The Electrical experimenter

m36 THE ELECTRICAL EXPERIMENTER May, 1917
CeN5TRUQTeR
An Electrical Paradox or Selective Lamp Controller
average person is always in-
THEterested in a puzzle. When that
])uzzle is electrical, it is certain
to appeal to the amateur experimenter.
Can any of you think
of an arrangement by means of which a
single pole, single throw, knife switch may
be made to operate three different lamps
individually, during three successive inter-
vals that the circuit is closed? For example,
if the switch is closed once, light No.
1 will light and remain lit until the switch
is opened again. It will then go out. If
the switch is again closed, light Xo. 2
OXLY will light and remain lit until the
circuit is again opened. Similarly with light
No. 3.
To secure the result described, an arrangement
is employed somewhat similar
to that used on the automatic block signaling
systems of single-track electric railroads,
and elsewhere. .\ commutator is
made to move from one contact segment to
another every time an electro-magnet
draws its armature down (or up).
Referring to Figs. 1 and 3, when the circuit
is closed, the magnets attract the armature,
pulling it down. The hook C
catches over a tooth of the ratchet wheel
R. By notin.g the direction of pitch of the
teeth, it will be seen that the movement of
the hook will not cause the ratchet to move.
The ratchet is rigidly attached to a shaft
B. on which a gear wheel K is also firmly
fastened (Fig. IV This cog meshes with
1 smaller one, J, which is tight on shaft A.
BY ALBERT H. BEILER
A vv'ooden cylinder, G, is fi.xt on A, which
has brass segments fastened along its perifery
as shown at E. It will be Seen that E
touches one of the brass strips I. This
closes a circuit and lights a lamp. If some
means could now be employed to move the
wooden cylinder Y} o{ a. revolution, another
segment seen slightly under the middle
brass strip would touch the strip, while the
Perspective View of Selective Lamp Control ler Built from a Telegraph Sounder, a Few
Gear Wheels and Other Odd Parts. At the Left Is Shown the Brushes and Commutator
Unit with Gear Attachment fo r Rotating the Segment Drum.
first segment would have moved away from
the end strip. Another third of a revolution
would cause the foremost segment to
touch the foremost I and close another cir-
cuit, while the other two circuits would remain
open. When the switch is closed,
the cylinder with the brass segments, called
the commutator, will not move, but the hook
will engage a tooth of the ratchet. Simultaneously
a lamp will light.
When the switch is now opened,
the lamp will go out and the
same instant the retractile
spring T will pull the armature
up again, since the magnets
have lost their power of attraction.
Hook C will pull the
ratchet up a distance equal to
its (the hook's) travel. This
distance is such that the ratchet
will have completed l/12th of a
revolution when the armature
shaft F strikes its stop screw
N. It must here be stated that the ratchet
has 12 teeth, gear K, 48 teeth, while
gear J has 12 teeth ; the ratio between
the two latter being 4 to 1. When the
ratchet makes l/12th of a turn, K will also
turn l/12th of a revolution. Thus the
third of a revolution movement, which is
necessary to bring each segment under its
respective contact, is accomplished.
It is possible that the reader who has followed
this explanation carefully w-ill ask
why the movement of the ratchet should be
accomplished by the retractile spring T
when the magnet exerts a greater force.
In other words, why should not the segments
change on the down stroke of the
armature instead oi on the up stroke-' The
answer is this : Suppose the commutator
turned if a circuit was closed
when it was opened, then, for
instead of
an instant
the lamp would light which had just previously
been lit. It is true that almost immediately
it would go out and tlie required
lamp would light but tlie result would very
obviously be unsatisfactory. The time taken
for the cylinder to commutate would be the
time required for the magnets to pull the armature
down. As this does not occur instantaneously,
the above described result
would occur. .Another objection to having
the commutator rotate on the down stroke
of the armature is that a segment and a
brass strip, each carrying current, would be
separated from each other by the movement
of the commutator and create a spark
v.'hich would soon pit the segments and
brass contacts and thus interfere with the
satisfactory operation of the device. With
the device arranged as just described the
commutator moves an instant .\FTER the
circuit has been opened, thus preventing any
arc from forming.
The wiring diagram is shown in Figure
8. B B B are the strips I of Figure 1.
C represents the commutator segments. M
is the electro-magnet. R is the rheostat,
made of salt water with carbon electrodes,
or sulfuric acid, and carbon or lead electrodes.
Two 100 watt lamps in jjarallel may
be connected
stead of the
in series
rheostat.
with the magnet in-
The magnets must
receive from IJj to 2 amperes, since they
have quite a pull to make. The smaller
circles B show where the wires from the
device are connected to the binding posts
seen in Fig. 1.
.\nyone sufficiently interested may tnake
one of these contrivances by following the
diagrams and instructions which follow.
Photo of Selective Lamp Switch or Controller as Built
by the Author, Together with Three Lamps to Be Controlled
and Main Circuit Switch.
Secure an old telegrapli sounder of the
sort that is generally sold to amateurs for
practising telegraphy. Unscrew the parts
from the base and mount the frame, mag-