US2549307A

US2549307A - Time-delay relay system

Info

Publication number: US2549307A
Application number: US590292A
Authority: US
Inventors: Milton W Griffes; Harold J Rathbun
Original assignee: Electric Controller and Manufacturing Co LLC
Current assignee: Electric Controller and Manufacturing Co LLC
Priority date: 1945-04-25
Filing date: 1945-04-25
Publication date: 1951-04-17
Anticipated expiration: 1968-04-17

Description

April 17, 1951 M. w. GRIFFES ET AL 2,549,307

TIME-DELAY RELAY SYSTEM l 4e l 6. 4 INVENTOK.

N/ra/v W. GRIFFEJ Y ,saw J. ,oT/MUN F/G. 5 "lm M. W. GRIFFES ET AL TIME-DELAY RELAY SYSTEM April 17, 1951 2 ShetsL-Sheet 2 Filed April 25, 1945 lllrll IN V EN TOR.

MM ra/v 61e /FFEJ M RA M50/v A T70 RNE v5 Patented Apr. 17, v1951 TIME-DELAY RELAY SYSTEM Milton W. Griffes and Harold J. Rathbun, Cleveland, Ohio, assignors to The Electric Controller & Manufacturing Company, Cleveland, Ohio, a

corporation of Ohio Application April 25, 1945, Serial No. 590,292

(Cl. F75-320) 11 Claims.

This invention relates to motor control systems, the illustrative examples hereinafter disclosed being improved control systems for automatically short circuiting the resistance in a circuit of an electric motor during acceleration of the motor and for introducing a time delay between the closing of successive starting switches, the extent of the time delay intervals being dependent upon the rate of energy accumulation of an electrical energy storage device such as a condenser.

Heretofore, in the control of translating devices other than motors by timing circuits, it has been proposed to connect a condenser, an adjustable resistor,'and the operating winding of an electromagnetic relay in series with each other across a source of constant unidirectional voltage, the electrical constants of the circuit being so proportioned that, upon initial application of voltage to the circuit terminals, the initial impulse of condenser charging current is suicient to cause pick-up or actuation of the relay which thereafter remains in its actuated or closed magnetic circuit position until the condenser charging current decreases to the drop-out current value oi the relay. A series connected condens-er, resistor, and relay winding circuit such as just described and in which all of the relay current passes through the timing condenser is not satisfactory when supplied with constant voltage for measuring the time relay intervals between the closing of successive motor acceleration switches because, when the resistance of the circuit is made low enough to permit the initial flow of charging current to be large enough to pick up the relay, the resistance is too low' to delay adequately the charging time of the condenser, and consequently the timing period is too short for many purposes including that of motor starting control. This disadvantage is aggravated by low Voltage conditions that often occur on industrial power supply systems. The time delay period can obviously be increased by using a condenser oi larger capacity, but this expedient is generally not justined both because of increased cost and because of the larger space required. Other disadvantages of suchprior series connected timing circuits are that relatively large variations in the resistance of the resistor have but little effect on the time intervals so that other means must be resorted to in order to obtain the usual required adjustment of the duration of the time interval, and that when two or more timingr circuits are used to control two or more acceleration switches, difficulty is encountered in arranging the circuits so that all possibilities of incorrect switching sequence are obviated.r

By taking advantage of the phenomenon that considerably less current is required to hold a relay in its actuated position than is required to actuate it, various modifications of the foregoing type of series connected condenser timing circuit have heretofore been proposed for in creasing the timing interval for unit of capacity. However, the switching sequences required in the prior modified timing circuits are such that the circuits are not suitable for controlling motor acceleration and in some instances also require the use of a relay having either a tapped operating winding or two separate windings.

