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Page 104

| Ignition Coils |

| The ignition coil in the ignition system of an internal combustion engine is essentially a two-winding transformer having a primary of a few turns operating usually at 6 or 12 volts with a secondary of many turns of fine wire, from 40 to 100 times the number in the primary (Fig. 6-14). An iron core serves to strengthen the magnetic field. The primary is connected to a battery with a mechanism in the circuit to open and close the circuit periodically. The dc from the battery builds up the magnetic field; as the circuit is open, the field collapses and cuts the secondary, thereby inducing a voltage in the secondary coil. The secondary circuit is completed through a spark gap at the end of the sparkplug in the cylinder; the induced voltage is high enough to cause a spark to jump across the spark gap and ignite the gasoline and air mixture in the cylinder. |

| Figure 6-14 Ignition system for internal combustion engine. |

| It is obviously impractical to describe all types of transformers and their application. Examples of representative types have been included above. For other special types or applications, references should be made to more complete technical texts, manufacturers' data, and instruction manuals. |

| Review. |

| 1. Autotransformers have only one winding, the entire winding being used as either primary or secondary, while a portion of it serves as secondary or primary (Fig. 6-1). It is used where ratios of transformation are low, usually less than about 5 to 1, and where the electrical isolation between the primary and secondary circuit is not essential. |

| 2. In the autotransformer, only a portion of the energy is transformed, and the remainder flows conductively through its winding; hence, it can be |

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