IMPROVEMENTS IN ELECTRICAL GENERATORS AND MOTORS
Year: 1882

page_text: LETTERS PATENT to Thomas John Handford of 42 Southampton Buildings in
the County of Middlesex, Patent Agent for an Invention of "IMPROVEMENTS
IN ELECTRICAL GENERATORS AND MOTORS" Communicated to him from
abroad by Thomas Alva Edison of Menlo Park in the State of New Jersey,
United States of America.
PROVISIONAL SPECIFICATION left by the said Thomas John Handford at
the Office of the Commissioners of Patents on the 27th December 1882.
THOMAS JOHN HANDFORD of 42 Southampton Buildings, in the County of
Middlesex, Patent Agent, "IMPROVEMENTS IN ELECTRICAL GENERATORS AND
MOTORS" a communication to me from abroad by Thomas Alva Edison of Menlo
Park in the State of New Jersey, United States of America,
In the working of continuous current dynamo-electric machines, or electro-
dynamic motors, the increase of the load of such machines causes the neutral line to
advance in the direction of rotation away from the line of maximum electromotive
force or work.
It has been found necessary heretofore to shift the commutator brushes or current
collectors forward to the neutral line, in order to prevent destructive sparks; but
the removal of the brushes away from the line of maximum electromotive force of
a generator, reduces the electromotive force of the machine.
With electro-dynamic motors the difficulties are greatly increased, since the load
may vary frequently and, if the brushes are adjusted for the average load, the
shifting of the neutral line away from the brushes will be productive of undue
sparking destructive both of the commutator, and the brushes.
Now this Invention has for its object the production of means whereby the
current collectors, or commutator-brushes may be retained at the points of maximum
electromotive-force or work of the generator or motor, without undue or destructive
sparking, the capacity of the machines being thereby largely increased.
It has been the universal practice heretofore, to use for the commutator brushes
of machines of this character, copper or other metal having good electrical con-
ductivity and making good electrical contact.

page_text: It has however been discovered that the copper brushes by reason of their great
conductivity, and good contact form circuits of very low resistance between the bars
of the commutator as they pass over them, and hence short-circuit in succession the
coils connecting the pairs of commutator bars, such coils then forming a local
dynamo and generating a powerful local current: the breaking of that short
circuit, which takes place when the brushes leave a commutator bar, causes the
destructive spark. The generation of the powerful local currents also causes the
heating of the machine, and the loss of energy due to such heating.
According to this Invention the current collectors or the commutator bars or both
are so constructed, and arranged that the bridge formed by each collector across the
cominutator bars has a large resistance compared with the local coils, the circuit of
which is completed within the machine by the bridging of the commutator bars;
hence the local current is very weak and the spark reduced to comparatively nil.
It is thus possible to keep the collectors at the points of maximum electromotive-
force or work, notwithstanding these may not be the neutral points, and by
providing a number of such collectors, the requisite total conductivity and contact
can be obtained to carry the main current without sparking
In carrying out this Invention the current-collectors, whether in the form of
wire brushes, plate springs, or of other form, are made of some metal or alloy
having inferior conductivity, and making inferior contact, compared with copper,
and preferably having a high melting point. Nickel, iron, steel, cobalt, platinum,
or palladium may be used or alloys such for example as phosphor bronze, or brass
but it is preferred to use German silver for the purpose, for the reason that it offers
very great resistance, and does not lose its stiffness by heat as is the case with
most alloys.
The current collectors, when made as brushes, are composed of layers of wires,
which are preferably separated by metal plates, the whole being soldered together
into a solid mass at one end.
For the purpose of increasing the resistance of the bridge formed by the brush,
the layers of wire are preferably insulated from each other. This may be accom-
plished by japanning the separating metal plates. The wires themselves may also
be japanned and the separating plates omitted, or not as desired.
The separating
japanned metal plates may be replaced by strips of mica or other suitable insulating
material, but the japanned metal is preferred.
The brush has its end bearing on the commutator cylinder, the ends of all or
nearly all the wires being in contact therewith. The current in passing from one
bar to another through the brush is forced to travel up part of the wires to the
solid end of the brush, and then down other wires to the other bar, the resistance
of the length of the wires being interposed in the local circuit.