The present invention involves timing circuits of the above indicated character and takes advantage of the fact that the drop-out current of a relay is less than the relay pick-up current, but the timing circuits are so arranged as to be eminently suitable for controlling motor acceleration and each of the timing relays requires but a single, untapped operating winding. More specifically, in accordance with this invention, circuit means are provided for temporarily bypassing the condenser and resistor portion of a series connected condenser, resistor, and relay winding timing circuit so as to supply, upon initial application of voltage to the circuit, suiiicient current to the relay winding to pick up the relay, the by-pass circuit means subsequently becoming inoperative due to closure of a motor starting switch or charging of a second condenser. After the by-pass circuit means becomes inop'- erative, the relay is held in its actuated position for a time interval by the charging current flowing through the timing condenser thereby to de- The by-pass circuit preferably conducts by itself suliicient current to pick up the relay, the circuit including the timing condenser either conducting substantially none or a very small percentage of the relay current during the time that the by-pass circuit is operative.

The improved series connected condenser and relay timing circuit disclosed herein not only provides a timing interval of longer duration for a given size of condenser than heretoforek obtainable with a circuit not provided with a by-pass circuit means so that the improved circuit is useable for the control of motor acceleration, but also greatly increases the range of adjustment of the timing interval and makes possible the use of simpliiied control connections for both single and multiple step motor starters which insure the proper sequence of operation and eliminate all close contact races.

For further increasing the time delay interval for microfarad of capacity in the circuit, an additional relay current path is provided in an alternative embodiment of the invention to permit a small amount of relay current, which is less than the drop-out current value of the relay, tc flow around both the temporary by-pass circuit and the series connected condenser and resistor circuit throughout the timing interval. The additional current path for supplying current to the relay winding permits the relay to remain in its operated position until the charging current iiowing through the condenser decreases to a value which is less than the difference between the current ilowing through the additional current path and the drop-out current value oi the relay.

An important object of this invention is to provide a motor control system having the foregoing advantages and features.

Another object is to provide an improved time delay control system especially adapted for motor control.

Another object is to provide an improved time delay control system in which an electromagnetic relay is temporarily held in its actuated or energized position by the charging current oi a condenser connected in series with the operating winding of the relay.

A further object is to provide a time delay control system in which a relay is temporarily held in its actuated position by the charging current of a condenser connected in series with a resistor and the relay winding kand in which a circuit temporarily ley-passing the condenser and resistor supplies substantially all of the current for initially actuating the relay.

An additional object is to provide an improved control system for an electric motor which includes means responsive to the charging current of a condenser for controlling the operation of electromagnetic switches.

Other objects include the provision of a plurality of cooperating time delay circuits of the character indicated above in which the time intervals are individually adjustable, the provision of a plurality of such circuits arranged for controlling acceleration switches for an electric motor, the provision of a plurality of such circuits in which the starting of the timing interval of one of the circuits is dependent upon the completion of the timing interval of another of the circuits` and the provision of a plurality of such circuits in which simplified connections are used for obtaining the proper secuence of operation.

A still further obiect is to provide a motor control system in which a relay, having normallyclosed contacts in series with the operating winding of a switch to be operated after a time delay, is operated to the open position of its contacts before a circuit to the switch can be completed and then is held in its operated position for a time interval measured by the charging time of a condenser.

Other objects and advantages will become apparent from the following description wherein reference is made to the drawings, in which:

Fig. l is a circuit diagram embodying the invention;

Fig. 2 is a circuit diagram of a modification',

Fig. 3 illustrates la further modicaticn;

Fig. 4 is a graph illustrating time-resistance characteristics of a prior art time delay circuit, and

Fig. 5 is a graph illustrating time-resistance characteristics obtainable with the time delay circuit of Figs. 1 and 2.

