Improvements in Variable Electric Resistances or Rheostats.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in Variable Electric Resistances or Rheostats.
We, R. WAYGOOD & Co. LIMITED, Hydraulic, Electrical, and General Engineers,
and PHILIP IBOTSON UNWIN, Electrical Engineer, both of Falmouth Road, Great
Dover Street, in the County of Surrey, do hereby declare the nature of this
invention to be as follows:-
This invention relates to resistances which are especially suitable for the electric
starting switches for the electric motors of lifts, cranes, and hoists, but are
suitable for other purposes.
It is well known that electrical motors must be started by means of a resistance
which is inserted in the circuit at the moment of starting and gradually removed in
order to allow the motor time to become magnetised and to prevent undue rushes of
current at the moment of switching on.
Water resistances in which a metallic rod or plate is gradually immersed in
water have often been used for this purpose.
Such resistances however have the disadvantage that when in frequent use the
water is liable to be heated to boiling and constant attention is required to supply
the loss by evaporation from this and other causes.
According to this invention these objections are overcome by substituting a
badly conducting powder for the water.
This powder must be such that its particles slide freely on each other. so as to
offer no undue impediment to the entrance of the conductor and lie in close contact
with it and at once close up together on its withdrawal so that no orifice is left.
A material admirably suited for the purpose is a peculiar form of graphite
largely used for lubricating purposes and known as "flake graphite."
Dated this 28th day of January 1898.

page_text: Dover Street, in the County of Surrey, do hereby declare the nature of this inven-
tion and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statement :-
This invention relates to resistances which are especially suitable for the electric
starting switches for the electric motors of lifts, cranes, and hoists, but are suitable
for other purposes.
It is well known that electrical motors must be started by means of a resistance
which is inserted in the circuit at the moment of starting and gradually removed in
order to allow the motor time to become magnetised and to prevent undue rushes
of current at the moment of switching on.
Water resistances in which a metallic rod or plate is gradually immersed in water
have often been used for this purpose.
Such resistances however have the disadvantage that when in frequent use the
water is liable to be heated to boiling and constant attention is required to supply
the loss by evaporation from this and other causes.
According to this invention these objections are overcome by substituting a
badly conducting powder for the water.
This powder must be such that its particles slide freely on each other so as to
offer no undue impediment to the entrance of the conductor and lie in close
contact with it and at once close up together on its withdrawal so that no orifice is
left..
A material admirably suited for the purpose is a peculiar form of graphite largely
used for lubricating purposes and known as "flake graphite."
This material is sold by the Joseph Dixon Crucible Company of Jersey City in
the United States of America and 28 Victoria Street Westminster.
Figures 1 and 2 are vertical sections (on the lines 1-1 and 2-2 Figures 2 and 1
respectively) of an electric switch made according to this invention.
a is a stand and 66 are two vessels of porcelain supported by it and filled with
flake graphite. cc are the conductors entering the bottoms of the vessels b and
connected to contact blades c¹ c¹ in them. d is the switch lever pivotted at d¹ to
the stand a and carrying a pair of copper blades e.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. A resistance consisting of a badly conducting powder and a conducting blade
or plunger which is inserted more or less into it.
2. A resistance consisting of flake graphite and a conducting blade or plunger
which is inserted more or less into it.
3. Variable electric resistances or rheostats substantially as described and
illustrated in the drawings.
Dated this 24th d
1000