The high resistance is due not only to the resistance offered by the metal of the
current-collectors, but largely to the inferior electrical contact of the collectors on
the commutator cylinder, which occurs when metal or alloys having a conductivity
inferior to copper are used for the collectors.
The contact resistance may be further increased by constructing the commutator
bars, or surfacing them with such a metal or alloy, as has been described, making
an inferior electrical contact compared with copper, or this method may be employed
in substitution for that previously herein before described.
In addition to the local sparking, there is the sparking due to the taking off of
the main current, which, (other things being equal) would necessarily be increased
by the inferior contact made by the current collectors, but by augmenting the
number of collectors or the component parts of the collectors to the requisite
extent the spark due to the main current may be reduced to the minimum by
division.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas John Handford in the Great Seal Patent Office on the
25th June 1883.
AND
THOMAS JOHN HANDFORD of 42 Southampton Buildings in the County of
Middlesex Patent Agent "IMPROVEMENTS IN ELECTRICAL GENERATORS
MOTORS" a communication to me from abroad by Thomas Alva Edison of Menlo
Park in the State of New Jersey, United States of America
In the working of continuous current dynamo-electric machines or electro-
dynamic motors, the increase of the load of such machines causes the neutral line
to advance in the direction of rotation away from the line of maximum electro-
motive force or work. It has been found necessary heretofore to shift the
commutator brushes or current collectors forward to the neutral line, in order
to prevent destructive sparks; but the removal of the brushes away from the line
of maximum electromotive force of a generator, reduces the electromotive force of
the machine.
With electro-dynamic motors the difficulties are greatly increased, since the load
may vary frequently, and, if the brushes are adjusted for the average load, the
shifting of the neutral line away from the brushes will be productive of undue
sparking destructive both of the commutator and the brushes.
Now this Invention has for its object the production of means whereby the
current collectors, or commutator brushes may be retained at the points of
maximum electromotive force or work of the generator or motor, without undue
or destructive sparking, the capacity of the machines being thereby largely
increased.
It has been the universal practice heretofore, to use for the commutator brushes
of machines of this character, copper or other metal having good electrical con-
ductivity and making good electrical contact.
It has however been discovered that the copper brushes by reason of their great
conductivity, and good contact, form circuits of very low resistance between the
bars of the commutator as they pass over them, and hence short-circuit in succession
the coils connecting the pairs of commutator bars, such coils then forming a local
dynamo and generating a powerful local current; the breaking of that short
circuit, which takes place when the brushes leave a commutator bar, causes the
destructive spark. The generation of the powerful local currents also causes the
heating of the machine and the loss of energy due to such heating.
According to the present Invention the current collectors are made of a material
of inferior electrical conductivity, and contact compared with copper and are
otherwise so constructed and arranged, that the bridge formed by each collector
across the commutator bars has a large resistance compared with the local coils,
the circuit of which is completed within the machine by the bridging of the
commutator bars; hence the local current is very weak and the spark reduced
to comparatively nil. It is thus possible to keep the collectors at the points
of maximum electromotive force or work, notwithstanding that these may not
be the neutral points, and, by providing a number of such collectors, the requisite
total conductivity and contact can be obtained to carry the main current without
sparking.
In carrying out the said Invention the current collectors, whether in the form
of wire brushes, plate springs, or of other form, are made of some metal or alloy
having inferior conductivity, and making inferior contact compared with copper,
and preferably having a high melting point. Nickel, iron, steel, cobalt, platinum,

page_text: or palladium may be used, or alloys such for example as phosphor-bronze or brass,
but it is preferred to use German silver for the purpose, for the reason that it
offers very great resistance, and does not lose its stiffness by heat as is the case
with most alloys.
The current collectors when made as brushes are composed of layers of wires
which are preferably separated by metal plates the whole being soldered together
into a solid mass at one end.
For the purpose of increasing the resistance of the bridge formed by the brush
the layers of wire are insulated from each other. This may be accomplished
by japanning the separating metal plates when such are employed, or the wires
themselves may be japanned, and the separating plates omitted or not as desired.
The separating japanned metal plates may also be replaced by strips of mica, or
other suitable insulating material, but the japanned metal is preferred.
