CA1064573A - Time-delay start winding cut-out circuit for an electric motor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This disclosure deals with a time delay cut-out circuit for the start winding of an AC electric motor.
The circuit includes an electronic switch which is con-nected in series with the start winding and which may be selectively closed to energize the start winding. Time delay means is provided which in response to current flow therethrough, provides a timing period. An auxiliary coil is wound on the motor stator and supplies current to operate the time delay means. The electronic switch is connected to respond to the time delay means which closes the elec-tronic switch to energize the start winding during the timing period. The components of the circuit, except for the coil, are mounted in a capsule which may be plugged into the motor from the exterior of the stator. The time delay means includes a heat responsive device, and the components are sized and arranged in the capsule to optimize the heat generation and dissipation properties and thereby obtain the desired operating characteristics.

Description

TIME~DELAY START WINDING CUT-OUT
_CIRCUIT FOR AN ELECTRIC MOTOR
DI SCLOSURE
Prior art U.S. Patents No. 3,832,612, August 27, 1974 to Woods; and No. 3,643,142, February 15, 1972 to McBride, Jr., describe various electronic control circuits for an AC induction motor having a main windiny and a start winding. The control circuits include a triac Coll-nected in series with the start winding and a -timing circuit connected to the gate of the triac ~or turning i-t on, ancl thus energizin~ the start winding, ~or a certain time interval measured from initial energization of the motor.
~he timing circuit includes a PTC resistor which heats to its transition temperature during the time interval and turns off the triac when heated to above its transition temperature.
While cixcui~s o~ this character operate satisfactorily, they haYe a numl~er of disadvantages. Such circuits include a sizable number of components, which makes the circuits

2~ relatlvely expensive, increases their chance of failure, and make~ them difficult to compactly package. Further, e length of time required Eor the transition of a PTC
resistor from its low resistance state to its hi~h resistance statè is relatively long, this transition taking place over a num~er o~ cycles of the AC power 5uppl.y. Since a triac normally i~ not a per~ectly sy~rnnetrical device, half~wave operation o~ten takes place during the transi tion. This is equivalent to intxoducing a direct current component in the power suppl~ lines, which makes a mo tor having ~:uch a control circuit noisy during the transition interval.
It is a general object of -the present invelltioll to ~ , .

~ provide an improved control circuit which does not have the .
oregoin~ disadvantages~

'~ , .~.

:~6~i73 A control circuit in accordance with the disclosed invention is designed to control energization of the start winding of an AC mo-tor which includes a main winding and a start winding. The con-trol circuit includes ~n electrollic bidirectional switch which is sellec-tively -triggerable into conduction, a timing circuit connected to trigger the switch for a timing interval or period after initial energization oE the motor, and an auxiliary coil for operating the timing circuit.
The control circuit is contained in a capsule which may be plugged into the motor from the exterior o~ the i stator, thus making the circuit readily accessible Eor replacement or servicing without dismantlin~ the sta-torO
The timing circuit includes heat responsive parts, and the physical layout of the electrical components in the capsule provides optimum heat generation and dis-sipation from the parts and optimum operating characteristics of the timing circuit.
Notwithstanding the above the invention in its ' 20 broader claimed aspect co~prehends a start winding cut-out circuit for an AC 01ectric motor including a stator, a main winding and a start winding, the main windin~ being adapted to be connected across AC power supply lines. The circuit comprises start wincling switch means connected in series with the start winding ancl connected across the rnain windiny and heat responsive switch means are connected to actuate the ~tart winding switch means. The heat xesponsive switch means include a self heatiny electrically conductive part which move5 upon self heating, and includes switch contacts which are actuated by the movement when the ~; ' ~ .

,',' .'. '" ,." ~, ' ~'''"', ' '," ', ' ' ' ' ' ' , '' ' .

part is heated to a selectecl temperature, the switch contacts being connected to and controlling actua-tion of the start winding switch means. A curren-t source is connected to the part and provides heating current Elow through the part, the current source being electric ally coupled to the mo-tor circuit and providing the heating current upon energization of the motor~ The heat responsive switch means actuates the start winding switch means after initial energization of the motor unkil the selacted temperature is reached.

The foregoing and other ob~ects and features of the present invention may be better understood ~rom ; the following detailed description taken in conjunction with the accompanying figures of the drawings, wherein:

Fig. 1 is a schematic diagram of a control circuit in accordance with the invention;

igO 2 i.s a view of a part of an electrical motor ;~ including a control circuit embodying the present invention;

Fig. 3 is a fragmentary sectional view oE a part of the motor;

' ~ ~

,~ . !
. 3 -is a view t~};en on the lirl~ 4-4 o.~ ~'iy.
5;
Fig. 5 i.s a sectional view taken on the line S-5 of YicJ. 4;
Fig. 6 is a sect-ional view taken on the line 6-6 O L ~iy. 5i Fig. 7 is a schematic diagram similar to Fiy. 1 but illustrating an alternate form of the invention, wi~h Fig. l;
Fig. 8 is a schema-tic diagram similar to Figs. 1 and 6 but illustrating still another alternate ~orm of the inventionr appearing with Fig. 1.
Fig. 9 is a sectional fragmentary view of a motor including a control ci.rcuit in accordance with another ~;
- embodiment oE the invention;
Fig. lO is an enlarged view of part of the motor shown in Fig. 9;
Fig. 11 is a sectional enlarged view o~ the con-trol circuit of khe motor of Fig. 9; and Fig. 12 is a sectional view taken OIl the line 12-~O ~o_ Pig. 11~
Fig. 1 schematically illustrates an AC~electric motor of the split-phase induction type, including a main . .
wind1ng lO and d start winding 11. Thetwo windings lO and 11 are wound on the stator (not shown) of an electric motor and are angularl~ displaced by 9O ~lectrical degrees. As is well known in the art, starting ~oxque :Eor the motor is attained by provi.ding the start wi.nding 11 with a diffexent reactance ~rom the m~in winding lO, thereb~ producincg a time .
:: .
or p~ase displacement in the two wind.ings. One side oE each ~ of the windingc; lO and 11 is connected to ~ power supply line ,~ ~
12, and the other side o the main winding lO is connected ::

