US2786965A - Starter for low-potential fluorescent tubular lamps - Google Patents

Description

F. KNOBEL March 26, 1957 STARTER FOR LOW- POTENTIAL FLUORESCENT TUBULAR LAMPS Filed Dec. 3, 1953 IN VEN TOR. Y filrz/flvasa t1 d 5m Per STARTER FOR LOW-POTENTIAL FLUORESCENT TUBULAR LAMPS Fritz Knobel, Ennenda, Glarus, Switzerland Application December 3, 1953, Serial No; 395,975

13 Claims. (Cl.315100) The present invention relates to astarter fora lowpotential fluorescent tube with series reactors or chokes, of the type in which a rest contactis connectedin series with the two electrodes of the tube, and in which a free hanging heat responsive wire coperates'with the arm of an actuating lever acting, upon passage of current through the heat responsive wire, on the'movable'portionof the rest contact so as to open thel atter and to cause, in combination with the choke and with a condenser connected between the two electrodes, arcing of thefluorescent tube, an additional resistance being connected inseries With the heat responsivewire, which resistance is short circuited when the rest contact is opened, so as to accelerate this opening by a sudden increase ofthe current through the heat responsive wire.

New such starters may under-certain circumstances-- e. g. when the fiuorescent-lamp-is old and worn-out, or when it is defective, when 'the'anibient temperature is unusually low, or at excessive-under-voltage in the n1ainsnot work satisiactoriiy so thatthe lamp is not lighted. The lamp flickers, i. e. it flashes at eachinterruption of the current and no continuous current flow corresponding to the one in a normally working lamp,is'attained. If this flickering lasts the contacts, the heat responsive wire and the starting condenserare overworked resulting'in a educed reliability of service of the starter.

According to the present invention this disadvantage is overcome by a bimetal strip secured to the movable portion of the rest contact, and cooperating with a catch provided at the casing of the starter in such away that the heating of the rest contact occurring at iiickeringoperation causes the bimetal stripto bend andto engage the catch so that the rest contact remains'open.

Thus at flickering operation the-starter'is automatically switched-off so that damagesoroverworkingof the parts of the latter are efiectively prevented.

The time for starting a starting device of theabove type depends mainly of the heat responsive properties of the heat responsive wire. For constructioual reasons, however, it is not possible to increaseat will this heat responsive properties, so thatinmany cases it isnecessary to artificially increase the cathode heating current-in order to supply the cathode with suflicient heating energy during the relatively short heating time. This artificial increase of the cathode heating current during the heating period could for example be obtainedby an opposing winding as described in Swiss'Patent 265,338. However, such opposing winding complicates 'the connection and, moreover, such extremely high cathode heating currents have several disadvantages resulting in their usebeing limited to the cases in which a'very short starting time is desired.

It is therefore a furtherobject'of the present invention to provide a starter of the above-mentioned-type, in which the additional resistance is formedof a conductor having a negative temperature coefficient inorder to increase the starting time of the starter.

if the mass of this conductor with negativetempera- Patented Mar. 26, 1957 ice "ture' coe'flicient would be "chosen as great as wouldbe necessary for the continuous load-present, the switchretardation would be too great 'forthepresentpurpose. Preferably the mass ofthe conductor with negative temperature coeflicient is chosen smaller as it would be-necessary for its continuous' load, inorder toobtain, as the conductor with negativetemperature coefiicientis shortcircuited, a desired switch-retardation. Simultaneously it is attained by short-circuiting' the'said conductor, that the latter is put out of circuit *at continuousservice and does not produce losses at is would be the case if acouductor with'negative temperature coeflicienbwouldbe continuously connected in series with'the heat' responsive wire for increasing the switch retardation.

