Design of an NGK double spark coil

Schematic diagram of the winding ration for ignition coils
Winding ratio for ignition coils: 1:150 to 1:200

Primary coil: made of copper wire, which is thicker in comparison with that of the secondary coil. However, the coil itself is shorter than the secondary coil; to put it another way: It has fewer windings than the secondary coil

Secondary coil: also made of copper wire, which is of a thinner consistency than that of the primary coil. An additional significant feature of this components is the number of windings, which is considerably greater in relation to the primary coil.

Diagram of the inside of an NGK double spark coil
Cross-section of a double spark coil

In order to prevent electric discharge and spark-overs in the interior of the coil or outward, the wires of the primary and secondary coils must be insulated.

This is satisfied by the quality of the winding on one hand, and the mould compound on the other hand

A high-quality winding of the coil can be seen in the cross-section, whereby the wires are precisely arranged above one another, so that there is no recognisable spacing between them.

Mould compound: With all coils, except for the cylinder coils, an epoxy resin is used for this purpose - cylinder coils are normally filled with oil. By nature, the resin only liquefies at very high temperatures, therefore the potting of the ignition coil plays an especially important role in the production, because no air bubbles may form in the mould compound and the components are subjected to a very high thermal load.

Magnetic core: The magnetic core represents a key component of the ignition coil. It is laminated, which implies that it is usually comprised of several thin ferromagnetic sheets.
The primary purpose of the magnetic core is the formation of the magnetic field in the ignition coil, which is amplified as soon as voltage is applied. Energy is stored in the magnetic field. As long as the primary current is not switched off, the coil is referred to as being charged.

Diagram of an NGK double spark ignition coil
Cross-section of a double spark coil

High-voltage connection: Depending on the angle at which it is viewed, this connection is the end of the secondary coil or the connection point to the distributor and/or spark plug. Through this connection, the ignition voltage travels to the spark plugs, where a spark-over occurs.

With distributor and block coils, the ignition voltage travels over the ignition cables to the spark plugs. As the term distributor coil suggests, an additional distributor is required for this purpose. Pencil coils, on the other hand, sit directly on the spark plugs. An ignition cable is then only required when the ignition coil generates ignition energy for a second spark plug.

Terminals 1 and 15: Low-voltage connections/ minus(1)- and plus(15)terminals. The ignition coil is provided with current through these terminals.