US2319144A - Gaseous discharge lighting apparatus - Google Patents

Description

May 11, 1943. E. G. LODGE GAsEous DISCHARGE LIGHTING APPARATUS Filed Aug. 3, 1942 llllflIxAllll INVENTOR.

NEKS.

nia-,M0101 444 ATroR Patented May 11, 1943 2,319,144 GAsEoUsmscnaaGE LIGHTING mm'rus Edmund G. Lodge, St. Marys, Pa., assigner to Stackpole Carbon Oompany, St. Marys, Ps., a corporation of Pennsylvania Application .august 3, 1942, serai No. 453.317

(ci. 11s-124) 8 Claims.

This inventon'relates to electric circuits for gaseous discharge lamps, and more particularly to those in which the lamp is operated from a source of direct current.

A gaseous discharge lamp is one containing a gas that is ionized by a pair of electrically heated filaments. An example oi' this type of lamp is the tubular fluorescent lamp. One terminal of each nlament is connected to a sourceof alternating current,'and the other terminals of the filaments are electrically connected by a normally closed automatic switch, such as a bimetallic switch. When the current is turned on, electricity flows through the filaments and switch until the filaments become hot enough to ionize the gas around them. At about the same time the electrically heated switch snaps open', and the resulting voltage surge, which may reach 800 or 900 volts or even higher, causes ionization of the gas in the tube and reduces the voltage to about 110 volts. An electrical device called a ballast is placed in the circuit to prevent the current from burning out the filaments while the switch is closed.

In many cases it is desirable to use fluorescent lamps and the like where there is no priary source of alternating current, such as in trains andr airplanes. It is therefore necessary to make special provision for producingv the alternating current necessary to operate the lamps.l

For this purpose it is common practice to generate alternating current by means of motor generators or dynamotors driven by the available direct current, but they are heavy, bulky, and expensive. Inthe case of dynamotors their fine and necessarily closely spaced windings often are destroyed when the load is suddenly removed. That is, to keep down the bulk and weight of dynamotors, the wire size and insulation thickness is kept at a minimum, so any unusual surge of voltage-caused by an open circuit tends to break through and destroy the insulation. Also, accidental shorts often cause the windings .to be burned open due to the small wire size. A multitude of delicate operations are lnecessary to con neet the armature windings to the commutator segments, causing hazards, and requiring close inspection with resulting high cost. All of these disadvantages become particularly objectionable in the case of airplanes, especially those used in warfare where reliability and reduction in weight are highly important. In warplanes the calibrations and needles on indicator dials are coated with fluorescent paints and the lamp tubes are.

left uncoated, resulting in the dials glowing while the black light from the lamps is invisible.

Vibrators also are used for the purpose of converting low voltage direct current into alternating current so that it can be stepped up by a transformer to a higher voltage. Vibrators have several undesirable features, one of the chief ones being unreliability. The vibration rate of the reed is so limited that fairly large transformers and filters are required. As the reed vibrates, the ilow of current removes contact material from one contact and deposits it on the adjoining one. 'I'his not only changes the characteristics of the vibrator but it causes the reed to stick. Once sticking begins it is generally necessary to replace the vibrator. Furthermore, vibrators are relatively expensive for their output because they require very careful adjustments to make them operable in the nrst place.

- It is among thev objects of this invention to provide gaseous discharge lighting equipment for battery or other direct current operation having means for converting the direct current into alternating current which is compact and relatively light in weight, which is easy and inexpensive to make, which is self-starting, which is hlighly emcient, and which is sturdy and dependa 1e.

In accordance with this invention the secondary coil of a transformer is connected to the iilaments of a gaseous discharge lamp, such as a :iluorescent lamp. The primary coil of the transformer has a center tap adapted to be connected to a source of direct current, such as a battery or direct current generator, that is to be converted into alternating current for lighting the lamp. By center tap is meant any tap on the primary coil between its end taps and is not to be understood as meaning a tap at the exact center of the winding. A pair of ilxed electric contacts are connected to or near the opposite ends of the primary coil for engagement by rotary contact means adapted when rotating to make electrical contact with each of the nxed contacts alternately. I'he rotary contact means are adapted to be electrically connected to the source of direct current to complete the primary circuit. When the rotary contact means are driven, the ilow of direct current to each half of the primary coil is interrupted alternately, and as this current alternately flows in opposite directions in the primary coil, it induces alternating current in the secondary coil connected to the lamp filaments. The transformer steps up the voltage of the converted current to a point where it ls sumcient to operate the lamp.

