Control circuit for a dual directional direct current motor employing a single alternating current power source

A control circuit operates a dual directional DC motor from an AC power source. A controller has first and second position indication inputs adapted to receive respective first and second position indications. The controller also has first and second direction outputs, which respectively energize one of two first relay coils having contacts outputting respective AC voltages responsive to the direction outputs. A full wave bridge rectifier receives the AC voltage and responsively outputs a DC voltage, which energizes a second relay coil. A contact thereof directs that voltage to two sets of first relay contacts, which are also responsive to the direction outputs, and which respectively provide a positive or negative DC voltage to the motor. Another second relay coil contact provides a braking action to the motor responsive to removal of the DC voltage from the rectifier output following removal of the AC voltage to the rectifier.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to control circuits and, more particularly, to control circuits for motors and, still more particularly, such control circuits for a dual directional direct current (DC) motor employing a single alternating current (AC) power source.

2. Background Information

Alternate power sources are provided for any number of applications, which cannot withstand a lengthy interruption in electric power. Typically, power is provided from a primary source with back-up power provided by a secondary source. Often, the primary source is a utility and the secondary source is an auxiliary power source, such as an engine driven generator or a second utility source. The transfers between the two power sources can be made automatically or manually.

In the case of a generator driven auxiliary power source, power must be stabilized before the transfer can be made to the secondary source. In any event, the two power sources cannot be connected to the load simultaneously unless they are in phase. Thus, an open transition transfer may be employed in which the previously connected source is disconnected from the load before the other source is connected.

Transfer switches are known in the art. Transfer switches operate, for example, to transfer a power consuming load from a circuit with a normal power supply to a circuit with an auxiliary power supply. Applications for transfer switches include stand-by applications, among others, in which the auxiliary power supply stands-by if the normal power supply should fail. Facilities having a critical requirement for continuous electric power, such as hospitals, certain plant processes, computer installations, and the like, have a standby power source, often a diesel generator. A transfer switch controls connection of the utility lines and the diesel generator to the facility load buses. In many installations, the transfer switch automatically starts the standby generator and connects it to the load bus upon loss of utility power, and reconnects the utility power to the load bus if utility power is reestablished.

Some transfer switches affect an open transition between the power sources, that is, one is disconnected from the load bus before the other one is connected. Other transfer switches provide a closed transition wherein the oncoming source is connected to the load bus before the other is disconnected, in order that both power sources are connected in parallel during the transition.

Transfer switches commonly used to connect alternate power sources to a load, including networks, utilize a pair of switches each connecting one of the sources to the load. In order to prevent connecting unsynchronized sources together, the operation of the two switches is coordinated, typically by a mechanical interlock, in order that only one switch at a time can be turned on. In many instances, it is desirable to operate the transfer switch remotely. Typically, electric motors have been used to operate the interlocks on transfer switches. See, for example, U.S. Pat. Nos. 5,081,367; 4,760,278; and 4,398,097.

A transfer switch typically comprises a pair of circuit interrupters combined with a drive input and a linkage system. The preferred types of circuit interrupters have been molded-case switches and molded-case circuit breakers because these types are commercially available in a wide array of sizes and are relatively economical compared to other options. The preferred type of drive input depends on the application for the transfer switch. Usually motors are preferred, but at other times there is a clear preference for manually-operated mechanisms.

One known automatic transfer switch employs a unidirectional motor. A motor-driven wheel rotates in one direction and employs a linkage to change the operating positions of two mounted switches (e.g., for a normal power source and an emergency power source) or two circuit breakers. The automatic transfer switch transfers between two power sources using a motor-driven arm that connects to a lever which operates both normal and emergency switches. The motor-driven lever operates in a ratchet-type operation. A rotational motion is created on an indicator wheel by the ratchet's operation.

There is room for improvement in control circuits for operating a dual directional direct current motor from a single alternating current power source.

SUMMARY OF THE INVENTION

These needs and others are met by the present invention, which allows automatic operation of, for example, a dual directional transfer mechanism with a single, high torque, direct current (DC) motor employing a single alternating current (AC) power source. An integral dynamic braking mechanism is included to instantaneously stop the rotation of the DC motor when the desired mechanism position has been obtained.

