March 1948 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
AC alternators replaced DC generators
back in the 1940s as demand for conditioned electrical power in vehicles rose beyond
that needed for ignition and lighting. Radios are the most notable additions, and
because amplitude modulation (AM) broadcasts were the dominant method of the day
for commercial stations, noiseless electrical supplies were required. Spark-induced
noise from ignition systems was bad enough since its frequency varied with engine
RPM, but the DC generator's commutator sparking noise - much of it right smack in
the audio frequency range - was just too much for the public to endure if widespread
acceptance of radio was to be realized. Remember that in the era, a radio was not
standard equipment in cars and trucks so customers needed to be convinced the extra
expense would be worth their hard-earned dollars. Use of a 3-phase alternator reduces
the component performance requirements for conversion to DC.
A. C. Generator for Automobiles
The alternating current motor car generator.
Rectifier shown in the schematic at bottom.
The old problem of how to maintain adequate charge in the automotive storage
battery used to operate mobile radio equipment and public address systems appears
to have been solved through the use of an a.c. alternator to replace conventional
d.c. generating equipment. Application of the alternator in combination with a voltage
regulator and dry disc rectifier results in obtaining much higher electrical output
at all engine speeds.
This new a.c. generating system was developed by The Leece-Neville Company, of
The use of d.c. in automotive equipment came about as the simplest solution to
the problem of a portable power supply: the wet cell type battery.
To eliminate the constant design compromise required in a d.c. generator, and
at the same time solve the problem of a flat output curve for wide variations of
engine speed, the designers turned to an alternator. Output of the alternator is
taken from a 3-phase stator, thus eliminating sparking and brush wear, the 2 major
problems of commutation in a d.c. generator. The stator is Y-connected, giving a
voltage conversion factor of 1.732 times that of any single leg. This a.c. output
is applied to the 3-phase full-wave rectifier unit, composed of pre-aged magnesium-copper-sulphide
plates which in effect replace the commutator of a d.c. generator, since d.c. output
The control unit of the system is composed of 3 sections: a voltage regulator;
load limiter; and load relay. The voltage regulator and load limiter are connected
to control the field current of the rotor as a function of load voltage or current
regardless of engine speeds above 575 r.p.m., and load demands within the capacity
of the system, where the alternator ratio is 2:1.
The Leece-Neville a,c. generating system provides a flat performance curve of
60 amperes from 11 1/2 m.p.h. up to a maximum speed of 120 m.p.h. with a 35-ampere
capacity at engine idling speeds. This is in comparison with the heavy-duty generator
system most commonly in use with the following performance: maximum output of 40
amperes from 19 1/2 m.p.h. to 53 m.p.h., and an 18-ampere output while idling at
450 revolutions per minute.
AC Generator &
Posted January 30, 2015