US2325142A - Current interrupting device - Google Patents

Description

July 27, 1943. E. G. LODGE 2,325,142

CURRENT INTERRUPTING DEVICE July 27, 1943. E. G. LODGE 2,325,142

CURRENT INTERRUPTING DEVICE Filed May 8, 1942 2 Sheets-Sheet 2 Ixr J 7 7 w/r/vfsscs. INVENTOR. @d/Maca BY (l. ML W. ma @/Lm'foMaaw# L.; ATTORNEYS.

Patented July 27, 1943 CURRENT INTERRUPTING DEVICE Edmund G. Lodge, St. Marys,

Stackpole Carbon Company,

Pa., assignor to St. Marys, Pa., a

corporation of Pennsylvania Application May 8, 1942, Serial No. 442,173

23 Claims.

This invention relates to electrical apparatus for interrupting direct current and converting it into alternating current so that it can be stepped up in voltage by a transformer. The embodiment of the invention disclosed herein is especially suitable as a substitute for ordinary synchronous and non-synchronous vibrators used in radio sets, and for dynamotors and motor-generators used for similar purposes.

Vibrators are used in radio sets 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, the a1- ternating current then being rectified or converted back to direct current at the higher voltage. As is well known, these vibrators contain an oscillating or vibrating armature or reed that is actuated by a solenoid so that contacts carried bv the reed alternately engage contacts on both sides of it. The vibrator is connected to the primary coil of a transformer in such a Way that the current flows first one way and then the other through the coil, thus producing in the primary an alternating current that is induced in the secondary. Such vibrators have several undesirable features. The bounce that occurs when the reed strikes the contacts at its sides produces an undesirable Wave form that contributes to hum and makes filtering difcult. Furthermore, the vibration rate of the reed is so limited that a fairly large transformer and filter are required. Asthe reed vibrates, the flow of current removes contact material from one contact and deposits it on the adjoining one, and this not only changes the characteristics of the vibrator but causes the reed to stick. Once sticking begins it is generally necessary to replace the vibrator. Vibrators are relatively expensive for their output because they require very careful adjustments to make them operable in the first place.

In the case of synchronous vibrators using two sets of contacts with very close adjustment for spacing and timing, the above-mentioned characteristics that cause the reed to stick are even more important. A further difliculty with synchronous vibrators is that it is difficult to control the timing, so they are often ineilleient in that respect, and changes in current load affect the synchronous characteristics and thereby alter the output.

Some of the chief objections to dynamotors are their cost, weight, and bulk. Because of their fine windings and necessary close spacing of all windings they 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. Due to the small size of the wire the regulation suffers, i. e., variations in load seriously affect the voltage output of the dynamotor. In fact, the regulation is so poor that in the military radio service at least two dynamotors are used, one for transmitting and one for receiving. In many cases a separate dynamotor has to be used for each stage. A multitude of delicate operations are necessary to connect the armature windings to the commutator segments, causing hazards and requiring close inspection with resulting high cost.

It is among the objects of this invention to provide current interrupting or converting apparatus which produces a relatively smooth wave form, which is self-starting, which is easy and inexpensive to make, which produces practically no hum, which produces current that is easy to filter, which can be operated at high frequencies so that small transformers and filters can be used with it, which has contact surfaces that are self-cleaning and will not stick, which has a minimum of arcing. which is sturdy and has a long life, which has a low cost in relation to its output, which is relatively light in weight, which gives positive timing in connection with its synchronous operation, which maintains substantially synchronous operation regardless of current load, and one embodiment of which makes use of a transformer as the actuating means for the current-interrupting armature.

In accordance with this invention a pair of fixed contacts are connected to the opposite ends of a transformer primary coil having a center tap connected to a source of direct current. A rotary contact member is mounted in such position that when rotating it makes electrical contact with each of the ilxed contacts alternately so that the direct current, which is also connected to the rotary contact members, flows through first one of the fixed contacts and then the other and thereby passes alternately in opposite directions through the primary coil. The rotary contact member is driven by an armature rotated by electromagnetic means which may consist of the transformer itself or a separate solenoid. 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 solenoid coil when a separate coil is used, is connected in the circuit in such a manner that as the rotary contact member engages rst o'n'e 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. A rectifier tube may be connected to the secondary of the transformer, or synchronous operation may be utilized by connecting fixed contacts to the ends of the secondary coil of the transformer and providing an extra set of rotary contacts, also driven by the armature, for alternately engaging each of the secondary contacts. The current induced in the secondary is taken out from a center tap of the secondary and from its ends. By center tap is meant any tap on a primary or secondary coil between its end taps and is not to be understood as meaning a tap at the exact center of the winding.