As one aspect of the invention, a control circuit operates a dual directional direct current motor from an alternating current power source, with the motor being operatively associated with a first position indication and a second position indication. The control circuit comprises: a first circuit structured to receive an alternating current voltage from the alternating current power source, the first circuit including a first output, a first direction input and the first position indication, the first output having a first alternating current voltage responsive to the first direction input and the first position indication, the first circuit further including a second output, a second direction input and the second position indication, the second output having a second alternating current voltage responsive to the second direction input and the second position indication; means for rectifying one of the first and second alternating current voltages from the first circuit and providing an output having a direct current voltage responsive to the first alternating current voltage and the second alternating current voltage; and a second circuit having an input energized responsive to at least one of the first and second outputs of the first circuit, the second circuit further having a first output when the input thereof is not energized and having a second output when the input thereof is energized, the first output of the second circuit enabling the means for rectifying to apply the direct current voltage to the motor at one of a first polarity and a second polarity, at least one of the first and second outputs of the second circuit providing a braking action to the motor responsive to removal of one of the first and second alternating current voltages of the first circuit.

The alternating current power source may be a redundant alternating current power source, and the first circuit may be structured for cooperation with the redundant alternating current power source.

As another aspect of the invention, a control circuit operates a dual directional direct current motor from an alternating current power source, the motor being operatively associated with a first position indication and a second position indication. The control circuit comprises: a controller including a first position indication input adapted to receive the first position indication, a second position indication input adapted to receive the second position indication, a first direction output and a second direction output; a first circuit structured for cooperation with the alternating current power source and the controller, the first circuit receiving the first direction output and the second direction output and including an output having an alternating current voltage responsive to one of the first direction output and the second direction output, the first circuit further including a first set of outputs responsive to the first direction output and a second set of outputs responsive to the second direction output; a rectifier receiving the alternating current voltage of the output of the first circuit and providing an output having a direct current voltage responsive to the alternating current voltage; and a second circuit responsive to the direct current voltage of the output of the rectifier, the second circuit providing a first output and a second output, the first output of the second circuit enabling the first set of outputs of the first circuit to provide the direct current voltage of the output of the rectifier to the motor at a first polarity, the first output of the second circuit alternatively enabling the second set of outputs of the first circuit to provide the direct current voltage of the output of the rectifier to the motor at a second polarity, the second output of the second circuit providing a braking action to the motor responsive to removal of the direct current voltage from the output of the rectifier following removal of the alternating current voltage from the output of the first circuit.

As another aspect of the invention, a control circuit operates a dual directional direct current motor from an alternating current power source, the motor being operatively associated with a first position indication and a second position indication. The control circuit comprises: a first circuit structured to receive an alternating current voltage from the alternating current power source, the first circuit including a first output, a first direction input and the first position indication, the first output having a first alternating current voltage responsive to the first direction input and the first position indication; a second circuit structured to receive the alternating current voltage from the alternating current power source, the second circuit including a second output, a second direction input and the second position indication, the second output having a second alternating current voltage responsive to the second direction input and the second position indication; a first rectifier receiving the first output of the first circuit and a ground or neutral of the alternating current power source, the first rectifier providing an output having a direct current voltage with a first polarity responsive to the first alternating current voltage of the first output of the first circuit; a second rectifier receiving the second output of the second circuit and the common or the neutral of the alternating current power source, the second rectifier providing an output having a direct current voltage with a second polarity responsive to the second alternating current voltage of the second output of the second circuit; and a third circuit having an input energized by the second alternating current voltage of the second output of the second circuit, the third circuit having a first output when the input thereof is not energized and having a second output when the input thereof is energized, the first output of the third circuit enabling the first rectifier to apply the direct current voltage with the first polarity of the output of the first rectifier to the motor, the second output of the third circuit enabling the second rectifier to apply the direct current voltage with the second polarity of the output of the second rectifier to the motor, the first output of the third circuit and the first rectifier providing a braking action to the motor responsive to removal of the second alternating current voltage of the second circuit.

The third circuit may be a relay having a coil energized by the alternating current voltage of the second output of the second circuit, a first contact which is closed when the coil thereof is not energized and having a second contact which is closed when the coil thereof is energized. The first contact of the third circuit may enable the first rectifier to apply the direct current voltage of the output of the first rectifier to the motor, and the second contact of the third circuit may enable the second rectifier to apply the direct current voltage of the output of the second rectifier to the motor.