The means by which the rotary contact means are driven preferably include an amature rotated by electromagnetic means that may consist of the transformer itself or a separate electromagnet. In the former. case the armature is journaled in such a position in the transformer that the leakage flux of the transformer rotates the armature. The primary coil of the transformer, or the electromagnetic coil when a separate coil is used, is connected in the circuit in such a manner that as the rotary contact means engage rst one fixed contact and then the other, the circuit through the coil is alternately energized and deenergized to produce the periodic magnetic impulses that rotate the armature. The transformer preferably is purposely made to have poor regulation characteristics, such as by winding the secondary with extra fine wire, so that the usual ballast wili be unnecessary. With such a transformer the load or resistance of the lamp laments before the automatic switch opens brings the alternating current voltage down to one proper for lament operation so that the filaments will not burn out. As soon as the switch opens and the gas in the lamp is ionized, the voltage increases to about 110 volts and the'lamp operates.

The preferred embodiment of the invention is illustrated in the accompanying drawing in which Fig. 1 is a side view of my current interrupting device by which direct current is converted into alternating current for operating a gaseous discharge lamp; Fig. 2 is a view of the opposite side of the device; Fig. 3 is an end view; Fig. d is a plan view; and Fig. 5 is a diagrammatic view of the entire lamp circuit. Y

Referring to Fig. 5 of the drawing, one terminal of each filament i of a gaseous discharge lamp 2, such as a'iiuorescent lamp, is electrically connected to a normally closed automatic switch 3 which may be a thermo-switch having a bimetallic element that opens the switch when it becomes heated by electric current flowing through it. The other terminals of the filaments are con-f nected by wires d to the opposite ends of the secondary coil 5 of a transformer 6. The ends of the primary coil i of the transformer are connected by wires 8 to a pair of xed electric contacts or brushes S and it that are engaged by a rotating contact member li. This contact member includes a pair of diametrically opposite live contact segments l2 and I3 which are electrically connected through a collector button i6 and a wire l5 to a source of direct curernt, such as a storage battery I6. The other side of the battery is connected by a wire Il to the center tap of primary coil 1. It will be seen that as contact member il rotates it connects the battery with rst one end and then the other of the `primary coil. The current thus ows alternately in opposite directions through the primary and thereby induces alternating current in the secondary coil. The transformer as a whole steps up the voltage of the alternating current to a point satisfactory for operation of the lamp.

For an understanding of the details of construction of the device by which direct current is converted into alternating current vfor operatingthe lamp, reference should be made to Figs. 1 to 4. As there shown, the transformer has an E-shape core 20 with a center leg on which is mounted a coil 2| that is a combination of primary and secondary windings 1 and 5, respecatraiga tively (Fig. 5). Projecting toward each other fromthe two end legs of the transformer core are core extensions 22 the inner ends of which are spaced apart above the center leg of the core.

- 'I'he metal laminations forming the core are clamped together at the bottom by bolts Z3 and at the top by bolts 2d.

Mounted on top of core 20 is avcover plate 2S of non-magnetic material, such as brass, which has downturned ears 27 at both ends that overlap the end legs -of the core. The lower edgeof each ear is notched topermit it to iit over upper bolts 2d and to be clamped by nuts zagainst the core.

YThe central portion of plate 25 is arched over the gap between core extensions 22, and this arched portionA projects from both sides of the core where it forms the upper portions of integral substantially cylindrical bearing supports 29.

Attached to the outer end of one of the bearing supports is an insulating plate 3i provided with a pair of outwardly projecting pins 32 on each of which one end of a contact arm 33 is pivotally mounted. The free ends of these arms carry brushes 9 and lil, preferably made from a mixture of powdered silver andy graphite, connected by wires 8 to the ends of the primary coil. The two brushes are held by springs (not shown) in engagement with the commutator-like member il mounted on the adjacent end of a horizontal metal shaft 34 journaled in bearings 35 mounted in metal bearing supports 29 of cover plate 2S.

