Improvements relating to the Conversion of Alternating into Direct Electric Currents.
Year: 1889

page_text: Date of Application, 22nd Oct., 1889--Accepted, 7th Dec., 1889
COMPLETE SPECIFICATION,
[Communicated from abroad by NIKOLA TESLA, of New York, in the County and
State of New York, United States of America, Electrician.]
Improvements relating to the Conversion of Alternating into Direct
Electric Currents.
I, HENRY HARRIS LAKE, of the firm of Haseltine Lake & Co. Patent Agents,
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 :—
In nearly all the more important industrial applications of electricity, the current
is produced by dynamo-electric machines driven by power, in the coils of whier the
currents developed are primarily in reverse directions or what is known as alternating.
As many electrical devices and systems, however, require direct current, it has been
usual to correct the current alterations by means of a comminutator instead of taking
them off directly from the generating coils:
The superiority of alternating current machines in all cases where their currents
can be used to advantage, renders their employment very desirable as they may be
much more economically constructed and operated, and the object of this invention is
to provide means for directing or converting at will at one or more points in a circuit,
alternating into direct currents.
Stated broadly, the invention consists in obtaining direct from alternating currents,
or in directing the waves of an alternating current so as to produce direct or
substantially direct currents, by developing or producing in the branches of the
circuit including a source of alternating currents, either permanently or periodically
and by electric, electro-magnet or magnetic agencies, manifestations of energy or
what may be termed active resistances of opposite electrical character, whereby the
currents or current waves of opposite sign or direction will be diverted through
different circuits, those of one sign passing over one branch and those of opposite sign
over another.
The case of a circuit divided into two paths only may be considered herein inas-
much as any further subdivision involves merely an extension of the same general
principle.
Selecting then, any circuit through which is flowing an alternating current, let
such circuit be divided at any desired point into two branches or paths. In one of
these paths is inserted some device to create an electro-motive force opposed to the
waves or impulses of current of one sign, and a similar device in the other branch
which opposes the waves of opposite sign. Suppose for example, that these devices
are batteries, primary or secondary, or continuous current dynamo machines. The
waves or impulses of opposite direction, composing the main current, have a natural
tendency to divide between the two branches, but by reason of the opposite electrical
character or effect of the two branches, one will offer an easy passage to a current of
a certain direction, while the other will offer a relatively high resistance to the passage
of the same current. The result of this distribution is that the waves of current of
one sign will-partly or wholly-pass over one of the paths or branches while those of
the opposite sign pass over the other.
There may thus be obtained from an alternating current two or more direct
currents, without the employment of any commutator such as it has been heretofore
regarded as necessary to use. The current in either branch may be used in the same
way and for the same purposes as any other direct current, that is, it may be made to
charge secondary batteries, energize electro-magnets, or used for any other analogous
purpose.
Some of the various ways in which this invention may be carried into practice is

page_text: Illustrated diagramatically in the accompanying drawings the ngures of which are
hereinafter referred to.
Figure 1 represents a plan of directing the alternating currents by means of devices
purely electrical in character. A designates a generator of alternating currents
and B B, the main or line circuit therefrom.
At any given point in this circuit at or near which it is desired to obtain direct
currents, the circuit B is divided into two paths or branches C. D. In each of these
branches is placed an electrical generator which for the present may be assumed to
produce direct or continuous currents.
The direction of the current thus produced is opposite in one branch to that of
the current in the other branch, or considering the two branches, as forming a
closed circuit, the generators E F are connected up in series therein, one generator in
each part or half of the circuit.
The electromotive force of the current sources E and F may be equal to, or higher
or lower than the electromotive forces in the branches CD or between the points X
and of the circuit B B. If equal, it is evident that current waves of one sign
will be opposed in one branch and assisted in the other to such an extent that all of
the waves of one sign will pass over one branch and those of opposite sign over the
other. If, on the other hand the electromotive force of the sources E, F, be lower
than that between X and Y, the currents in both branches will be alternating, but the
waves of one sign will preponderate.
One of the generators or sources of current E or F, may be dispensed with, but it
is preferable to employ both, if they offer an appreciable resistance, as the two
branches will be thereby better balanced. The translating or other devices to be
acted upon by the current are designated by the letters G, and they are inserted in
the branches CD in any desired manner, but in order to better preserve an even
balance between the branches, due regard should be had to the number and character
of the devices as will be well understood.
Figures 2, 3, 4 and 5 illustrate what may be termed electro-magnetic devices for
accomplishing a similar result. That is to say, instead of producing directly by a
generator an electromotive force in each branch of the circuit, a field or fields of
force is established, and the branches led through the same in such manner that an
active opposition of opposite effect or direction will be developed therein by the
passage or tendency to pass of the alternations of current.
In Figure 2, for example, A is the generator of alternating currents BB, the line
circuit, and C D the branches over which the alternating currents are directed. In
each branch is included the secondary of a transformer or induction coil, which, since
they correspond in their functions to the batteries of the previous figure are designated
by the letters E F.
The primaries H H of the induction coils or transformers are connected either
in parallel or series with a source of direct or continuous current I, and the
number of convolutions is so calculated for the strength of the current from I that
the coils JJ, will be saturated.
The connections, are such that the conditions in the two transformers are of opposite
character, that is to say, the arrangement is such that a current wave or impulse
corresponding in direction with that of the direct current in one primary as H, is of
opposite direction to that in the other primary H³, hence it results that while one
secondary offers a resistance or opposition to a passage through it of a wave of one
sign, the other secondary similarly opposes a wave of opposite sign. In consequence,
the waves of one sign will, to a greater or less extent, pass by the way of one branch,
while those of opposite sign in like manner pass over the other branch.
In lieu of saturating the primaries by a source of continuous current, they may be
included in the branches C, D, respectively, and their secondaries periodically short-
circuited by any suitable mechanical devices, such as an ordinary revolving
commutator. It will be understood of course, that the rotation and action of the
commutator must be in synchronism or in proper accord with the periods of the
alternations in order to secure the desired results.

