IMPROVEMENTS IN ELECTRIC ARC LAMPS
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Leslie Bradley Miller at the Office
of the Commissioners of Patents on the 9th April 1883.
LESLIE BRADLEY MILLER of 34 Darnley Road, Hackney in the County of
Middlesex Electrical Engineer "IMPROVEMENTS IN ELECTRIC ARC LAMPS
"
My invention relates to Improvements in Electric Arc Lamps whereby I obtain
in a simple manner great steadiness in the light.
The class of lamps to which my invention relates is that in which the electro
magnets or solenoids used to regulate the descent of the carbon fall with the latter
as it is consumed. The great steadiness and certainty of action of my lamp is
chiefly due to the employment of two three or more armatures which act as friction
brakes. When the lamp is burning under normal conditions these brakes are never
all removed at the saine instant by the electro magnetic attraction so that the
friction of one or more will always prevent the too sudden descent of the carbon.
This is not the case when one armature only is employed as a brake and the
descent is retarded merely by an uncertain mechanical friction not controlled by
electro magnetic action as in this lamp. In practice I find that when three
armatures are employed they all vibrate under the varying electro magnetic
attraction and the time during which more than one brake is removed is so
infinitesimal that the descent of the carbon is imperceptible.
One form of this lamp which I employ with separately excited or shunt wound
dynamo machines consists of two vertical guide rods suitably insulated from one
another and connected together by horizontal cross pieces at the top and bottom.
Between these guides I arrange a rectangular frame of brass capable of being moved
up and down and which has rollers or grooves on each side to guide its movement.
These rollers or grooves are insulated from the rectangular frame on one side.
Within this frame I arrange two three or more small horizontal electro magnets
one above the other and in front of each I place a small armature working on a
pivot fixed in the frame. The shape of armature which I prefer is one that has
à flat surface next to the electro magnet whilst that in contact with the guide rods
is bevelled and curved in a suitable manner to act efficiently as a sliding friction
brake. Also I prefer the pivot to be placed in such a position that the descent of
the rectangular frame tends only to turn the said armature on its pivot. These
armatures are pressed by spiral springs which can be accurately regulated against

page_text: the guide rods and may pass through the hollow cores of the electro magnets being
carried by small rods attached to the frame and on which the regulating nuts work.
The pressure of the springs is sufficient to uphold in position the frame with the
electro magnets and carbon. I screw the core of these electro magnets at the end
opposite the armatures into a vertical plate of iron fixed in the frame This plate
is bent at right angles at the bottom and forms a polar extension beneath the
electro magnet. 1 may also employ a similar extension from one or more of the
opposite poles to increase the magnetic effects. Through this polar extension and
the bottom of the brass frame there passes a rod terminating at the top in an
armature and to the bottom of which is attached the upper carbon holder. This
armature with the carbon holder is raised an adjustable distance above the polar
extension by means of a spiral or other spring which is capable of regulation. *The
upper carbon is made to pass between guide wheels which are also contact wheels;
the lower carbon is fixed to the lower cross piece. The electro magnets are wound
with wire which forms a shunt of high resistance between the poles of the lamp
one end being connected to the frame and the other to the insulated groove and
thus to the other pole.
The action of this lamp is as follows:
The carbons being apart in the first instance the current passes round the electro
magnets pulling down the armature above the polar extension and with it the
upper carbon and removing the pressure of the brakes against the guide rods as
previously described. The whole frame together with the upper carbon now slowly
slides down the guide rods until the carbons are in contact when, the current being
almost entirely diverted from the electro magnets, the pressure of the spring acting
on the armature attached to the upper carbon causes the latter to ascend and strike
the arc.
At the same time the pressure of the brakes is renewed and the frame
held in position. As the arc increases in length the current round the electro
magnets is increased causing the brakes to vibrate in the manner before described
and allowing the upper carbon and frame gradually to descend as required.
Besides making the springs of this lamp adjustable I may wind the electro
magnets with a different number of turns of wire on each make the distance
between the pole and armature in each different, or vary the mass of iron, in order
that the pressure of all the armatures against the slide rods shall not be taken off
at the same instant. I may insulate one of the slide rods by insulating the upper
carbon from the electro magnet frame and the guido wheels from the slide rod
causing the current to enter the carbon by the guide wheels only and connecting
one end of the shunt circuit to the carbon.
When I wish to start with the carbons in contact I suppress that part of the
iron plate which is bent at right angles and which I have called the polar extension
and also its armature and employ an electro magnet in the main circuit which I
cause either to raise the upper or lower the lower carbon for the purpose of striking
the arc. In that form in which I raise the upper carbon I prefer to employ a
horizontal electro magnet wound so as to form a consequent pole in a mass of iron
in the middle. Through this mass passes a rod to the bottom of which is attached
an armature and the upper carbon holder. The distance of the armature below the
'mass of iron may be made adjustable by a nut and a spring regulated by a screw
may be employed to press the upper carbon down. By making use of the polar
extension of the shunt electro magnets and placing an armature above as well as
below the electro magnet in the main circuit I can make the action differential.
In this construction I insulate the guide wheels and pass the current from the
guide rod through the electro magnet down the carbon or I may make metallic
connection between the upper carbon holder and the guide wheels in any suitable
manner. By the use of hollow guide rods in which a resistance is placed I may
cause part of the main current to pass through the electro magnet and part through
the guide wheels to the carbon.
The form of electro magnet which I prefer to use for striking the arc by pulling
down the lower carbon is circular, having a hollow core to contain the adiustable

page_text: spring and the small rod to the top of which the armature and lower carbon holder
is attached. This electro magnet may be surrounded outside with a ring of iron
to increase the attractive pull and for protection. With this lamp I may employ a
cut off formed by an armature which is usually upheld by a spring but which,
when the attraction of the shunt magnet becomes unusually great pulls down the
armature and in so doing throws the arm of a weighted lever over a projection on
the end of the armature making a contact which short circuits the lamp. The
armature is then pulled up by the spring and makes the contact secure, the
projection on the armature preventing the lever from returning to its original
position.
In a form of this lamp in which the arc is struck by pulling down the lower
carbon I make use of one electro magnet which has three or more brakes and
springs similar to those first described and a cut off arranged in the following
manner: An extension from one of the poles is brought above the electro magnet
and over this there is an armature, which when the pole caused by the shunt
current becomes very strong owing to the arc being broken or nearly broken from
any cause, is pulled down against the action of a spring and makes a contact that
diverts the main current round through a coil of thick wire on the electro magnet.
This increases the attractive pull on the brakes and tends to bring the carbons
together again. Tho instant they retouch the current is diverted for the most part
from the coil brought into action by the cut off the attractive pull of the polar
extension is not sufficient to maintain the contact, the whole current again
passes through the carbons the arc is struck and the lamp again brought into
action.
I may wind any of the electro magnets differentially and combine any part of
one form of lamp with any part of another.