~ 6~LS'~3 to a p~w~r li.ne 13. ~i~h~ two lin~s 12 and 13 cl.re adapted to be connected to an ~C power supply 14 such as a 60-cycle single phase AC power source.
While the main windin~ lO is connected di.rectly across the two power supply lines 12 and 13, the start winding ll is connectable across the twcl supply lines b~t a control circuit which enables energizati..on o~ the star~ windin~ 11 during a short t:iming interval or peri.od at in.itial energi-zation of the motor. This time interval may, for example, be one-hal~ second in length. As will be described hereinafter, the start winding 11 may also be reenergized if the motor : stalls. The control circuit comprises a selectivel~ closable bi~directional electronic switch commonly known as a triac, indicated by the raference numeral 16. The triac 16 com-j prises a first main or power terminal 17, a second main or power terminal 18, and a gate l9. As is well known in the : art, the triac 16 offers a low resistance path between ~he ; main terminals 17 and 18 when, in each AC hal~ cycle, a ~ - .
~: ~ potential appears across the main terminals and a trigger 0~ ~ignal appears on the gate l9. The triac 16 othexwise :: , ~
presents a very high resistance, or open circuit, to current flow between the main terminals 17 and 18. The main terminal 17 is connected to the start winding ll and the other main ~ terminal 18 is connected to the power line 13. It will be :~ apparent therefore that the start w.inding 11 and the triac ~ 16 are connected in series and that they are connected across : ~ ~
; the power lines 12 and 13 in parallel with the ~ in winding lOt and when the triac 16 is closed or triggered, the start winding ll will be energiæed.
~ time delay circuit 21 is a:Lso provided in the ~: . , ~ 5~

5~73 control c:ircui~ to tri~cler ~ C~ ~r~ c 16 into concluction.
The time delay circuit 21 comprises a biMetallic therrnally responsive me~ber 22 which, in the present illustra.io~, i5 generally U~shaped. rrhe member 22 comprises two lay~rs 23 and 24 of metals which have difLerent rates of thermal expans;on, as is well known in the art. The'10~7er ends of the legs 26 and 27 of the membex 22 are rlxed or h~ld stationary, and a movable cont-act 28 is secured to the web or cross portion o~ the member 22. A stationary or fixed contact 29 is positioned adjacent the member 22 and the contacts 28 and 29 are normally c~osed. ~Iowever, when the member 22 is heated, it flexes and moves the contact 28 away from and out of engagement with the ~ixed contact 29.
While the contact 29 is referred to herein as a ixed contact, it may also ~e-movable to some e~tent~ The co~ltact ~9 may bè fastened to a flexlble bimetal member 30 ,~ which moves the contact 29 in the same direction as the contact 28 when heated. This arrangement compensates ~or :
~ changes in ambient temperature without otherwise affecting , ' 20 the operation o~ t'he circuit.
i , . . .
` ~ ; The fixed contact 29 is electrically connected to the gate 19 o the triac 16~ The leg 27 o~ the member 22 '~
: :
is eIectrically conzlected to the main terminal 18 of the triac 16 and the other leg 26 is electrically connected to a current sourae which in the present ins~ance comprises an auxiliary coil 31. The coil 31 is connected between the le~ 26 and the power line'13~ and it w;ll be apparent that ; when a voltage is induced in the coil 31, current will flow 'through the loop including the coil 31~ the bimetallic mem'her 22, the line 13, and return to the coil 31. The coil 31 is ' '' ~6- ' moun-ted on the motor stator concentri~ with or on tl-le a~is of the start windiny 11.
In ~ddition to the foregoiny circuit components, a snubbing resistor 32 and capaci-tor 33 may be connected across the main terminals 17 and 18 of the triac 16 to prevent self-triggerillg of -the tr~c, as is well known in the art~
Considering the operation of the circuit illustrated in Fig. 1, when the power lines 12 and 13 are connected to an AC power suppl~, current flows through the main winding 10. Xnitially, the member 22 is cool and the contacts 28 and 29 are in electrical engage~ent. In a particular half cycle of the supply voltage, as the supply voltage crosses zero and starts to increase, substantially the full line potential app~ars across the main terminals 17 and la of the triac 16. The potential across the main terminals results in current flow from the main terminal 17, through the internal triac resistance between the terminal 17 and the gate 19, through the contacts 28 and 29, the ~ember 22 20~ and to the power line 13. As the supply voltage increases in the AC half cycle, the current flow between the teirminal ;17 and the gate 19 increases and the potential across the terminals~17 and 18 also increase~. When the gate current reaches, ~or example, 20 to 30 milliamps, the triac 16 is `~ triggered on and full start winding current :elOws through ~ : `
the winding 11 and the triac 16. This accurs very early in the halr cycle, and current flow continues ùnt~l the end of the AC half cycle, but the triac 16 turns off at the next zero crossing. Of course, the fore~oing series o~ events 30~ occurs oncie again during the next ~C halE cycle and continues . : : ~

::
:
.

.

. . . , ~ ,, i. " ' : . ' until the contcl~ts 2~ clnd 29 open -to br~ak the pal.h ~
current flow througll the gate 19. While this ga~e current flows through the m~mher 22, it is not sufficient to materiall.y hea-t the member 2~D Once the triac 16 fires, the current through the yate 19 is lirnited because of the short circuit formed by the tr~ c main terminals. The only voltage across the gate 19 i5 the triac Eorward voltaye drop which of course is very low. Therefore there is no need for a gate resistor as is usually required in convention~l circuits. Damaging current surges in the gate circuit are prevented by the start wi.nding 11 inductance.
As shown in Fig. 1, the auxiliary coil 31 is mounted concentrically with or on the axis of the start winding 11, and consequently current flowing through the start winding 11 induces a voltage in the coil 31. The induced voltage results in current flow through the coil 31 and the legs 26 and 27 of the member 22.
This current results in resistance or self-heating :
of the two layers 23 and 24 of metal of the member 22, and after a time interval or period, the member 22 is heated ~: :
sufficiently that it flexes and opens the normally closed contacts~8 and 29. Th~ length of the -time interval or period is determined primarily by the size and mass of the member 22, the types of metal, the number of turns o-E the coil 31, and the amount o~ heat lost Erom the member Z2.
This length is chosen to co.inc.ide with the lenyth of time required for the motor to reach the normal cut-out speed : ~ :
when driving the loàd for which the motor is designed. For a motor designed to dri7~e a water well pump for example, ~ he cut-out speed is reached at the end of approximately ~: ~ . : :

.:

: . .. : , .. , ..