The coil may not be energized when the first contact is closed. The first rectifier may be adapted to providing braking to the motor. The first rectifier may include a pair of diodes, which are electrically connected in series with the first contact, with the series combination of the pair of diodes and the first contact being adapted to be electrically connected in parallel with the motor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a control circuit2for operating a dual directional direct current (DC) motor (M)4from an alternating current (AC) power source6. The motor4is operatively associated with a first position indication8(e.g., clockwise) and a second position indication10(e.g., counter-clockwise) for such motor. The control circuit2includes a first circuit12, a rectifying mechanism14and a second circuit16. The first circuit12is structured to receive an AC voltage18from the AC power source6. The first circuit12includes a first output20, a first direction input22(e.g., clockwise) and the first position indication8. The first output20has a first AC voltage24responsive to the first direction input22and the first position indication8. The first circuit12further includes a second output26, a second direction input28(e.g., counter-clockwise) and the second position indication10. The second output26has a second AC voltage30responsive to the second direction input28and the second position indication10.

The rectifying mechanism14(e.g., an AC/DC converter; a single rectifier, such as a full wave diode bridge; a pair of rectifiers) rectifies one of the first and second AC voltages24,30from the first circuit12and provides an output32having a DC voltage34responsive to the first and second AC voltages24,30.

The second circuit16has an input36energized responsive to one or both of the first and second outputs20,26of the first circuit12. The second circuit16further has a first output38when the input36thereof is not energized and has a second output40when the input36thereof is energized. The first output38of the second circuit16enables the rectifying mechanism14to apply the DC voltage34to the motor4at one of a first polarity42and a second polarity44. One of the first and second outputs38,40of the second circuit16provides a braking action to the motor4responsive to removal of one or both the first and second AC voltages24,30of the first circuit12.

The AC power source6may be any suitable AC power source, or may be a redundant AC power source (e.g., as shown with power source46ofFIG. 2or power source48ofFIG. 3). The first circuit12is structured for cooperation with the AC power source6.

Referring toFIG. 2, a control circuit50operates a dual directional DC motor (M)52from the AC power source46. The motor52is operatively associated with a first position indication54and a second position indication56. The control circuit50includes a suitable controller58, a first circuit60, a rectifier62and a second circuit64.

The controller58(e.g., a microprocessor-based controller; a logic controller; a programmable logic controller; relay logic; digital logic; analog logic; any suitable control mechanism or circuit) includes a first position indication input (IN1)66adapted to receive the first position indication54(e.g., a clockwise (CW) position indication normally open contact), a second position indication input (IN2)68adapted to receive the second position indication56(e.g., a counter-clockwise (CCW) position indication normally open contact), a first direction output70(e.g., a clockwise normally open contact output) and a second direction output72(e.g., a counter-clockwise normally open contact output).

The first circuit60, which is structured for cooperation with the AC power source46and the controller58, receives the first direction output70and the second direction output72and includes an output74having an AC voltage76responsive to one of the first direction output70and the second direction output72. The first circuit60further includes a first set of outputs78responsive to the first direction output70and a second set of outputs80responsive to the second direction output72.

The rectifier62receives the AC voltage76of the first circuit output74and provides an output82having a DC voltage83responsive to the AC voltage76.

The second circuit64is responsive to the DC voltage83of the rectifier output82and provides a first output84and a second output86. The second circuit first output84(e.g., when normally open contact KVDAis closed) enables the first circuit first set of outputs78(e.g., when normally open contacts KV1B, KV1Care closed) to provide the rectifier output DC voltage83to the motor52at a first polarity (e.g., positive). The second circuit first output84(e.g., when normally open contact KVDAis closed) alternatively enables the first circuit second set of outputs80(e.g., when normally open contacts KV2B, KV2Care closed) to provide the rectifier output DC voltage83to the motor52at a second polarity (e.g., negative). Also, the second circuit second output86provides a braking action (e.g., when the normally closed contact KVDBis closed) to the motor52responsive to removal of the rectifier output DC voltage83following removal of the AC voltage76from the first circuit output74.

As shown inFIG. 2, the motor52may be operatively associated with a suitable position indication circuit, such as a dual directional transfer mechanism88, which provides the position indications54,56.

The AC power source46, in this example, is a redundant AC power source. The first circuit60is structured for cooperation with the power source46. The contact outputs70,72are electrically connected in series with a common terminal90, which is adapted to receive an AC voltage92from the AC power source46.