The invention is illustrated in the accompanying drawings in which Fig. l is a side view of my current interrupting device built into a transformer as it appears from the primary commutator side; Fig. 2 is a view of the opposite side thereof; Fig. 3 is an end view; Fig. 4 is a plan view; Fig. 5 isa perspective view of the armature and commutator-like contact members at both ends of the armature shaft, showing the circuit diagrammatically; Fig. 6 is an end view of a modification in which a separate solenoid is used; Fig. 7 is a plan view thereof; Fig. 8 is a transverse section taken on the line VIII-V111 of Fig. 6; Fig. 9 is a diagrammatic view showing the electric circuit for the modified embodiment;

Figs. 10 and 11 are views similar to Figs. 6 and 8, respectively, of a further modification; and Fig. 12 is an enlarged section through the commutator taken on the line XII-XII of Fig. 10. Referring to the drawings, a transformer has an E-shape core I with a center leg on which is mounted a coil 2 that is a combination of primary and secondary windings 3 and l, respectively, (Fig. 5). Each of these windings is center tapped, the center tap of the primary being adapted to be connected by a wire 5 to a source of direct current, such as a battery 6 (Fig. 5), and the center tap of the secondary being adapted to be connected by a wire 1 to the apparatus with which this device is to be used. The other wire B for the same apparatus is connected to ground, which in this case is the metal core I. Wire 5 is also connected to a lter condenser 43 -mounted on one side of the core to which it is grounded. Projecting toward each other from the two end legs of the transformer core are core extensions Ia the inner ends of which are spaced apart above the center leg of the core. The metal laminations forming the core are clamped together at the bottom by bolts 9 and at the top by bolts I0.

Mounted on top of core I is a cover plate II of non-magneticgmaterial, such as brass, which has downturned ears I2 at both ends that overlap the end legs of the core. The lower edge of each ear is notched to permit it to t over upper bolts I0 and to be clamped by nuts. I3 against the core. The central portion of plate Il is arched over the gap between core extensions Ia, and this arched portion projects Afrom both sides oi' the core where it forms the upper portions of integral cylindrical bearing supports Il.

Attached to the outer end of each of these shown) in engagement with commutator-like members mounted on the opposite ends of a horizontal metal shaft 29 journaled in bearings 29 mounted in metal bearing supports I4 of cover plate II. Each commutator consists of a pair of diagonally opposite electric contact segments 3I and 32, or 33 and 34, and enough insulated metal segments 36 to complete the cylinder without at any time bridging the adjoining brushes. It -is preferred to divide each commutator into six segments with all of those of the primary commutator the same size. Thus, each segment forms approximately 60 of a cylinder. For a reason that will be explained later, it is4 desirable to make the live contact segments 33 and 34 of the secondary commutator only 54, as shown in Fig. 2. Each commutator is provided at its inner end with a projecting hub tightly engaging shaft 28 and integral with the live contact segments but separated from segments 36. Engaging the hub 31 of the 'primary commutator is a small collector button 39 carried at the center of a fiat spring 39 supported at its ends by pins 4I projecting from bearing supports I4. The pins are so positioned relative to the shaft that spring 39 must be bowed slightly so that button 33 makes good contact with hub 31. The contact segments of the two commutators are-thus grounded to cover plate II and core I, through button 38, spring 39 and pins 4I.

It will thus be seen that as the commutators revolve, theirlive segments engage rst one brush and then the other. In the case of the primary brushes I9 and 20- this causes the current from battery 6 to pass alternately through each contact so that it flowsv through the primary coil flrst in one direction and then the4 other to give an alternating current effect. In the case of thesecondary brushes 2| and 22 the current induced in the secondary coil 4 ows through rst one brush and then the other in the same direction so that the current in the wires 'I and 3 connected to the center tap of the secondary coil and ground, respectively, flows continually in only one direction and thus again becomes direct current.