~ 0~4~73 .5 sec~nd. ~s will b~ discussed hereina:Ete.r, -the lay~ut or moun~iny oE the componen~s has an e-fect on the tirne interval because the layout determines the amount o:E heat loss Lrom the member 22.
As previously mentioned, the conta~-ts 2~ and 29 open at the end of the presel.ect:ed time interval. Ther~-after, the bimetallic member 22 is maintained in its heated condition in order to hold the contacts open by reason of the voltage induced in t~.e coil 31 and the resultant current ~low throuyh the member 22. During running of the motor, .:
the turning rotor induces current in the coil 31 and this induced current is suf~icient to maintain the element 22 .
in the heated condition:and to hold the contacts 28 and 29 ~ .
open.
At the time that the contacts 28 and 29 open the only current flow through them is the residual curren.t fbw ..
in the gate 19 circuit:a~t~r the traic has fired, which is extremely low. Consequently, the contacts 28 and 29 may be made very small and will last a long time.
.
2~ ~ While the au~iliary coil 31 may be inductivel~ :
coupled with the start windiny 11 as shown in Fig. 1, or with~the main winding 10 as shown in Fig~ 7, or in a position inbetween as shown in FiyO ~, the positi~n illustrated in Fig. 1 i5 pre~erred for most rnotor appli-~:~:: cations. In the event that the motor is stall.ed, -the main , windinJ lO will continue to be energized but the rotor will : rlot turn and current will no lonyer be induced in the coil 31.~ As 900n as cuxrent stops flowing through the auxlliary coil 31 dnd the member 22, the member 22 becJins to cool.
30;~ When it cools su~iciently, the contacts 28 and 29 again lose and th~ ~tart winding l.l will be reenergi~.ed due .

to triycJering or firi.ny o:E the triac 16 as prev1ou~ly described. Normally the rnotor will start up ayain and the member 2~ will be heated and the timing interval will be repeated. Of course, an overload device should be provided bet~7een the lines 12 and 13 to protect t'he motor against damaye in the case where the motor continues to be stalled ,~
after the start winding i.s reenergized.
The circuit of Fig. l,has numerous advantages.
The bimetal member 22 may be made very small because it carries only a small proportion of the start winding current.
With such a small si~e it wil]. have little thermal inertia, :.
and consequently the member ~2 will heat rapidly and it will cool relatively rapidly if the motor is stalled in order to trigger the triac 16 and reenergize the start winding.
By way of a specific example, the total length of the legs 26 and 27 may be approximately one-quarter inch long, and the overall width o~ the member 2~ in the other direction ma~ be approximately one-eighth inch. The two layers 23 and 24 may be made extremel~ thin.
~ A ~urther advantage derived from the small. size of the bimetal member ~2 is that little current is required to heat it. The coil 31 may consist of one or a few turns around several teeth o~ the stakor which provides sufficient current to heat, the member 22 and to ma:intairl i-t heatecl after the contacts 28 and ~9 open. To preverlt damage to the member 22 f'rom overheating after the contacts 28 and 29 open, heat sin~s and the other circuit components may be mounted adjacent the membcr 22. Such heat sin]cs and components would not materially affect operation during :
ini.tial ener~ization however because the member 22 heats ~: " ': : ' . .

, so qu:ickl.~ that i.t does not ~ose an ap~rec:i,ab.~e amount of ~eac.
A sti:L.L further advantage o~ the circui-t is due to ~he fact that, at the instant oE initial energization of the motor, the ~ull power supply vol-tage is applied : across the contacts 28 and 29, ~nd consequently there is n.o problem due to failure to ma'ke adequate electrical con-tact. ~evextheless, there is no problem due to current buildup in the gate 19 circuit because the current is limi-ted by the rapid energization of the triac 16, thereby pre venting damage to the contacts 28 and 29. --Figs. 2-6 illustrate one method of mounting the components of the control circuit and the installation of the control circuit in an electric motor, The parts illus-trated in Figs. 5 and 6 are approximately twice actual size . in a typica1 embodimen-t o~ the invention.
: . With reference to Figs. 2 and 3, the refererlce numeral.36 illustrates an annular end ring o:E a stator of an induction motor, the end ring closing one end of a stator ~: 20 cavi~y which houses the stator windings (not shown). ~he ~end ring 36 has a hole 37 formed therethrough, and -the end of the hole 37 which is ad~acent the stator cavity receives a co~nector part 38 (Figs. 3 and 5). q~he support 38 is - ~ secured to,the stator at the inner end o~ the opening 37 and supports three fernale connectors or sockets 41, 42 and 43 .,. ~, ich extend downwcardly i.nto -the cavityO Fig. 1 schemati-cally illust.rates the sockets and as shown the socket 41 is connected to the awriliary w.inding 31~ the soc~cet 42 is con-nected to the main winding 10, and 'che soc~cet 43 is connected to ~he start wincling 11. '' :
~: :
~ , . .

; ~

, . . .
, .

5~3 The opening 37 in the end ring 36 receives a capsule 44 tFigs. 3 to 5) which houses the electrical components of the control circuit. The capsule 44 comprises a generally cylindrical housing 46 which is closed at its upper end and open at its lower endj and a connector base 47 which is fas-tened in the open lower end of the housing 46. As shown in Figs. 2 and

3, a vertically extending slot 48 is formed on the base 47 and extends upwardly from the lower side of the base at one side thereof, and a polarizing projection 49 (Fig. 3) is formed on the connector part 38, which is adapted to be received in the slot 48. As shown in Fig. 3~ to ensure proper alignment of prongs on the capsule 44 with the sockets 41 to 43, the capsule 44 is positioned with the slot 43 over the projection 49, and the capsule is then pressed downwardly into place.

With reference to Fig. 3, the upper portion 51 of the hole 37 is enlarged and the upper portion of the housing 46 is also enlarged. The upper and lower portions of the housing 44 fit snugly into the upper and lower portions of the hole 37. A
sealing ring 52 is positioned in the hole 37 at the lower end oE
~i 20 the enlaxgement 51, and when the capsule 44 is pressed into the ~: : , j hole 37, the sealing ring 52 is compressed ancl forms a seal between the capsule 44 and the end ring 36.

The electric motor Eurther includes an end bell 54 (Fig. 3) having a hole 56 ~ormed therein in aligmnent with the end ring hole 37. A thin cylindrical shell 55 is preferably also provided to cover the exterior of the stator.