Referring to Fig. 1, a direct current motor IU having an armature winding IOa and a series field winding Iub is arranged to be connected between a pair of supply conductors II and I2 through series connected accelerating resistors III and i5 when normally open main circuit contacts 16a, of an electromagnetic contactor or switch I6 are in their closed position. The switch I additionally has normally closed auxiliary contacts I6b, normally open auxiliary contacts I6c and ld, and an operating winding Iw the energization of which is controlled by a pilot device or master switch shown as a push button i8 having normally open contacts ISa and normally closed contacts I8b. The accelerating resistors I4 and I5 are arranged to be short circuited upon closure of normally open main circuit contacts I9a and 20a, respectively, of electromagnetic contactors or switches I9 and 29, respectively. The switch I9 is additionally provided with a pair of normally closed auxiliary contacts 19h and I9c, a pair of normally open auxiliary contacts I9d and ISe, and an operating winding ISw. The switch 20 is additionally provided with normally closed auxiliary contacts 2%, normally open auxiliary contacts 20c, and an operating winding 20w. The energization of the windings Ilsw and 2llw is controlled respectively, in a manner to be described, by normally closed .contacts 2Ia oi an electromagnetic relay 2l and normally closed contacts 22a of .an electromagnetic relay 22.. The relays 2I and 22 have operating windings 2Iw and 22w, respectively, and are preferably designed, as by having moving part-s which are relatively smaller than the moving parts of the switches i6, IB and 29, so that they respond'more quickly upon energization of their respective windings than do the switches. That is, when the winding ci a switch and the winding lof a relay are energized concurrently, the relay moves to its operated or actuated position before the switch. Any suitable type of relay may be used Afor the rela-ys 2I and 22 so long as it has a drop-out current value which is less than its pick-up current value, but preferably the relays 2l and 22 are of the clapper type having either a iixed drop-out current value or having means for adjusting the drop-out current value, it being understood that the representation of the switches and relays in the drawings is merely schematic. i

.For controlling time delayed drop-out of the relay 2I, a condenser 24 and an adjustable resistor 25 are connected in series with each other and with the winding 2 Iw between the conductor I2 and a conductor I Ia which is electrically connected to the conductor .II when the contacts IEc and/or Illa are closed. Time delayed dropout of the reay 22 is controlled by a condenser 28 :and an adjustable resistor 29 connected in series with each other and with the winding 22w between the conductors Ila and I2. A vby-pass circuit around the condenser 24 and the resistor 25 extends through the contacts IBb, and a similar by-pass circuit around the condenser 28 and the resistor 29 extends through the contacts I9b. Preferably in Fig. 1 the by-pass circuits are of relatively low resistance and, as shown, constitute short circuits of the respective series connected condensers and resistors. Other details ,tors I4 and I5.

tacts Ita to connect the motor I0 to the source of power in series with the accelerating resis- Concurrently with completion of the energizing circuit for the winding |6w, closure of the contacts I8a also completes an energizing circuit for the winding 2|w from the conductor |I through conductors 3| and IIa, the

I0. Closure of the contacts I 9d completes 'a discharge circuit for the condenser 24 through a portion of the resistor 25, the contacts |9d, and a conductor 40 to the conductor Ila, and opening of the contacts |9c prevents any possible operation of the relay 2| as a result of the closure of the contacts |9d.

Closure of the contacts |9c has no effect at this time because the contacts 22a in series therewith are open, but opening of the contacts |91) interrupts the by-pass circuit around the condenser 28 which thereupon starts to draw a charging current lwhich temporarily holds the relay 22 in its energized position. The path of the charging current for the condenser 2B is from the conductor Ila, through `the condenser 28, the resistor `29, the winding 22u), the contacts 20h, and

still closed contacts |61 in the by-pass circuit, f

a conductor 34, the winding 2|w, a conductor f '35, and the normally closed contacts I9c to the conductor I2.

Upon energization of its winding 2 lw, the relay 2| moves to its actuated position and opens its contacts 21a, the contacts '|619 subsequently opening after a predetermined short interval of time to interrupt the by-pass circuit. Having been moved to a closed position of its magnetic circuit by the relatively large current flowing through the Icy-pass circuit, the relay 2| is held temporarily in its actuated or energized position after the opening of the contacts |6b by the relatively smaller and gradually decrescent charging current which starts .to flow through the condenser 24 and there- -sistor 25 as soon as the contacts IEb open. `The rate of decline in the charging current ofthe condenser 2d is determined by its microfarad ca'- pacity, the applied voltage and the ohmic resistance of the resistor 25 and the winding 2Iw. Closure of the contacts I6c completes a circuit around the contacts I8a from the conductor II to the conductor Ila so that the contacts I8a may be opened at this time without operative elicot, and closure of the costacts |6d has no immediate eect because by the time the-contacts Id have closed the contacts 2 Ia in series therei with and with the winding ISw have opened. It should be noted that the relay 2| need respond but a very short time before the switch I6 operates to open the contacts IBD, since even ir" the contacts 2Ia and |6d move concurrently, I

contacts |9b, a conductor 38, the winding 22w,

the contacts 20h, and a conductor 39 to the conductor I2. Operation of the relay 22 to its energized position consequent upon energization of the winding 22u; has no effect at this time since the contacts 22a are in series with the still open contacts |96.