The commutator includes the pair of electric contact segments l2 and i3 and enough metal segments 35 insulated from them to complete the cylinder without at any time bridging the adjoining brushes. It is preferred to divide the commutator into six segments of equal size embedded in a core 3l of insulating material. The commutator is provided at its inner end with a project ing hub 38 tightly engaging shaft 3d and integral with the live contact segments but separated from segments 36. Engaging this hub is the smai. collector button It carried at the center of a flat spring 39 supported at its ends by metal pins di projecting from bearing supports 2t. The pins are so positioned relative to the shaft that spring 39 must be bowed slightly so that button is makes good contact with hub 38. The contact segments i2 and i3 of the commutator are thus grounded to cover plate 26 and core 2@ through button tl, spring 39, and pins t l As the battery is ground-= ed to core 20 by wire l5, the contact segments are electrically connected to the battery at all times.

It will thu's be seen that, as the commutator revolves, its live segments engage first one'brush and then the other. This causes the current from battery I6 to pass alternately through each brush so that it ows through the primary coil rst in one direction and then the other to give an alternating current effect. Also, due to the break in the circuit every time a live segment of the commutator leaves a brush and before the other brush is engaged by a live segment, the transformer is alternately energized and deenergized.

The'commutator is rotated by means of an armature 'd5 rigidly mounted on the central portion of shaft 36. The armature has a plurality of radial projections or wings, preferably four, spaced at intervals over where two live commutator contacts are used. When either one of the two primary contact segments is in engagesions 22. .This leakage iiux or magnetic impulse attracts the adjacent projection of the amature and draws it toward it, thereby rotating the armature. This moves the live contact of the commutator out of engagement with the adjoining brush and breaks the circuit through the transformer. rotating armature carries the other live contact segment into engagement with the other brush so that the transformer is again energized and another impulse thus given to the armature. In this manner thearmature is rotated at high speed.

Referring more specifically to Fig. 1, the rotor, which consists of the armature, commutator and supporting shaft. is shown in one of the four similar positions it should be in for starting and forrotation in a clockwise direction. The lower right-hand projection of the armature is closer to the center leg of the transformer core than is any other part of the armature, and contact segment I2 is in contact with upper brush I0 but about to leave it. When the current from battery I6 is turned on, the transformer is energized and the lower right-hand projection of the armature drawn around toward the center leg of the transformer due to the effort of the -ux set up in the transformer to close the gap between its center leg and the armature or to find the path of least resistance. By the time the armature projection points within about 2 'of straight down so as to afford a low resistance path for the flux, contact segment I2 hasleft brush I0 so that the transformer is deenergized, but momentum continues the rotation of the armature until contact segment I3 makes contact with brush 9 so that the transformer 'is again energized and the cycle repeated. Shortly after segment I3 leaves brush 8 it moves across brush I0, after which contact I2 engages brush 9, whereby the armature is continuously rotated at high speed.

In order that the rotor will always be selfstarting, means is provided for stopping the armature with one of its projections in the position shown in Figs. 1 and 2 whenever the current to the device is turned oif. For this purpose, as shown in Fig. 2, a hollow cylinder 41, mounted on the side of the transformer opposite t that from which the commutator member projects, contains a solenoid coil 48 that is connected in series in wire I1 between the battery and a filter condenser Il connected to that wire and grounded to the transformer core. A fixed core 49 is disposed in the lower half of the solenoid inside of a tube SII that projects above the coil. 'I'his tube guides a vertically reciprocable movable core I that extends above cylinder 41 and that is urged upwardly by an encircling spring 52 compressed between the top of the tube and the bottom of a disc l2 rigidly mounted on the upper portion of the movable core. The upper endY of the movable core is bifurcated and receives the slotted outer end of an arm 54 the inner end of which is pivoted to the lower portion of a bearing support 29. The arm and core are pivotally connected by a pin 55. The arm is provided near its inner end with an upwardly extending integral projection 56 from the upper end of which a roller 51 projects outwardly. This roller is adapted to engage the edge of a disc-like cam il rigidly mounted on the projecting end of rotor shaft 3l. The cam is more or less square with a central depression in each edge, and it is so `positioned relative to the armature that when roller 51 engages the cam in any one of its four depres- However, the momentum of thesions the armature is in starting position, which is shown in Figs. 1 and 2.

