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
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 Cleveland, Ohio.
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
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 is
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 & Rectifier Schematic
Posted January 30, 2015