page_text: Such a disposition is represented diagrammatically in Figure 3. Corresponding to
the previous Figures, A is the generator of alternating currents, B, B, the line
and CD, the two branches for the direct currents. In branch C are included two
primary coils E, E¹, and in branch D are two similar primaries F, F¹. The corre-
sponding secondaries for these coils and which are on the same subdivided cores J or J¹,
are in circuits, the terminals of which connect to opposite seginents K, K¹ and L, L',
respectively of a commutator. Brushes bb bear upon the commutator and alternately
short-circuit the plates K and K and Land L¹ through a connection c. It is obvious
that either the magnets and commutator or the brushes may revolve.
The operation will be understood from a consideration of the effects of closing or
short-circuiting the secondaries. For example, if at the instant when a given wave
of current passes, one set of secondaries be short circuited nearly all the current flows
through the corresponding primaries, but the secondaries of the other branch being
open circuited, the self-induction in the primaries is highest and hence little or no
current will pass through that branch. If as the currents alternates, the secondaries
of the two branches are alternately short-circuited, the result will be that the
currents of one sign pass over one branch and those of the opposite sign over
the other.
The disadvantages of this arrangement which would seem to result from the employ-
ment of sliding contacts, is in reality very slight, inasmuch as the electromotive
force of the secondaries may be made exceedingly low so that sparking at the brushes
is avoided.
Figure 4 is a diagram partly in section of another plan of carrying out the
invention.
The circuit B in this case is divided as before and each branch includes tha coils
of both the field and revolving armatures of two induction devices. The armatures () P,
are preferably mounted on the same shaft, and are adjusted relatively to one another
in such manner that when the self-induction in one branch as C is maximum, in the
other branch Dit is minimum.
The armatures are rotated in synchronism with the alternations from the source A.
The winding or position of the armature coils is such that a current in a given direc-
tion passed through both armatures would establish in one, poles similar to those
in the adjacent poles of the field, and in the other, poles unlike the adjacent field
poles, as indicated by n, n, e, s, in the drawing.
If the like poles are presented as shown in circuit D, the condition is that of a
closed secondary upon a primary, or the position of least inductive resistance, hence
A half revolution of
a given alternation of current will pass mainly through D.
the armatures produces an opposite effect and the succeeding current impulse passes
through C.
Using this figure as an illustration it is evident that the fields N, M, may be
permanent magnets or independently excited and the armatures O, P, driven as in
the present case so as to produce alternate currents which will set up alternately,
impulses of opposite direction in the two branches D. C, which in such case would
include the armature circuits and translating devices only.
In Figure 5 a plan alternative with that shown in Figure 3 is illustrated. In
the previous case illustrated, each branch C and D contained one or more primary
coils, the secondaries of which were periodically short-circuited, in synchronisin with
the alternations of current from the main source A, and for this purpose a commutator
was employed. The latter, may, however, be dispensed with, and an armature with a
closed coil substituted.
Referring to Figure 5, in one of the branches, as C, are two coils M¹ wound on
laminated cores and in the other branches D are similar coils N¹. A subdivided or
laminated armature 0 carrying a closed coil R is rotably supported between the
coils MN as shown.
In the position shown, that is with the coil R¹ parallel with the convolutions of the
primaries NN, practically the whole current will pass through branch D, because
the self-induction in coils M¹ M' is maximum. If, therefore, the armature and coil