The two commutators are rotated by means of an armature 45 rigidly mounted on the central portion of shaft 28. The armature has a plurality of radial projections or wings, preferably four spaced at intervals of Where two live contacts per commutator are used. When either one of the two primary contact segments is in engagement with one of the primary brushes I9 and 20, current iiows through the transformer and produces a leakage flux in the gap between core extensions Ia. This leakage ux or magnetic impulse attracts the adjacent projection of the armature and draws it toward it, thereby rotating the armature. This moves`the live contact of the primary commutator out of engagement with the adjoining primary brush and breaks the circuit through the transformer. However, the momentum of the rotating armature carries the other live contact segment into engagement with the other primary brush so that the transformer is again energized and another impulse thus give to the armature. In this manner the armature is rotated at high speed. The current induced in the secondary coil passes through the secondary commutator in the same manner so that for every impulse of electricity through the primary coil an induced impulse leaves the secondary coil.

Referring more' specifically to Fig. l, the rotor, which consists of the armature, commutatore and supporting shaft, is shown in the position it should be in for starting and for rotation in a clockwise direction. The lower right-hand projection of the armature is closer to the center leg of the transformer than is any other part of the amature, and contact segment ll is in contact with upper primary brush 20 but about to leave it. When the current from battery l is turned on the transformer is energized and the lower righthand projection of the armature drawn around toward the center leg of the transformer due to the effort of the flux set up in the transformer to close the gap between its center leg and the amature or to find the path of least resistance. By the time the armature projection points straight down so as to afford the lowest resistance path for the flux, contact segment Il has left brush 20 so that the transformer is deenergized, but momentum continues the rotation oi' the armature until contact segment I2 makes contact with brush I9 so that the transformer is again energized and the cycle repeated. Shortly after segment 32 leaves brush Il it moves across brush 20, after which contact ll engages brush I9, whereby the armature is continuously rotated at high speed.

Due to the slight lag in inducing current in the secondary coil from the primary, the secondary commutator is mounted on shaft 2l with its live segments at an angle to those of the primary commutator, so that a secondary contact does not make contact with a secondary brush until after a primary contact has engaged a primary brush. A ready-to-start position of the secondary commutator is shown in Fig. 2. In the particular example illustrated in the drawings, secondary contact 34 will not engage secondary brush Il until after primary contact 1| has left brush 2l. This sequence of electrical contacting is controlled by transformer design, taking into consideration the materials used, the number of turns selected, the general efficiency of design, and the size of the buffer condenser 4B mounted on one side of core l as shown in Fig. 2 and connected to the two wires 24 of the secondary circuit. If electrical contact is held too long with either live segment of the secondary commutator, the contact would be carried over into the reverse cycle of the wave and the correct wave form of rectified A. C.; hence the reason for making the secondary live segmens 33 and 34 shorter than segments Il and I2 of the primary commutator.

It is not necessary to have two commutators,

I because the device will operate with both sets of brushes engaging the same commutator. In such a case the secondary brushes engage the commutator a few degrees behind thf` primary brushes to compensate for the current lag between the primary andl secondary coils of the transformer. Two commutators are preferred, however, because with two the device is better balanced, the brushes are not so crowded, and there is less heat.

In order that the rotor will always be self-starting, means is provided for stopping the armature in the position shown in Illgs. 1 and 2 whenever the current to the device is turned ofi'. For this purpose, as shown in Fig. 2, a hollow cylinder I1, mounted on the side of the transformer from which the secondary commutator projects, contains a solenoid coil 48 that is connected in 'series in wire l between the center tap of the primary coil and the battery. A fixed core I8 is disposed in the lower half of the solenoid inside of a tube ll that projects above the coll. 'This tube guides a vertically reciprocable movable core Il 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 53 rigidly mounted on the upper portion of the movable core. 'Ihe upper end of the movable core is bifurcated and receives the slotted outer end of an arm Il the inner end of which is plvoted to the lower portion of a bearing support H. The arm and core are pivotally connected by a pin B5. The arm is provided near its inner end with an upwardly extending integral projection I6 from the upper end of which a roller 51 projects outwardly. This roller is adapted to engage the edge of a disc-like cam IB rigidly mounted on rotor shaft 28 directly behind the secondary commutator. 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 l1 engages the cam in any one of its four depressions the armature is in starting position, which is shown in Figs. 1 and 2.

