Patent Publication Number: US-11394202-B1

Title: Alternating current time-sharing outlets and switch box

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Patent Application No. 62/820,439, filed Mar. 19, 2019, the contents of which are herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention relate generally to electrical power supplies. More particularly, embodiments of the invention relate to methods and apparatus for a time-shared outlet that can be connected to two distinct power loads and switched to provide power selectively to one of the two distinct power loads. 
     2. Description of Prior Art and Related Information 
     The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon. 
     If a user has a high current capacity 240 volts alternating current (VAC) or a 480 VAC/600 VAC outlet but has two loads that could draw power from these sources, it is often expensive and time consuming to wire a new outlet. Simply providing an extension cord-like apparatus that splits the outlet into two risks drawing current over the rated maximum current through the wire, which could result in overheating and even fire. 
     As can be seen, there is a need for an economical way to time-share an existing high current capacity 240 VAC or a 480 VAC/600 VAC outlet that is unique in a location to run two different loads/appliances one at a time. 
     SUMMARY OF THE INVENTION 
     The typical 240/250 VAC and 480/600 VAC wirings in the USA are depicted in  FIGS. 6 through 11 . A two-pole, double throw (2PDT) switch can be used to physically move the two active wires L1, L2 of the 240/250 VAC wirings or the 480 VAC/600 VAC-1PHASE wirings from one source to two different locations/receptacles/outlets. It should be noted that a single-pole, double throw (1PDT/SPDT) switch can break the current flow to a 240 VAC or 480 VAC/600 VAC-1PHASE system but is not safe since either 120 VAC or 240 VAC/300 VAC is still present at one leg of the connector when the connector is supposed to be OFF. 
     An appropriate three-pole, double-throw (3PDT) switch can be used to physically move the three active wires PHASE-A, PHASE-B, PHASE-C of the 480 VAC/600 VAC-3PHASE wirings from one source to two different locations/receptacles/outlets. 
     The 3PDT switch can be used to safely switch the 240/250 VAC, 480 VAC/600 VAC-1PHASE, and 480 VAC/600 VAC-3PHASE active wires to two different locations/receptacles/outlets. 
     Similarly, an appropriate three-pole (3P) slide or rotary switch can be used to physically move the above-mentioned 240 VAC, 480 VAC/600 VAC-1Phase, and 480 VAC/600 VAC-3Phase active wires to more than two locations/receptacles/outlets. 
     The ground and neutral wires can be directly tied together at all receptacles/outlets. 
     The methods described above can be used to time-share as many outlets as the availability of the components (switches and receptacles) that meet the load requirements. 
     The same methods can also be used for any AC wiring in the world that has 2 or 3 active lines using the appropriate connector type(s) (3-, 4-, or 5-prong) to time share outlets. By providing such a switching mechanism, a user can be assured that only one load is powered at a time, thereby not exceeding the maximum rated current of the circuit. 
     These methods can be used to build a 240V/480V AC Switch Box with two receptacles/outlets and a 3PDT switch—rated at 30 A at 250 VAC—that can switch both 240 VAC and 480 VAC (limit set by component selection) and an optional AC meter to provide voltage, current, and power measurements. The existing outlet wiring can be connected to the 3PDT switch that will, upon the user&#39;s selection, move the active AC lines to the selected receptacle/outlet. The user can plug up to two loads in the two receptacles/outlets, and select the active side using the switch to run two different loads/appliances from one wired outlet. 
     While the user can, alternately, unplug and swap the two loads to time-share the existing outlet, this may become tedious over time and may wear out the existing outlet leading to the need for expensive repairs. 
     Embodiments of the present invention provide an alternating current (AC) switch device comprising a cord and plug configured to electrically connect to an existing outlet; a housing containing a first receptacle and a second receptacle; and a switch configured to deliver power from the cord and plug to at least one of the first receptacle and the second receptacle. 
     Embodiments of the present invention further provide an alternating current (AC) switch device comprising a cord and plug configured to electrically connect to an existing outlet; a housing containing a first receptacle and a second receptacle; and a manually activated switch configured to deliver power from the cord and plug to one of the first receptacle and the second receptacle, wherein the housing has a length and width of less than seven inches and a depth of less than 2.5 inches; and the first receptacle and the second receptacle are configured for at least 240 volts AC. 
     Embodiments of the present invention also provide an automatic alternating current (AC) switch device comprising a cord and plug configured to electrically connect to an existing outlet; a housing containing a first receptacle and a second receptacle, the first receptacle and the second receptacle receiving power from the cord and plug; and a microcomputer-controlled electronic switch configured to disconnect power from being delivered to the second receptacle when the first receptacle is above a predetermined maximum amperage, wherein the first receptacle and the second receptacle are configured for at least 240 volts AC. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present invention are illustrated as an example and are not limited by the figures of the accompanying drawings, in which like references may indicate similar elements. 