When the charging current iiowing through the condenser 24 had decreased to the drop-out current value of the relay 2|, the relay 2| drops out, i. e. returns to its normal position, and the contacts 2|a reclose to complete an energizing circuit for the winding |910 from the conductor IIa through the now closed contacts Id, the contacts 2m, and the Winding |910 to the conductor I2. Operation of the contacter I9 consequent upon the energization of its winding |9w closes the contacts I9a, I9d, and I9e and opens the contacts |919 and |9c. Closure of the contacts I 9a short circuits the resistor I4 thereby increasing the voltage impressed on the motor the conductor 39 to the conductor l2. After the expiration of a time interval determined by the applied Voltage, the capacity of the condenser 28, and the combined resistance of the resistor 29 and the winding 22w, the charging current of the condenser 28 decreases to the drop-out current value of the relay 22 which thereupon returns to its normal position in which the contacts 22a are closed. Closure of the contacts 22a completes an energizing circuit for the winding 20w from the conductor Ila. through the contacts 22a, the winding 20w, and the now closed contacts |9e to the conductor |2. The switch 20 in response to the energization of its winding 20w closes its contacts 20a to short circuit the resistor I 5, closes its contacts 20c to complete a discharge circuit for the condenser 28 through a small portion of the resistor 29, the contacts 2|lc, and the conductor 40 to the conductor lla, and opens its contacts 20h to prevent any possible operation of the relay 22 as a result of the closure of the contacts 20c.

yShort circuiting of the resistor I5 connects the motor directly across the conductors and 2, the time delay provided by the circuits including thecondensers 24 and 28 having delayed the successive operation of the switches I6, I9 and 20 so as to effect proper acceleration of the motor I0. It should be noted that the circuit of Fig. 1 is so arranged that the windings |610 and 2Iw are both energized before the circuit to the winding |9w can be completed, and that so long as the contacts 2|a open before the contacts I 6d close there can be no false operation of the switches due to a contact race.

The motor IIl may be stopped at anytime by opening the contacts |319 to interrupt the energizing circuit for the winding |6w which permits the switch It to return to its normal position wherein the contacts |6a are open. The 'switches I9 and 20 return to their normal position upon drop-out of the switch I6 because the circuit to their energizing windings is interrupted at the contacts I'Ec, the contacts |8a having previously been opened. Since the condensers 24 and 28 are almost instantly discharged upon pick-up of the switches I9 and 25, respectively, immediate pick-up of the switch I5 after dropout thereof does not prevent the full acceleration time intervals from occurring. Ii the motor |Il for any reason does not slow down rapidly, the relatively low resistance discharge Icircuits for the condensers 24 and 28 through the cont-acts |911 and 20c may be dispensed with since reclosure of the contacts lb completes a discharge circuit for the condenser 24 and reclosure of the contacts |912 completes a discharge circuit for the condenser 2-8. These latter circuits are of relatively high resistance so that a longer time is required for complete discharge of the respective condensers. So long as the duration of the discharge interval of the condenser 24 is less than the deceleration time of the motor i, the motor will be properly re-accelerated since, if the motor has not stopped, its countervoltage will limit the motor current peaks during reacceleration so that the shortened time delay interval resulting because the condenser 24 has not been fully discharged will be of no material consequence.

In Fig. 4 which illustrates the operation of a condenser timing circuit merely having a condenser, a resistor, and a relay winding connected in `series and without the by-pass circuit -for initially supplying substantially all of the current required to pick up the relay, the time during which the relay is picked up is plotted against the ohmic value of the series connected resistor.