page_text: be rotated in synchronism with the alternations of the source A the same results are
obtained as in the case of Figure 3.
Figure 6 is an instance of what may be called in distinction to the others, a magnetic
ineans of securing the results arrived at in this invention. V and W are two strong
permanent magnets, provided with armatures V1 W₁ respectively. The armatures are
inade of thin laminae of soft iron or steel, and the amount of magnetic metal which
they contain is so calculated that they will be fully or nearly saturated by the magnets.
Around the armatures are coils E F, contained respectively in the circuits C and D.
The connections and electrical conditions in this case are similar to those in
Figure 2, except that the current source I of Figure 2 is dispensed with and the
saturation of the core of coils E F obtained from the permanent magnets.
In the illustrations heretofore given, the two branches or paths containing the
translating or induction devices are in each instance shown as in derivation one to
the other, but this is not always necessary. For example, in Figure 7, A is an
alternating current generator; B, B, the line wires or circuit. At any given point in
the circuit two paths as D D¹, are formed, and at another point two paths as C C¹.
Either pair of group of paths is similar to the previous dispositions with the electrical
source or induction device in one branch only, while the two groups taken together
form the obvious equivalent of the cases in which an induction device or generator
is included in both branches.
In one of the paths as D are included the devices to be operated by the current.
In the other branch as D is an induction device that opposes the current impulses
of one direction and directs them through the branch D. So also in branch C are
translating devices G and in branch C' an induction device or its equivalent that
diverts through (, impulses of opposite direction to those diverted by the device in
branch D.
A special form of induction device for this purpose is also shown. J Jare the
cores formed with pole pieces upon which are wound the coils M N. Between these
pole pieces are mounted at right angles to one another the magnetic armatures O P,
preferably mounted on the same shaft and designed to be rotated in synchronism
with the alternations of current. When one of the armatures is in line with the
poles or in the position occupied by armature P, the magnetic circuit of the
induction device is practically closed, hence there will be the greatest opposition to
the passage of a current through coils N N. The alternation will therefore pass by
way of branch D; at the same time, the magnetic circuit of the other induction
device being broken by the position of the arinature O, there will be less opposition
to the current in coils M, which will shunt the current from branch C.
A reversal of the current being attended by a shifting of the armatures the opposite
effect is produced.
There are many other modifications of the means or methods of carrying out this
invention, but it is not deemed necessary herein to specifically refer to more than
those described as they involve the chief modifications of the plan. In all of these it
will be observed that there is developed in one or all of the branches of a circuit from
a source of alternating currents an active (as distinguished from a dead) resistance,
or opposition to the currents of one sign, for the purpose of diverting the currents
of that sign through the other or another path, but permitting the currents of opposite
sign to pass without substantial opposition.
Whether the division of the currents or waves of current of opposite sign be
effected with absolute precision or not is immaterial to the invention since it will be
sufficient if the waves are only partially diverted or directed, for in such case the
preponderating influence in each branch of the circuit of the waves of one sign secures
the same practical results in many if not all respects as though the current were direct
and continuous.
An alternating and direct current have been combined so that the waves of one
direction or sign were partially or wholly overcome by the direct current, but by this
plan only one set of alternations are utilized, whereas by this system the entire current
is rendered available.
t

page_text: By obvious applications of this discovery, it is possible to produce a self-exciting
alternating dynamo, or to operate direct eurrent meters on alternating current
circuits, or to run various devices, such as are lamps, by direct currents in the same
circuit with incandescent lamps or other devices run by alternating currents.
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 be
by my foreign correspondent I declare that what I claim is :-
First. The method herein set forth of obtaining direct from alternating currents,
which consists in developing or producing in one branch of a circuit from an alter-
nating current source an active resistance to the current impulses of one direction,
whereby the said currents or waves of current will be diverted or directed through
another branch.
Second. The method of obtaining direct from alternating currents, which consists
in dividing the path of an alternating current into branches and developing in one of
said branches, either permanently or periodically, an electrical force or active resistance
counter to or opposing the currents or current waves of one sign, and in the other
branch a force counter to or opposing the currents or current waves of opposite sign,
as set forth.
Third. The method of obtaining direct from alternating currents, which consists in
dividing the path of the alternating current into branches, establishing fields of force
and leading the said branches through said fields of force in substantially the
manner set forth, whereby electro-motive forces of opposite direction will be produced
therein.
Fourth. The combination with the branches of a divided circuit carrying alternating
currents, of devices included in or connected with the said branches and capable of
developing or exerting an active opposition or electro-motive force counter to the
current waves of one direction or sign, as herein set forth.
1000
ed this na
22nd day
October 1800.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.