US1348171A - Switching-over device for electrical lighting installations for railway-trains and the like - Google Patents

Description

H. GROB. SWITCHING-OVER DEVICE FOR ELECTRICAL LIGHTING INSTALLATIONS FOR RAILWAY TRAINS AND THE LIKE.

APPLICATION FILED NOV- 9. I9I5.

1,348,171. PatenteaAug. 3,1920.

HUGO GROIB, OF ZURICH, SWITZERLAND.

SWITCHING-OVER DEVICE FOR ELECTRICAL LIGHTING INSTALLATIONS FOR RAILWAY-TRAINS AND THE LIKE.

Specification of Letters Patent.

Patented Aug. 3, 1920.

Application filed November 9, 1915. Serial No. 60,507.

To all whom it may concern:

Be it known that I, H oo GROB, a citizen of the Republic of Switzerland, residing at Zurich, in the Canton of Zurich, Republic of Switzerland, have invented certain new and useful Improvements in Switching Over Devices for Electrical Lighting Installa: tions for Railway-Trains, and the like; and I do hereby declare the following-to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same, reference being had to the accompanying drawings, and to letters of reference marked thereon, which form a part of this specification.

This invention relates to electrical lighting installations for railway trains, and with regard to certain more specific features, to a train-lighting system utilizing an axle-driven generator for lighting the train and charging one or more storage batteries which serve to light the train when the generator is at rest or is operating at too low a speed to generate sufficient voltage for the purpose.

One of the objects of; the invention is to provide a simple and eflicient train-lighting system in which the parts are automatically effective to accomplish their functions without the necessity for manual operation.

In axlelighting systems for railway trains, it is ordinarily necessary to switch over or change over the circuits as the train comes to rest. Usually the diminishing potential of the dynamo is utilized in some way to effect this switching of the circuits. In such cases, when the potential is regulated by purely electrical action, as is done in installations constructed according to U. S. Patent N 0. 994,510, and U. S. patent application, Serial No. 605,629, certain practical difficulties arise, and consequently it has been customary in effect the changing over by means dependent upon the speed of the dynamo or train. But

the necessary mechanical connection with the revolving dynamo shaft has rendered-it often impracticable to accommodate the switching apparatus in the interior of the vehicle for, the purpose of facilitating the control thereof. Accordingly, a further object of the present invention 1s to provide an improved switching-over effected by means such installations to or .changingover device for electric lighting installations wherein the dynamo and storage battery are alternately and temporarily in operation and wherein the changing over in the connections between battery and generator is dependent on the variation in the strength of the exciting current of the generator. Obviously a system employing means of this character permits of great freedom in the placing of the switching-over apparatus. 7

Another object is to provide in trainlighting apparatus of the above general type certain details of construction whereby the above and other advantageous results are attained.

Other objects will be in part obvious and art pointed out hereinafter.

he invention accordingly comprises the features of construction, combinations of elements and arrangements of parts which are to be exemplified in the structure hereinafter described, and the scope of the ap: plication of which will be indicated in the following claims.

The accompanying drawing shows one of various possible embodiments of this invention and is a diagrammatic general view of .the improved apparatus used in connection with a train-lighting installation in which there is provided a dynamo A of ordinary construction, with two independent armature windings represented by commutator circles, 2, 3 of which the larger one 2 gen crates, for example, thirty-two volts, and the smaller one 3 about seven volts. At B is shown conventionally the exciting Windthe dynamo A. A battery is shown as comprising the two equal halves C C which are interchanged at suitable' intervals, as after each stoppage of the train. The work circuit is illustrated at D. The switches F, G, whose armatures are preferably polarized, serve to effect'the circuit changes to accompany the changes in generator speed, as will be pointed out hereinafter. The switch E limits the voltage upon the work circuit, as hereinafter described.

At the initial conditions with the train at rest, switches F, G are inclined toward the right, whereby the two batteries C C are connected in parallel to supply current to the work circuit D through the low resistance coil H of the switch G. The coil 8 of switch E, responsive to dynamo voltage, is of course deenergized, so that the blade 28 of said switch is in its lower position. The field winding B is likewise deenergized.