A curve 4I is the time-resistance characteristics of such a, circuit having a condenser of a given capacity C, and curves 42 and `43 are timeresistance characteristics for circuits having a condenser of capacity two times C and our times C, respectively. It will be noted that as the size of the condenser is increased, increased periods of time delay are obtained, and that by increasing the ohrnic value R of the series connected resistor, only slight increases in time delay are the initial impulse of condenser charging current alone is used to pick up the relay, there is a limit beyond which it is impossible to increase the resistance of the circuit. This limit for a rated Value of supply voltage and for a given relay is represented by a curve 45 in Fig. 4, and it is obvious that if the supply voltage is decreased, the limiting resistance curve 45 moves to the left in Fig. 4.

Referring now to Fig. 5, which illustrates the time-resistance characteristics of the time delay circuit of Fig. l, the time scale is the same as that of Fig. 4, but the resistance scale represents an ohmic value ten times as large, hence the indication of the abscissa point ten times R. The same relay and relay winding were used in obtaining the data for Figs. 4 and 5, and in Fig. 5 curves 45, 4'1, and 48 are plotted for the same values of capacity as the curves 4|, 42, and 43, respectively, of Fig. 4. Due to the fact that in accordance with this invention the pick-up current of the relay flows through a circuit of low resistance which temporarily by-passes the condenser charging circuit, there is no limiting value of series resistance, such as indicated by the curve 45 o `Fig. 4, and, as is apparent from the steepness of the curves 4B, 4l, and 4S of Fig. 5 as compared with the

corresponding curves

4I, 42, and 43 of Fig. 4, much greater changes in time delay period can be obtained by simply adjusting the value of the series resistor.

In the form of the invention illustrated in Fig. 2, the normally closed contacts lh of the switch I6 of Fig. l are replaced by a condenser 5B and a resistor 5I which are connected in series with each other and in parallel with the condenser 24 and the resistor 25 between the conductors 2a and 34. Similarly the normally closed contacts .|9b of the switch I9 of Fig. l are replaced by a condenser E2 and a resistor 54 which are connected in series with each other and in parallel with the condenser 28 and the resistor 29 between a conductor IIb and the conductor 38. The conductor I Ib is connected to the conductor |Ia when thecontacts I9e of the switch I9 are closed. The capacity of each of the condensers 50 and 52 may be, and preferably is, considerably less than the capacity of either of the condensers 24 and 28. The resistors 5| and 54 serve only to limit the inrush current of their respective relay windings and may be omitted if the resistance of the windings 2Iw and 22w is suiiicient for this purpose. Other differences between the control system of Fig. 2 and that of Fig. l are pointed out in the following description of operation of the system of Fig. 2.

With power available at the conductors Il and I2, closure of the contacts ISa causes operation of the switch i6 and permits an impulse of charging current to flow from the conductor I I, through the conductors 3| and Ia, the condenser 5U, the resistor 5I, and the operating winding 2 Iw to the conductor 35 which is sufficient to cause the relay 2i to operate and open its contacts 2 Ia. After a relatively short interval of time, the condenser 50 becomes fully charged and current no longer ows therethrough to the winding 2|w, but the relay 2| is temporarily held in its picked-up position by the charging current flowing through the condenser 24 and the resistor 25. Consequent upon the accumulation of suflicient charge on the condenser 24 to cause the current iiowing therethrough and through the resistor 25 to the `winding 2li() to be reduced belenr the drop-out current vaine of the relay 2|, the relay 2| returns to its normal position and the contacts 2Ia reclose to effect energization of the winding |9w as described in connection with Fig. l. Operation of the switch I9, due to energization of its winding |9111, causes closure of the contacts |9a, ld, and |96 and opening of the contacts |9c. Closure of the contacts i941 causes an increase in the voltage applied to the motor i8, closure of the contacts ld and opening of the contacts |9c completes a discharge circuit for the condensers 24 and 50, and closure of the contacts |98 completes the circuit from the conductor I Ia to a conductor Ill).