Other objects andadvantages of the invention will-become apparent from the description now -to follow, of

preferred embodiments thereof, given "by" way of example,

and in which referencewill be had to the accompanying drawings, inwhich:

Fig. 1 is a view illustrating"a 'thermaI circuit breaker;

Fig. 2 is an enlarged fragmentary view ofthe thermal circuit breaker of 'Fig. 1;

Fig. 3 is an enlargedfragrnen'tary view-similar tothe oneof Fig. 2, with' the circuit-breaker in anotherworking position;

-tionary portionl and the movable portion *3 of a rest contact or starter switchand the connecting lugs'4 and 5' associated therewith. An arm '6 and a pivot7' are connected with connectinglugss'and 9. *Rotatably' mounted on pivot 7 is a bushing *lilwhich carries an actuating lever 11. "Reference numeral 12 designates'a heat responsive wire, which has its one end connected tothe arm 6 while its other end iswound around the bushing 10. The additional resistance consists of'a loop 37, which'is formed by a portion of the-heat responsivewire leading from "the bushing 10 to the connecting 111g 9. Into this loop 37 is connected at conductorB having anega'tive temperature coeflicient. The operation of such'a conductorB with negative temperature coefl icient will be explained in detailin connection-With Figf9. A copper wire-connection 38 is connectedwith a contact39 insulated with respect "to the portion' 3 ofthe rest contact. "This'copper wire connection 38 serves to short-circuit the 'additional"re sistance 37 when the rest contact isopened. "The'iheat responsive wire 12is heldstrained'by a'spring 13 acting uponthe lever 11.

A bimetal strip '14is fixed to the movable portion 3 by means of a contact rivet 18 in such away that in the case of the contact growing warm the heat is transmitted to the bimetal"strip"14 and causes the 'latterto 'bend in the direction'indicated by the arrow in Fig. 2. The bimetals'trip 14 cooperates with a catch 15 provided with a hook 16 and secured in'the-'-"groove17 of the casing. 1 by means of a suitable adhesive such: as for example synthetic resin. This catch 15 may be of-bim'etal 'too, so

that:- at variation of the ambient'tcmperaturefrom -25 C. up to Clit bends inthesamedirecfion and to the same extentas st'rip'14,-:as clearlywisible.inFFigJZ. As may be seen. fromthe wiringascheme ofQFig. 7 .the

heat responsive wire 1211's connected :to some turns of -t-he choice 25. Moreoverthe rest contact 2;.3 is connected between the heatingelectrqdes 28, 29 of the lamp 27, i. e. it is connected in series with the choke 25 to the mains 32, 33. Reference numeral 24 designates a condenser connected between' the electrodes 28, 29. The rest contact 2, 3 may be bridged by a contact 23.

The operation of the described starter is the following:

If, for example, an alternating potential of 220 v. is switched on the terminals 32 and 33, a current flows from the terminal 32 through the choke 25, the lamp elec trode 28, the lug 5, the closed rest contact 2, 3, the lug 4, the lamp electrode 29 and back to the second mains terminal 33. Simultaneously a current is induced in the choke windings lying between the lugs 8 and 9, which current flows from lug 8 to the arm 6 through the heat responsive wire 12, bushing 10, pivot 7 and to the lug 9. The heat responsive wire 12 is heated by this current flowing through it and expands itself so that the lever 11 moves downwardly in direction of the arrow in Fig. l under the action of the spring 13 and removes the portion 3 of the rest contact, electrically connected with the lug 5, from the stationary portion 2 of the rest contact,

electrically connected with the lug 4. The opening of the contacts 18 causes a sudden interruption of the current and a high induction voltage in the choke 25, which normally is suflicient for arcing the fluorescent tubular lamp 27, the electrodes 28 and 29 of which have been heated by the preceding current flow to a temperature of approximately 600 C. Now it may occur that even with intact electrodes 28, 29 and in spite of a high induction voltage the lamp 27 is not lighted. The reasons therefor may be of various origins such as worn-out old or defective lamps, unusually low ambient temperature, excessive under-voltage in the mains etc. 'In such a case the starter of the lamp tries without-success to light the lamp by continually opening and closing the contacts 18. This leads to the so-called flickering of the lamp, as the latter flashes at each current interruption owing to the high induction voltage, while no continuous current flow according to the one in a normally working lamp is attained. If such a flickering lasts for a longer time the contacts 18, the heat responsive wire 12 and the condenser 24 of the described starter are heavily overworked resulting in the reliability of service of the starter being substantially reduced. This drawback is avoided in the afore-described starter as the heating of the rest contact causes the bimetal strip 14 to bend in direction of the arrow, whereby, as this bending has attained a certain extent, the bimetal strip will engage the catch 15 and be retained by the hook 16 of the latter as shown in Fig. 3 to maintain the contact parts 2, 3 of the starter switch separated. The dimensions of the parts 14 and 15 are such that the distance between the contact elements 18 is about mm.