As soon as the train starts, the residual magnetism in the dynamo A builds up in the windings associated with the low voltage commutator 3 a voltage which sends current by way of the lead 46, thence through the ballast or constant current resistance R the blade 28 of switch E, in its lower position, lead 29, field winding B, and lead-39, thus enabling the dynamo A to excite itself. Since the two commutators 2, 3 are connected in series, the lead 46 is at a potential equivalent to the sum of the voltages across the two commutators; assuming the negative lead 7 to be at zero volts potential, the normal pressure of thirty-two volts across the brushes of the commutator 2 would maintain the lead 39 at thirty-two volts, and the further normal pressure of seven volts across the brushes of the commutator 3 would maintain the lead 46 at thirty-nine volts. As soon as the potential at the lead 46 becomes higher than the potential at the blade 9 of the switch F, the coil H thereof will change the direction of its current flow and will cause the switch blade 9 to move toward the left and establish a charging connection between the dynamo lead 46, through the ballast charging resistance R current coil H blade 9, to the battery (1. The charging current which enters the battery C as the dynamo volta e increases, flows through the current coil 1% and holds the switch G firmly in its left-hand or charging position. At this moment only the battery C is connected to the external lighting circuit. a

The switch blade 27 is connected mechanically to the blade 9 of the switch F. The blade 30 is likewise connected mechanically The blade 27 when in its left-hand position, connects the dynamo lead 46 through the lamp resistance R blade 27, lead 31, and blade 30, to the load D in parallel with the battery C As the dynamo voltage increases, the load is assumed gradually by the dynamo, resulting in a corresponding decrease in the discharge current from the battery until finally the dynamo begins todeliver charging current into the battery C The to the blade-1O of the switch Gr.

resulting reversal of current in the current coil H of the switch G causes the blades 10 and 30 of the switch to be shifted into their left-hand positions, whereby, first, the battery C is disconnected from the work circuit D and connected to the exciting winding B, and, second, the dynamo is made now to deliver the lighting current directly through switch blade 30, instead of through lead 46 and lamp resistance R By this connection of the battery C to the exciting winding B, the dynamo A is converted from a self-exciting erator into a dynamo of constant voltage, the voltage of which is regulated on the principle embodied in my U. S. patent application, Serial No. 605,629. The regulation is accomplished by the use of the ballast or constant current resistance R which is in series with the field winding B across the leads 46 and 39, the battery C being connected to the junction between this resistance and field, with the other terminal of the battery connected to the lead ,7. The ballast resistance R permits a limited predetermined quantity of current to pass through it, and this current divides between field winding and battery. At a predetermined dynamo speed, the bat tery may be assumed to be floating. If now, the dynamo speed increases, the dynamo voltage tends to increase, and the battery takes an increasing amount of charging current. Since, however, the sum of the current to battery and field is constant (limited by the resistance R the field current is reduced, thus reducing the dynamo voltage to its former and constant value. The dynamo voltage thus adjusts itself at every speed to such a degree that the regulating battery C will take away from the constant current passing through the ballast resistance R just such an amount that the remaining current flowing through the exciting coil B is just sufficient to produce the proper dynamo voltage. It will be readily understood that even at an excessively high speed of the dynamo, its voltage (disregarding residual magnetism) cannot rise high enough to cause the regulating battery C to take the entire current which is allowed to pass through by the resistance B since then the exciting current would have become equal to zero in the field circuit B.

In consequence of the smallness of the charging current which flows into the battery C the counter electro-motive force of the battery will remain for a certain space of time in the neighborhood of about 2 to 2.2 volts per cell according to its condition of charge. The voltage across the brushes of the large commutator remains, practically uninfluenced by the speed of the dythe uppermost lead and shunt gennamo, within these limits, but is reduced by the voltage drop of about one volt in terminal is connected to the the exciting winding B; this also applies to the lighting voltage. Then owing .to the addition of the voltage of the small commutator, the battery C also receives an approximately constant of suitable intensity. The low ballast resistance R is inserted'in the charging lead for the purpose of settingan upper limit to the charging current.

Although the quantity of current flowing into the regulating battery C is small, the counter electromotive force of this battery and therefore the voltage of the work circuit would in time assume a high value. In order to avoid this, thereis inserted in the lead 31 the blade 28 of a switch E which comes into operation as soon as the voltage in the work circuit has attained a predetermined maximum value. Then the current supply through the resistance R to the exciting winding B ceases, and the dynamo voltage drops until the battery C is delivering current, through the current coil H, blade 10, lead 6 and field winding B, thereby replacing the former arrangement of obtaining the field current from the dynamo lead 46 through the ballast resistance R The regulation of the voltage is now effected in accordance with my U. S. Patent No. 994,510. The negative terminal of the field winding B is connected to the lead 39 as before, and the positive terminal 6 of the field is connected, as-before, to the positive terminal of the battery C whose negative dynamo return lead.7. At the minimum operative dynamo speed, the battery may be assumed to be supplying a maximum current to the field.

