Modeler's Corner

Winding Coils, Part II

| December 2005

Hello again, everyone. This month we will go through part two of David Metzs' letter on coil winding. Last month he explained Ohm's Law and how it applies to ignition coils. This month he discusses resistance, measurements and tolerances. Next month we'll get back to normal and I'll have more on the Gade build. Is this hobby great, or what?

Wire Resistance

David Metz writes: Let us now go back to the beginning and look at wire resistance. The resistance of a conductor is directly proportional to its cross-sectional area. My wire chart doesn't give figures for 18-1/2-gauge, but it does give the following for standard 18-gauge enamel covered wire:

Ohms per 1,000 feet = 6.3860 ohms
Current carrying capacity in bundles: 10 amps

To obtain more resistance for a given wire diameter, you have to use more wire. Or, to obtain more resistance (and more inductance) you can use a smaller diameter wire. Let's look at 20-gauge wire:

Ohms per 1,000 feet = 10.1280
Current carrying capacity in bundles = 7.5 amps

Thus, with a smaller wire, you would have more resistance for a given volume of wire, and since you can fit more turns on the core, you would have more inductance, giving you more "kick" to make your spark.