A New or Improved Method of Converting a Direct or Continuous Electric Current Into an Alternating Current, and Improvements in or relating to Apparatus therefor.
Year: 1890

page_text: Date of Application, 21st Jan., 1890-Accepted, 22nd Feb., 1890
COMPLETE SPECIFICATION.
A New or Improved Method of Converting a Direct or Continuous
Electric Current Into an Alternating Current, and Improvements
in or relating to Apparatus therefor.
A communication from abroad by Ludwig Gutmann, of Pittsburgh, Allegheny County,
State of Pennsylvania, United States of America, Electrical Engineer.
I, WILLIAM PHILLIPS THOMPSON F.C.S. M.I.M.E., of the Agency for Foreign Patent,
Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street, Manchester both in the
County of Lancaster, and 323, High Holborn in the County of Middlesex, Civil
Engineer, 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:―
Heretofore it has been common to generate alternate or alternating electric currents
by means of the well known alternating electric current generator, or by merely
rapidly reversing the direction of any given electric current from a direct current
generator such as a dynamo or galvanic battery.
This device relates to or, rather, embraces means for changing a direct or continuous
current into an alternating current which is not only merely alternating but resembles
in every respect the alternating current generated by the well known alternating
current generator. The current obtained by the invention is not simply constituted
of impulses of alternate direction, but each impulse varies gradually from zero to
maximum of the given strength of current of the direct current dynamo or battery,
and then gradually from maximum to zero.
In the accompanying drawings the invention is fully illustrated so that it can be
constructed by those versed in the art.
Figures 1, 2, 3, and 4, show the device in the successive stages or phases reached
during the rotation of the shaft upon which the device is mounted.
Figure 6 represents the normal condition of the device.
Figures 5 and 7 are modifications of the device illustrating that the domain of
the invention is not confined to the exact construction shown in the remaining
Figures.
j
The normal condition of the device is first described, reference being had to
Figure 6. It may be noticed that the system therein shown consists of the com-
bination of two commutators a and b fixed upon a common shaft c, and suitably
insulated therefrom; a continuous or direct current generator or dynamo or electric
battery (primary or secondary) d of which a portion, such as two of the cells, is in
circuit with the small motor e, employed in rotating the shaft c through the medium
of the belt and bearings g for the shaft c.
The commutator a consists of the com-
bination of two conductor discs h and i, having respective projections h¹, h" and h
etcetera, and , i", and 111, etcetera, which discs and projections are separated by
insulating pieces j, j and j¹¹, etcetera, which are equal in width to the plates or
projections, 11, and 111, etcetera. For the sake of simplicity in the explanation, the
semi-cylindrical surface of each commutator is evolved upon a flat or plane surface,
thereby showing the true relative dimensions of the commutator plates and insulation.
The commutator b consists of the combination of two discs and m, having respectively
projections or conducting plates 1, 111, 11, and so forth, and m³, m", and m, etcetera,
the discs and plates being separated from each other by insulation n. As this insula-
tion is so thin as merely to separate the two sets of plates and the discs, and as the
commutators are represented as of equal diameter, it is evident that there are twice as
many plates on commutator b, as there are on commutator a, o is a choking magnet
consisting substantially of a core p of iron upon which is wound a coil 9 of a suitable
conductor of electricity. When a current is passed through the magnet there occurs