; ~ . .
The capsule 44 is held securely in the holes 37 and 56 ~ ' as by a shoulder 53 (Fig. 3) which i5 formecl on the inner periphery of the hole 56 and extends inwardly over t,he upper end of the capsule 44. The hole 56 has an internal dimension which is equal to the enlarged part 51 oE the hole 37, and the vertical dimension of the end bell is great enough that the upper end of the housing 46 is recessed below the upper surface of the end bell 54. While the hole 56 may be a blind hole extending upwardly from the lower surface 57 of the end bell, Fig. 3 illustrates an arrangement where a hole 58 is formed concentrically with the hole 56 and extends from the hole 56 upwardly to the upper surface of the end bell 54. With this arrangement, the upper end of the capsule 44 is exposed to the ambient temperature and it can dissipate heat. The housing 46 preferably has a close fit with the end bell 54 and the end ring 36 so that the latter members can conduct heat Erom the housing ~, 46.
' ~
me mounting of the electxical components shown ,, in Fig. 1 is illustrated in Figs. 4 to 6. The stationary ' contact 29, the bimetal member 22, and the triac 16 are ' ~, supported on the base 47. The two terminals 17 and 18 and '~
the gate 19 of the triac 16 are in the form of three prongs "
which extend downwardly from the body oE the triac. Three pron~s 61, 62 and 63, which are electr:ically connected to the circuit components extend downwardly from the base 47 and mate with the three sockets ~1, 42 and g3. The pronys 61 and 62 are electrically connected to the ~,wo legs of the bimetal member 22,i and the prong 63 is electrically connected by a lead 64 to the main terminal 17 of the triac 16.
The gate 19 is connected by leads 66 to ~he stationary ':
' , ~ -13-, ~ " . . , . , ,, , : . :

S~3 contact 29, th~ m~in t~rminal 18 is connected to prony 62 a lead 67. ~he main terminal 18, in addition to bei.ny connec-ted to one of the downwardly extending prongs sho~,m in Fig. 6, is also connected to an upwardly extending mount-ing tab of the triac lG, in~icated b~ the numeral 71 (~ig.
S). Where the snubbing resistor 32 and capacitor 33 are ~rovided, they are mounted, above the other components and are connec~ed by leacls 72 to the tab 71 and by leads 73 (Figs. 5 and 6) to the prong 63.
The tah 71 of the triac 16 is fastened to a metal heat sink 74 by a screw 75 which extends through a hole in the tab 71. The part 38 and the support 47 are of course made of an insulating material. .The sink 74 is supported by the base 47 and is made of a good heat conducting material such as copper. The housing 46 is made o~ a metal, such as copper, and it is separated from some of ~he components b~
~a generally cylindrical member 76 which is made of a good heat conducting material, but which is also an electrical insulator. ~ne me~er 76 extends from the base 47 upwardly to the capacitor 37, and it is positioned around the contact 29, the member 2~ and the triac 16. ~he member 76 extends to and is part of a thin layer 77 of insulation between the , triac: 16 and the sink 74. ~s shown in Fig. 4, the outer side of the sink 74 is curved, and the cylindrical portion of the member 76 and khe sink 74 are in tiyht engag~ment :~ with the housiny 46 for yood heat conductivity. Tne very hin layer 77 of insulation separates the triac from the sink 74! buk heat conducts through the layer 77 because o its thinness. The adjacent surfaces of the tab 71 and the : :~sink 77 are~lat except for a counters.ink 80 in the sink 77 ;

~ 5 ~ 3 a.councl the hole ~or the screiJ 75, and tlle tab 71 ana the sinX 77 are :in good heat conducting rel~tion l:hrou~h -the insulation member 77.
~ s will be apparen~ ,rom Figs~ 2-6, the capsule

4~ is ~rotected against damage by being recessed into the motor. By first removin~ the end bell 54, the capsule may be readily removed for testing or servicing, without requiring complete disassembly o~ the motor~ A still furt'ner advantage of mounting the control cîrcuit outside the motor stator is that this location reduces the ef~ect on the circuit operation, o~ the heat generated by the motor windings 10 and 11. At the exterior location sho~m, the bi~etal member 22 will be influenced by the ambient temperature and t'nerefore, if the motor is stalled, the metal 22 will cool much more rapidly than if the me~er 22 ~~~ were mounted in.the motor stator .
: since the bimetal member 22 is mounted closely . adjacent the base 47 and the other components, particularly the triac 16, hea-t leaXed from the member 22 and absorbed ~20 ~ by the other parts will px~vent damage to the member 22 . ; after the start winding has been deenergized. The member 22 i5 very small and it is supported by conductors 61, 62 ~and 66 closely adjacent the base 47, and consequently heat ~from the member 22 will be conducted to t'ne ~ase and dissi-:~ pated. The member 22 f~exes in the direction of the txiac 16 w'nich also acts as a heat sink, and a5 the member 22 lexes, more of its heat will be radiated to tha triac~ If necessary to pxotect the mel~ber 22 or to ach.ieve the desixed ~ ,~
speed o~ operation, other heat sinks in addition to tha triac .
~30 and the sink 74 may be mounted adjacent the member 220 For . :
: ~ .

69~573 e~ram~)le, a copper he~t s:Lnlc coulc~ be mounted ~here :i-t woulcl'be enc~aged by the memb~r 22 a~er it has'been, heate~. As a specific example, when from one to -two amps. current flow thrvugh the member 22 it will be heated to the contact openiny temperature in .5 isecond, but sufficient heat will be lea~ed from the mem'ber 22 that it ~Jill not be heated to above the temperature where it will be damaged. Upon initial energization the member 22 is heated so quickly that little heat is lost, but , duriny continuous operation, a balance is maintained be-tween t'ne energy into the member 22 and the heat dissipated.
Fig. 7 illustrates an alternate form of control circuit for use with an electric motor including a main winding 81 and a start winding 82 which are connected to AC power supply lines 83 and 84. The start winding 82 is connected in series with a triac 86 and across a main wind-ing 81. The triac 86 includes a main terminal 87 which is connected to the start winding 82, another main terminal 88 which is connected to the power supply line 84, and a gate 89 which is connected to a stationary contact 91 o~ a time delay circuit. A u-shaped thermal member 92 having a movable contact 93 is positioned adjacent the stationary conkact 91, the ~ember 92 and the contacts 91 and 93 being generally similar to the member 22 and the contacts 28 and 29 illustrated in F:iy~ 1. The bimetal member 92 is connec~
ted to an auxiliary coil 94 and to the power supply line 84, ~he auxiliary coi:l 94 in khis embodiment of the invention being mounked on the stcltor concentrically with or on the axis o~ the main winding 81. A resistor 96 connects t~e stationary contact 91 with the junction between the staxt .:

~,: ~ .
; ~ .

