IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES
Year: 1883

page_text: LETTERS PATENT to Professor George Forbes of 34 Great George Street in
the City of Westminster for an Invention of "IMPROVEMENTS IN DYNAMO
ELECTRIC MACHINES
PROVISIONAL SPECIFICATION loft by the said George Forbes at the Offico
of the Commissioners of Patents on the 22nd June 1883.
Professor GEORGE FORBES of 34 Groat George Street in the City of Westminster
"IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES
"
This Invention has for its object improvements in dynamo-electric machines.
The armature of my machine is a revolving mass of iron without coils and my
field magnet is continuous all around. the armature which it completely encloses
except that there is a central hole by which the axis passes. The magnet presents
a continuous North pole to one side and a continuous South pole to the other sido
of the armature whose polarity is also continuous.
In the form which I prefer the armature is a disc mounted upon an axis and
confined within a soft iron box. The cavity of the box is only of sufficient width
to permit the armature to revolve without contact. The periphery of the disc is
surrounded by a ring serving as the conductor by which the current is drawn
off: Good contact is ensured with this conductor by means of a little mercury
which is retained in its place by centrifugal force. I may make this conductor
hollow for the circulation of water if found necessary. The circuit connection
is made with the ring in any convenient manner, the magnetizing coils are
immediately exterior to the ring and enclosed within the box like mass which,
as well as the disc they serve to magnetise. The axis of the disc serves to convey
the current from the centre of the disc and a metal brush bearing upon the axis
may serve as the second terminal of the machine. I prefer however to duplicate
the apparatus and have two armatures on the same axis. I then so arrange the
winding of the magnets that the two conducting rings surrounding the armatures
may serve the one as the positive and the other as the negative terminal of the
machine.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said George Forbes in the Great Seal Patent Office on the 22nd December
1883.
°
Professor GEORGE FORBES of 34 Great George Street in the City of Westminster
"IMPROVEMENTS IN DYNAMO ELECTRIC MACHINES"
This invention has for its object improvements in dynamo electric machines.
The armature of my machine is a revolving mass of iron without coils and my
field magnet is continuous all around the armature which it completely encloses
except that there is a central hole by which the axis passes: The magnet presents
a continuous North pole to one side and a continuous South pole to the other side
of the armature whose polarity is also continuous.
In the form which I prefer the armature is a disc mounted upon an axis and
confined within a soft iron box. The cavity of the box is only of sufficient width
to permit the armature to revolve without contact. The periphery of the disc is
surrounded by a ring serving as the conductor by which the current is drawn off.
Good contact is ensured with this conductor by means of a little mercury which is
retained in its place by centrifugal force I may make this conductor hollow for the
circulation of water if found necessary. The circuit connection is made with tho
ring in any convenient manner, the magnetizing coils are immediately exterior to
the ring and enclosed within the box like mass which as well as the disc they serve
to magnetise. The axis of the disc serves to convey the current from the centre of
the disc and a metal brush bearing upon the axis may serve as the second terminal
of the machine. I prefer however to duplicate the apparatus and have two
armatures on the same axis. I then so arrange the winding of the magnets that
the two conducting rings surrounding the armatures may serve the one as the
positive and the other as the negative terminal of the machine.
The annexed drawing is a section of the double machine.
▲ ▲ are two iron discs with grooved edges.
BB is a spindle of bronze to which they are screwed one with a right handed
the other with a left handed screw.
C. C. is a central mass of soft iron.
D. D are two masses of soft iron.
The discs A A fit as closely as possible in the spaces between C. C. and D D.
E E are annular spaces between C. C. and D D. Each of these spaces contains
a thin copper casing (coated with insulating material) within which is a coil of
insulated wire.
FF are the ends of one of these coils. These ends pass through a hole in the
copper casing and through another in the iron masses.
GG are the positive and negative terminals of the machine. They are attached
one to each of the copper casings and pass through holes in the iron masses lined
with insulating material.
HH are iron supports for the bearings attached to the iron masses D D by the
bolts K K.
LL are the bearings screwing into the supports H H and secured by nuts M M.
NN are the bolts to connect the three iron masses CDD
PP are rings of insulating material e. g. india rubber: they form fluid tight
joints with the walls of the copper case on which they abut.
Q. Q. are holes insulated inside for mercury to be poured into and out of the
space between the discs A A and the copper casings. This surface of the copper
casing is not insulated but may be electro plated with nickel to prevent