page_text: at the completion and at the interruption of the current an induced or counter current
in the circuit carrying the said curient.
Pressing upon the commutator a are brushes or contact plates or terminals r, s, t,
and ; and t being on the cylindrical surface, and s and u on and in contact with
the opposite discs of the commutator a.
Upon the commutator bare brushes v, w and and y all upon the cylindrical
surface.
All the brushes are connected in circuit by suitable conductors so that the circuit
may be followed in this manner. The circuit starts from one pole of the generator d,
through the brush, to the plate m", to the brush y, to and through the magneto, to
the brush v, to the plate to the brush w, to the brush s, to the disc h, to the
insulation where it stops. From the other pole of the same generator, circuit is
through the brush u, to the disc i, to the insulation and there stops. The present
following out of the circuit is in reference to Figure 6. In the main lines, containing
the converter A, and lamps B, the brush is upon the insulation ; and the brush
upon the insulation j¹. It is evident that in this condition of the commutator and
circuits, the current is zero. When the shaft c rotates, the relative positions of the
commutators and brushes undergo a change.
The first change is indicated in Figure 1. The changé consists in the brush
coming upon the plate i¹, and the brush t upon the plate h, so that it may be noticed
that a circuit is completed from one pole of the generator, to the other, including the
choking magnet and the main line. At the first instant, the counter-electromotive
force caused by the choking magnet maintains the current at zero. The self
induction or counter-electromotive force gradually diminishes while the direct or
original current from the generator gradually increases to a maximum, but not fully
to the strength of the original current. To all practical points of consideration it does
become equal to the original current in strength as there is only the ohmic resistance
of the wire surrounding the core, it being a well known principle that there is no
self induction produced by a choking magnet unless there is a variation of some kind
in the current.
The next change which occurs as soon as the current has reached the above named
maximum is represented in Figure 2, this change consists in the brushes v and y
connecting two contiguous plates of the commutator b, thereby short-circuiting the
choking magnet o. The current in this manner becomes the absolute maximum, the
resistance of the magnet being entirely eliminated. It, the current, remains at
maximum only for a short period of time dependent only upon the rate of rotation and
of the length of the commutator plates and insulation. The change is shown in
Figure 3. It may be noticed that the brushes v and y entirely leave the plates they
were formerly on, and come upon the plates m¹ and respectively, while the brushes.
and w remain on the original plates. This change in position of brushes and y
produces simultaneously two changes of action. The one is the introduction into the
circuit of the choking magnet, thereby reducing the strength gradually from maximum
to zero, according to the principle already noted, and the other is the reversal of the
direction of the current in the choking magnet. The latter action is caused by the
brushes and y which have changed their relation to the brushes and w. During
the next instant of time, the brushes x and w change their relation respectively to the
brushes and y, and brushes t and r break the circuit at this same moment, that is, an
instant after the current, by re-introduction of the choking magnet, has been reduced,
by the self induction, to zero.
v
By this invention, the current is changed from a continuous or direct current into a
true alternating current, and in such a manner that there is no sparking or arcs
produced at the commutators or elsewhere. The reason of this advantage is due to
the fact that there is no current flowing at the brushes and t, at the time when those
brushes pass from the commutator plates to the insulation, that is when they cause the
circuit to be interrupted. Also that current which would otherwise be formed and
existing at the brushes to and is counteracted and destroyed by self induction in the
magnet o. This self induced current flows in opposition to the current from the

page_text: source or generator, because the connection of the brushes from positions shown
in Figure 3, have been so changed that they occupy the positions shown in
Figure 4.
Should there be a longer time interval necessary for the change of the brushes .c
and w, across the insulation to allow the current to rise again, then it is preferable to
place in the main circuit a choking magnet R¹, whose one coil is C and the other D.
The coil C is in the main line and the coil D is terminated by one brush E at the
lower part of the plate and by another brush F at the lower part of the plate h¹.
When the brushes r and t make contact or close the circuit, the brushes E and F
break or open their circuit; while they close their circuit when the brushes r and t
open the circuit. This equal and opposite action reduces the current in the main line
to zero and there will be no sparking at the brushes r and t.
Referring to Figure 7, it will be noticed that a choking magnet is similarly inserted
in the other main conductor, the said choking magnet having coils (and D'. The
terminals of the coil D' are connected to the same brushes as those of the coil D.
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 declare that what I claim is :-
1. The method of obtaining an alternating electric current, consisting in
generating a continuous electric current of a given strength; gradually diminishing
the strength of the current to zero; reversing the direction of the current; increasing
the strength of the current from zero to maximum or normal strength; gradually
decreasing the strength from maximum to zero, again reversing the direction, and so
on until the continuous current is permanently interrupted.
2. A device consisting of two coinmutators and a choking magnet all normally in
circuit with a continuous current generator, whereby the terminals of the main line
from the generator, are so arranged as to touch alternately a positive pole of the
generator, insulation, a negative pole of the source, insulation, and so on in a similar
manner; and the terminals or brushes of the choking magnet being electrically
connected to the other commutator.
3. A device for automatically producing an alternating electric current from a
continuous current generator, consisting of an arrangement, whereby the current
is gradually reduced to zero, then reversed, then gradually increased to maximum
or normal, then gradually reduced to zero then simultaneously reversed and com-
pleted through the device and the main line, and then gradually increased to
maximum and so on.
4. The combination of a generator of a continuous electric current; one or more
choking magnets electrically connected having its contact points of positive and
negative polarity organised alternately around a common centre, and main line
terminals in electrical contact with the said commutator.
5. A device for producing an alternating current from a given continuous electric
current substantially as set forth in the description and illustrated by the accom-
panying drawings.
6. A commutating device in which the commutating plates and insulation between
then, are so arranged that when included as described in an electric circuit
carrying a continuous electric current, the said continuous current will be trans-
formed into a current formed of currents of short duration and of alternate
direction, and each impulse consisting of a current which gradually varies from zero
to maximum and then from maximum to zero.
Dated this 20th day of January 1890
WM. P. THOMPSON & Co.,
Liverpool, Manchester, and London, Patent Agents