Year: 1897

page_text: Date of Application, 25th May, 1897
Complete Specification Left, 17th Feb., 1898-Accepted, 16th Apr., 1898
I, PETER VALENTINE MCMAHON, of 195, Clapham Road, in the County of Surrey,
Engineer, do hereby declare the nature of this invention to be as follows:-
My invention relates to improvements in the switching gear generally known
as a series parallel controller for starting motors in series and after a certain
speed has been attained placing the motors in parallel, as in the case of an electric
locomotive or other electrically propelled vehicle.
The switch or controller may be described as a combination of an ordinary
rheostat switch preferably of circular form; (but the contacts may be arranged in
straight lines or other convenient form) containing a number of contacts depending
upon the capacity of the switching gear, and a separate parallel switch both
preferably secured to the same base and worked by the same handle. Arranged
concentric with the rheostat switch are the necessary contacts for changing the
motors from the series to the parallel position. On an insulated disc or arm also
concentric, are secured the parallel brushes or contact fingers, this disc with its
brushes is moved by the handle of the rheostat switch at predetermined positions
only, but in other positions of the rheostat switch the handle is free to move without
operating the parallel switch.
This arrangement allows the starting resistance to be inserted, cut out of circuit,
and inserted again where necessary; before the motors are changed from series to
parallel; without using long contacts, as the parallel switch is not operated until
the motors are about to be placed in parallel. Again when the motors are running
in parallel, and it is required to switch the current off, the parallel switch is
allowed to remain with the motors in parallel until all or nearly all the starting
resistance is placed in circuit when the handle of the rheostat operates the parallel
switch placing the motors back in series, the current flowing at this period being
reduced to a minimum the circuit is then broken through the rheostat switch.
the moment of changing from the series to the parallel position any sparking that
may take place is transferred from the parallel switch contacts to a spring or
quick breaking contact outside or apart from the parallel switch contact."
Dated this 25th day of May 1807
At
I, PETER VALENTINE MCMAHON, of 195, Clapham Road, in the County of Surrey,
Engineer, do hereby declare the nature of this invention and in what manner the
[Price 8d.]

page_text: same is to be performed to be particularly described and ascertained in and by the
following statement:-
―
My invention relates to improvements in the switching gear generally known as
a series-parallel controller for starting motors in series, and after a certain speed
has been attained placing the motors in parallel, as in the case of an electric
locomotive, or other electrically propelled vehicle, and has for its object to provide
a switch of simple construction and operation whereby the liability of damage
through sparking is reduced to a minimum.
The switch or controller may be described as a combination of an ordinary
rheostat switch, preferably of circular form; (but the contacts may be arranged
in straight line or other convenient form) containing a number of contacts,
depending upon the capacity of the switching gear, and a separate paralleling
switch both preferably secured to the same base and worked by the same handle.
Arranged concentrically with the rheostat switch are the necessary contacts for
changing the motors from the series to the parallel position. On an insulating' disc
or arm also concentric, are secured the parallel brushes or contact fingers. This
disc with its brushes is actuated by the handle of the rheostat switch, at predeter-
mined positions only, but in other positions of the rheostat switch the handle is
free to move without operating the parallel switch.
This arrangement allows the starting resistance to be inserted, cut out of circuit
and inserted again, where necessary before the motors are changed from series to
parallel without using long contacts as the parallel switch is not operated until
the motors are about to be placed in parallel. Again when the motors are running
in parallel and it is required to switch the current off, the parallel switch is allowed
to remain with the motors in parallel until all or nearly all, the starting
resistance is placed in circuit, when the handle of the rheostat operates the parallel
switch placing the motors back in scries the current flowing at this point being
reduced to a minimum; the circuit is then broken through the rheostat switch.
At the moment of changing from the series to the parallel position any sparking
that may take place is transferred from the parallel switch contacts to a spring or
quick breaking contact outside or apart from the parallel switch contacts.
In order that my invention may be better understood and more readily carried
into effect, I will now describe it with reference to the accompanying drawings in
which the same letters refer to the same parts in all the figures.
Figure 1 is a plan of the complete switch, and
Figure 2 a section through the centre.
A A are the contact blocks of the rheostat switch secured to an insulated base E,
with a suitable resistance between each block. The current is led into the circular
ring B, in the centre also secured to the base E, and then through the spring contact
piece C, to the blocks A the amount of resistance in circuit depending of course
upon the position of the arm 1) and the contact piece C.
The parallel switch is arranged concentrically with the rheostat switch, and con-
sists of an insulating disc G, secured to the spindle F, upon which the handle 1)
also revolves, the disc G being prevented from moving by the lock nuts shown; on
the spindle I is another insulating disc or set of arms H free to revolve and actuated
by the handle D at predetermined positions only. To this disc are secured the
parallel contact makers or brushes J1 J2 J3, in this case three in number. The
brushes (J1 J2 J3) make contact with the conducting segments L1 L2 L³ L4 & L³,
five in number in this present case, but the number may be decreased or increased
as and when necessary. These segments are secured to the disc G and are insulated
from and connected to one-another as shown in Figures 3, 4, 5 and 6.
On the outside of moveable disc H or side removed from the brushes Ji J2 J3,
are projections M.M', with which another projection N on the handle D, 'engages H
as hereinafter described.
•
The brushes J1 J2 J3 are so arranged that their contact making piece has only a