Upon energization of the conductor l ib, an impulse of current flows through the condenser 52, the resistor 54, the conductor 33, the winding 2220, the contacts 2Gb, and the conductor 39 to the conductor I2 which is suiiicient to cause the relay v22 to move to the open position of its contacts 22a. The contacts 22a of the relay 22 open before theswitch 2|) can operate due to the temporary but ineective energization of its windings 20w which occurred at the instant of closure of the contacts ite. After the condenser 52 is charged, the by-pass circuit therethrough is, in operative effect, interrupted, and the relay 22 remains in its picked-up position due to current which ilows through the condenser 2S and the resistor 29. After the accumulation of a predetermined charge on the condenser 28, the current flowing therethrough to the winding 22w decreases beloW the drop-out current value of the relay 22 which thereupon recloses its contacts 22a to complete the energizing circuit for the winding from the conductor I IIJ to the conductor I2. Operation of the switch 2-3 consequent upon the energization of its winding 2G10 causes closure of the contacts 20a which short circuit the remaining acceleration resistance section I5, and causes closure of the contacts 2Bc and opening of 9 the contacts 20h which complete a discharge circuit for the condenser 28 and 52.

The time-resistance characteristic curves of Fig. are also illustrative of the operation of the timing circuit of Fig. 2 because, since the resistors 5I and 54 have a low resistance and the condensers 50 and 52 have a small capacity, the condensers 50 and 52 become fully charged almost instantly and have very little effect on the respective time periods controlled by the condensers 24 and 28.

In Fig. 3 a portion of one of the previously described timing circuits has been reproduced, and a resistor 55 is shown as added thereto. The resistor 55, which is shown as connected in parallel with the contacts |612 and in parallel withthe condenser 24 and the resistor 25, has an ohmic value such that when the contacts I6b are opened and the condenser 24 is substantially fully charged, insufficient current flows therethrough to hold the relay 2| in its picked-up position. The shunt circuit including the resistor 55 supplies current to the relay winding 2 Iw which is in addition to that supplied through the condenser 24 so that the condenser 24 becomes more fully charged before the total current flowing through the winding 2|w decreases to the drop-out current value of the relay 2 I. The time delay period that is obtainable by using the circuit with the resistor 55 is longer for a given size of condenser than that obtainable by using the circuits of Figs. 1 and 2. It is readily apparent that if desired a resistor 55 may be added in a similar manner to one or both of the timing circuits illustrated in Fig. 2.

We claim:

1. In a motor controller, a resistor of relatively high resistance, a timing condenser of relatively large capacity, an electromagnetic switch having an operating winding, connections forming a series circuit including said resistor, condenser, and winding, a by-pass circuit of relatively low resistance connected in parallel with said series connected resistor and condenser and in series with said winding, switch means operable to connect said series circuit across a source of unidirectional voltage, a control condenser of relatively small capacity interposed in said by-pass circuit and chargeable within a predetermined time after operation of said switch means and while said timing condenser is substantially uncharged to prevent the flow of current in said Icy-pass circuit, and the electrical constants of said circuits being related to each other and to the voltage of said source to permit suiiicient current to flow in said circuits to pick up said electromagnetic switch when said switch means is operated and before said control condenser becomes charged. f

'2. In a motor controller, a resistor of relatively high resistance, a condenser, an electromagnetic switch having an operating Winding, means for connecting said resistor, condenser, and winding in series with each other to form a series circuit, switch means operable to connect said series circuit across a source of unidirectional voltage, the electrical constants of said electromagnetic switch and said resistor being so related to each other and the voltage of said source that insufficient current lows through said series circuit to operate said electromagnetic switch upon connection of said series circuit across said source when said condenser is substantially uncharged, a bypass circuit of relatively low resistance connected in parallel with said condenser and resistor and 10 in series with said winding, the electrical constants of said by-pass circuit, said resistor, and said electromagnetic switch being so related to each other and to the voltage of said source that the by-pass circuit is operative to prevent material charging of said condenser and that said circuits are operative while said condenser is substantially uncharged to allow suiicient current to flovv through said Winding to operate said electromagnetic switch, by-pass circuit interrupting means interposed in said by-pass circuit and rendered operative consequent upon and after operation of said switch means and while said condenser is substantially uncharged to prevent current from ilovving through said by-pass circuit, and the electrical constants of said electromagnetic switch, said condenser, and said resistor being so related to each other and to the voltage of said source that the condenser charging current that flows upon cessation of current flow through said by-pass circuit is sufficient to hold said electromagnetic switch in operated position for a time interval.

