US2436400A - Fluorescent tube lighting system - Google Patents

Description

Feb. 24, 1948..-

M. NATHANSON 2,436,400 FLUORESCENT TUBE LIGHTING SYSTEM Filed March 20, 1947 2 Sheets-Sheet 1 17 E 15 10 V 3 I? K I? F \NVENTOR MAXNATHANSON ATTQRN E Feb. 24, 1948. M. NATHANSON 2,4

FLUORESCENT TUBE LIGHTING SYSTEM Filed March 2o, 1947 2 Sheets-Sheet 2 24 INVENTOR MAX-NATHANSON ATTORNEYS,

Patented Feb. 24, 1948 UNITED STATES PATENT OFFICE FLUORESCENT 'lifiliiilHTING SYSTEM.

Max N athanson, Montreal, Quebec, Canada Application March 20, 1947; Serial No. 736,009;

This. invention. relates to improvements. in

fluorescent tube lighting systems of the type set forth in my co-pending application Serial No. 692,906, filed August 24, 1946..

The principal feature of the systems described in said applicationis the operation of a pluralityof series connected fluorescent tubes ata voltage not substantially greater than that required for operating the same tubes when connected in parallel with each other. This is accomplished by the provision of suitable by-pass or bleeder connections through the agency of'which arelatively low voltageimpressed across the terminals ofthe tube circuit is rendered effective to ionize said tubes in rapid succession and to establish and maintain in all of said tubes the current density required for efficient and satisfactory operation. The purpose of the present invention is to provide simplified circuit arrangements whereby a standard type of auto-transformer may be utilized in conjunction with suitable bypass connections and current-limiting means to operate a single tube load consisting of two or more fluorescent tubes connected in series with each other in the secondary circuit of the transformer.

Other purposes, advantages and characteristic features of the present invention will be more readily understood from the following detailed description of the accompanying drawings, in which Fig. 1 is a diagrammatic elevational view of an auto-transformer and other component elements of a fluorescent. lighting system embodying my invention.

F? g. 2 is a wiring diagram shown in Fig. 1.

Fig. 3 is a view similar to Fig. 2 but showing a slight modification; and

Fig. 4 is a view similar to Figs. 2 and 3 but showing a further modification.

In the system shown in Figs. 1 and 2, an autotransformer 5 is employed, in conjunction with condensers 6 and I, to operate two series connected fluorescent tubes 8 and 9 ata voltage not substantially greater than that required for operating the tubes in parallel with each other.

Transformer 5 is shown as an auto-transformer having two laterally spaced core legs in and H connected by end pieces l2. The primary winding comprises a coil section l3 arranged on core leg I and a second coil section l4 arranged on core leg II. The secondary winding comprises coil sections l and l! arranged on core leg Hi and coil sections l6 and I8 arranged on core leg ll. Thes primary and secondary coil sections are electrically connected in auto-transformer relationship as indicated at 9, 29, 21, 22 and 23. The transformer is designed so that the secondary coils l5, l6, l1 and I 8 have a high inductive reactance- 2 Claims. (Cl. 315-278) The primary coils l3. and I l are energized by a so rce. of alternating current energy which may be of any suitable voltage and frequency rating.

Condensers 6 and 1 are connected in the transformer, secondary circuit so that condenser 6 is in series with both tubes Sand 9 while condenser is in series with tube 9 and in parallel with tube 8.

In tracing the circuit connections as shown in Fig. 2, it will be. noted that primary coils l3 and.

Id of transformer 5 are connected across the alternating current potential source 24by leads 25 and 21. The left hand end of primary coil is is connected, at junction 28, tolead 26 and to the right hand end of secondary coil I 5. The right hand end of primary coil l3.is connected at 19' to the left hand end of primary coil 54. The right hand end of primary coil I4 is connected, at junction 25, to lead 2?. The left hand end of secondary coil I5 is connected, at 21, to the right hand end of secondary coil t5 which has its left hand end connected, at 22, to the right hand end of secondary coil IT. The left. hand end of secondary coil I1 is connected, at 23, to the right 8 by lead 32. The left hand electrode of tube 8' is connected to the left hand electrode of tube 9 by lead 33. The right hand electrode of tube 9 is connected, by lead 35, to the right hand end of coil I 4 at junction 25. The tube side of condenser l is connected, by lead 35, to lead 33 at junction 36. From this tracing of the circuit connections for tubes 8 and 9 and condensers 6 and 1, it will be seen that condenser l, with its. connectingleads 30, and. 35, provides a current limit-- ing by-pass through which current is shunted around tube 8 and through tube 9;

In the operation of the system shown in Figs. 1 and 2, the line voltage impressed across primary coils l3 and I 4 by way of leads 2B and 2? is increased, by transformation, to a higher. output voltage across the terminalsof thesecondary circuit in which the tubes and condensers are connected. This higher secondary output potential is maintained Within the maximum limits prescribed for safe operation and, in fact, corresponds to the potential (approximately 450 to 500 volts for a 40 watt tube.) ordinarily employed for. operating fluorescent tubes connected in parallel with each other.