When the current is turned ofi', the spring l2 lifts movable core lil and thereby swings arm 54 upwardly to press roller 61 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 in starting position. As soon as the current is turned on again the magnetic pull on the armature is suflicient to cause a high part of the cam to force roller l1 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 field of magnetic attraction of the fixed core 49. The latter continues to draw the movable core downwardly and the roller is thus entirely freed from the cam so that the rotor is free to rotate.

In the embodiment of the invention shown in Figs. 6 to 9 the direct current is interrupted by rotary contact means driven by a separate solenoid, and the alternating current induced in the secondary coil of the transformer is rectified by a rectifier tube, although this device with slight alteration can be made to rectify the current by synchronous operation as in the first embodiment. A frame is formed from two side plates spaced apart at their lower ends by a bottom plate 8| above which there is a spacing rod 82 that also serves as a tie rod for the side plates. Moimted on the bottom plate is a solenoid coil B3 having a core M extending upwardly with an opening in its upper end through which the tie rod extends.

Disposed above the solenoid is a shaft 06 the ends of which are journaled in bearings I1 mounted in openings in the side plates of the frame. The central portion this shaft carries an armature preferably formed from four equally spaced radially projecting prongs 08. The outer end of each of these projections has an integral circumferential extension that is tapered toward its outer end.

Mounted on shaft 66 at each side of the armature is a ring carrying two diametrically opposite contact members 1l and 12. The contact members at one side of the armature are set at 90 to those on the other side. Likewise, there is an electric contact member 13 disposed on each side of the armature where it is supported in any suitable manner, such as by a retaining member 'i4 attached to the adjacent side of the frame. These last two contacts are so positioned that every time the armature makes a quarter turn one or the other of them is engaged by one of the contacts rotating with shaft GB.

As shown in Fig. 9, this device is adapted to be l connected to a transformer in an electric circuit by connecting one end of its solenoid 69 by a wire 16 to a battery 1l, and by connecting the two fixed brushes 13 by wires 18 and 'I9 to the opposite ends of the primary coil 80 of the transformer. The center tap of the primary coil is connected by a wire 8| to the battery, and the rotating contacts 1l and l2 and the other end of the solenoid are'grounded to the frame.

When one of the rotary contacts engages one of the xed contacts current ows through the primary and the solenoid. This energizing of the solenoid causes it to attract the adjacent end of one of the armature prongs 68. The attempt of the magnetic flux to nd the path of least resistance to its iiowy tends to pull the thicker end of the prong extension toward the solenoid core and thereby rotates the armature and the shaft. This breaks contact between the rotating contact and the xed one, but the inertia of the rotating armature carries a. rotating contact on the other `side of the armature into engagement with the xed contact on that side. This again energizes the solenoid but causes the current to iiow in the opposite direction through the primary coil of the transformer, and the cycle is repeated.

The alternating current induced in the secondary coil 82 of the transformer may be rectified by an ordinary rectifier tube 83 connected to a lter 84. The center tap of the secondary is grounded by means of wire 85.

As shown in Figs. 8 and 9, rotary contacts Il and 12 are so positioned relative to the rotor prongs 68 that one of the contacts isjust starting to engage a fixed contact 13 when the pointed end of a rotor prong is above the solenoid core. The attempt of the magnetic ux to find the path of least resistance draws the radial or wider portion of the adjacent prong toward the solenoid and thereby rotates the rotor. By the time the radial portion of the prong is in line with the solenoid core the rotary contact has left the adjacent xed contact and the solenoid is deenergized, but inertia causes the rotor to continue to rotate and bring a contact on the opposite side of the armature into engagement with the xed contact on that side. The cycle is then repeated with the current owing first in one direction and then the other through the transformer primary coil. Suitable means, such as shown in connection with the next embodiment of the invention, can be used for stopping the rotor in the starting position shown in Figs. 8 and 9 when the battery current is turned off.