!, ' ' ;' ' ; ' ' ' ' ' ~ ~ ' ' ' ' ' ' ~ ' ' ' ~inclincJ 82 ~nd th~ ~riac -termillal 87.
cons.iderincJ the operation of tlle form of t'he invention illustrated in Fiy. 7, the circuit will operate generally similar to that o:E the ~ig. 1 circuit except that the bimetal member 92 ~`7ill be heated both by curren-t generated in the auxillary coil 94 and also by current flowing thxough the start wind.ing 82. consequen-tly, the me~'oer 92 may be heated more quickly than the membe.r: 22 of .he Fig. 1 circuit. At the instant the motor is ener-gized b~ connecting the power lires 83 and 84 to an AC
power supply, current flows through the main winding 82 and curxent will also flow through the star~ winding 82, the resistor 96, ~he contacts 91 and 93, the two legs of the bimetal member 92 and to the power supply line 8 .
~he voltage drop or potential across the resistor 96 pro-duces triac,tr.igyering current which flows through the gate 89 of the triac 86 and thus triggers ~he triac 86 into conduction in each AC half cycle. As soon as the triac 86 starts.to conduct, nearly all of the start wLn ding current flows through it, the resistor 96 and the ...
bimetal member 92 being essentially shorted by the triac ':.
but the bimetal member 92 continues to be heated by current which is induced in the auxiliary coil 94. Thus, the.bi-.
metal member 92 is heated both by a portion of the start winding current and by current from the auxiliar~ co.il 94.

As soon as the bimetal mem~er 92 'has been suf- , ~icientl~ heated, the bimetal member 92 moves the contact .~ :
- : .
: 93 out o~ engagement with the fixed or stationary contact 91 and the triac 86 ceases to be, triggered into conduction :' ~:~ 30 because of the loss of the potential across the resis-tor 96.

' ~ ' :~ . ~17-

5~3 Furtl-~er, since t'lle contacts 91 and 9~ are out of engayem~nt, ~tar-c ~7indin~ curren-t no long~ flo~s through the pa-th pre-viously ~orme~ by the resistor 96 and the bimetal mer~er 92 Even though the start winding cur:rent no longer heats the bimetal member 92, the curren~ induced in the auxiliary coil 94 is suf~icient to m~intain the hime~al member 92 in heated condition and hold the two contacts 91 and 93 separated. In some cases, more current is re~uired to open the contacts thàn is requirea to hold them open, and in this construction adequate current is provided ~or both stages o~ operation.
When the contacts 91 and 93 open, the triac 86 is conducting and substantially all of the start winding current flows through the triac. ~he amount of current flowing through the contacts 91 and 93 when they open is therefore very low, and conseguently ~he contacts may have a véry .small size and will have a long life.

- . .
In the event the motor is stalled,: current will con~inue to flow through the main winding 81 and conse~

: quently current will be induced in the auxiliary coil 94.

: 20 ~ The bimetal member 92 will continue ko be heated by the ~ .
induced current and the contacts 91 and 93 will he held out of engagement. Tl~ere*ore, an overload device tnot showl1~ should be provided to prevent ~ontinued energization of the motor which might overheat and d~nage the motor.
; : :. In the circuit shown in Fig. 7, it will be noted that the current induced in the auxiliar~ coil 94 will 10w in the loop formea by the coil 94 and both lecJs of the ~i-: ~ metal member 92. The direction of current flow in o.ne o~
~ .the two legs will be opposed to that of the star-t winding ;~ 30; current flowing through the resistor 96 and the bimetal '~ :

691~5~3 mer(lber 92, and the direc-tion o:~ curr~nt flo~ throuyh th~
other of the two legs will be added to th~ star~c windiny current. To prevent uneven heating o~ the t~ legs of the bimetal member in such circumstances, the circuit s'nowll in Fig. 8 may be utilized. rrhe Fig. 8 cixcuit corn prises a motor including a main wlnding 101, a start ~7in-ding 102, power supply lines 103 and 104, and a con-trol circui~ 106. once again, the control circuit comprises a triac 107 connected in series with the start winding 102 and across the main winding 101, the triac 107 inclu-ding main terminals 108 and 109, and a gate 111. A resist~
112 is also connected .in series with the start windin~ 102 and the triac 107. The gate 111 is connected to receive triggering current from a delay cixcui.t including a bimetal - - .
element 113 ~hich has one leg 113b connected to the power :.
supply line 103 and the other leg 113a connected to an auxiliary coil 114, ~he other side of the coil 114 also being connected to the line 103. A stationary or fixed .
~ contact 117 is positioned adjacent -the bim~Qtal member 113, , and a movable contact 116 is ~astened to the bimetal member ~:
113. :A. resistor 118 connects the fixed contact 117 with .
the start winding 102, and another resistor 119 connects :
: the ~ixed contact 117 with the gate 111.
The aux.iliary coil 11.~ is wounc1 on the stator such . ::
.
. ~ that it has an angular displacement ~rom the ma.in winding :~ ~ 101, and it is electrically between the motor windings 101 ;~ ~ and 102. T'ne winding 114 is located on the stator at the point where the current it causes to ~low t'nrough the t~o legs of the membex 113 is as closely as possible 90O in ;~ 30 phase angle displ~cement from the phase angle of the start ~ , : ~ I q ~

