While some import electronic ignitions mount a power transistor directly onto the coil, the power transistor in most ignitions is incorporated into a separate Dwell angle and duty cycle begin when the primary circuit is grounded and ends when the primary circuit is interrupted. The primary circuit on-time is generally referred to as “dwell angle” on distributor ignitions and “duty cycle” on distributorless ignitions. The PCM then commands the power transistor to interrupt the primary circuit and collapse the magnetic field, which then creates an ignition spark. To create a spark, the power transistor is commanded by the powertrain control module (PCM) to form a magnetic field in the coil by grounding the primary circuit.Ĭoil “saturation” occurs as the magnetic field is formed. Primary Notes An ignition coil primary circuit includes the battery voltage or B+ terminal attached to a 12-volt current source and a ground or B- terminal attached to a power transistor that controls primary current flow. In general, lean A/F ratios and high cylinder pressures tend to increase the voltage requirement at the spark plug. Keep in mind that the actual output voltage of the coil depends upon the air/fuel (A/F) ratio and the running compression of the engine at the spark plug gap. When the current flowing through a few hundreds of turns of primary winding is interrupted, the resulting magnetic field collapses into many thousands of turns in the secondary winding.īy “cutting” the magnetic field many thousands of times, the secondary winding multiplies or transforms low battery voltage into the voltages needed to create an ignition spark. Whatever the configuration, an ignition coil has three parts: a primary circuit, a secondary circuit and a soft-iron core.Ī magnetic field is created around the soft-iron core when an electric current flows through the primary circuit or winding. Keep in mind that, because many different factors affect the voltage multiplication process, the ultimate voltage output will vary according to design and operating conditions. To illustrate, an oil-filled ignition coil might require about 4 amperes of current at 12 volts to produce 20-30 kilovolts (kV), while a modern e-core or coil-on-plug configuration might require about 7 amperes of current at 12 volts to produce 30-60 kV of high-intensity spark. Whatever the configuration, an ignition coil creates a spark by transforming amperage into volts.
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