Tulsa daily world. [volume] (Tulsa, Indian Territory [Okla.]) 1905-1919, 1917-04-29

chine as above will not do. Then what
can be done to make the current
direct" II each end OF the wire
were fastened to half ring, as shown
IN Fig ?, the brush ID, as the wire
and half rings reVolve. would always
be rubbing against the half ring at
tached TO the wire cutting upward,
and the brush r. to the half ring
attached to the wire cutting down
ward. Thus the current would always
flow out (say) from the brush II and
so the current in the wire + would
be of direct current. or always flowing
IN one direction.
The half rings to which the ends
of the wire are attached would have
TO be separated by some insulating
material, so as to prevent the
brushes catching; to give strength
and to prevent dirt, oil etc, getting
between them and causing short
circuit. As you will see later. these
half rings are reduced TO small seq
ments of circles in practice. These
segments with the insulation be-
tween them are called the commu-
tatOr.
OF course, one loop of wire as
shown in Fig >, will not give suf-
ficient and a steady enough voltage
to be practical and so number of
loops arranged in a circle, as shown
in Fig. 3. are used. Instead of at
taching the ends of the loops to
large semicircular segment as in Fig.
?, a number of small segments are
used Sometimes each loop has its
own segment, hut more often a few
of the adjacent a loops are attached.
to one segment
For mechanical reasons, and also
to intensity the current generated,
the loops of wire are wound on "a
soft iron core This core is made
up of a large number of discs, or is
laminated The core with the loops
or winding is called the armature.
Figure 4 shows "A complete armature
with the commutator at the right.
So much for the armature Now
as to the magnets. You have had
brought to your attention two kinds
of magnets; namely, the permanent
magnet made of hard steel, and the
electro magnet, made of soft iron,
with coil of wire wound about It,
which is flowing thru the wire. The
latter type of magnet Is used in prac
tically all the generators used in the
starting and lighting systems of today.
From where can we get the cur
rent which must flow thru the wire
wound on this core? Why, from the
armature, as shown in Fig. g. Here n
wire is connected to one of the
brushes, then wrapped about one
core, then the other and then re-
turns to the second brush, while sep
arate wires go out of the machine TO
the battery, lights, etc. When por-
tion of the current is so shunted from
the main line, we say that the gem
orator is shunt wound. The coil of
wire around the magnets is called the
field coil, as the magnetic field is
due to 1t.
In stationary dynamos Cor gener-
ators) as are used in large power
plants and in some Of the small gem
orators used on the automobile, in
addition to the shunt winding as ex-
planned above, the main current, be-
fore leaving the machine, is first
made to flow thru few turns of wire
placed on the field magnets, the field
coil thus being in Series with the
outside units. Where the field coil
has two windings, one shunt and the
other a series, ii is said to be COM
| pound wound.
Perhaps a question has come to
| you, namely. il the current generated
| by the armature is due to the arma-
| ture windings cutting thru the mag
! netic field, and IL the core is magnet
! only when current is flowing thru its
| stopped, there will be no magnetic
| field, as no current will be flowing
! thru the field coils and so when the
| armature is started revolving there
will be no field and so no current will
| be generated. This problem is taken
care of by having the material of
which the core is made such that
| once II is magnetiZed ii will always
retain a small amount of magnetism,
| nc ~
| yield n slight current at starting and
then this current, by flowing thru the
| field coils, will increase the magnet
ism, this magnetism thus being built
| up until the maximum, for that speed
of armature revolution, Is reached.
! In some generators instead of there
| being only two magnets with their
coils, there are four, six, eight, etc.
placed equal distances apart, in cir
Gle, the first being a positive pole, the
| second negative. next positive, next
negative and so on.
As to the collector brushes which,
by rubbing against the commutator,
collect the current generated by the
armature? These, while sometimes
made of copper. are most always
made of prepared carbon. In order
to allow for wear, they are mounted
in pivoted arm or in such n way
that they can slide back and forth,
and are held against the commutator
by means of springs.
The generator armature and field
coils will practically never give trou-
BILE, but the commutator and brushes
will sometimes be the cause of the
generator giving but little or an irreg-
ular current. In time the brushes
will wear out and will have to be re-
Observation-Disclosures