If now, the dynamo speed increases, the

voltage across the leads 39-7 tends to increase; and since the voltage across the field isequal to the (constant) battery voltage minus the voltage 39-7, it is obvious that this increase in the voltage 39-7 reducesthe voltage across the field, thus reducing the field current and thereby reducing the dynamo voltage to its former andconstant level. In this manner the dynamo voltage at every speed is automatically adjusted to a value so much less than the voltage of the battery C that a voltage diiference is produ'ced at the terminals of the exciting winding B, which difference is just sufiicient to cause that amount of exciting current in the winding B which is necessary for enerating the proper dynamo voltage. ince as hereinbcfore stated, thepotential across the field B for full generator load at minimum operative generator speed need not exceed one volt, the dynamo voltage across the leads 397 need never be more than one volt lower than the voltage across the battery C even at the lowest operative speed of the charging voltage functional value of connection between this latter circuit and v the dynamo is broken.

7 In order to do this automatically,

the present invention provides for, the control of the disconnecting devices by the change in the value of the exciting current flowing in the winding B. For this purpose, the operation of the switch G is made to take place responsively to a the exciting current. The exciting current is led directly through a current coil H associated with the switch 'G so that the action of the latter is dependent upon the regulating current flowing through the battery C. This current flows into the regulating battery C as long as the armature of the switch E is not attracted; when the coil 8 of the switch E is energized, the regulating battery C then begins to discharge; as explained above.

' Hence the switch G is operated under either of two conditions; First, with switch E not fully energized and the blade 28 in its lower position, the field current is equal to the difference between the current through resistance R and the automatically varying charging current to battery C if the dynamo speed is sufficiently high, or, as in the present case, when the dynamo speed is assumed to be nearing its lower operative limit, the field current is equal to the current through this resistance R plus the automatically varying discharge current from said battery C Assuming for example ten amperes as the maximmn permissible field current, and eight amperes as the current constantly delivered through the ballast resistance R then the witch G should operate as soon as the battery current reaches two amperes. Second, with switch E enercharging current from the battery C so thatthe switch G should operate when the battery current attains ten amperes. This operation of the switch G at two or ten amperes is effected by providing a voltage coil H on the switch G, to be traversed by current only when the switch E is energized. This winding H adds as many negative ampere turns as are necessary to counteract the action of eight amperes in the current coil H If the switch G is operated when the switch E is not sufficiently energized, the dynamo becomes an ordinary shunt dynamo,

, diately afterward.

whose potential drops with diminishing speed. After sullicient drop in the dynamo voltage a reverse current flows from the battery to the dynamo. and the switch F is thrown to the right by the reversed current in the coil H the battery C being thus connected again to the work circuit 1).

()n the other hand, if the switch G is operated when the switch E is energized, the dynamo is suddenly deprived of its excitation, and therefore its voltage fallsvery quickly. The switch I is operated imme- In such a case the battery which has been on charge, is connected suddenly to the work circuit D, and an upward flickering of the lights would occur. In order to avoid this, the switch (i may be combined with a device which will interrupt the circuit of the coil 8 of switch E momentarily at every reversal of the switch G. This interrupting device is represented diagrammatically in the drawing by the pairs of contacts 2-l and 26, and the insulated short circuiting piece 25. If the switch G changes its position while the coil 8 is energized. the latter will release its armature 2S, and thereby connect the dynamo field to the dynamo lead 46 for selfexcitation, and the voltage of the battery C willfall so slowly as to give the battery time to reduce its own voltage before the operation of the switch F, thus avoiding a flickering of the lights. By providing for a closin of switch 28 prior to shifting of switch ti, an interruption of the exciting current and consequent injurious sparking at the point of interruption is avoided.

Since both batteries have to supply the lighting current connected in parallel when the train is stationary, both batteries must naturally be charged; this is effected by interchanging the connections of the, two

batteries atsuitable intervals, as for instance after every stoppage of the train, in the manner illustrated in my U. S. Patent No. 994,510 above mentioned.