In the modication shown in Figs.v 10, 11 and 12, the side plates 86 of the frame are held apart by top and bottom plates 8l and are clamped together by a tie rod 88 passing through the upwardly projecting core 89 of a solenoid coil 99 mounted on the bottom plate. As in the `preceding embodiment, a shaft 9| is journaled above the solenoid, and anarmature is mounted on the shaft directly above the solenoid core. The armature is provided with a plurality, preferably eight, of radial projections or prongs 92 as shown in Fig. 11. Also mounted on the shaft is a commutator-like member provided With as many contacts 93 (Fig. 12) as the armature has prongs. 'I'hese contacts are grounded to the shaft and the space between them is filled with insulating material 94 such as Bakelite or the like to make a continuous cylindrical surface. The commutator is engaged by a pair of fixed contacts or brushes 9E and 91 one of which may be horizontal and the other of which is disposed at an angle of about 271/2" to the horizontal. The brushes can be held in place by supports 98 projecting from the frame. When this device is connected in a circuit like that shown in Fig. 9, lthe engagement of any one of the commutator contacts with either ofthe brushes energizes the solenoid which thereby attracts an adjacent prong of the armature and rotates the armature and commutator. As the contact leaves the brush the circuit is broken for a moment until a contact on the opposite side of the commutator engages the other brush. The result is that the current fiows iirst in one direction and then the other through the primary coil of the transformer and solenoid is energized and deenergized.

Figs. 10 and 11 also illustrate a way in which self-starting of any of the rotors disclosed herein can be assured. The-rotating shaft 9| is provided with a square portion engagedv by a weak spring strip 99 extending down from the top plate of the frame. Whenever the battery switch is opened so that the armature ceases rotation, the spring strip causes the armature to stop with one of the flat sides of the shaft against the spring. When in this position one of the commutator contacts 93 is in engagement with brush 9'1 so that when the main switch is closed again the solenoid immediately will be energized to start the armature rotating. Furthermore, when a :dat side ofthe shaft lies against the spring strip one of the armature prongs is close tothe solenoid core and closer to it than is any of the other prongs. The magnetic attraction of the solenoid is thus suicient to draw the prong toward it, and the rotor always starts rotating in the same direction.

It has been found that a better wave form can be produced if there is not an abrupt break in the circuit every time one of the commutator contacts 93 leaves a brush. A less sudden decrease in current can be produced by mixing graphite particles with the Bakelite that forms the insulating segments 94 of the commutator, as shown in Fig. 12. Consequently, as aV commutator contact leaves a brush the circuit is not broken completely at once, but the current decreases substantially to zero and then increases again as a contact on the opposite side of the commutator approaches the other brush.

Current interrupting and converting apparatus constructed in accordance with this invention produces a smooth Wave form because there is no bounce caused by contacts reciprocating between xed contacts. Therefore, there is practers can be used than heretofore.

their life is prolonged. There is no reed to loseits spring or to break, and the entire apparatus is sturdily built. It likewise is neither bulky nor heavy for its output. Positive timing is assured when synchronous operation is utilized, regardless of variations in the current load. Unlike a dynamotor in which the armature windings have to be soldered to many segments of a commutator, the only connections here are to the opposite ends and the two center taps of the transformer coils. The use of a transformer permits layer winding and layer insulation, which are the easiest. withou thought of bulk and weight.

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

I claim:

1. A currentl interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected to said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit ilows through the iirst one of said contacts and then the other, and a rotatable armature operatively connected to said rotary contact means and adapted to be rotated by periodic magnetic attraction of said electromagneticmeans i'or driving said rotary contact means.

2. A current interrupter for use with a transformer primary coil having a center tap connected to a source of direct current that is to be converted into alternating current, said interrupter comprising a pair of xed contacts adapted to be electrically connected to the opposite ends of said coil, rotary contact means for connection to said source of direct current and adapted when rotating to make electrical contact with each of said ilxed contacts alternately with a break between whereby the circuit is periodically broken, a rotatable armature operatively connected to said rotary contact means for driving said means to interrupt the now of current to each half of said coil alternately, and means for stopping said rotary contact means in electrical contact with one of said fixed contacts when the source oi' direct current is turned on to thereby assure starting of the armature when said direct current is turned on again.

3. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected with said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit ilows through iirst one of said contacts and then the other, a rotatablearmature having a plurality of radial projections adapted to be successively attracted by periodic magnetic impulses of said electromagnetic means, and means connecting the rotary contact means to said armature for rotation thereby.

4. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected with said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit ilows through first one of said contacts and then the other, a rotatable armature having four ilat radial projections adapted to be successively attracted by periodic magnetic impulses of said electromagnetic means, and means connecting the rotary contact means to said armature for rotation thereby.

5. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected with said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit ows through ilrst one of said contacts and then the other, a rotatable armature having a plurality of radial projections provided with outer end portions extending circumferentially in only the direction of rotation of the armature and adapted to be successively attracted by periodic magnetic impulses of said electromagnetic means, and means connecting the rotary contact means to said armature for rotation thereby.

6. A current interrupting device for use with electromagnetic means and a pair of electric contacts, adapted to be electrically connected with said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit ilows through nrst one oi' said contacts and then the other, a rotatable armature having a plurality of radial projections provided with outer end portions extending circumferentially in only the direction of rotation of the armature yand adapted to be successively attracted by periodic magnetic impulses of said electromagnetic means, and means connecting the rotary contact means to said armature for rotation thereby, each of said circumferentially extending outer end portions being tapered toward its free end.

7. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected with said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit flows through iirst one of said contacts and then the other, a rotatable amature operatively connected to said rotary contact means and adapted to be rotated by periodic magnetic attraction of said electromagnetic means for driving said rotary contact means,and means for stopping said rotary contact means in electrical contact with one or said contacts when the curcomprising rotary contact means rent to said electromagnetic means is shut oi to thereby assure self starting of the armature electrically connected to the opposite ends of.

said coil, of rotary contact means adapted'to be connected to said source of direct current and adapted when rotating to make electrical contact with each of said'xed contacts alternately with a break between, a core for said coil having two ends facingeach other, and an armature rotatably mounted between said core ends and adapted to be rotated by the periodic magnetic attraction of said core, said armature beingfoperatively connected to said rotary contact means for driving the latter whereby to interrupt the flow of current to each half of said coil alternately and to alternately energize and deencrgize said core.

9. In an electric circuit for converting direct current into alternating current, the combination with a transformer primary coil having a center tap adapted to be connected to a vsource of direct current, a pair of fixed contacts electrically connected to the opposite ends of said coil, and a magnetic core vextending through-the coil, of rotary contact means adapted to be elec-` trically connected to said source of direct current and adapted when rotating to make electrical contact with eachv of said xed contacts alternately, and a rotatable armature mounted adjacent said core and having a plurality of radial projections adapted to besuccessively attracted by periodic magnetic impulses vof the core, said armature being operatively connected to said rotary. contact means for rotation thereof whereby to interrupt the iiow of current to each half of said coil alternately and alternatelyy energize and deenergize the coil.

10. A current interrupter for use with a transformer having center tapped primary and secondary coils and a source of direct current connected to the center tap of the primary coil, said interrupter comprising a pair of iixed contacts for connection to the opposite ends of each coil, rotary contact means adaptedA to be connected to said source of direct current and adapted when rotatingto make-electrical contact alternately with eachl o1 the said contacts connected to the ends of the primary coil, rotary contact means adapted when rotating to make electrical contact alternately with each of theI said contacts connected to the ends of the secondary coil, a solenoid adapted to be electrically connected with said source of directcurrent, and a rotatable armature operatively connected to said rotary contact means and adapted to 'be rotated by periodic magnetic attraction of the solenoid for driving said rotary contact means to interrupt the flow of current to each half of said primary coil alternately and tointerrupt the'fiow of currentv` from each half .of said secondary coil alternately.