The first circuit60includes a first relay94having three contacts KV1A,KV1B,KV1Coperated by a first coil KV1and a second relay96having three contacts KV2A,KV2B,KV2Coperated by a second coil KV2. The first coil KV1is energized by the closed first direction output70, and the second coil KV2is energized by the closed second direction output72. The first relay contact KV1Aprovides the output74having the AC voltage76responsive to the first direction output70, and the second relay contact KV2Aprovides the same output74having the AC voltage76responsive to the second direction output72. The pair of contacts KV1B,KV1Cof the first relay94provides the DC voltage83from the rectifier output82to the motor52at a positive polarity, and the pair of contacts KV2B,KV2Cof the second relay96provides the DC voltage83from the rectifier output82to the motor52at a negative polarity.

The exemplary rectifier62is a full-wave diode bridge, although any suitable AC to DC rectifier or other suitable AC to DC converter may be employed. The rectifier62includes a first terminal98receiving the first circuit output74, a second terminal100adapted to receive a ground or neutral102from the AC power source46and the first circuit60, and third and fourth terminals104,106providing the DC voltage output82responsive to the first circuit AC voltage76.

The exemplary second circuit64is a relay110having a coil KVD, a normally open first contact KVDAand a normally closed second contact KVDB. The second circuit relay coil KVD is responsive to the rectifier output DC voltage83, with the contact KVDA, when closed, enabling the contacts KV1B,KV1C, in order to provide the DC voltage83from the rectifier62to the motor52at a positive polarity, or enabling the contacts KV2B,KV2C, in order to provide the DC voltage83from the rectifier62to the motor52at a negative polarity. Also, the second circuit relay contact KVDB, which is electrically connected in parallel with the windings (not shown) of the motor52, when closed, provides a braking action to the motor52.

The first circuit60obtains directional inputs, clockwise (CW) or counter-clockwise (CCW), from the two respective contacts70or72of the controller58. Zero or one (and at most one) of such directional inputs is closed at any one time. In this example, AC power to the control circuit50is supplied from a “voting” circuit112, with the AC voltage92being common to both of the directional inputs CW,CCW. Also, in this example, the directional inputs CW,CCW are controlled via the outputs70,72in view of the two respective position indication (e.g., limit) switches54,56. For example, these switches54,56signal the controller58that the mechanical motion of the motor52is satisfied. In response, the controller58opens the corresponding one of the directional inputs, CW or CCW, such that both such directional inputs are open, in order to remove power from the first circuit60. In turn, the dynamic brake, contact KVDB, stops the motor52by shorting the motor windings (not shown).

The control circuit50provides counter-clockwise direction control as follows. Initially, the CW position indication54is closed, and both of the CW and CCW outputs70,72are open. Hence, the first circuit60is without AC power and, thus, the relay coils KV1and KV2are both de-energized. The normally open contacts KV1Aand KV2Aare both open and no AC voltage is applied to the rectifier62. As a result, the relay coil KVD is de-energized. Therefore, the normally closed contact KVDBis closed, which brakes the DC motor52.

Next, for CCW operation, the CCW output72closes (e.g., due to a command from the controller58). This supplies AC power from the voting circuit112to the relay coil KV2. In response, the normally open contacts KV2A, KV2Band KV2Cclose. Then, AC power is supplied through the, now closed, normally open contact KV2Ato the rectifier62, which converts the AC power into DC power. The rectifier62energizes the relay coil KVD. In response, the normally open contact KVDAcloses and the normally closed contact KVDBopens. It will be appreciated that the normally open contact KVDAand the normally closed contact KVDBare “break before make”. When the normally closed contact KVDBopens, this releases the dynamic brake on the motor52. When the normally open contact KVDAcloses, a positive DC voltage is applied through closed normally open contact KV2Cand a negative DC voltage is applied through closed normally open contact KV2B. This polarity configuration applies a negative voltage to the motor52, which allows such motor to rotate in a counter-clockwise direction in order to do mechanical work.

Once the mechanical motion of the motor52is completed, the CCW position indication56closes. The controller58senses this closure and opens the CCW output contact72. This removes AC power from the voting circuit112to the relay coil KV2. In response, the normally open contacts KV2A, KV2Band KV2Copen. The open state of the normally open contact KV2Aremoves AC power from the rectifier62, which removes DC power from the relay coil KVD. In response, the normally open contact KVDAopens and the normally closed contact KVDBcloses. This, first, removes DC power from the motor52after which the normally closed contact KVDBshorts out the motor windings (not shown) and dynamically brakes the motor52to stop rotation.

The control circuit50provides clockwise direction control in an analogous manner as counter-clockwise direction control. Initially, the CCW position indication56is closed, and both of the CW and CCW outputs70,72are open. Hence, the first circuit60is without AC power and, thus, the relay coils KV1and KV2are de-energized. The normally open contacts KV1Aand KV2Aare open and no AC voltage is applied to the rectifier62. As a result, the relay coil KVD is de-energized. The normally closed contact KVDBis closed, which brakes the DC motor52.

