IMPROVED MEANS FOR ESTABLISHING ELECTRIC CONNECTION BETWEEN SURFACES IN RELATIVE MOTION APPLICABLE TO THE COLLECTORS OF DYNAMO MACHINES to be as follows:
Year: 1885

page_text: I, Professor GEORGE FORBES of 34 Great George Street in the City of West-
minster do hereby declare the nature of my invention for "IMPROVED MEANS FOR
ESTABLISHING ELECTRIC CONNECTION BETWEEN SURFACES IN RELATIVE MOTION
APPLICABLE TO THE COLLECTORS OF DYNAMO MACHINES to be as follows:-
"
This Invention has for its object improved means for establishing electric
connection between surfaces in relative motion applicable to the collectors of
dynamo machines.
In dynamo machines generally there is difficulty in making the contact in a
satisfactory manner and this is especially the case in continuous current dynamo:
machines in which the current has to be led away from the circumference of a
rapidly revolving disc. I have employed mercury for the purpose and mercury
can be used under circumstances in which the application of a metallic brush is
unsuitable.
According to my present Invention I am able to take off the current from the
circumference of such a disc much more conveniently than by either of the methods
mentioned above and this I do by means of plumbago or hard carbon applied with
moderate pressure to the disc. The friction resulting from this contact is small
and a very satisfactory electrical connection is established-A convenient way to
employ the carbon contact maker is to set a block of this material into a holder
made of copper. Such contact makers are applicable for use in electric propulsion
or wherever contact between a metallic conductor and a contact maker the one in
movement relatively to the other is required.
They may also be applied in substitution for metallic brushes in ordinary dynamo
machines.

page_text: Improved means тог
Establishing
Micctric Como
DCTW COR
Surfaces in Relative Motion Applicable to the Collectors of
Dynamo Machines.
I, Professor GEORGE FORBES of 34 Great George Street in the City of West-
minster 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 its object improved means for establishing electric
connection between surfaces in relative motion applicable to the collectors of
dynamo machines.
In dynamo machines generally there is difficulty in making the contact in a
Satisfactory manner and this is especially the case in continuous current dynamo
machines in which the current has to be led away from the circumference of a
rapidly revolving disc. I have employed mercury for the purpose and mercury
can be used under circumstances in which the application of a metallic brush is
unsuitable. According to my present invention I am able to take off the current
from the circumference of such a disc much more conveniently than by either of
the methods mentioned above and this I do by means of plumbago or hard carbon
applied with moderate pressure to the disc. The friction resulting from this contact
is small and a very satisfactory electrical connection is established. A convenient
way to employ the carbon contact maker is to set a block of this material into a
holder made of copper. Such contact makers are applicable for use in electric
propulsion or wherever contact between a metallic conductor and a contact maker
the one in movement relatively to the other is required.
They may also be applied in substitution for metallic brushes in ordinary
dynamo machines.
By the use of my improved contacts the friction wearing away and heating which
generally result when contact is made by metal surfaces in relative motion is to a
a great extent avoided. Various forms of carbon either in a natural state or
manufactured may be employed.
I prefer however to employ plates of carbon such as are commonly used in
galvanic batteries and I strengthen them and increase their conductivity by backing
them with copper. I apply the copper to the carbon by electro-deposition either
to the full thickness required or to a sufficient thickness to admit of convenient
attachment by soldering or by screws of another metallic support.
Where it is an object to reduce the resistance of the contact as far as may be
I employ as thin a carbon plate as I conveniently can (one eighth of an inch will
be found suitable) and I deposit copper over the whole or nearly the whole of the.
surface excepting that which actually touches the opposed conductor.
In my non-polar dynamos for which patents have been granted to me N° 311583
and 11244 I arrange the contact makers in the following manner :-the rapidly
revolving metallic disc or armature is surrounded by a stationary copper ring in
which are notches or recesses; the carbon slabs backed as already described are

page_text: inserted into these recesses and behind them are coiled springs pressing them
obliquely both towards the centre of the disc and adversely to the movement of the
portion of the disc on which the contact maker bears.
To replace the metallic brushes of ordinary dynamos I employ carbon slabs say
of an eighth of an inch in thickness. I deposit copper on both the faces and if
desired further strengthen the slab by a backing as already described. I then
clamp the slab firm in a metal clip which I fix to the usual brush holder of the
dynamo. The carbon slab then takes the place of the metallic brush and it is
used in a similar manner; its end makes contact with the revolving part of the
commutator. These contact makers can also be employed in electrical railways to
take the current for propelling the train from an insulated rail or bar: in this case
the current may advantageously be divided between several contact makers.
Plumbago either in the pieces or nodules in which it is found in nature or
prepared in such a manner as not to seriously impare its conducting property may
when the cost is not too great, be very advantageously employed in contact makers
according to my invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed I declare that what
I claim is
1. My improvement in contact makers applicable to the collectors of dynamo-
machines and other contact makers establishing electrical connection between parts
in rapid relative motion and consisting in the employment of carbon therein
substantially as described.
2. A contact maker establishing electrical connection between parts in rapid
relative movement in which one of the rubbing surfaces is of carbon and the other
of metal substantially as described.
3. A contact maker establishing electrical connection between parts in rapid
relative movement in which one of the rubbing surfaces is of carbon backed with
metal substantially as described.
4. The combination, with a dynamo-machine of a collector consisting of a
surface of carbon and a metallic surface maintained in electrical connection there-
with whilst the said surfaces are in rapid relative motion substantially as
described.