Improvements in Alternating Current Motors.
Year: 1894

page_text: nate of Application, 23rd Oct., 1894-Accepted, 24th Nov., 1894
[Communicated from abroad by EDWARD ANDREWS CLARK, of Jamaica Plain,
Boston, in the County of Suffolk and State of Massachusetts, United States
of America, Broker.]
Improvements in Alternating Current Motors.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent
Agents, 45 Southampton Buildings, in the County of Middlesex, do hereby
declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement :-
It has long been known that when two coils are in proper relation to a magnetic
circuit an alternating current in one induces an alternating current in the other,
and motors on this principle have been devised, the field magnet coils being
commonly the primary coil, or the coil carrying the impressed current, and the
armature coils the secondary coil, or the coil carrying the induced current, but
such motors are practically worthless because of their lack of efficiency; that is
only a small per cent. of the power expended in generating the impressed current
can be given out by the motor. The apparently insuperable difficulty with all such
motors is that the induced current is necessarily altogether too great in quantity if
the resistance of the armature coils is as small, as it must be practically; for in
order to attain any approach to a commercial efficiency the difference of potential
between the terminals of the primary coils multiplied by the amperes in that coil,
must nearly equal the difference of potential between the terminals of the
secondary circuit multiplied by the ampere in that circuit; and if the amperes
in the secondary circuit be cut down by a resistance which is extraneous
to the armature coil forming part of the secondary circuit the result is excessive
waste of energy; and it is wholly unpractical to make the armature coil so that it
shall have in itself sufficient resistance.
My invention consists of a motor in which the secondary coils are in close relation
with one or more masses of iron between the poles of the field magnet, as will
hereinafter be explained.
In the accompanying drawing
Figure 1 illustrates one form of my invention, and
Figure 2 illustrates a modification.
A represents the field magnet; B its coils; D the armature core and F its
coils. The coils B are in circuit with a generator of alternating currents, and
therefore are in this case the primary coils. The coils F form two loops of
a closed circuit in the manner familiar in all closed circuit armatures; for the
brusbes G G¹ rest upon plates of the commutator H, and the contiguous ends
of any two contiguous coils go to the same plate of the commutator, so that
the current splits at the brushes one-half flowing through part of the coils, the other
half through the other part of the coils, as will be clear without further description.
The coils B are, of course, wound to produce opposite salient poles, and bence the
projections J J, shown in Figure 1, are not consequent poles, and must be without
polarity to serve their function, except that polarity due to induction from the
armature coils. It will also be clear that the adjustment of the brushes G G will
determine the direction of rotation of the armature; and, indeed, up to this
point I have described nothing more than has long since been suggested but
which is wholly inoperative, for were it not for the masses of iron J, J', the
current in coils B, and the current induced in the armature coils F would soon

page_text: heat them sufficiently to destroy their insulation, and make the machine worthless.
This will be clear if it be assumed that there are 100 turns in the field coils B, and
a like number in the armature coils F, and that a constant difference of potential of
50 volts be maintained between the terminals of the field coils, and if it also be
assumed that the wire used in the coils B and F be so small that it will have about
one ohm resistance, and that it will not bear more than 5 amperes of current
without becoming unduly heated. Under these assumptions the current in the
coils B and F would be nearly 50 amperes if the armature did not rotate, and if
the bodies JJ' were absent; and although the rotation of armature D will diminish
the current in coils B and F materially, it is practically impossible for armature D
to attain the very high speed necessary to diminish the current in coils B and F
sufficiently to prevent excessive heating of these coils. If the length of wire in
coils F be increased, to increase the resistance, the difference of potential between
the terminals of coils F will also be increased, as there will necessarily be more
turns or spires in coils F; and if the diameter of the wire in coils F be decreased,
to increase the resistance, the wire will be too small to carry the desired current.
I have discovered that if masses of iron J J¹ be used between the poles N S of the
field magnet, as indicated in the drawing, the current in coils F and B will be
reduced so that when the desired speed of rotation is reached the coils will not be
unduly heated, and what is still more important the efficiency of the motor will
be high.
My theory is that the self induction of those of the coils F which are between
the core D of the armature and the masses J J¹ of iron is so greatly increased as
to cut down the current flowing in the coils B and F.
I find in practice that it is not essential that the masses of iron J J¹ be connected
with the field magnet A; as they may be separated by a wide air gap from
magnet A as shown in Figure 2.
Whatever may be the correct theory, the fact is that the addition of the iron
masses J J cuts the current down in the coils B and F, and makes any extraneous
resistance in circuit with coils F unnecessary and also converts a machine which
would be self destructive and wholly worthless without the masses J J¹, into an
alternating current motor of marked efficiency at usual speeds.
I have shown masses of iron J and J' diametrically placed with reference to the
armature but obviously one mass will answer a good purpose, although the
diametrical position is better.
Another advantage of my invention is that I am able by reason of the use of
masses of iron J J'as above described to make the number of turns in the armature
coils F several times greater than the number of turns in the field coils B; thereby
greatly increasing the torque, and decreasing the requisite speed of the armature
to give the best results.
In a small motor with a difference of potential of 50 volts between the terminals
of the field coils B, and a total of about 200 turns in both field coils, I have used
over 400 turns in the armature coils; the brushes being connected by a conductor
of trifling resistance; so that the total resistance of the field coils was less than
one ohm, and the total resistance of the secondary circuit, the armature coils,
commutator brushes and conductor short circuiting the brushes, about two ohms;
and under these conditions the current in the field coils was about three amperes
when the arinature had a speed of about 2000 per minute; the current in the
armature coils being about one and a half amperes.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me by
my foreign correspondent, I wish it understood that I do not claim a motor com-
prising a field and an armature, with a commutator and brushes electrically connected
to close the secondary circuit through the armature coils, nor do I claim a field
magnet with salient and consequent poles, but what I clain is :-
An alternating current motor consisting of a field magnet with alternating and

page_text: opposite poles; a closed circuit armature and its core with alternating and opposite
poles; a commutator, and its brushes short circuiting the armature coils; and
masses of iron as J J¹ between the alternating and opposite poles of the field
magnet, to reduce the current which is induced in the armature coils by the
alternating current in the field coils substantially as set forth.
Dated this 23rd day of October 1894.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.