When the current is turned off, the spring 52 lifts movable core 5I and thereby swings arm il upwardly to press roller 51 against the edge of the cam. The rotating cam comes to rest with the roller disposed in one of its four depressions, and the armature thus is ir. starting position. As

' soon as the current is turned on again the magnetic pull on the armature is sufcient to cause a high part of the cam to force roller 51 outwardly. This action swings the outer end of the arm down and thereby forces the movable core down into the solenoid far enough to bring it into the eld of magnetic attraction of the fixed core 49. The latter continues to draw the movable core downwardly and the roller is thus entirely fleed from the cam so that the rotor is ree to rotate. Lever 54 then is in the dotted-line position shown in Fig. 2.

Another feature of this invention is that the transformer is preferably wound to provide poor electrical regulation. This may be done by winding the secondary coil with extra fine wire. The

regulation is most suitably such that when the current is rst turned on the voltage of the secondary coil can be held down to about 20 volts by the electrical resistance of the lamp filaments. With this voltage there is no danger of burning out the filaments. As soon as the automatic switch opens there is a surge in voltage up as high as 900 volts or higher. This causes ionization of the gas in the lamp tube, after which the current drawn is such that the voltage output of the transformer is raised and stabilized at about 110 volts A. C. With this type of transformer it is not necessary to use a ballast and therefore the cost and weight of such an element are eliminated. n

Gaseous discharge lighting equipment constructed in accordance with this invention makes use of a current converting device that is neither bulky nor heavy for its output. The device is inexpensive to make and is dependable in opera-l y to the opposite ends lof the two transformer coils and to the center tap of the primary coil. The use of a transformer permits layer winding and layer insulation,.which are the easiest, without thought of bulk and weight.

According to the provisions of the patent statutes, I have explained the principle and operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

l. The combination with a gaseous discharge lamp provided with spaced filaments, of a transformer having its secondary coil connected to said filaments, the primary coil of the transformer having a center tap adapted to be connected to a source of direct current that is to be converted into alternating current, a pair of fixed electric -contacts connected to the opposite ends of the primary coil, rotary contact means for connection to said source of direct current and adapted connected to said rotary contact means for driving said means to interrupt the flow of direct current to each half of said primary coil alternately whereby said secondary coil supplies alternating current to said lamp filaments, and means for stopping said rotary contact means in electrical contact with one of said fixed contacts when the direct current to the primary coil is shut oi to thereby assure self-starting of the armature when said current is turned on again.

2. The combination with a gaseous discharge lamp provided with spaced filaments, of a transformer having its secondary coil connected to said filaments. the primary coil of thc transformer having a center tap adapted to be connected to a source of direct current that is to be converted into alternating current, a pair of fixed aeiaiie electric contacts connected to the opposite ends of the primary coil, rotary contact means for connection to said source of direct current and adapted when rotating to make elcctricalcontact with each of said iixed contacts alternately with a break between, a rotatable armature operatively connected to saidrotary Contact means for driving said means to interrupt the flow of direct current to each half of said primary coil alternately whereby said secondary coil supplies alternatingr current to said lamp filaments, means for stopping said rotary contact means in electrical contact with one of said fixed contacts when the direct current to the primary coil is turned oli, and means vfor automatically moving said stopping means out of operative position when said direct current is tuined o n again.

3. The combination with a gaseous discharge adapted to be successively attracted by periodic magnetic impulses of said transformer, means connecting-the rotary contact means to said armature for rotation thereby, a cam connected to said armature for rotation thereby, spring-biased means 'for engaging said cam when the direct current is turned oi whereby to stop said armature with one of its projections adjacent said transformer and with said rotary contact means in engagement with one of saidiixed contacts, and electromagnetic means for withdrawing said spring-biased means from said cam when 'said primary coil is energized.

