Since the battery ignition system in early gas engines is a subject covered by few present-day publications, this information is being presented here especially for the old time gasoline engine enthusiast.
The earliest system was the low voltage make-and-break battery ignition system using a "kick-coil," which consists of a single winding of insulated copper wire on a soft iron core. The main disadvantage of this system was the difficulty in maintaining the mechanical actuating linkage, as well as the resultant low-voltage spark produced. The standard power source in the past consisted of four or more number 6 dry cells, however for present-day service a 6-volt storage battery works very well. When the internal breaker points close, an electric current flows through the circuit. Then when the points opened, self-inductance in the kick-coil caused an induced current to flow for an instant, in the form of a spark, across the gap between the points. This self-inductance is the result of a rapid breakdown of the magnetic flues-flux field within the induction ('kick') coil which causes an induced voltage, many times greater than the original 6 volts, to be built up within the winding of the coil. This induced voltage may run as high as 200 to 300 volts, depending on the size of the coil.
The high-voltage ignition system was an improvement over the low-voltage system, in that not only was a much hotter spark achieved, but the moving contact points were removed from within the cylinder. This system utilizes two electric circuits instead of one. The primary circuit consists of a 6-volt battery, switch, a primary winding on a soft iron core, vibrating breaker points with a condenser shunted across them, and a timer. The operation of the primary circuit is similar to the low-voltage system, except that the internal contacts with accompanying linkage has now been replaced by a much simpler timer. The build-up of voltage within the primary, instead of arcing across the timer or vibrating points, charges the condenser which then discharges back through the primary coil after the points have opened. This discharge back through the primary coil aids in the rapid change and reversal of the magnetic flux which in turn induces a current of 10,000 to 20,000 volts into the secondary coil, which in turn produces a series of very hot sparks across the points of the spark plug. In these engines as well as with the early slow-running automobile engines, a coil assembly with vibrating points was used in with the slow moving timer, so that instead of getting just one spark across the points of the spark plug (as with the modern high-speed multi-cylinder engines) several sparks jumped the gap during the period of time that the points of the timer were in contact, thus better insuring ignition of the gas-air mixture.