         FIG. 1  illustrates front view of a power switch box according to an exemplary embodiment of the present invention; 
         FIG. 2  illustrates a side perspective view of the power switch box of  FIG. 1 ; 
         FIG. 3  illustrates a back view of the power switch box with a back side of its housing removed; 
         FIG. 4  illustrates a schematic representation of an automatic power switch box according to another exemplary embodiment of the present invention; 
         FIG. 5  illustrates a schematic representation of a MOSFET gate driven switching circuit usable with an automatic power switch box according to an exemplary embodiment of the present invention; 
         FIG. 6  illustrates a conventional power connection wiring diagram for a three-pole, three-wire 240/250 VAC outlet; 
         FIG. 7  illustrates a conventional power connection wiring diagram for a three-pole, four-wire 240/250 VAC outlet; 
         FIG. 8  illustrates a conventional power connection wiring diagram for a two-pole, three-wire single phase 480 VAC outlet; 
         FIG. 9  illustrates a conventional power connection wiring diagram for a four-pole, four-wire three phase 277/480 VAC outlet; 
         FIG. 10  illustrates a conventional power connection wiring diagram for a four-pole, four-wire three phase 347/600 VAC outlet; and 
         FIG. 11  illustrates a conventional power connection wiring diagram for a four-pole, five-wire three phase 347/600 VAC outlet. 
     
    
    
     Unless otherwise indicated illustrations in the figures are not necessarily drawn to scale. 
     The invention and its various embodiments can now be better understood by turning to the following detailed description wherein illustrated embodiments are described. It is to be expressly understood that the illustrated embodiments are set forth as examples and not by way of limitations on the invention as ultimately defined in the claims. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS AND BEST MODE OF INVENTION 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well as the singular forms, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     In describing the invention, it will be understood that a number of techniques and steps are disclosed. Each of these has individual benefit and each can also be used in conjunction with one or more, or in some cases all, of the other disclosed techniques. Accordingly, for the sake of clarity, this description will refrain from repeating every possible combination of the individual steps in an unnecessary fashion. Nevertheless, the specification and claims should be read with the understanding that such combinations are entirely within the scope of the invention and the claims. 
     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one skilled in the art that the present invention may be practiced without these specific details. 
     The present disclosure is to be considered as an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated by the figures or description below. 
     As is well known to those skilled in the art, many careful considerations and compromises typically must be made when designing for the optimal configuration of a commercial implementation of any system, and in particular, the embodiments of the present invention. A commercial implementation in accordance with the spirit and teachings of the present invention may be configured according to the needs of the particular application, whereby any aspect(s), feature(s), function(s), result(s), component(s), approach(es), or step(s) of the teachings related to any described embodiment of the present invention may be suitably omitted, included, adapted, mixed and matched, or improved and/or optimized by those skilled in the art, using their average skills and known techniques, to achieve the desired implementation that addresses the needs of the particular application. 
     Broadly, embodiments of the present invention provide methods and apparatus to turn an existing 240 VAC or 480 VAC/600 VAC outlet into two or more time-sharing, i.e., one operating at a time, outlets. An AC switch box with two time-sharing outlets can be made with either a mechanical switch for switching which load receives power, or automatically by, for example, a microcomputer system. In the automatic AC switch box, the non-favored outlet may be typically powered on unless a load is detected at the favored/default outlet, when power to the non-favored outlet is automatically disconnected until the load is reduced or eliminated. 
     Referring now to  FIGS. 1 through 3 , a manual AC switch system  10 , also simply referred to as a switch box  10 , can include an outer housing  12  with a first receptacle  14  and a second receptacle  16  accessible through openings in the housing  12 . A manual switch  18 , or simply switch  18 , may be disposed outside the housing  12  to permit a user to choose between the first and second receptacles  14 ,  16 . A reset button  22  may be accessible from outside the housing, where the reset button  22  may be used to bring the microcomputer to a known start-up state in the event of illogical or fault conditions. For example, both LEDs indicating power to each receptacle are on or flashing, or the like. Finally, the switch box can include a meter  20  for providing a reading of the voltage, current, or the like, of the selected receptacle. A power cord  24  can provide an electrical connection between an existing power outlet (not shown) and the switch box  10 . In some embodiments, the switch box  10  may include blades extending from a back side thereof for a direct plug into the existing power outlet. The elements of the switch box  10  are discussed in greater detail below. 