5. The combination with a gaseous discharge lamp provided with spaced laxnents, of a transformer having its secondary coil connected to said filaments, the primary coil of the transformer having a center tap adapted to be connected to a source of direct currect that is to be converted into alternating current, a core for said coils having two ends facing each other, a pair of nxed electric contacts connected to the opposite ends of the primary coil, rotary contact means for connection to said source of direct current and lamp provided with spaced filaments, of a transformer having' its secondary coil connected -to said filaments, the primary coil of the trans- VUV nately with a break between, a rotatable armature operatively connected to said rotary contact means for driving said means to interrupt the now of direct current to each half of said coil altei-nately whereby said secondary coil supplies al` teinating eurent to said lamp filaments, a stop member mounted for automatically stopping said armature in a predetermined position when the direct current is turned off, and electromagnetic means for moving said stop member out of stopping position when said primary coil is energized.

e. The combination with a gaseous discharge lamp provided with spaced filaments, of a transformer having its .secondary coil connected to said nlaments, the primary coil ol' the transformer having acenter tap adapted to be connected to a source of direct current that isto be converted into alternating current, a pair of fixed electric contacts connected to the opposite ends oi the primary coil, rotary contact means for con'- nection to said source of direct current and adapted when rotating to make electrical contact with each of said fixed contacts alternately with a break between whereby the circuit througn the primary is periodically deeneigized and tlie current in said circuit liows througn first one of said contacts and then the other to induce alternating current in said secondary, a rotatable armature having a plurality of radial projections adapted when rotating to make electrical contact with each of said nxe'd contacts alternately with a break between, and an armature rotatably mounted betweensaid core ends and adapted te be rotated by the periodical magnetic attraction of the core, said armature being operatively connected to said rotary contact means for driving the latter whereby to interrupt the iiow of direct 4 current to each haii of said primary coil alternately and to alternately energize and deener- .gize that coil.,

6. The combination withV a gaseous discharge lamp provided with spaced laments, of atransformer having its secondary coil connected to of the primary coil, rotary contact means adapted' to be electrically connected to said source o dlrect current and adapted when rotating to make electrical contact with each of said fixed contacts alternately, and a rotatable armature mounted I adjacent said core and having a plurality of radial projections adapted to be successively attracted by periodic magnetic impulses of the core, said armature being operatively connected to said rotary contact means for rotation thereof whereby fto interrupt the :dow of direct current to each lamp provided with spaced filaments, of a transformer including concentric primary and secondary coils, the secondary coil being connected to said filaments and the primary coil of the transformer having a center tap adapted to be connected to a source of direct` current that is to be converted into alternating current, a magnetic core common to both coils, a pair of nxed electric contacts connected to the opposite ends of the primary coil, a rotatable shaft, an armature rigidly mounted on said shaft and adapted to be rotated by periodic magnetic attraction of said core, and a commutator-like contact member rigidly mounted on one end of said shaft and adapted to be connected to said source of direct current, said contact member being adapted when rotating to maire electrical contact alternately with each of the xed contacts connected to the primary coil, whereby to interrupt the flow of direct current to each half of the primary coil alternately and to alternately energize and deenergize that coil.

8. The combination with a gaseous discharge lamp provided with spaced filaments, of an auto matic switch electrically connecting the filaments and adapted to open when said laments reach a predetermined temperature. to strike an arc between the iilaments, a transformer having its secondary coil connected to said laments, the primary coil of the transformer having a center tap adapted to be connected to a source of direct current that is to be converted 'into alternating current, a pair of xed electric contacts connected to the opposite ends of the primary coil, rotary contact means for connection to said source of direct current and adapted when rotat ing to make electrical contact with each of said nxed contacts alternately, and means for driving said rotary contact means to interrupt the ilow of direct current to each half of said primary coil alternately whereby said secondary coil supplies alternating current to said lamp iilaments, said transformer having poor regulation characteristics to thereby cause the electrical resistance of the filaments before said switch opens to reduce the voltage of said alternating current to a point at which it will not burn out the filaments.

EDMUND G. LODGE.

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