Ignition Coil

Assignment

The ignition coil should convert a primary voltage of 12 V with several Amperes of current, into a high tension of 15000 - 30000 V at an accordingly lower current. For the following explanation, change over to the 'Older type'.

Function

The plus pole on the battery is connected to the igintion switch through terminal 15 (on the left). When closing the power switch, the terminal 1 (on the right) is connected to the earth, the primary circuit is now closed. In the following closing period the magnetic field is built up. It breaks down when the power switch is opened. The high tension flows through the cable 4 (center on top) and the high tension distribution to the spark plug.

In an ignition coil there is no visible movement. Here, there are two, very different windings coiled around the same iron core. The primary coil, supplied by the battery, causes changes in the iron core. It consists mainly of laminated iron plates which have easily changeable mini magnets, called dipoles. These are abruptly aligned by the magnetic field and cause in the second, the secondary winding, an induction voltage. If the magnetic field breaks down through the switching off of the primary current, this can be compensated, with a much higher voltage, e,g., at the spark plug.

By which amount the voltage is increased, depends on the ratio between the primary- and the secondary windings. Of course, the expected voltage increases also with the time which was available for the charging by the primary winding, or with the time taken for the change of the magnetic flow. Thus, e.g., the generated secondary voltage is distinctly higher, if it is connected to a spark plug in a dense medium. Even a greater drop in compression is noticable by the voltage deviation.

The primary winding can be recognised by the distinctly thicker wire with less coils, the secondary winding by its thin wire and great many coils. An ignition coil can, particularly through the primary windings, become quite warm, which is why this is more often installed around the secondary windings. Older ignition coils even have a fuse against overheating, this however, is only a protection against fire and cannot be reset. From the safety point of view, one should touch neither the primary- nor the secondary circuit during operation, the danger could be fatal … 02/10