The brush has its end bearing on the commutator cylinder, the ends of all or
nearly all the wires being in contact therewith. The current in passing from one
bar to another through the brush is forced to travel up part of the wires to the
solid end of the brush, and then down other wires to the other bar, the resistance
of the length of the wires being interposed in the local circuit
The high resistance is due not only to the resistance offered by the metal of the
current collectors, but largely to the inferior electrical contact of the collectors on
the commutator cylinder, which occurs when metal or alloys having a conductivity
inferior to copper are used for the collectors
The contact resistance may be further increased by constructing the commutator
bars or surfacing them with such a metal or alloy, as has been described making
an inferior electrical contact compared with copper.
In addition to the local sparking, there is the sparking due to the taking off
of the main current which, (other things being equal) would necessarily be
increased by the inferior contact made by the current collectors, but by augmenting
the number of collectors, or the component parts of the collectors to the requisite
extent the spark due to the main current may be reduced to the minimum by
division.
And in order that the said Invention may be perfectly understood I shall now
proceed more particularly to describe the same and for that purpose shall refer to the
several figures on the accompanying sheet of drawings, the same letters of reference
indicating corresponding parts in all the figures.
Figure 1, of the accompanying drawings illustrates a part of a dynamo-electric
machine, or electro-dynamic motor, with commutator brushes, arranged in accordance
with the said Invention;
Figure 2, is a view of the commutator, showing several brushes;
Figure 3, a view on a larger scale of two bars of a commutator and the improved
brush;
Figure 4, a cross section of the brush;
Figure 5, an illustration of the course taken by the local current through the
electrically divided brush; and
Figure 6, an illustration showing the course of the local and main currents.
P, N, (figure 1) are the polar extensions of the field magnet of the generator or
motor, A, being the armature, B the commutator cylinder, and C, C, the commu-
tator brushes. The varying neutral line on the commutator cylinder is represented
by the dotted line x, x, and the line of maximum electro-motive force by the dotted
line y, Y.
Heretofore in order to prevent sparking it has been found necessary
to shift the brushes on to the line x, x, but it is possible by reason of the peculiar
construction and arrangement of the current collectors, or commutator brushes
according to the said Invention, to keep them on the line y, y, without sparking.
Two or more commutator brushes connected together are used on each side of the
commutator cylinder to carry the current, as shown in figure 2.
Each brush is constructed of layers of wires a (figures 3 and 4) of German
silver, or other inferior conducting metal or alloy, the layers being divided by

page_text: metal plates or strips b. The wires a and plates bare formed into a solid mass
by soldering at the outer end c of the brush. The plates b, are japanned as
are also the wires a, so as to insure a good electrical division of the brush.
The brush rests with the ends of all its wires bearing on the commutator
cylinder as shown
The course of the local current is indicated by the arrows in figure 5, and by the
small arrows in figure 6. while the course of the main current is indicated by the
large arrows in figure 6.
The local coil d (figure 6) has its circuit closed at the commutator by the bridge
formed by the brush. This bridge however is of high resistance compared with
the coil d. It is made so by the inferior electrical contact of the brush on the
commutator, by the inferior conductivity of the metal of which the brush is
made, and also by the electrical division of the brush at its inner or bearing end.
It will be noticed that the local current in addition to being forced to overcome
the resistance offered by the length of the wires has to overcome the main current
in one side of the bridge formed by the brush.
The bars e of the commutator B may also be made of or surfaced with German
silver or other suitable alloy or metal making inferior electrical contact compared
with copper. This increases the resistance of the contact and makes the bridges
formed by the brushes of higher resistance.
Having now described and particularly ascertained the nature of the said
Invention and the manner in which the same is or may be used or carried into
effect, I would observe in conclusion that what I consider to be novel and original
and therefore claim as the Invention secured to me by the hereinbefore in part
recited Letters Patent, is :-
The electrically divided current collector, made of a material having an inferior
conductivity, and making inferior contact compared with copper, in conjunction
or not, with commutator bars constructed of or surfaced with a material making
inferior contact compared with copper, substantially as hereinbefore described.
In witness whereof I the said Thomas John Handford have hereunto set my
hand and seal this twentyfifth day of June in the year of our Lord one
thousand eight hundred and eighty three.