Improvements in connection with Brushes and their Holders for Dynamos.
Year: 1897

page_text: PROVISIONAL SPECIFICATION.
Improvements in connection with Brushes and their Holders for
Dynamos.
I, WILLIAM MORRIS MORDEY, of Redholm, Loughborough, in the County of
Leicester, Electrical Engineer, do hereby declare the nature of this invention to
be as follows:-
This invention has reference to a new or improved construction and arrange-
ment of dynamo brushes whereby sparking is considerably lessened or prevented.
In constructing such brushes I take thin plates or laminæ (hereinafter called
plates) of carbon or graphite arranged parallel with each other to form blocks of
the required thickness to constitute the complete brush, the direction of lamination
being such as to be parallel, when the brush is in use, to the division lines of the
commutator. The plates are electrically separated or insulated from one another
throughout most of their length, being electrically connected only at the ends or
sides that will be remote from the commutator when applied thereto. The plates
are held together in any convenient manner. I prefer for this purpose to cement
or stick them together by some adhesive insulating cement or varnish containing
powdered or finely divided plumbago or other form of carbon, the amount thereof
used being insufficient to seriously impair the insulating properties of the cement.
Other substances may be used instead of the carbon, such as mica, talc, asbestos
or steatite, or these may be mixed with the carbon powder, but I prefer to add
carbon alone to the cement or separating material as it acts as a lubricant without
danger of forming a badly conducting film on the surface of the commutator.
The separating material between the plates extends from the working or rubbing
surface or end of the brush to within a short distance of the other end or side
where, as herein before stated, an electrical connection is made between them. This
connection may be obtained by making the carbon plates a little thicker at that
end so as to bring them into contact with each other, or by placing between them
at that end pieces of thin metal foil. They may be held together by rivets or
screws, or by both rivets and screws, but, as will hereafter appear, I do not consider
this a good plan.
Instead of building up the brush in the manner above described, or in some
substantially similar manner, I may make it in one block, obtaining the separation
or lamination by sawing or otherwise cutting or dividing it from the working or
rubbing surface or end back nearly to the other end, and I may fill in these
dividing spaces by an insulating cement, such as I have described above, or by plates
or sheets of any suitable insulating material.
The effect of using brushes constructed as described is to greatly reduce the
current which circulates through the armature coil or coils which is or are being
short-circuited by the brush. This lessens the heating of the brush and enables a
smaller brush to be used than usual. The reduction of short-circuit current also
lessens armature reaction and therefore decreases the movement of the brushes
about the commutator necessary to the best collection. It also reduces the field
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page_text: excitation both by decreasing armature reaction and by. allowing a more backward
collection than would otherwise be possible.
In using brushes constructed according to this invention I may use any ordinary
form of clamp or brush holder, but I prefer to employ one of special form or arrange-
ment. Hitherto it has been usual to make as good an electrical contact as possible
between brush and brush-holder by clamping the brush as a whole between metal
_ clamping_plates. _ I have found by experiment that sensibly improved results are
obtained by departing from this customary method and adopting in lieu thereof
the improved method which I will now describe. Instead of making contact with
the brush as a whole I insulate it from the holder or clamp on the side facing the
direction of rotation and connect it to the holder on the side opposed to the direction
of rotation. By this arrangement the resistance is least between the commutator
and the brush-holder by way of the rear portions of the brush, and greatest through
the front portion.
The special object of the one-sided connection of the brush to its holder is to
cause the current to pass into the brush mainly by the rear plates thus reducing the
tendency to spark at the tip of the brush as the sectors of the commutator pass in
succession from under the brush.
In generators or motors required to run indifferently in either direction, I prefer
to so arrange the brushes that the current passes respectively to or from the holder
by the middle instead of by one side of the brush.
I do not limit myself to the foregoing methods of carrying out my invention.
For example instead of carbon or graphite I may use carbon and metal built up
together. To increase the effect of the separation of the plates or laminæ I may
make them narrower or thinner at the parts remote from the rubbing surface.
Dated this 18th day of February 1897.
COMPLETE SPECIFICATION.
Improvements in connection with Brushes and their Holders for
Dynamos.
I, WILLIAM MORRIS MORDEY, formerly of Redholm, Loughborough, in the
County of Leicester, but now of 66, Victoria Street, Westminster, Electrical
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:-
This invention has for object to construct in an inexpensive practical and
convenient. form dynamo brushes of carbon or graphite (hereinafter included in
the term carbon) comprising plates or laminations separated from one another for
a portion of their length but electrically connected together at the end not designed
to be placed in rubbing contact with the commutator.
In the accompanying drawings Figs. 1 and 2 are perspective views showing two
constructions of such brushes. Fig. 3 shows partly in cross section and partly in
side elevation, a brush with metal clamp or holder according to this invention.
Fig. 4 shows in side elevation, a modified construction of brush. Fig. 5 shows a
further modified construction of brush according to this invention.
The brush shown in Fig. 1. comprises thin plates of carbon arranged parallel
with each other to form a block of the required thickness to constitute the complete.
"

