This occurs when the breaker points ( points ignition ) are "closed" and while the transistor ( electronic ignition ) is "on". When the primary circuit is interrupted ( points "open" or transistor switches "off" ), the magnetic field collapses and a high voltage is induced in the secondary windings. The high voltage is then directed to the correct spark plug by the distributor cap and rotor.

Breaker points : Within the distributor is a cam mounted on the distributor shaft. The mechanical points are opened and closed by the rotation of the cam. The time the points are closed is termed "dwell". At this time primary current flows and coil saturation begins .A longer "dwell" creates better coil saturation which results in a higher secondary voltage.

Condenser : Used in breaker point ignition systems to prevent arcing across the contact faces as the points open and to dampen the high voltage spike induced in the ignition primary when it collapses. If the contacts were allowed to arc, premature failure of the contacts would occur resulting in poor vehicle performance or a no start condition.

Electronic Ignition Primary Components

Due to increased demand for better fuel economy and stringent emission standards electronic ignition systems are used. By utilising a better control over higher voltage output for a longer duration these standards are being met. Many electronic ignition systems also adjust timing and vary the dwell according to engine speed and primary source voltage.

Components that make up a typical electronic ignition systems include : Ignition module or igniter, armature wheel/magnetic pickup and a hall effect switch.

Armature/Magnetic pickup : The armature is fitted to the distributor shaft instead of a cam. The armature has one trigger arm per cylinder. A magnetic sensor, located next to the armature wheel generates a magnetic field. When the point of the trigger arm passes by, a voltage is induced in the pickup which then signals the ignition module to interrupt the current flow to the coil.

Hall Effect Switch : The Hall Effect will produce a voltage when the sensor is in a magnetic field. This type of distributor has a fixed permanent magnet and a sensor with a narrow air gap between them. If the shutter ( sometimes a part of the distributor rotor ) is between the sensor and the magnet, the magnetic field is interrupted and zero voltage occurs, signalling the ignition module. As the shutter moves away from the air gap, voltage is again produced.

Ignition Module : This is a solid state device that switches the primary current on and off based on the signals from the magnetic pickup. In most applications, the module varies dwell with engine speed and controls ignition timing.

Electronic ignition systems have been developed greatly over the years to increase ignition system performance and reliability. Types of systems include : Breaker Triggered Inductive Ignition, Pulse Generator Ignition, Hall Generator Ignition, Capacitor Discharge ignition, Electronic Spark Timing Ignition, Thick Film Intergrated Ignition and the latest innovation is the Distributorless Ignition System.