~6~S~73 ~Ji ndin~ current ~lowin~ throuyh the le~s o~ th~ member 113. The coil 114 may be located such t'nAt its current either leads or la~s the start winding current by 90O.
considering the operation of the circuit shown in Fig. 8, upon initial energizat:ion of the motor by con-nec.ing the power suppl~ lines 103 and 104 to a source of AC po~/er, AC current -Elo~s through the main winaing 101.
Current also flows through the start winding 102~ t'ne re-sistor 118, the t~o legs 113a and 113b of the number 113 to the line 103. Some current also flows throuyh the gata circuit of the triac 107 because of the drop across the rasis-tor 118 and this yate current serves to trigger the triac, as previously explained. In addition, curxent is induced in the auxiliary coil 114 and this current flows through the loop comprising the coil 114, the two legs 113a and 113b o~ the bimetal member 114, and the power . ~ :
supply line 103 In a partieular AC half cycle, start winding current flows from the start winding 102, ~hrough the ;~ 20 resi3tor 11~, and through both lPgs 113a and 113b to ~he .
line~103. The curxent caused by the coil 114 will flow rom the coil 114, through the leg 113a, the leg 113b, : the line 103 and return to the coil 114. If the start :~ winding current and the auxiliary coil curr~nt were in phase, the auxiliar~ coil current would add to ~he start w~lnding current in one of the legs of the meimber 113 and . .:
subtract from the start winding current in the other o~
~ .
: the two legs and d~ferent amounts of current would flow in the two legs 113a and 113b~ However, due to the fact , ~ 20-that the au~iliary coll 114 is located on the stator at a point where the curren-t ~low in the member 113 due to the coil 114 is displaced 90 from the start winding, the current through the bimetal member 113, the total current, and the heating effect, will be the same in each leg 113a and 113b.
While the triac 107 is conducting, start winding current flows both through the branch includiny ~he triac 107 and the resistor 112, and through the branch including the resistor 118 and the bimetal member 113. The pr~por-tions of the start winding current flowing through these two branches may therefore be adjusted by an appropriate selection of the relative resistances in the two branches to ~btain the desired amount of current through the member 113 and the speed of opening of the contacts. This is con~
veniently accomplished by means-of the resistors 172 and 118.
The two resistors 112 and 118 may be part of the internal motor winding resistance and/or external resistors.
Figs. 9 to 12 illustrate an alternate and preferred ~ ,: , 20~ mounting arrangement of the electrical components of a con-trol circuit in a capsule. The preferred control circuit shown in Fig. 1 .is illustrated in Figs. 9 to 12.
The ~apsule is designed to be mounted in an electric motor including an upper end bell 120, an annular end ring 121, and a cylindrical outer shell 122. The riny 121 and the shell form parts of the motor stator which further in-cludes stator windings 123 an~ a cylindrical inner liner 124.
The end bell 120 is secured to the end ring 121 by mounting studs 126 and it supports a motor shaft 127. ~ spline seal ~128 and a rotary shaft seal 129 are mounted on the end bell ~, .

~ '~

120 and enga~e the shaft 127. An outer corrosi.on resistant cover 131 is :Eastened to -the exterior of the end bell 120 to protect the end bell from corxosion. F~rther, the end bell supports a shaft bearing 132 and an O-riny 133.
A longitudinal].y extending hole 136 (E'igs 9 and 10) is formed through the end bell 121, and a blind hole 137 is formed in the end bell 120 in alignment with the hole 136. The end of the hole 136, which is in the cavity o~ the sta~or, is enlarged or counter sunk as indicated at 138. A
capsule 141, shown in detail in Figs. 11 and 12, is mounted in the hole 136 and extends into the blind hole 137.
With reference to Figs. 11 and 12, the capsule 141 includes an inverted cup-shaped housing or enclosure 142 which is mad~ of a metal having good heat conducting properties~ The lower end ~ the .housing 142 is supported by a base 143 and a connector part 144, both of which are .
~` made of an electrical insulating material. The upper end .

o~ the part 144 is secured in the counter sink 138 as shown in Figs. 9 and 10. Three soc~ets 146 are mounted on the 20 ~ ~ part 144, and wires 147 connect the lower ends o~ the sockets 146 to~the motor wi.ndings. The sockets 146 of course correspond to the sockets 41 to 43 shown in Figs. 2 and 5.
.The upper side of the part 144 is recessed as indicated at .148, and the recess 148 snugly receives the base 143~
The base I43 supports the components of ths con-trol circuit~ I'hree pronys 149 extend downwardly from the .
underside of the base 143 and engage the socket~ 146. A

projection and slot arran~ement ~not shown) may ~e provided .
to properly align ~he prongs 149 and sockets 145, similar 30~;~ to the projection 49 and the slot 48~ On the upper side : ~ :

, ~ ~2~-~ 6~i73 of the base 143 are moun-ted a triac 151, a U-shclped bi-metallic heat-resp~nsive me~ber 152, and a contact member 153, which correspond and are similar to the mernbers 16, 22 and 29. The members 151, 152 and 153 are electrically con~
nected to the prongs 149 as explained in connection with E'igs. 2 to 6. The triac includes a mounting tab 154, and a heat sinX 156 is secured to the tab 154 by a rivek 157.
Holes are ~ormed in the tab 154 and the sink 156 ~or the rivet, and the sink hole is countersunk at 158 such that the head o~ the rivet will be flush with the outer surface o~ the sink.
Above .the heat sink 156 is a disc 159 which is made of an insulating material and supports a snubbi~g capacitor 161 and resistor 162. A lead 163 is secured to the rivet 157 and is folded th~ough holes 164 formed in.the . . ..
disc 159, thus holding the disc in place on top o~ the sink 156. On~ lead 166 of the capaci~or 161 is connectea to the :~ lead 163 (Fig. 12), the other lead 167 of the capacitor is connected to one side of the resistor 122, and the cther :;20~. side of the resistor i5 connected by a conductor 168 to a ~ . lead of the triac 151.
;~ : : The inner sux~ace of the housing 142 is electrically insulated fxom the components o~ the control circuit by a thin liner 171 o~ insulat:ing material. In the present in-stance, the liner 171 consists o~ a thin ~ilm o~ plastic insulation sold under the trademarX Kapton which has an .
~ : e~ectrical insulating rating of 5500 to '7000 volts per mil :
and a thermal conductivity o~ .004 watts per square inch per degree centigrade. This film thus pos.sesses good heat :30 :~ trans~er charact:eristics and high dielectric characteristics, ~ ~ .
: ~ :: ::
.