As may be seen from Figs. 4 and 5 the movable portion 3 of the rest contact may be provided with an elongated slot 20, which reduces the heat transmission to the rear portion of the portion 3 so that .a quicker heating of the bimetal strip 14 is attained.

In the modified form shown in Fig. 6 the portion 3 of the rest contact is shortened and the bimetal strip 14 is secured to it by a rivet 19 while the contact 18 is only riveted to the bimetal strip 14 so that the whole heat of the contact is immediately transmitted to the strip 14 and a quick and strong bending is attained.

Of course, the locked starter must, subsequent to repair or the lamp, be brought back into its normal working position. This could be obtained very easily by a mechanical release device, however, as such starters are normally built together with the choke 25 they are not accessible without else so that such a device would not be satisfactory. A more satisfactory solution of this problem is shown in Fig. 7 in which an electrical restoring contact 23 which may be a push-button switch known per se is arranged on the switch-board and connected with the lugs 4 and 5. If subsequent to the repair of the defective lamp and to the switching-inof the mains 32, 33 the contact 23 is short-circuited, which in fact corresponds to a bridging of the open contacts 18, the normal preheating current flows again through the lamp 27 and through the choke 25. The heat responsive wire 12 is again heated and the lever 11 moves in the direction indicated by the arrow to the maximum opening position of the contact, in which position the opening is larger than it is in the locked position shown in Fig. 3. The bimetal strip 14, which has rapidly adapted itself to the ambient temperature and therefore exerts a releasing force upon the hook 16, is released in the very moment in which the opening of the contact is such as to permit for the hook 16 to return into its starting position. The starter is now again in its normal working condition.

In the modified form according to Fig. 8 such a restoring contact is provided on the casing 1 of the starter. The contact spring 21 has its one end connected to the lug 4 and its other end provided with a contact rivet 22 adapted to cooperate with a similar contact rivet 22 at the lug 5. The contacts 22 are closed for restoring the locked starter by means of a button provided on the contact spring 21.

As stated before with respect to Fig. 1, the additional resistance 37 may comprise a conductor B with negative temperature coeflicient. Fig. 9 now represents the wiring scheme of a modified form of a starter for a low-potential fluorescent tubular lamp R in which the additional resistance is such a conductor with negative temperature coeflicient.

The Wiring scheme represented in Figure 9 of a starter of a low-potential fluorescent tube R comprises a circuit coming from a main circuit wire P over a main switch C, a choke D, a cathode K1, a rest contact an, a cathode K2 and back to the main circuit wire 0. A conductor B with negative temperature coeificient, which may be shortcircuited by a contact :11, and a heat responsive wire A are connected in series to some turns of the choke D. The wiring scheme of Fig. 9 contains parts which are shown in Fig. 1. The heat responsive wire A of this scheme corresponds to the heat responsive wire 12 of Fig. 1. Further the contact al corresponds to the contacts 11, 39 of Fig. 1 and the contact a2 corresponds to the contacts 2, 18 of Fig. 1. As the heat responsive wire A grows warm its heat expansion firstly closes, by means of an actuating lever an auxiliary contact a1 and then opens the rest contact :12, which, in known way per se, owing to the quick interruption of current, causes an induction voltage at the choke D and thereby starts the arcing of the fluorescent tube. The actuating lever mentioned above may be lever 11 of Fig. 1 which operates the contacts a1 and a2 of Fig. 9. When the heat responsive wire A of Fig. 9, or 12 of Fig. l actuates by heat expansion, the lever 11 then closes first the auxiliary contact a1 of Fig. 9, or 2, 18 of Fig. 1.