It is important that the connection of the two batteries C, C established during the stoppage of the train, does not contain the current coil H of the switch G, since otherwise the switch G might be operated to its left-hand position by a compensating or equalizing current flowing between the batteries.

Great advantages are effected bychanging the shunt excitation of the dynamo (switch G to the right) to regulation for constant voltage (switch G to the left), not before the dynamo has taken the entire load of the work circuit. In this manner, the belt reaches the limit of its capacity for transmitting power, before the dynamo has assumed the entire load, 2'. 0., while the dynamo is still running with shunt excitation; upon further increase of speed, the

belt begins to slip in a perfectly stable manner, since when the belt slips the speed of the dynamo falls, and with shunt excitation the dynamo output will fall more rapidly than the speed, so that the dynamo will thereafter deliver just an amount of currentcorresponding to the power-transmitting capacity of the belt.

In the other case. 6., if the shunt excitation will be replaced by regulation for constant voltage before the dynamo has assumed the entire load, and if the belt is not capable of transmitting the entire load, then the slipping of the belt will be unstable. The more the speed of the dynamo falls, in consequence of belt-slipping, the more the retarding force of the dynamo increases, owing to the constancy of the power (constant volts X constant amp'eres) delivered by the dynamo. After a sufiicient decrease of the speed, the dynamo will be switched out again, i. (5., completely discharged of load. Afterward a new rise of speed will take place until the dynamo is switched in again and so forth. In this manner there may take place an oscillating switching-in and switching-out of the controlling apparatus.

lly disconnecting the dynamo from the external circuit only after the dynamo output has been reduced practically to zero, the belt is never slipping at the time the dynamo is disconnected, and no repeated operation of the cut-out switches occurs.

If the work circuit were connected to the terminals 39, 7 during the shunt excitation period, (switch F to the left, switch G to the right, and switch E deenergized), then with falling dynamo voltage the work circuit voltage would drop to its permissible minimum of about 32 volts (and should be disconnected) sooner than the voltage at the charging battery C drops to its permissible minimum of two volts per cell (32 volts), since the battery is across the high "oltage mains 46, 7 this would'require two switches, for load and battery respectively, operating at different times. According to the present invention however, the work circuit is connected to the high voltage terminals 46, 7, through the series resistance R during the shunt excitation period, so that with falling dynamo voltage the work circuit voltage reaches its lower limit of 32 volts at the same time that the battery voltage reaches its lower limit of 32 volts, so that both the work circuit and the battery may be disconnected by a single switch mechanism as indicated at F. 9, 27. By this means it is possible to dispense with one of the prior art switches, and thus in spite of simultaneous connection of the charging circuit and work circuit to the dynamo, to effect a gradual transfer of the load to the dynamo during the starting vehicles, such as motor veassumed first, that the train is at rest. At

this time switch F is in its right-hand position, switch Gr is at the right, and switch 15 is de'nergized; hence both batteries C and C are connected in parallel to supply the work circuit D. If now the train starts, the

dynamo field B is self-excited by virtue of its connection to the mains 39, 46 of the generator, through the ballast resistance R switch blade 28 and leads 6, 29; the batteries C and. C are still in parallel with the load. When the train speed is high enough so that current flows in the direction from the main 46 through the voltage coil H to the positive terminal of battery C switch F is shifted automatically to the left: this does not disturb the connections frombattery C to load through coil H and switch blade 10, but it disconnects battery C from the load, and connects this battery to the high-voltage or charging main 46 of the generator through the current coil H and the ballast charging resistance R Simultaneously the high-voltage main 46 of the generator becomes connected to the load in parallel with the batte C through the load or lamp resistance switch blade 27, lead 31, and switch blade the generator is still selfexcited through the circuit 46, R 28, 6, B, 39. When the train speed is high enough so that current flows from the main 46 through the lamp resistance R switch blade 27, lead 31, switch blade 30, switch blade 10, and current coil H into the positive terminal of battery C the olarity of the coil H4 is reversed and switch ,is shifted automatically to the left. The battery C is now still on charge throu h the ballast resistance R, current coil the ballast field resistance ,yvinding B, so that with variations of dynamo and switch blade 9; the the high voltage main 46 of the generator and the battery C and loadD is broken at the switch blade 30, and instead, the low voltage or intermediate main 39 of the generator is connected to the load D through connection between switch blade 30,- without any intermediate.

