An automotive coil seems like a very unique component and could have a great deal of applications, especially if it could be used as a (very tough, resilient) step up transformer.
It seems that an automotive coil is designed to work with DC, yet from it's design (I'm talking about the old standard, oil filled cylinder type w/ primary & secondary, etc) - superficially, it seems like a transformer. Could it handle AC as well? Does anyone know anything about it's design history?

 

Google offers up 1,900,000 hits on "ignition coil". This link is pretty informative - http://www.familycar.com/CLASSROOM/ignition.htm.

The structure is a bit odd internally, as the primary and secondary share a common point. This makes it more like an autotransformer. As the coils are not ohmically isolated, it cannot be used as a conventional transformer.

 

It is a true transformer, but it was not designed for continous service. It was designed for the short bursts of current it gets from a car. Feed it that and it is happy.

I have burned up my share making electric fences.

 

Many of the early electronic ignition systems merely used the ignition coil as a step up transformer for power invertor.

As such they were subject to continuous duty. Of the several I built, the Marston circuit proved the most successful, running for the several years I had the vehicles involved, in the late 1960s and early 1970s.

Essentially they worked by improving the energy supply available to the spark plug in what was known as a capacitive discharge ignition.