11. In an electric circuit for converting direct currentinto alternating current and rectifying the latter, the combination with center tapped primary and secondary coils, a pair of fixed contacts electrically connected to the opposite ends of each coil, and a magneticcore 'common` to both coils with the center tap oi the primary coil adapted to be connectedto a source of directV current, of rotary contact means adaptedto be connected to said source ofdirect current and. adapted when rotatingto make electricalxcom tact `alternately with each of the said contacts connected to the primary coil, rotary lcontact means adapted when rotating to make electricaly contact alternately withf'eachof the saidrcontacts connected to the secondary coil, and a rotatable armature mounted adjacent said core and adapted .to be rotated by periodic` magneticimpulses` of the core,said armature being oper` atively connected to said vrotary contact means for rotation thereof.

12. In an electric circuit for converting directv current -intov alternating current and rectifying the latter, the combination with center tapped primary and secondary coils, a pair of fixed contactselectrically connected to the opposite ends of each coil, and a magnetic core common to bothcoils with the centertap of the primary coil adapted to be connected to a source of direct current, of a rotatable shaft, an armature rig-y 13. A current inerrupting device for use withv`r electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected with said electromagnetic means and adapted when rotating t0 make electrical contact with each of said contacts alternately, whereby the circuit through 4the electromagnetic means is periodically deenergized and the current in said circuit iloWs through first one of said contacts and then the other,r a rotatablearmature operatively'connected to said .rotary contact means and adapted to be rotated by periodic magnetic attraction of said electromagnetic means 'for driving said rotary contact means, means for stopping said rotary contact means in electrical contact with one of said contacts when the current to said 'v electromagnetic means is shut o'to thereby assurel self starting of the armature when said current is turned on again, and means for automatically moving said stopping means out lof opelectromagnetic erative position when said I means is energized. f 14. A current interrupting contacts, comprising rotary contact `vmeans adapted to be'electrically connected with said electromagnetic means and adapted` when rotating yto make electrical contact Witheach of said contacts alternately, wherebythe circuitY throughy the electromagnetic means is Vperiodically dee'nergized vand the current in said circuit `iiows through first one of said contacts and then the l other, a rotatable armature operatively connected to said rotary contact means and adapted'to be rotated by periodic magnetic attraction of said' electromagnetic means for driving said rotary` contact means, a stop member mounted for yauto-v matically stopping said armature in a predetere mined position when said device is not operating, and velectromagnetic means for moving saidy devicefor use with electromagnetic means and 'a'A pair of electric f stop member out of said stopping position when said first-mentioned electromagnetic means is energized.

l5. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected with said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit flows through iirst one of said contacts and then the other, a rotatable armature having a plurality of radial projections adapted to be successively attracted by periodic magnetic impulses of said electromagnetic means, 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 operation of said device is terminated whereby to stop said armature with one of its projections adjacent said electromagnetic means and with said rotary contact means ln contact with one of said electric contacts, and electromagnetic means for withdrawing said spring-biased means from said cam when said device is energized.

16. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising a rotatable shaft having a flat side, rotary contact means carried by said shaft and adapted to be electrically connected to said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the current in said circuit flows through iirst one of said contacts and then the other, an armature rigidly mounted on said shaft and adapted to be rotated by periodic magnetic attraction of said electromagnetic means, and resilient means engaging the shaft and adapted to stop its rotation with the flat side against the resilient means when said device ceases operation.

17. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising a commutator having a plurality of segments adapted to be electrically connected to said electromagnetic means and adapted when rotating to make electrical contact with each of said contacts alternately, whereby the circuit through the electromagnetic means is periodically deenergized and the cur-1 rent in said circuit fiows through first one of said contacts and then other, insulating material between said commutator segments for engagement by said contacts, electrical conducting material mixed in said insulating material, and a rotatable armature operatively connected to said commutator and adapted to be rotated by periodic magnetic attraction of said electromagnetic means for driving the commutator.