3. In a motor controller, a resistor of relatively high resistance, a condenser, an electromagnetic switch having an operating winding, means for connecting said resistor, condenser, and winding in series with each other to form a series circuit. switch means operable to connect said series circuit across a source of unidirectional Voltage, the electrical constants of said electromagnetic switch and said resistor being so related to each other and to the voltage of said source that insuiiicient current iiows through said series circuit to operate said electromagnetic switch upon connection of said series circuit across said source when said condenser is substantially uncharged, a, by-pass circuit of relatively lov1 resistance connected in parallel with said resistor and in series With said winding, the electrical constants of said by-pass circuit and said electromagnetic switch being so related to each other and to the voltage of said source that said by-pass circuit is operative while said condenser is substantially uncharged to allow suiiicient current to flow through said winding to operate said electromagnetic switch, bypass circuit interrupting means interposed in said by-pass circuit and rendered operative consequent upon and after operation of said switch means and while said condenser is substantially uncharged to prevent current from iiowing through said by-pass circuit, and the electrical constants of said electromagnetic switch, said condenser, and` said resistor being so related to each other and to the voltage of said source that the condenser charging current that flows upon cessation of current flow through said by-pass circuit is suicient to hold said electromagnetic svvitchin operated position for a time interval.

4. In a motor controller, a timing control system for delaying the sequential operation of a switch means and a contactor, said system com,- prising a resistor, a condenser, an electromagnetic relay having an operating winding and normally-closed contacts, a series circuit in which said condenser and resistor are connected in series with each other and with saidk winding, a by-pass circuit connected in parallel with said series connected condenser and resistor and in series with said winding, a switch means, an electromagnetic contactor having a winding, a contactor operating circuit connecting said normally-closed contacts and said contactor winding in series, means operatively connecting said switch means to said contactor operating circuit 1l and said series circuit so that upon closure of said switch means said contactor operating circuit, said series circuit, and said by-pass circuit are connected across a source of unidirectional voltage whereby said circuits are initially energized, said by-pass circuit including means rendered operative consequent upon and after operation of said switch means for interrupting current flow in said by-pass circuit, said by-pass circuit being of such low resistance that said condenser does not accumulate an appreciable charge while said by-pass circuit is conducting current, energization of said series circuit and said by-pass circuit causing pick-up of said relay before, and permitting charging of said condenser after, said by-pass circuit ceases to conduct current, and pick-up of said relay opening said normally-closed contacts before said contactor is operated as a result of current owing in its operating winding, whereby said contactor does not operate until its winding is energized after drop-out of said relay resulting from the charging of said condenser.

5. A timing control system comprising an electromagnetic switch and a pair of electromagnetic contactors, electromagnetic relays having normally-closed contacts in energizing circuits respectively for said contactors respectively, operating windings for said relays respectively, series connected condenser and resistor combinations connected in series with said windings respectively, by-pass circuits connected in parallel with said series connected condenser and resistor combinations respectively and in series with said relay windings respectively, means for energizing said electromagnetic switch and operable concurrently to energize said relay windings through said by-pass circuits respectively, means rendered operative consequent upon energization of said electromagnetic switch to interrupt one of said by-pass circuits thereby causing a charging current to start to ilow through one of the condensers and the winding associated therewith, diminution of the charging current as said one of said condensers charges causing drop-out of one of said relays thereby to cause said contacts of said one relay to close to complete the energizing circuit of one of said contactors, means rendered operative consequent on operation of said one of said contactors to interrupt said other by-pass circuit thereby causing a charging current to start to flow through the other of said condensers and the winding associated therewith, diminution of the charging current as said other condenser charges causing drop-out of the other relay thereby to cause said contacts of said other relay to complete the energizing circuit of the other of said contactors.

