IMPROVEMENTS IN REGULATORS FOR ELECTRIC MOTORS.
Year: 1881

page_text: PROVISIONAL SPECIFICATION left by John Henry Johnson at the Offico
of the Commissioners of Patents on the 15th October 1881. A commu-
nication from abroad by La Société Anonyme La Force et la Lumière
Société Générale d'Electricite, of Brussells, in the Kingdom of Belgium.
JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of Middlesex,
Gentleman. "IMPROVEMENTS IN REGULATORS FOR ELECTRIC MOTORS.
A con-
munication from abroad by La Société Anonyme La Force et la Lumière Société
Générale d'Electricite, of Brussells, in the Kingdom of Belgium.
•
This Invention relates to apparatus for regulating or controlling the speed and
power of electric motors.
It is well known that an electric contact formed by causing two conducting
bodies to touch each other opposes a resistance to the passage of the current, which
resistance varies with the nature and dimensions of the two conducting bodies, and
with the amount of pressure with which the said bodies or conductors are pressed
together. The electrical resistance of a transversely divided conductor may
consequently be increased or diminished at pleasure by increasing or diminishing
the pressure between the several parts of the said conductor. When a series of
contacts are employed the diminution or increase in the resistance corresponding
to a certain variation of pressure will increase in proportion to the number of
contacts.
The essential part of the improved regulator or rheostat consists of an ordinary
metallic chain. This device presents a series of approximately similar points of
contact capable of being pressed together simultaneously, with a force which
admits of being readily applied or removed by straining or slackening the chain.
When the chain is tightly stretched the resistance is comparatively slight, but
when it is slackened or allowed to hang loosely the resistance is considerably
increased.
The degrees of tension intermediate between these two conditions produce
corresponding variations in the resistance, so that by means of a conductor of this
description all degrees of resistance may bo obtained between the two extreme limits.
The range between the two limits increases in proportion to the number of links in
the chain.

page_text: In carrying out this Invention the chain rheostat is interposed in a circuit
connected with the electric motor, as hereinafter described.
In the case of electric motors working with soft iron or with polarised
armatures, and with permanent magnets or electro magnets, the chain rheostat is
inserted in the line of the conductor, which unites one of the poles of the source
of electricity with the corresponding pole of the electric motor. By altering the
tension of the chain thus interposed its resistance is modified, and consequently
the total resistance of the circuit and the intensity of the current is also corre-
spondingly modified, thereby producing corresponding variations in the power of the
maguetic and inducting reactions of the motor, and enabling the speed of the
latter to be controlled with facility.
In the case of motors working with electro magnets, whether the said magnots
are placed in the general or main circuit, or in derivation on the circuit of the
polarized armature upon which the magnets react, the two extremities of the chain
rheostat are respectively placed in electrical communication with the two extremni-
ties of the circuit of the electro magnets, so that the chain establishes a derived
or branch circuit upon this line. The resistance of the chain when slack must bo
considerably greater than the resistance of the circuit of the electro magnets, and
must be capable of being rendered relatively slight by stretching the chain. The
working of the rheostat will be readily understood; when the chain is slack the
amount of electricity passing along it is small, and the maximum effect is produced
by the magnetic and inducting reactions in the motor, but when the chain is drawn
as tight as possible nearly all the current from the electro-magnets leaks away,
passing along the chain, and the actions are consequently enfeebled. All the inter-
inediate degrees of power between these two extreme conditions are readily
obtained by altering the tension of the rheostat.
In lieu of placing the chain rheostat in derivation on the circuit of the electro-
magnets of the motor, the chain may be similarly arranged on the circuits of the
coil.
When the source of electricity is an electrical machine, the rheostat may bo
placed in derivation either on the circuit of the electro magnets of this machine or
on the circuit induced by it.
The chain may be formed with links of any convenient shape, but it is preferred
to employ circular links made of round wire and connected together in the ordinary
manner. One extremity of the chain is connected to a fixed or stationary metallic
contact piece, and the opposite extremity is connected to a moveable metallic
contact piece capable of being acted upon by the hand or by the foot of the
operator. For example:-
The extremities of the chain are connected with the electrical apparatus or
motor through these contact pieces, according to one of the modifications herein-
before described. It is generally preferable to attach the moveable contact piece
to a lever in order to facilitate the working, and it is desireable to support this
lever by means of a counter spring. Under these conditions tho play or motion of
the lever or pedal is extremely small, on account of the inelastic nature of the
chain.
A more delicate adjustment of the pressure or tension is obtained by imparting
a certain amount of elasticity to the apparatus, and increasing the range of motion
of the lever. This is effected by interpolating a tension spring between the
stationary contact piece and the end of the chain, the said spring being weaker
than the counter spring. By pressing on the lever the tension spring is extended,
and the strain upon it and consequently upon the links of the chain may thus be
gradually increased or adjusted with great precision.
In order to diminish the effect of the incidental resistance of the tension spring,
and to prevent the latter from becoming heated, it is adviseable to connect the
extremity of the chain with the fixed contact piece by means of a flexible
conductor.
It is evident that the lever may be worked directly by the foot or by the hand,

page_text: or through the intervention of a screw or other suitable device; or again, the lever
may be dispensed with, and any other convenient mechanical arrangement capable
of producing a similar effect may be employed.
In lieu of a single chain a number of chains or lengths of chain may be
employed, either for the purpose of increasing the average resistance of the rheostat
or for the purpose of diminishing its resistance by increasing the extent of cooling
surface. In the first case the lengths of chain are electrically connected by a
tension arrangement, and in the second case by a quantity arrangement.
The tension or pressure is uniformly distributed between all the lengths by
coupling them together in pairs at their upper or lower extremities by means of
lovers jointed at their contres to another lever or to a series of lovers combined,
after the manner of whiffle trees, in order to employ any desired number of pairs
of chains.