page_text: amalgamation. The holes are furnished with plugs by which they may be
closed.
RR are channels to drain away the surplus oil, the bearings being lubricated by
any ordinary lubricators.
The coils of wire in E E are so connected that the magnetizing current goes in
opposite directions in the two coils. The current may be derived from a separate
source or the coils of wire in E E may form part of the circuit through which the
useful current passes, or they may be a shunt on that circuit.
S. S. are rings for lifting the iron masses.
The pulley is of lignum vitae (or other insulator) with an iron tyre attached by
one set of bolts and a central tube attached by another set of bolts to the lignum
vitae.
These
When the shaft is rotated a difference of electric potential is created between the
centre and circumference of each of the discs A A tending to set up a current in
one of them towards the centre and in the other towards the circumference.
being connected by the shaft at the contres and by the mercury (which is driven
out by centrifugal force) by the copper casings by the terminals G G and by the
circuit or line a current.is set up.
It is not necessary to uso mercury any sort of metallic contact would do.
I sometimes cut slots in the discs from the circumference half way to the centre
of the discs which get filled with mercury when the machine is at rest this drains
the upper part of the disc space of mercury and so the mercury cannot reach the
shaft.
The parts DD are so proportioned that any line drawn from E to the exterior
and rotated about the axis will generate a surface of an area not less than the face
of the disc A and similar proportions are given to the mass C.
This is important to observe in order to avoid crowding together of the lines of
force emanating from the face of the disc which would be injurious to the efficiency
of the machine.
All of the lines of magnetic force in the machine represented pass continuously
through iron and this is an important feature of the invention.
A single machine may be similarly constructed it is unnecessary that I should
represent it by a separate drawing as the single machine is substantially the half
of that shown by the drawing the second terminal being electrically connected
with the axis through a metallic brush or being upon the mass D which is
electrically connected through the bearing with the axis.
My invention admits of variation without departure from its spirit thus the
disc A may be altered in its proportions and may so be converted into a shaft
revolving within a coil or again the masses CD in place of being brought together
in the simplest manner and thereby boxing in the edge or periphery of the disc
may be connected by an exterior horse shoe bar of sufficient sectional area and the
coils may be wound upon this bar. The machine of the form represented by the
Drawings is however that which I prefer.
Having thus described the nature of my said invention and the manner of
performing the same I would have it understood that I claim as my improvements
in dynamo electric machines:—
First The combination of a rotating magnetised mass included in an induced
electric circuit and a mass magnetically connecting the poles of the rotating
magnetised mass substantially as described.
Second-The combination of a rotating magnetised mass included in an induced
electric circuit a magnetizing coil surrounding the said mass and a box like mass
magnetically connecting the poles of the rotating mass and enclosing it and also
the magnetising coil substantially as described.
Third The combination constituting the double machine in which there are
two rotating magnetised masses and an induced electric circuit passing through
them in opposite directions substantially as described.

page_text: Fourth The use of inercury to establish electrical contact between the periphery.
of a rotating mass and a ring conductor encircling it substantially as described.
Fifth The construction of dynamoelectric machines substantially as described
and represented in the annexed drawings.
•
cj
In witness whereof. I the said Professor George Forbes have hereunto-set my
hand and seal this twenty first day of December in the year of our Lord One
thousand eight hundred and eighty three.
J
GEORGE FORBES (I.S.)