18. In an electric circuit for converting direct current into alternating current and rectifying the latter, the combination with center tapped primary and secondary coils, a pair of fixed contacts electrically connected to the opposite ends of each coil, and a magnetic core common to both coils with the center tap of the primary coil adapted to be connected to a source of direct current, of a rotatable shaft, an armature rigidly mounted on said shaft and adapted to be rotated by periodic magnetic attraction of the core, and commutatordike contact members rigidly mounted on both ends of said shaft, one of said members being adapted to be connected to said source of direct current and adapted when rotating to make electrical contact alternately with each of the contacts connected to the primary coil, and the other of said members being adapted when rotating to make electrical contact alternately with each of the contacts connected to the secondary coil, the live segments of the commutator-like contact member for the secondary coil being shorter in the direction of rotation than the live segments of the other member.

19. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected to said electromagnetic means and adapted when rotating to make electric contact with each of said contacts alternately with a break between, whereby the circuit thrmigh the electromagnetic means is periodically broken and the current in said circuit flows through first one of said contacts and then the other, a rotatable armature operatively connected to said rotary contact means and adapted to be rotated by periodic magnetic attraction of said electromagnetic means for driving said rotary contact means, and means for stopping said rotary contact means in electrical contact with one of said contacts when the current to said electromagnetic means is shut off to thereby assure self-starting of the armature when said current is turned on again.

20. A current interrupting device for use with electromagnetic means and a pair of electric contacts, comprising rotary contact means adapted to be electrically connected to said electromagnetic means and including spaced conductors adapted when rotating to make electrical contact with each of said contacts alternately with a break between, whereby the circuit through the electromagnetic means is periodically broken and the current in said circuit flows through first one of said contacts and then the other, a rotatable armature having a plurality of radial projections adapted to be successively attracted by periodic magnetic impulses of said electromagnetic means, means connecting the rotary contact means to said armature for rotation there by, and means for stopping said rotary contact means with one of its electric conductors in contact with one of said contacts when the current to said electromagnetic means is shut off to thereby assure `starting of the armature when said current is turned on again.

21,. In an electric circuit for converting direct current into alternating current, the combination with a transformer primary coil having a center tap adapted to be connected to a source of direct current, and a pair of xed contacts electrically connected to the opposite ends of said coil, of rotary contact means adapted to be connected 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, a core for said coil having two ends facing each, other, an armature rotatably mounted between said core ends and adapted to be rotated by the periodic magnetic attraction of said core, said armature being operatively connected to said rotary contact means for driving the latter whereby to interrupt the flow of current to each half of said coil alternately and to alternately energize and deenergize said core,

and means for stopping said rotary contact means in electrical contact with one of said xed contacts when the source of direct current is shut olf to thereby assure self-starting of the armature when said direct current is turned on again.

22. In an electric circuit 4for converting direct current into alternating current, the combination with a transformer primary coil having a center tap adapted to be connected to a source of direct current, a pair of xed contacts electrically connected lto the opposite ends of said coil, and a magnetic core extending through the coil, of rotary contact means adapted to be electrically connected to said source of direct currentl and including spaced electrical conductors adapted when rotating to make electrical contact with each of said iixed contacts alternately with a break between, a rotatable armature mounted ad.- Jacent said core and having a plurality of radial projections adapted to be successively attracted by periodic magnetic impulses of the core, said amature being operatively connected to said rotary contact means for rotation thereof whereby to interrupt the ilow of current to each half of said coil alternately and alternately energize and deenergize the coil, and means for stopping said rotary contact means with one of it's electrical conductors in contact with one of said iixed contacts when the source of direct current is shut oi to thereby assure self-starting of the armature when the direct current is turned on again.

23. In an electric circuit for converting direct current into alternating current and rectifying the latter, the combination with center tapped primary and secondary coils, the center tap of the primary coil being adapted to be connected to a source lof direct current, and a pair of xed contacts electrically connected to the opposite ends of each coil, of rotary contact means adapted to be connected to said source of direct current and adapted when rotating to make electrical contact alternately with each of the contacts connected to the primary coil, rotary contact means adapted when rotating to make electrical contact alternately with each of the contacts connected to the secondary coil, a magnetic core common to both coils and having two ends facing each other, and an armature rotatably mounted between said core ends and adapted to be rotated by the periodic magnetic attraction of said core, said armature being operatively .connected to said rotary contact means for rotation thereof.

EDMUN'D G. LODGE.

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