~ ~. ~23 .
. ~ . . , , " . .. .
. . , ~, "

~645~3 as well as good physical strength. The liner 171 includes a rectan~ular sheet which is folded against the inner sur-face of the cylindrical part of the housing 142, and a circular sheet which is positioned against the inner sur~ace of the upper end o~ the housing.
With re~erence to Fig. 11, the outer periphery o~
the base 143 is recessed adjacent: its upper surface, as indicated at 172. The lower end edges of the housing 142 and the liner 171 ~it snugly in the recess 172 and ayainst the inner surface ffl the recess 148 oE the part 144. The outer diameter of the disc 159 is slightly less than the inner ~iameter of the liner 171, so that the disc lS9 fits snuyly in the liner~ The outer surface o~ the sink 156 has an arcuate shape, similar to the sink 74, and its radius is ',' ,~-, ,~approximately e~ual to the,radius of the ~inner su~ace of the liner 171.
It is advantageous to have the sink 156 held tightly~against the liner 171 so that thare will be good heat transrer from ~he sink 156, throug~ the liner 171, to ~ the housing 142 This is attained in the ~ollowing manner.
The;~triac 151 is securely fasterled to the base 143 and suppo~rts the sink 156 which has a thickness such that it fits snugly between the triac 151 and the liner 171. Further~ ' , he lead or concluctor 163 connecting the tab 154 with the "
disc 159 is quite stiff due to its width and thickness, as '' shown in Figs. 11 and 12~ As previously mentioned, the : :~ ~: , ' lead 163 is tightly connected to both the disc 159 and the tab 154, and thq outer peripheries o~ the disc 159 and the sink 156 are flush with each other. As a consequence, the 30 ~ ~disc~159 ~Eitting snugly inside the liner 171~ holds ~he ~, ~

~,: , :

~6~S~t'3 upp~r ~nd of the tab 156 tightly ayainst the liner 171.
There~ore, the disc 159 at the upper end of the sink and the snug ~it of the housing 1~2 between the base 143 and the part 142 adjacent the lo~er end of the sink, cooperate to maintain the sink 156 tigh,ly against the liner 171. A
good heat conduction path is thereby established fxom the triac 151, through the sink 156 and the liner 171, to the housing 142 and the end ring 121.
The bimetallic member 152 is mounted closely ad-jacent the triac 151 and the triac acts as a heat sink for heat radiated by the member 152. The member 152 is designed to bend in the direction of the triac 151 when it is heated, and consequently the amount of heat lost by the member 15 to the triac lSl increases as the member 152 is heated.
This is very important because it ser~es to protect the '- - m~mber 152 against damage that might be caused by overheating.
~urther,' this location and direction of bending of ~he member 152 helps to maintain a balance, during operation of th~ motor, between the amount of heat generated by the member 152 and the amount of heat dissipated by the member 152 to the surrounding parts, such tha~ the member 152 will e maintai.ned out of c~ntact with the contact 153 'but will not be damaged by over'heating.
; The capsule is mounted i.n the hole 136 'in the end ring 121 as previously mentioned, and a water tight seal is provided between them to prevent any leakage of liquid through the hole 136 into the stator cavity~ This is ~` ~ important in the ~ase o~ a submersible motor for a water pump. In the present instance the seal iæ provided by ~:
~ 30 enlarging the upper end o~ the hole 136 as indicated at 181 ~ .

~64!~73 and po~itioning an annular resilient seal mernber 182 at the bottom of the enlargement :L81. A metal sealing ring 183 is pressed into the enlar~ement 181 over the member 182, and the bwer surface of the end bell ].20 holds the ring 183 in place. The ring 183 has an enlarged rim :l84, and the enlarye-ment 181 is recessed at 186 to receive the rim 184. The upper surface of the rim 184 is substantially flush with the upper sur~ace of the end ring 12:1 and it is engaged by the lower surface of the end bell 120 to hold the ring 183 in place.
It will be apparent from the ~oregoing description that a novel and use~ul motor control arrangement has been provided. The circuits described herein use a relatively small num~er o~ components and the components are relatively inexpensive and reliable~ Further, the disconnection o~
the switch and consequent deenergization of the start winding occurs very rapidly and does not result i~ half wave oper-ation of the motor. Still ~urther, the circuit components . .
. : may~be conveniently packaged and installed in an electric ~20 motor at a location ~here they may be readily removed for inspection or servicing without disassembly of the entire motor~. The capsuIe is mounted at a location where it is expo~ed to the ambient temperatura and is not unduly in-: fluenced by the motor operating temperature.
: The present constructions are particularly suited : ~ox use in motors which are raquired to be rapidly turned ~: on and ofE. In such a motor i.t is neceAssary that the bi , :: metal element he heated very rapidly to disconnect the start ~ winding durin~ start up, and also that it cool rapidly : 30 upon deenergization o~ the motor so that the motor may be .:

:

~ ~26-, .. . :: . , . : . . . . . .

~:116~3 started again in a short tim~ urther, it is necessar~
that the bimetal element not be overheated during continuous operation of the rnotor. The size and mass of the bi~etal and the number of turns of the sensing coil, are selected to obtain the heating and cooling times necessary for a particular motor requirement. Another important Eactor affecting the heating and cooling of the ~imetal is its pro~imity to heat sinks. In the present construction the triac serves as a heat sink and the bimetal is mounted as closely as possible to the triac. The bimetal bends in the direction o~ the triac when heated, thus absorbing more heat durin~ continuous motor operation. In a speci~ic example, the parts are sized and mounted to provide a rate o~ temperature rise in the range of 37 C to 150 C per second, and a minimum temperature decay of 25~C per second.
~- It should~be understood that certain modifications may be made in the ~oregoing constructions without departing from the scope of the invention, For example, in both of the Flgs. 1 and 7~circuits, the auxiliary coils 31 and 94 may 20 ~ be wound conce~trically wikh the start winding, or concen- -trically with the main winding, or at a location between the start and main windings~ Further, instead of providing detachable sockets 41 to 43 and prongs 61 to 63, Leads having soldered or crimped connections~ for example, could be provided between the capsule 44 and the stator windings and the auxiliary coil. Such connections are of course removable or detachable similar to the prong and socket connections i1lu~trated in the drawings, ~o that the capsule may be removed when desired. Instead of providing a U-shaped ; 30 ~ bimetallic element, a plain strip of bimetal could be used : , ... .. .