page_text: limited, travel outwards so that when a brush comes off a segment as shown, the
contact piece does not come out far enough to prevent it mounting the next
segment. The segments L1 L2 L3 L & L are easily renewable, as they are secured
to the brackets on the fixed disc G, with countersunk screws.
The insulating disc G prevents any sparking that may obtain at the rheostat
contacts from reaching the parallel contacts or vice versa..
The operation of the switch is easily followed by reference to Figures 3, 4, 5 & 6.
The current enters the ring B, (Fig. 3), and in the position of the contact C
shown, all the external resistance is cut out of circuit, when this contact C moves
farther round in the direction of the arrow (Figure 3), resistance is again inserted
before changing the motors from the series to the parallel position. When C
reaches the double block O all the "change over" resistance is then in circuit
and the projection N on the handle D is just. touching the projection M³, on the
disc H carrying the parallel brushes J1 J2 J3 (Figure 1). A further movement of
the handle carries the disc H with it and places the motors in parallel.
Figure 4 shows diagramatically the segments of the parallel switch, the brush J₁
connecting the segments L' and L3; in this position the motors are in series and
the brushes J2 J3 are clear of the segment. A slight movement of the disc H
brings the brush J2 into contact with segments L L and momentarily short-
circuits No. 2 motor. (Figure 3) and puts No. 1 motor across the mains with the full
line voltage at its terminals; the next instant the brush J3 comes in contact with
segments L and L3 and puts No. 2 in parallel with No. 1, both motors now
receiving the full line voltage except an amount lost in the regulating resistance
which can be controlled by the handle 1). Figure 5 shows both motors in parallel
with all regulating resistance in circuit and Figure 6 shows the same condition of
the motors with all regulating resistance cut out.
.
At the moment of short-circuiting No. 2 motor and putting it into parallel
there niay be a slight spark at the contacts, but by short-circuiting and
placing No. 2 motor in parallel with a proper value of current (found by trial with
the switch in practice) flowing, this spark may be eliminated.
In switching off, if the disc H and brushes J1 J2 J3 were rigidly attached to the
handle. D. In addition to the contact C, putting external resistance in the circuit,
the parallel brushes J1 J2 J3 would make a series of contacts with the segments L'
LL L & L in the reverse order to that described above, when disastrous sparking
would result. This is avoided by having the disc H independent of the handle 1)
and only operating it by the projection N, engaging projections M M on disc H.
ין
The handle D in coming back in a clockwise direction allows the disc H to remain
in the parallel position until the projection N on the handle D engages with M.
This takes place before all the resistance in the rheostat switch is cut out, farther
travel of 1 carries H round, but on account of the length of the segments L¹ L³
L3 L&L, no change of electrical connections takes place until the contact
maker C (Figs. 1 & 3) is on the last block A¹ of the rheostat switch and a minimum
current flowing; a slight additional movement now breaks the circuit on the
rheostat switch and places the motors back in series. Any slight sparking at the
parallel contacts can be transferred to a quick break, but I prefer 'to break the
circuit on the rheostat switch and pause for an instant just before placing the
motors back in series. In this manner all trace of sparking at the parallel contacts
can be avoided.
In order to prevent the disc H from moving accidentally I provide a cam or
ratchet X (Figs. 1 & 2) secured to the disc G, a pawl Y attached to disc H and
moving to and from the centre thereof being held against the ratchet X by a
spring. It will thus be seen that a certain extra pressure on the switch handle D
is required when the parallel switch changes from series to parallel and vice versa.
In some cases it may not be convenient to use the rheostat and parallel switches
in a circular form; I then arrange the contact blocks of the rheostat switch in a
straight line with resistance between them as before. The segments L L L L L³

page_text: of the parallel switch are also arranged so as to form a flat instead of a circular
surface, on which the brushes J1 J2 J3 make contact as before. A suitable
insulating substance is interposed between the rheostat contacts and the parallel
contacts to prevent any sparking that may obtain on the rheostat switch reaching
the parallel switch or vice versa. Projections are fixed on the arm or support of
the brushes J1 J2 J3 which engages with the projection on the arm or handle that
moves the rheostat contact and the result already obtained with the circular form
in changing the motor from series to parallel and back into series again is arrived
at as hereinbefore described.
Another very great advantage arises from having the parallel brushes J¹ J2 & J³
operated by the projections already described, namely, when dealing with large
electric motors as used on electric locomotives it is very often necessary to switch
on the current for a few seconds only, as in the case of a locomotive "setting back"
on a train in which case it may be necessary to move the locomotive only a few
inches. In switching off the current again considerable sparking takes place at
the contacts of the rheostat switch, unless the number of contact blocks is great
and the resistance between each block small. With my switch the number of
blocks and the resistance between them on the rheostat switch can be regulated to
any extent without in any way interfering with the parallel switch. Obviously
this advantage applies to starting any large motors and switching off the current
again before they get up to speed, whether for locomotives or motors used for
winding engines.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is:-
1. The combination of rheostat and parallel switches on the same hase, but
separated by a diaphragm or disc of insulating material whereby any sparking on
the rheostat switch is prevented from reaching the parallel switch or vice versa,
substantially as herein described and for the purposes specified.
2. In a series-parallel controller for electric motors, the combination of rheostat
contacts and parallel contacts, a disc or piece of insulating material separating said
contacts, and parallel contact brushes or strips adapted to be operated at pre-
determined positions only by means of a projection on the handle of the rheostat
switch engaging with a projection or projections on the parallel contact brushes
or their support or supports, substantially as herein described for the purpose
specified.
בד
111
1
0 TA
1000
JOHN P. O'DONNELL, Fell. Chart. Inst. P.A.,
Agent for the said Applicant,
70 and 71, Palace Chambers, Westminster, S.W.