lamp resistance; the battery C? is now connected, throu h the current coil H, switch blade 10 and ead 6, to the jllzmction between and the field spee a varia e amount. of. the s ant any but may be adapted,

ships and the like, and also in sta rent flowing through resistance R verted from the field B into the battery C and thus constant voltage is maintained at the generator irrespective of the generator speed, as hereinbefore explained. After a length of time depending upon the condition of the slowly charging battery C the voltage of this battery reaches the point where the voltage coil 8 (whose strength is proportional to the voltage of battery C becomes sufiiciently energized to lift its switch blade is operation disconnects the field winding B from the resistance R and hi hvoltage main 46, and as a result the field is now excited by discharge current pass' from the battery C through the coil H, switch blade 10, main 6, and field winding B, to the intermediate or low-voltage main 39 of the generator, and, as hereinbefore explained, the exciting current is automatically decreased with any speed increase and the dynamo voltage thus maintained constant irrespective of the dynamo speed. If the dynamo speed drops below its operative value at a time when the batte C is thus discharging through the field B to the main 39 (switch E energized), the field current passing through the .coil H naturally increases with decreasing dynamo speed and when said current attains a predetermined maximum, such as for example, ten amperes, the switch G is automatically shifted to theright. The voltage coil H is at this time energized and opposes the flux generated by current coil H to such an extentthat ten amperes of current through coil H is re uired to shift the switch G toward the rig t; thisshifting of the switch G toward the right interrupts for a moment at the contacts 26 the circuit of voltage coil 8 of switch E, which is thus compelled to retract its blade 28 and reestablish the selfexciting field circuit 46, R 28, 6, B, 39. In

this manner, the'field circuit B is notopened and the objectionable, spar g attendant upon the opening of a field circuit is avoided.

Upon further decrease of d amo speed, the switch F shifts to the right when reverse current from battery G nto main 46 reverses the eflect of the current coil H and the conditions existing with the train at rest (switches F and G ener ized) are thus restored. If, however, the dynamo speed drops below its minimum operative value at a time when the batte C is connected to the junction between field resistance R and field winding B (switch E denergized) the field current, part of which (for example, eight amperes) is sufi plied by the constant current resistance 3 and the rest of which is supplied b the battery C, naturally increases with ecreasing dynamo speed, and when said field current. attains a predetermined maximum, such as ten -P b We emr is to the right, switch E de-' ing through the coil H from thebattery C the switch G is automatically shifted to the right. The-voltage coil H is at this time de energized, and therefore offers no opposition to the coil H, so that two amperes of discharge current flowing through the coil H from the battery C is sufficient to shift the switch G toward the right. Upon further decrease in train speed, the reverse current, from battery 'C into the main -16 reverses the current coil H and shifts the switch F to the right. The conditions corresponding to yero train speed, are thus restored, namely, switches F and G to the right, and switch E deenergized, with the two batteries in parallel serving the load.

From the above it will be seen that the several objects of the invention are realized and other advantageous results obtained.

As various changes might be made in the above construction, and as the above invention might be embodied in diiferent forms, it is intended that all matter set forth in the above description and in the accompanying drawings, shall be interpreted as illustrative and not in a limiting What I claim is 1. In apparatus of the class described, in combination, a generator, a field coil therefor, a .suhstantially constant current resistance connecting one end of said coil to one of the terminals of said generator, a battery connecting said same end to another terminal of said generator, and protective means for disconnecting said battery when a maximum field current is reached.

2. In apparatus of the class described, in combination, a generator, self-exciting and externalexciting means therefor, adapted to operate separately or conjointly, and a de vice controlling said external means, to limit the maximum total' excitation of said generator to apredetermined value whether said external means is operating solely or conjointly with said self-exciting means.

3. In apparatus of the class described, in combination, a generator having two commutators in series, providing thereby a positive, intermediate and negative terminal, an exciting winding, one pole of which is connected to said intermediate terminal, a battery, one pole of which is connected to said negative terminal, means for connecting and disconnecting the other pole of the exciting winding and the other pole of the battery, and means for disconnecting the exclting from the battery when the exciting current has attained a redetermined value.