Next, the CW output70closes (e.g., due to a command from the controller58). This supplies AC power from the voting circuit112to the relay coil KV1. In response, the normally open contacts KV1A, KV1Band KV1Cclose. Then, AC power is supplied through the, now closed, normally open contact KV1Ato the rectifier62, which converts the AC power into DC power. This energizes the relay coil KVD. In response, the normally open contact KVDAcloses and the normally closed contact KVDBopens. When the normally closed contact KVDBopens, this releases the dynamic brake on the motor52. When the normally open contact KVDAcloses, a positive DC voltage is applied to closed normally open contact KV1Band a negative DC voltage is applied to closed normally open contact KV1C. This polarity configuration applies a positive DC voltage to the motor52, which allows such motor to rotate in a clockwise direction in order to do mechanical work.

Once the mechanical motion of the motor52is completed, the CW position indication54closes. The controller58senses this closure and opens the CW output contact70. This removes AC power from the voting circuit112to the relay coil KV1. In response, the normally open contacts KV1A, KV1Band KV1Copen. The open state of the normally open contact KV1Aremoves AC power from the rectifier62, which removes DC power from the relay coil KVD. In response, the normally open contact KVDAopens and the normally closed contact KVDBcloses. This, first, removes DC power from the motor52after which the normally closed contact KVDBshorts out the motor windings (not shown) and dynamically brakes the motor52to stop rotation.

Although a voting circuit112for two (e.g., S1and S2) AC power sources is disclosed, the invention is applicable to a one-input AC power source (e.g., S1or S2), which does not employ a voting circuit, or to two, three (not shown) or more AC power sources, which employ suitable AC power source selection logic (not shown).

The individual AC power sources (e.g., S1; S2) may employ any suitable AC line-to-line voltage, any suitable AC line-to-neutral voltage (e.g., between (e.g., S1-A and S1-B), or any suitable AC voltage (e.g., as obtained from the secondary of a transformer).

Referring toFIG. 3, a control circuit150operates the dual directional DC motor (M)52from the AC power source48. The control circuit150includes a first circuit152, a second circuit154, a first rectifier156, a second rectifier158, and a third circuit160. The exemplary rectifiers156,158are full-wave diode bridges, although any suitable AC to DC rectifier or other suitable AC to DC converter may be employed. The first circuit152is structured to receive an AC voltage162from the AC power source48. The first circuit152includes a first output164, a first direction input165(e.g., CW) and a first position indication166. The first output164has a first AC voltage167responsive to the first direction input165and the first position indication166.

The second circuit154is structured to receive the AC voltage162from the AC power source48. In this example, the power is common to both of the CW and CCW directional inputs165,170. The second circuit154includes a second output168, a second direction input170(e.g., CCW) and a second position indication172. The second output168has a second AC voltage173responsive to the second direction input170and the second position indication172.

The first rectifier156receives the first circuit first output164and a ground or neutral174of the AC power source48. The first rectifier156provides an output176having a DC voltage178with a positive polarity (with respect to the motor52) responsive to the first AC voltage167.

The second rectifier158receives second circuit second output168and the common or the neutral174of the AC power source48. The second rectifier158provides an output180having a DC voltage182with a negative polarity (with respect to the motor52) responsive to the second AC voltage173.

The third circuit160is a relay, which includes an input, such as coil KA, energized by the second AC voltage173, a first output, such as normally closed contact AUXB, which is closed when the coil KA is not energized, and a second output, such as normally open contact AUXA, which is closed when the coil KA is energized. The normally closed contact AUXBenables the first rectifier156to apply the positive DC voltage178to the motor52. The normally open contact AUXAenables the second rectifier158to apply the negative DC voltage182to the motor52. The normally closed contact AUXBprovides a braking action to the motor52through the first rectifier156responsive to removal of the second AC voltage173of the second circuit154, which de-energizes the coil KA. The first rectifier156includes the diodes200,201, which are electrically connected in series with the normally closed contact AUXB, with the series combination of the diodes200,201and that contact being electrically connected in parallel with the motor windings (not shown) of the motor52.

The first rectifier156includes a first terminal184receiving the first circuit first output164, a second terminal186adapted to receive the ground or neutral174, and third and fourth terminals188,190providing the first output DC voltage178.