page_text: brush, the direction of lamination being such as to be parallel, when the brush
is in use, to the division lines 6 of the commutator c, with which it is used. The
plates are electrically separated or insulated from one another for a part of their
length, being electrically connected only at the ends A that will be remote from
the commutator when applied thereto. The plates a are held together in any con-
venient manner. I prefer for this purpose to cement or stick them together, as
shown at d, by fish-glue or isinglass or by some other suitable adhesive insulating
cement or varnish which may contain powdered or finely divided plumbago or other
form of carbon, the amount thereof used being insufficient to seriously impair the
insulating properties of the cement. I may use thin tissue paper with the cement
to further ensure insulation. Other substances may be used instead of the carbon,
such as mica, talc, asbestos or steatite, or these may be mixed with the carbon
powder, but I prefer to add carbon alone to the cement or separating material
as it acts as a lubricant without danger of forming a badly conducting film on the
surface of the commutator.
The separating-material between the plates a extends from the working or
rubbing surface or end B of the brush to within a short distance of the other.
end A where, as herein before stated, an electrical connection is made between
them. This connection may be obtained by making the carbon plates a little
thicker at that end so as to bring them into contact with each other, or by placing
between them at that end pieces e of thin metal foil. They may be held together by
rivets or screws, or by both rivets and screws, but, as will hereinafter appear, I do not
consider this a good plan.
Instead of building up the brush in the manner above described, or in some
substantially similar manner, I may make it in one block as shown in Fig. 2,
obtaining the separation or lamination by sawing or otherwise cutting or dividing
it from the working or rubbing surface or end B back nearly to the other end A,
and I may fill in these dividing spaces with an insulating cement & such as I.
have described above, or by plates or sheets of any suitable insulating material.
A convenient way of forming such carbon blocks is to mould them with sheets of
asbestos cloth or paper or other suitable insulating material in the positions shown
in the drawings.
The effect of using brushes constructed as described is to greatly reduce the current.
which circulates through the armature coil or coils which, for the time being, is or are
being short-circuited by the brush. This lessens the heating of the brush and
enables a smaller brush to be used than usual. The reduction of short-circuit
current also lessens armature reaction and therefore decreases the movement of the
brushes about the commutator necessary to the best collection. It also reduces the
field excitation both by decreasing armature reaction and by allowing a more back-
ward collection than would otherwise be possible.
In using brushes constructed according to this invention, I may use any ordinary
form of clamp or brush holder, but I prefer to employ, one of special form or
arrangement. Hitherto the common practice has been to make as good an electrical
contact as possible between the brush and brush-holder by clamping the brush as
a whole between metal clamping plates. I have found by experiment that
sensibly improved results are obtained by departing from this customary method
and adopting in lieu thereof the improved arrangement which I will now describe
with reference to Fig. 3. Instead of making contact between the brush and metal
holder or clamp f, on both sides as usual, I insulate the brush from the holder
or clamp on the forward side or that facing the direction of rotation, as for example
by a strip g of insulating material, and connect it to the holder on the rear side or
that opposed to the direction of rotation, as for example by letting it rest against.
the metal holder as shown. By this arrangement the resistance is least between
the commutator c and the brush-holder f by way of the rear portions of the brush,
and greatest through the front portion.
The special object of this one-sided connection of the brush to its holder is to
cause the current to pass into the brush mainly by the rear plates thus reducing

page_text: the tendency to spark at the tip of the brush as the sectors of the commutator pass
in succession from under the brush.
In generators or motors required to run indifferently in either direction, I prefer
to so arrange the brushes that the current passes respectively to or from the holder
by the middle instead of by one side of the brush. This arrangement is shown
_diagrammatically in the construction of brush represented in Fig. 4, whereby the
connection to the brush holder can be made by the middle plate or plates h.
I do not limit myself to the foregoing methods of carrying out my invention.
Thus instead of using carbon plates alone, carbon and metal may be built up
together, the insulated laminations a¹ of metal being at the rearward portion of
the brush and the carbon laminations a at the forward portion of the brush as shown
for example in Fig. 5. To increase the effect of the separation of the plates or
lamine, I may make the insulating divisions 'd of different lengths, also as shown
in Fig. 5; or I may make them narrower or thinner at the parts or end A remote
from the rubbing surface B.
I am aware that various proposals have been made to construct dynamo brushes
of insulated strips or plates of conducting material but so far as I am aware no
one has succeeded practically in introducing in a convenient and useful form a
brush on this principle prior to my application for Letters Patent.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is:-
1. A dynamo brush consisting of a block comprising plates or laminations of
carbon separated from each other by insulating material throughout most of their
length but electrically connected at their outer ends, substantially as described.
2. A dynamo brush having laminations of carbon integral with each other but
separated and insulated from each other throughout most of their length.
3. Holding or supporting a dynamo brush of the kind referred to in the preceding
claims in such a manner that the current tends to pass into the said brush mainly
at the rearward side thereof, as set forth.
4. Dynamo brushes constructed and arranged as herein before described with
reference respectively to and shown in Fig. 1; in Fig. 2; in Fig. 3; in Fig. 4;
and in Fig. 5 of the drawings annexed. .
Dated this 18th day of November 1897.