Extension Leaflet 330
1951
FARM ELECTRIC MOTORS
"Selection of Electric Motors"
by
B.  A.  McKenzie, Agricultural  Engineering
G. W. Isaacs, Agricultural Engineering
THE APPLICATION of electricity to the agricultural industry has been a determining factor in the type of life which farm people can
enjoy. Not only has it raised the general standard
of living, but it has also eliminated a large portion
of the hard work and drudgery of the occupation.
The electric motor has been the captain of the
team of electrical applications to lead the way to
easier ways of doing things. For instance; "an
electric motor, for 5 cents, will milk 20 cows, cool
25 gallons of milk, pump 1000 gallons of water,
or shell 20 bu. of corn." Yet, just as a captain of
a basketball team may not be qualified to guide the
football team, so may one type of electrical motor
not be fitted to do all the jobs it is called upon to
perform. You, as the coach of your team of motors,
should select them according to their abilities, just
as the coach of a team selects his players.
Types of Electric Motors
There are four main types of electric motors
which make the team normally found in agricultural
uses. These are (1) split phase start-induction run
(2) capacitor start-induction run (3) repulsion
start-induction run (4) and universal or series
wound motor. These types will be considered in
the preceding order.
The Split-Phase Motor—The split-phase start-
induction run motor usually ranges in size up to
one-half horsepower. The most common speed of
this motor is 1725 rpm. but it is available for other
speeds, namely 860, 1140, and 3450 rpm. It is
built to operate at a voltage of 115 or 230 volts,
but must be selected for the voltage desired.
The lower cost split-phase motors have high
starting currents which will often cause lights to
dim or fuses to burn out. The ability of this type
motor to start a hard-starting machine is extremely
low. It is, therefore, limited to easy-starting applications, such as household fans, washing machines,
shop tools, etc.
The better split-phase motors have lower starting
currents. These models are usually more efficient
than those of lower cost and are suited for applications on fans, blowers, stokers, etc.
A split-phase motor is usually reversible by interchanging the wires to the starting winding. This
type motor has few parts to give trouble, and with
the proper service and application, it should be relatively trouble free.
The Capacitor Motor—
The capacitor start-induction run motor is the
most popular type for
farm applications. It is
readily recognized by the
presence of the capacitor.
This unit looks like a
small can, and, in small
motors, is usually clamped to the motor frame.
See Fig. 1. In some of
the newer models, it is
located inside the motor
housing, but it is visible
through the ventilation
ports. On large motors,
the unit will often be
placed inside the terminal
box. Capacitor motors are
built to operate all but
the hardest starting loads,
and yet their initial cost
is relatively low.
Fig. 1. Three ways in
which the capacitor may
be attached to a motor.
First two pictures illustrate the method usually
used on small motors and
the third denotes the
method normally applied
to motors larger than 2
HP. Some small motors
enclose the capacitor in
the base plate.