The second rectifier158includes a first terminal192receiving the second circuit second output168, a second terminal194adapted to receive the ground or neutral174, and third and fourth terminals196,198providing the second output DC voltage182.

The two directional inputs165,170(e.g., clockwise (CW) and counter-clockwise (CCW)) may be controlled by two separate contacts from any suitable circuit or controller (not shown) (e.g., the microprocessor-based controller58ofFIG. 2). Power from the power source48is preferably supplied via a suitable “voting” circuit202, although a single AC power source may be employed.

In this example, the CW and CCW directional inputs165,170are controlled in view of two position indication (e.g., limit) switches CW position and CCW position166,172, respectively. These position indication switches166,172signal that the mechanical motion of the motor52is satisfied. The circuits152,154then remove power from the rest of the control circuit150.

The control circuit150provides clockwise direction control as follows. Initially, the normally closed CCW position indication172is open, the normally closed CW position indication166is closed, and both of the CW and CCW outputs165,170are open. As a result, the coil KA of the auxiliary relay160remains de-energized and the corresponding normally open AUXAand normally closed AUXBauxiliary contacts do not change state.

The contacts AUXB, AUXAisolate the first and second rectifiers156,158from one another. Hence, the purpose of the auxiliary relay160is to isolate the two rectifiers156,158. This is employed because the positive output176of the first rectifier156would otherwise, be directly electrically connected to the negative output180of the second rectifier158and visa versa. Thus, without the auxiliary relay160, a direct short would occur anytime power was supplied to either of the two rectifiers156,158.

Next, the CW output165closes (e.g., due to a command from a controller (not shown)). This supplies AC power from the voting circuit202through the closed CW output165and through the normally closed CW position indication166. As a result, AC power is supplied to the first rectifier156, which converts the AC power into DC power, which is supplied to the DC motor52though the normally closed contact AUXB. This polarity configuration allows the motor52to rotate in a clockwise direction. Once the mechanical motion is completed, the normally closed CW position indication166opens, which removes power from the first rectifier156. For example, the CW contact165may be controlled by a suitable controller (not shown) or by manual operation. The motor52is not stopped dynamically in this direction.

Except for braking operation, the control circuit150provides counter-clockwise direction control in an generally analogous manner as clockwise direction control. Initially, the normally closed CW position indication166is open, the normally closed CCW position indication172is closed, and both of the CW and CCW outputs165,170are open. As a result, the coil KA of the auxiliary relay160remains de-energized and the corresponding normally open and normally closed auxiliary contacts AUXA, AUXBdo not change state.

Next, the CCW output170closes (e.g., due to a command from a controller (not shown)). This supplies AC power from the voting circuit202through the closed CCW output170and through the normally closed CCW position indication172. As a result, the auxiliary relay coil KA is energized and the corresponding normally open and normally closed auxiliary contacts AUXA, AUXBchange state.

As a result, AC power is supplied to the second rectifier158, which converts the AC power into DC power, which is supplied to the DC motor52though the, now closed, normally open contact AUXA. This polarity configuration allows the motor52to rotate in a counter-clockwise direction. Once the mechanical motion is completed, the normally closed CCW position indication172opens, which removes power from the second rectifier158. For example, the CCW contact170may be controlled by a suitable controller (not shown) or by manual operation.

As one difference from the clockwise direction control, the motor52is dynamically stopped in the counter-clockwise direction through the first (CW) rectifier156. This is because when the normally closed CCW position indication172opens, the relay coil KA is de-energized. As a result, the now closed, normally closed contact AUXBprovides an electrically conductive path from the motor52and through the two lower diodes200,201of the first rectifier156. Since one or both of the normally closed CW position indication166and the CW output165are open, there is no external DC voltage applied to the motor52.

Although CW and CCW output contacts165,170are shown, any suitable contacts or other suitable mutually exclusive outputs may be employed to control the direction of a motor from any suitable switching device.

The normally closed position indications CW166and CCW172are employed to remove power from the respective rectifiers156and158when the desired mechanical position is obtained.

The present control circuits50,150are for use with, but not limited to, dual directional transfer mechanisms, such as transfer mechanism204ofFIG. 3. Such a transfer mechanism204may employ, for example, a double-pole, double-throw contactor/switch or other like switching device (not shown). For example, the motor52rotates both clockwise and counter-clockwise, in order to change the state of the switching device. Alternatively, the control circuits50,150may be employed with any suitable transfer switch (e.g., employing two circuit breakers (not shown)).