6. In a motor controller, a resistor of relatively high resistance, a condenser, an electromagnetic relay having an operating winding, a series circuit in which said condenser and said resistor are connected in series with each other and with said winding, a by-pass circuit of relatively low resistance connected in parallel with said series connected condenser and resistor and in series with said winding, a switch means, means operatively connecting said switch means to said series circuit so that upon closure of said switch means said series circuit and said by-pass circuit can become connected across a source of unidirectional voltage whereby said circuits can be initially energized concurrently, by-pass circuit interrupting means interposed in said bypass circuit and rendered operative consequent upon operation of said switch means for preventing the iiow of current in said by-pass circuit, said by-pass circuit interrupting means including means operative to impart a time delay period between the operation of said switch means and the operation of said by-pass circuit interrupting means, and the electrical constants of said circuits and said relay being so related to each other and to the voltage of said source that said condenser does not accumulate an appreciable charge while said by-pass circuit is conducting current, that energization of said series circuit and said by-pass circuit causes pick-up of said relay during said time delay period, and that the charging current of said condenser that ows after said by-pass circuit interrupting means operates is sufficient to hold said relay closed for a time interval.

7. A motor controller in accordance with claim 6 characterized in that said by-pass circuit interrupting means comprises normally closed switch contacts interposed in said by-pass circuit and means responsive to operation of said switch means are arranged to open said switch contacts to interrupt said by-pass circuit.

8. A motor controller in accordance with claim 7 characterized in that said switch means comprises a momentary contact push button which upon closure can connect said series circuit and said by-pass circuit across said source and an electromagnetic contactor having an operating winding arranged to be energized from said source upon momentary closure of said push button, said contacter including normally open holding f circuit contacts which close upon energization of said operating winding to complete a holding circuit around the contacts of said push button, said switch contacts, and means to effect opening of said switch contacts upon said energization of said operating winding.

9. A motor controller in accordance with claim 6 characterized in that a shunting resistor is connected in parallel with said by-pass circuit and in series with said winding and has an ohmic value so related to the voltage of said source and the drop-out current value of said relay that the additional current that can be supplied through said shunting resistor to said winding during the charging period of said condenser is less than the drop-out current value of said relay.

l0. In a motor controller, a resistor, a timing condenser, an electromagnetic switch having an operating winding, means for connecting said resistor, condenser, and winding in series with each other to form a series circuit, switch means operable to connect said series circuit across a source of unidirectional voltage, the electrical constants of said electromagnetic switch and said resistor being so related to each other and to the voltage of said source that insuicient current flows through said series circuit to operate said electromagnetic switch upon connection of said series circuit across said source when said condenser is substantially discharged, a, normally completed oy-pass circuit connected in parallel with said condenser and resistor and in series with said winding, the electrical constants of said by-pass circuit and said electromagnetic switch being so related to each other and to the voltage or" said source that upon connection of said series circuit across said source said by-pass circuit is operative to prevent operative charging of said condenser and is operative while said condenser is substantially uncharged to allow sucient current to flow through said winding t0 operate said electromagnetic switch, by-pass circuit interrupting means interposed in said bypass circuit and rendered operative consequent upon and after operation of said switch means to prevent current from iiowing through said bypass circuit, and the electrical constants of said electromagnetic switch and said resistor being so related to each other and to the voltage of said source that the condenser charging current that iiows upon cessation of current flow through said by-pass circuit is sucient to hold said electromagnetic switch in operated position.

11. The motor controller of claim 10 characterized in that said timing condenser is of relatively large capacity, said by-pass circuit interrupting means is a condenser of relatively small capacity, and the resistance of said by-pass circuit is materially less than the resistance of said switch means said condenser in said by-pass cir- REFERENCES CITED The following references are oi record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,555,893 Thomson Oct. 6, 1925 2,223,163 Boeker Nov. 26, 1940 2,273,988 Pinto Feb. 24, 1942 2,279,849 Warrington Apr. 14, 1942 2,394,294 Giuseppe Feb. 5, 1946 FOREIGN PATENTS Number Country Date 56,246 Norway Mar. 2, 1936 481,054 Great Britain Mar. 4, 1938