4. In apparatus of e class described, in combination, a generator having two commutators in series, providing thereby a posisense.

tive, intermediate and negative terminal, an

exciting winding, one pole of which is connected to said intermediate terminal, a battery, one pole of which is QQmlQQted to said ed to said intermediate terminal and negative terminal, and means for connecting the other pole of the exciting winding to the other pole of the battery automatically when the generator has assumed the load, said connection from exciting winding to battery being automatically broken upon a sufiicient decrease of generator speed.

5. In apparatus of the class described, in combination, a generator having a positive terminal, a'negative terminal, and a terminal of voltage intermediate the voltage of the positive and negative terminals, an exciting winding for the generator connected to the intermediate terminal and the positive terminal through a constant-current resistance, means for interrupting the connection between said winding and said positive terminal when the generator voltage has attained a predetermined value, and a battery whose poles are connected respectively to the negative terminal of the generator and to the positive terminal of the exciting winding.

6. In apparatus of the class described, in combination, a generator, an exciting winding therefor connected to said generator through a constant-current resistance, a hattery connected to said exciting winding and to said generator so that the battery voltage and the generator voltage are opposed to each other, and means for interrupting the connection between said winding and a terminal of said generator when the battery voltage has attained a predetermined value,

7. In apparatus of the class described, in combination, a generator having a positive terminal, a negative terminal, and a terminal of voltage intermediate the voltage of the positive and negative terminals, an exciting winding for the generator connected to the intermediate terminal and the positive terminal through a constant-current resistance, whereby the current through said resistance normally divides between exciting winding and battery to maintain the generator voltage constant with varying speed, and means for interrupting the connection between said winding and said positive terminal, whereupon the current in said winding is proportional to the difference between battery voltage and the voltage across the intermediate and negative terminals of the generator, whereby the generator voltage is maintained constant with varying speed.

8. In apparatus of the classdescribed, i1 combination, a generator having two com mutators in series, providing thereby a posi tive, intermediate and negative terminal, an exciting winding for the generator connect to battery whose other le is connected to th negative terminal oi the generator, a con nection between the positive terminal of th generator and the junction between excit mg winding and battery, voltage-controlle means for breaking said connection, and means for restoring said connection automatically prior to disconnection of the battery from the exciting winding.

9. In apparatus of the class described, in combination, a generator, a field winding therefor, a battery adapted to be automatically connected to the generator for charging thereby, means for simultaneously connecting the generator to a work circuit through a resistance, means automatically effective after the generator has assumed the load, for breaking said connection to the work circuit and connecting said work circuit to generator terminals carrying only a fraction of the total generator voltage, and means for re-connecting the work circuit to the generator-through said resistance prior to disconnection of the generator entirely from the work circuit.

10. In apparatus of the class described, in combination, a generator having three terminals, namel a negative terminal, an intermediate terminal and a positive terminal, the voltage between negative terminal and positive terminal being higher than the voltage between negative terminal and intermediate terminal, an exciting winding, one pole of which is connected with said intermediate terminal and the other pole with said positive terminal, a resistance in the connection between said positive terminal and said exciting winding, a magnetic interrupter adapted to break said connection between positive terminal and exciting winding, said interrupter having a voltage coil across the negative terminal and the intermediate terminal, a battery whose negative pole is connected to said negative terminal of the generator, a work circuit whose negative pole is connected to said negative terminal of the generator, an auxiliary con necting line, a magnetic switch connecting in its working position the positive pole of said battery with the second pole of said exciting winding and connecting the positive pole of the work circuit with the intermediate terminal of the generator, said switch connecting in its rest position the positive pole of the battery with the positive pole of the work circuit and connecting the latter with said auxiliary connecting line, said switch shifting to its working position when current flows into said battery,

circuit which is closed when said interrupter has interrupted said connecting line, said second coil opposing said first coil; a second battery whose negative pole is connected to the negative pole of the generator, a second switch connecting in its working position the positive pole of the second battery with the positive terminal of the generator and connecting said auxiliary connecting line with the positive pole of the generator, said second switch connecting in its rest position the positive pole of the second battery with the positive pole of the first battery, means for shifting said second switch into its working position when the voltage of the positive terminal of the generator exceeds the voltage of the positive pole of the second battery, means for shifting said second switch into its rest position when reverse current flows from said second battery to said generator, a resistance in the connecting line between the positive pole of the generator and said second switch, and a resistance in said auxiliary connecting line.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

HUGO GROB.

Witnesses HERMANN HUBER, CARL Goran.

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