Improvements in Electrical Switches or Variable Resistances.
Year: 1897

page_text: Date of Application, 14th Dec., 1897-Accepted, 19th Mar.,
1898
COMPLETE SPECIFICATION.
Improvements in Electrical Switches or Variable Resistances.
We, WILLIAM BENJAMIN SPIKINS, of 34, Western Road, Hove, Sussex, Merchant,
and ALFRED HERBERT MAYES, of 51, Upper Westbourne Villas, Hove, Sussex, Electrician,
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 refers to improvements in electrical switches and variable resistances
for motors, dynamos and the like.
In designing the form of variable resistance switch, described in this specification,
mny aim has been to construct a simple and very compact form of switch, eminently
adapted for starting and stopping electro motors and which by means of a slight
modification could be made to form an excellent adjustable resistance, suitable for
placing in circuit with the field winding of dynamos or motors for regulating
purposes.
I claim to have introduced a novelty by the employment as a resistance material,
of a substance which has such a retarding action upon the flow of the electric
current, that an extremely short length of it, interposed between the conducting
terminals or heads of the switch, will have a power of resistance, equal to that
obtained by using an immensely greater length of the material usually employed for
the purpose. The advantage and novelty of my arrangement will be rendered even
more obvious when I explain that a simple and compact form of my switch as shewn
in the drawings will answer the same purpose, and be equally efficient as a switch
constructed in the usual manner and occupying, roughly ten times the room and
space.
To further render clear the novelty of my idea, we will enumerate the methods
usually and at present employed to effect the same purpose.
The materials usually
employed where resistance is required, are generally connected between the contact
heads of the switch, and usually consist of either iron or platinoid wire.
To obtain the necessary amount of resistance to the flow of the electric current, a great
length of the aforesaid wire has to be used, and even when coiled in spirals and
arranged upon a suitable frame occupies a large space.
With reference to the composition and method of employment of the resisting
material we proceed as follows:-
We procure some form of carbon (preferably retort carbon and in practice we have
used arc lamp carbons) and having reduced the same to a more or less fine powder
we pack or place the same in between the contact heads of switch, or arrange the
powder in such a way that it is interposed in the path of the current and a portion
of it may be cut in or out of circuit by a movement of the switch finger or moveable
contact.
The resistance of the powder becomes less in proportion to the pressure exerted
in forcing it into its place in consequence of the particles coming into more intimate
contact.

page_text: In practice we frequently find it necessary to combine one or more of the
substances hereafter specified with the carbon in order to increase its resistance on
high voltage circuit.
We should also explain that where the resistance of the resisting material is
mentioned it is to be taken at 60° Fahrenheit.
We will now describe the invention with reference to the accompanying drawings
in which-
Fig. 1 shows a plan and elevation of one form of switch to which our system of
variable resistance is applied.
Fig. 2 shows a plan and elevation of a second form of switch in which the contact
blocks are raised and project up from a strip of resistance material beneath.
Fig. 3 shows a third form of switch as hereafter described.
Referring to Fig. 1, A is the contact plate of the switch formed by preference in
segmental shape and composed of metallic contact blocks A¹ A¹ which alternate with
resistance blocks B to B of high resistance material. C is the switch arm or finger
centred at C¹ to a suitable base. D and E are the positive and negative cables.
Thus by moving the switch arm backwards or forwards upon the contact plate the
resistance to the electric current will be increased or diminished, and the resistance
will be less when C is in the position shown, than if it were at B5. Preferably the
different blocks would be of variable resistance by reason of their varying composition; :
thus B might have double that of B³.
Referring to Fig. 2, F is a strip of resistance material upon which the contact
blocks A¹ A¹ may be screwed or otherwise fastened.
Referring to Fig. 3, G is a strip of resistance material forming the contact plate,
at one end of which a single contact block A¹ may be placed. The switch arın would:
in this case slide upon the resistance material G.
We may manufacture the necessary high resistance material from a combination
of such substances as powdered carbon, or any form of retort carbon, vegetable
charcoal, metallic oxides, peroxides or sulphates, oxide of manganese, or plaster of
Paris, or other suitable substances. The substance or substances used would be such
as would create a resistance to the passage of the electric current equal to, or
exceeding 3 ohms per cubic inch. A suitably arranged form of our variable
resistance may be inserted in the shunt coils of dynamos for regulating purposes.
:
Having now particularly described and ascertained the nature of our said
invention, and in what manner the same is to be performed, we declare that
what we claim is :-
1. The use or combination of any or all of the following substances or the like;
namely vegetable charcoal, powdered carbon, or any form of retort carbon, the
metallic oxides or peroxides, or sulphates, oxide of manganese, or plaster of Paris or
other suitable substances, so as to form a material having a resistance equal to, or
exceeding 3 ohms per cubic inch, substantially as herein described and set forth.
2. The use or combination of any or all of the above named substances for the
purpose of obtaining variable resistances constructed or applied; substantially as
.herein described and set.forth.
3. The use or combination of such of the foregoing substances (mentioned in
Claim 1) as would create a resistance to the passage of the electric current equal to,
or exceeding 3 ohms per cubic inch, as herein described and set forth.
S. S. BROMHEAD,
Patent Agent, 171, Queen Victoria Street.
Lon HOLY SO novo