The current limiting condenser l and its connecting leads 30 and 35 afford a high impedance by-pass or bleeder connection through which a of giving the same effects.

limited amount of.current is shunted around tube 8 to initially establish an ionized or conductive condition of tube 9. The impedance of tube 9 is thus reduced to a value at which the voltage drop across said tube is approximately low in comparison with the voltage required to establish an ionized or conductive condition of the tube. In this connection, it will be understood that condenser I is designed so that its capacitive reactance or impedance is high enough to limit the flow of by-pass current in tube 9 to an amount of current which is just suflicient to establish and maintain the ionized or conductive condition of said tube. As will hereinafter be apparent, this limitation of the amount of bypass current supplied to tube 9 is necessary to keep the ultimate flow of operating current in this tube within proper limits.

In the ionized and conductive condition of tube 9 the potential available across the electrodes of tube 8 is immediately eiiective to establish an ionized and conductive condition of tube 8 and to cause sufiicient operating current to flow through the series connected condenser 8 and tubes 8 and 9 to establish and maintain in both of said tubes the current density required for satisfactory operation. In this connection it will be understood that condenser E is designed to act as an impedance limiting current flow in tubes 9 and 9 to the current limits for which the tubes are designed. For example, in the case of a 40 watt tube the current limit is approximately 430 milliamperes.

An important characteristic of the system described in the foregoing is that the high inductive reactance of the transformer secondary coils 55 to I8 inclusive is balanced against the high capacitive reactance of condensers 9 and l to give a high power factor (over 90%). Another important advantage of this system is that both tubes are ionized and illuminated almost instantly at an operating voltage which is little more than that required to ionize one tube alone and this enables a substantial saving in transformer costs to be realized.

The condensers 6 and I may be replaced by other suitable current limiting devices capable For example, the condenser 1 may be replaced by a suitable resistor or reactor of the linear or non-linear type. In practice we have found that the best results are obtained by using a condenser l of approximately 0.3 mfd. capacity for 118 volt (40 watt tube) 60 cycle supply (24). Such a condenser would allow a current of approximately 50 milliamperes to flow through lamp 9 and would be satisfactory for initially establishing the desired ionized or conductive condition of said tube.

The arrangement shown in Figs. 1 and 2 is merely illustrative of one of numerous arrange.-

ments whereby a plurality of fluorescent tubes may be economically operated in series in accordance with principles of my invention within permissible voltage limits and with a minimum increase in the size of the transformer.

In Fig. 3 I have shown a slightly modified system in which the transformer side of condenser I is connected, by conductor 39, to a junction point 38 between the secondary coils l1 and I8. This modification has the effect of increasing the output emciency of the system.

The system shown in Fig. 4 is the same as that shown in Fig. 2, except for the addition of a third tube 39 and an additional bleeder or by-pass condenser 49. In the arrangement shown in Fig.

4 the right hand electrode of tube 9 is connected by lead 4! to the right hand electrode of tube 39. Theleft hand and of tube 39 is connected, by lead 42, to the right hand end of coil M at junction 25. The transformer side of condenser 49 is connected to junction 3| by lead 43. The transformer side of condenser 49 is connected by lead 44 to lead 4| at junction 45.

In the operation of the system shown in Fig. 4, the condenser 49 and its connecting leads 43 and 44 afford a highimpedance bleed or by-pass connection through which a limited amoimt of current is shunted around tubes 8 and 9 to initially establish an ionized and conductive condition of tube 39. A similar ionized and conductive condition of tube 9 is then established by virtue of the by-pass or bleeder connection afiorded by condenser 1 and its connecting leads 39 and 35.

When both tubes 39 and 9 are illuminated the voltage across tube 8 is effective to immediately establish an ionized and conductive condition of tube 8 and to cause sufficient operating current to flow through the series-connected condenser 6 and tubes 39, 9 and 8 to establish and maintain in the three tubes the current density required for satisfactory operation.

The condensers shown in Figs. 3 and 4 may be replaced by any suitable equivalent current limiting devices as previously pointed out in connection with the system shown in Figs. 1 and 2.

Having thus described the nature of my invention and several preferred embodiments, it will be understood that various modifications may be resorted to within the scope and spirit of the invention as defined by the appended claims.

I claim:

1, In a fluorescent tube lighting system, a source of alternating current energy having a plurality of voltage connection terminals includmg end terminals and an intermediate terminal, a plurality of fluorescent tubes connected in series with each other across said source, and a high by pass impedance connected respectively to said intermediate terminal of the said source and to a series connection between adjacent tubes, and a low impedance in series with all of said tubes and connected to one of said end terminals of said source, the impedances being in series across one of said tubes, and being of such values that after the remainder of said tubes have become conductive the break-down voltage will be applied to said one of said tubes, all of said tubes being operated in series with each other at a voltage substantia-lly lower than the sum of the break-down tion between adjacent tubes, and a low impedance in series with'all of said tubes and connected to an end terminal of said source, the impedances being in series across one of said tubes, and being of such values that after the remainder of said tubes have become conductive the break-down voltage will be applied to said one of said tubes. all of said tubes being operated in series with each other at a voltage substantially lower than the sum of the break-down voltages required for each tube.

MAX NATHANSON.

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