Electrical characteristics of spark generators for automotive ignition Page: 3 of 30
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REPORT No. 241
ELECTRICAL CHARACTERISTICS OF SPARK GENERATORSI FOR
By R. B. BRODE, D. W. R notra, and F. B. SILSBEE
This paper reports the results of an extensive program of measurements on 11 ignition
systems differing widely in type. The results serve primarily to give representative data on
the electric and magnetic constants of such systems, and on the secondary voltage produced by
them under various conditions of speed, timing, shunting resistance, etc. They also serve to
confirm certain of the theoretical formulas which have been proposed to connect the perform-
ance of such systems with their electrical constants, and to indicate the extent to which certain
simplifed model circuits duplicate the performance of the actual apparatus.
For several years the Bureau of Standards has carried on a study of ignition systems for
the National Advisory Committee for Aeronautics and other branches of the Federal Govern-
ment. Much of this work has been devoted to the solution of special problems of immediate
urgency, but throughout the work the need has been felt for the formulation of a systematic
basic theory of operation of such apparatus, and whenever opportunity permitted the work has
been directed toward the foundation of such a theory. National Advisory Committee for
Aeronautics reports No. 58, "Characteristics of High Tension Magnetos," and No. 123,
"Simplified Theory of the Magneto," together with Bureau of Standards Scientific Paper No.
424, "TMNathematical Theory of Induced Voltage in the High Tension M agneto," constitute
steps in this work. In 1922 a program of measurements was undertaken on a group of spark
generators for the purpose of determining (1) their performance under various conditions of
operation, (2) the electrical and magnetic characteristics of the apparatus, and (3) the extent
to which the theoretical relations set forth in the reports listed above could be applied to these
particular types of spark generators. The principal results of this investigation are here
The ignition systems used in this work were all of the jump-spark type, and included both
battery-coil and magneto systems. The systems were selected so as to give as great a variety
as possible in the arrangement of the magnetic circuit. A detailed description of the systems
will be found in the section under " Description of the spark generators studied," of this report.
In considering the results of this work it should be borne in mind that the tests given cover
only the electrical performance and not the mechanical quality of the apparatus, and further-
more that the data were all obtained with apparatus which was new and in good condition. In
finally judging the relative merits of different types of spark generators such features as mechan-
ical workmanship, resistance to wear, waterproofness, and other qualities which could be demon-
strated only by protracted endurance tests are of great importance. These factors, however,
have not been dealt with in the present paper. It should also be mentioned that, in order to
cover apparatus differing as much as possible in the type of magnetic circuit, machines have
been included which differ greatly in size and cost, and which would not normally enter into
competition with one another in any single application. Still another point that should be
1 Following British practice the term "spark generater" is here used to designate the electrical equipment which directly serves to produce the
ignition spark; and includes both the high-tension magneto and the battery, induction coil, and breaker of a battery-coil system.
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Brode, R. B.; Randolph, D. W. & Silsbee, F. B. Electrical characteristics of spark generators for automotive ignition, report, 1927; (digital.library.unt.edu/ark:/67531/metadc65894/m1/3/: accessed January 15, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.