In this wiring scheme the additional resistance used is not an ohmic resistance with neglectable temperature conductor B having when cold a resistance which is approximately 5 to 20 times superior to its resistance when warm, the initial current through the heat responsive wire. 'A is limited to such a small value that the latter is practically not heated and therefore does not expand itself. On the other hand this current sufices for heating up the relatively small mass of the conductor B. Owing to this warming the resistance of the conductor is reduced and the current increases resulting into increasing temperature of the conductor B and further reduction of its resistance etc. The greater current now also results in a heating up and expanding of the heat responsive wire A, so that after a determined switch retardation the auxiliary contact an is closed and thus the conductor B is short-circuited. Moreover, as already mentioned, the

arcing of the fluorescent tube is started by opening of the rest contact. Owing to the fact that the conductor B is short-circuited it is not necessary for it to have a mass chosen for continuous load. This mass may on the contrary be much smaller and adapted to the desired switch retardation.

I claim:

1. In a starter for a low-potential fluorescent lamp having a pair of electrodes, a casing of insulated material, contacts for conducting current to said electrodes and through at least one of the electrodes, a heat responsive wire connected in series to one of said contacts, a starter switch comprising a movable contact portion and a stationary contact portion normally in contact with each other and in series with one of the contacts for one of the electrodes and one of the contacts for the other electrode and responsive to changes in the length of said heat responsive wire, a bimetal strip secured to the movable portion of said starter switch and adapted to bend to open said switch when the starter switch grows warm, and a catch secured to the casing and adapted to cooperate with said bimetal strip upon bending of the latter so as to keep the starter switch open.

2. A. starter as set forth in claim 1 wherein the catch is formed of bimetal material, said bimetal strip and said bimetal catch bending in the same direction and to the same extent under the influence of the ambient temperature, and said bimetal catch engaging said bimetal strip upon bending of the latter when the starter switch grows warm.

3. A starter as set forth in claim 2 wherein the movable contact portion of the starter switch is provided with an elongated slot for reducing the heat transmission to the end of this portion opposite said bimetal strip.

4. A starter as set forth in claim 1, wherein said bimetal strip is secured to the movable portion of the starter switch by means of the contact rivet of the latter.

5. A starter as set forth in claim 1, wherein said bimetal strip is secured to the movable portion of the starter switch by means of a separate rivet, and wherein the rivet at the bimetal strip provides for direct heat transfer to the bimetal strip.

6. A starter as set forth in claim 1, wherein the means for securing the catch to the casing comprises an adhesive substance.

7. A starter as set forth in claim 1, including an electrical restoring contact bridging said starter switch and adapted upon actuation to open the movable contact portion of the starter switch to release the bimetal strip out of engagement with the catch.

8. A starter as set forth in claim 1, including a push contact switch adapted to bridge said starter switch for releasing the bimetal strip out of engagement with the catch.

9. A starter as set forth in claim 7, wherein said restoring contact is mounted on the casing.

10. A starter as set forth in claim 1, including a resistance formed of a conductor having a negative temperature coefficient and connected in series with said heat responsive wire and adapted to be short-circuited upon opening of the starter switch.

11. A starter as set forth in claim 10 wherein the mass of said additional resistance having a negative temperature coefi'icient is adapted to the desired switch retardation and is smaller than it would be necessary for continuous load.

12. A low-potential fluorescent lamp comprising in combination, a series choke, a tube having a pair of tube electrodes, a casing of insulating material, a heat responsive wire mounted in said casing and connected in series with said electrodes, a starter switch comprising a movable and a stationary portion connected in series with said electrodes and responsive to changes in the length of said heat responsive wire, a bimetal strip secured to the movable portion of said starter switch and adapted to bend when the starter switch groves warm, a catch secured to said casing and adapted to cooperate with said bimetal strip upon bending of the latter so as to keep the starter switch open, and an additional resistance adapted to be shortcircuited upon opening of the starter switch, said additional resistance being formed of a conductor having a negative temperature coeflicient.

13. A low-potential fluorescent lamp as defined in claim 12 wherein the movable portion of the starter switch is provided with an elongated slot to reduce heat transmission to the end of this portion opposite said bimetal strip, and wherein the catch is formed of bimetal material, said bimetal strip and said bimetal catch bending in the same direction and to the same extent under the influence of the ambient temperature, and said bimetal catch engaging said bimetal strip upon bending of the latter when the starter switch grows warm.

References Cited in the file of this patent UNITED STATES PATENTS 2,170,457 Lord Aug. 22, 1939 2,231,999 Gustin Feb. 18, 1941 2,266,616 Scott Dec. 16, 1941 2,284,407 Edwards May 26, 1942

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