~6~ 3 by adding a shunt connec-ted to the contact, which would s~r~e as return path for current flowing through the bi-metal element.
The liner 171 could be in the form of a coating on the inner surface of the housing 142, instead of separate films as described.
Another important advantage in placing the sensing coil substantially concentrically with the starting winding as shown in Figure 1, arises from the Eact that the current flowing in the sensing coil when the motor is at standstill or low speed, is much lower than the current flowing when the motor is at running speed. This low current flow at start up in the sensing coil and in the bi-metal element results in slow heating of the bi-metal element. This gives the motor time to rise to running speed before the start winding is disconnected, even though there may be a heavy motor load at start up. Further, when the motor has been running and is switched off, the bi-metal element will start to cool. If the motor is quickly swltched on again, the bi-metal element will slowly reheat because of the low current flow in the coil at start up, which enables the motox to rise to running speed. If the coil current ,",, ,!';V
were hlgh at start up, the bi-metal element would ~uickly reheat and open the start winding circuit before the motor rose to running speed, but advantageously this is not the case.

~ ' ': :
,:

.

~ ` . , ~~,' .

Claims (25)

WHAT IS CLAIMED IS:

1. A start winding cut-out circuit for an AC electric motor including a stator, a main winding and a start winding, said main winding being adapted to be connected across AC power supply lines, said circuit com-prising start winding switch means connected in series with said start winding and connected across said main winding, heat responsive switch means connected to actuate said start winding switch means, said heat responsive switch means including a self heating electrically conductive part which moves upon self heating, and switch contacts which are actuated by said movement when said part is heated to a selected temperature, said switch contacts being connected to and controlling actuation of said start winding switch means, and a current source connected to said part and pro-viding heating current flow through said part, said current source being electrically coupled to the motor circuit and providing said heating current upon energization of said motor, and said heat responsive switch means actuating said start winding switch means after initial energization of said motor until said selected temperature is reached.

2. A circuit as in Claim 1, wherein said current source comprises an auxiliary coil wound on said stator and adapted to have a voltage induced therein.

3. A circuit as in Claim 2, wherein said coil is wound on the axis of said start winding.

4. A circuit as in Claim 2, wherein said coil is wound on the axis of said main winding.

5. A circuit as in Claim 2, wherein said coil is wound electrically between said start and main windings.

6. A circuit as in Claim 1, wherein said self heating part is further connected to receive current flowing through said start winding, said self heating part thus responding both to current from said auxiliary coil and to start winding current.

7. A circuit as in Claim 1, wherein said self heating member comprises a bimetal member which heats and flexes in response to said heating current flowing there-through, and said switch contacts include a movable contact which is moved by flexing of said bimetal member, and fixed contact adjacent said movable contact.

8. A circuit as in Claim 7, wherein said fixed and movable contacts are normally closed when said self heating member is cool, and said trigger current flows only while said contacts are closed.

9. A circuit as in Claim 7, wherein said bimetal member is generally U shaped, said current source is con-nected across the legs of said U, and said movable switch contact is attached to the cross part of said U.

10. A circuit as in Claim 7, wherein said current source comprises an auxiliary coil wound on said motor and connected to said bimetal member.

11. A circuit as in Claim 10, wherein said current source further comprises a connection from said start winding to said bimetal member, said connection including a resistor and said switch contacts.

12. A circuit as in Claim 11, wherein said coil is wound on said motor at a location where the current flow in said bimetal member caused by said coil is displaced substantially 90° from the current flow in said bimetal member caused by current flow from said start winding.

13. A circuit as in Claim 11, and further in-cluding a second resistor connected in series with said start winding switch means, the sizes of said two resistors being proportioned to produce a predetermined amount of heating current through said bimetal member.

14. A circuit as in Claim 1, wherein the electric motor includes a stator having a stator end member, said end member having a hole formed therethrough, said circuit further comprising a first connector part adapted to be secured to said end member in said hole, a capsule for housing said heat responsive switch means and said start winding switch means, said capsule including a second connector part which mate with said members of said first connector part, said capsule being movable into said hole in said end member to couple said second connector part with said first connector part.

15. A circuit as in Claim 14, and further including means on said end member for holding said capsule in said hole.

16. A circuit as in Claim 14, wherein said first and second connector parts include polarizing means for aligning said connector parts.

17. A circuit as in Claim 14, and further including seal means between said capsule and said end member.

18. A circuit as in Claim 14, wherein said start winding switch means includes an electronic solid state switch means and said capsule includes a base, said heat responsive switch means and said solid state switch means being mounted closely together on said base, and said capsule fur her including a thermally conductive outer housing.

19. A circuit as in Claim 18, and further including a thermally conductive member in tight engagement with the inner surface of said outer housing and in relatively close relation with said solid state switch means and with said heat responsive switch means.

20. A circuit as in Claim 18, and further including heat sink means in said capsule closely adjacent said heat responsive switch means.

21. A circuit as in Claim 1, wherein said start winding switch means comprises an electronic switch having a pair of power terminals and a gate, a low resistance current path between said power terminals being selectively established when a potential is across said power terminals and trigger current appears on said gate, said start winding and said power terminals being adapted to be connected in series and across said power supply lines, and trigger current supply means connected to said gate and including said heat responsive switch means and said current source, said source comprising an auxiliary coil, said coil being adapted to be wound on the stator of said motor and being connected to said heat responsive switch means, current generated in said coil during energization of said motor flowing to said heat re-sponsive switch means, said heat responsive switch means being connected to said gate and to at least one of said power lines and forming a trigger current flow path to said gate, said heat responsive switch means when current flow there-through having a substantially constant time period during which said trigger current flows to said gate along said flow path, said trigger current flow being interrupted at the termination of said time period, and said current generated in said coil flowing to and energizing said heat responsive switch means.

22. A circuit as in Claim 1, wherein said start winding switch means comprises a triac including first and second main terminals and a gate, said main terminals being adapted to be connected in series with said start winding and connected across said power supply lines, said self heating part including a U-shaped thermally responsive member, one of said contacts being attached to the center portion of said member, one of the legs of said member being connected to one of said main terminals of said triac, and said current source being connected across the legs of said member.

23. A circuit as in Claim 20, wherein self heating part flexes toward one side upon current from said source flowing therethrough, and said heat sink means is positioned adjacent said part on said one side, whereby said part flexes toward said sink means when heated and heat is dissipated from said part to said base and to said sink means.

24. A circuit as in Claim 230 wherein said sink means includes said start winding switch means.

25. A circuit as in Claim 24, wherein said sink means further includes a heat absorbing and conducting sink member secured to said start winding switch means.