     The AC switch system  10  can be housed in the housing  12  that is typically formed of plastic, such as ABS or polycarbonate. In one embodiment, the housing  12  may have a length and width between 5 and 10 inches, with a depth of 2 to 4 inches, typically, with a length and width of 6.30 inches and a depth of 2.37 inches. 
     The housing  12  can include two receptacles, the first receptacle  14  and the second receptacle  16 , typically NEMA receptacles with either 3-, 4- or 5-prongs, with appropriate voltage and amperage ratings that are used for 240 VAC or 480 VAC connections. Some examples of receptacles  14 ,  16  include NEMA 10-30R (240 VAC, 30 A), 14-30R (240 VAC, 30 A) and L16-20R (480 VAC, 20 A). One receptacle  14  can be named side/port A and the other receptacle  16  can be named side/port B. The receptacles  14 ,  16  may be the same or different in configuration. Typically, the receptacles  14 ,  16  may be rated at the same current, however, in some embodiments, the receptacles  14 ,  16  may be rated at different currents, provided that none of the receptacles  14 ,  16  are rated greater than that of the existing receptacle from which the switch box  10  draws power. 
     The housing  12  can include one switch  18 , such as a 3PDT switch that allows both 240 VAC and 480 VAC switching. Typically, the switch  18  will have a 30 A rating, but other switch ratings may be used depending on the particular application. One exemplary switch is the NKK 5832 switch (30 A at 250 VAC). The switching is physical and is typically performed by a quality switch component so any change/variation in electrical DC characteristics is minimal. For example, at a 30 A resistive load, a drop of −0.3V occurs due to −0.01-ohm switch resistance. The AC frequency (50 or 60 Hz) and the phase of the AC signals would not change due to the switch. 
     The housing  12  can further include an optional AC panel meter  20 . The meter  20  may be selected with various specifications, such as ±1% accuracy for current measurements, ±1% accuracy for voltage measurements and ±2% accuracy for power measurements. 
     The housing  12  can include a fuse box and fuse to protect the AC panel meter  20  and enhance the user&#39;s safety. The fuse box and fuse may be placed at one side of or inside the housing  12  for maximum user&#39;s safety. The fuse may be a slow-blow/time-delay type with ratings 0.5 A, 250 VAC. 
     Should a high current condition or short-circuit occur in the power section of the electronics, the fuse can instantly break the current to preclude damage and/or fire hazard. 
     In some embodiments, the housing  12  can include indicators, such as LED indicators to indicate that side A (the first receptacle  14 ) or side B (the second receptacle  16 ) is activated. 
     Inside the housing  12 , the appropriate wiring may be used to support the current loads. For example, a 10 AWG copper wire may be used for a 30-amp load. 
     The wires from the existing/original outlet can be distributed/connected to the 3PDT switch and can support the respective receptacle/plug (3-, 4- or 5-prong) type and the desired voltage type (either 240 VAC or 480 VAC with 2 or 3 active wires). For example, as shown in  FIGS. 1 through 3 , a first line wire  28 , a second line wire  30  and a neutral wire  26  may be disposed inside the housing  12  to connect each receptacle  14 ,  16  to each throw side of the switch  18 . Each housing  12  can be built to a set configuration of connector and voltage type, e.g., 3-prong receptacles and 240 VAC or 4-prong receptacles and 480 VAC. Different box configurations/models can be pre-built for different receptacles and voltages. 
     A cable with plug  24  can be provided to ensure the connectors of the existing outlet are correctly connected to the first and second receptacles  14 ,  16 . 
     Optional safety features can be included, such as arc-fault circuits, ground-fault circuits, or the like. 
     To use the switch box  10 , the operator can connect the cable with plug  24  to an existing 240 VAC or 480 VAC outlet (not shown). The operator may connect two loads to the AC switch box  10  at the first receptacle  14  and the second receptacle  16 . The loads can be any 240 VAC or 480 VAC load that is less than the safe limit of the switch and the receptacle, typically about 80% of the current rating. For example, for a 30 A system, this would limit the loads to about 24 A at 250 VAC. Electric dryers and EV chargers are typically within this limit. Either receptacle  14 ,  16  can be used for the electric dryer or the EV charger, for example. 
     The switch  18  can determine at what receptacle, the first receptacle  14  or the second receptacle  16  the 240 VAC or 480 VAC is connected. If the first receptacle  14  (side A) is selected, the 240 VAC or 480 VAC is present at the first receptacle  14 . If the second receptacle  16  (side B) is selected, the 240 VAC or 480 VAC is present at the second receptacle. 
     The meter  20  can be designed to have two display modes, where a first display mode may show a user the voltage, current, and power, measurements when the second receptacle  16  is selected. The meter  20  may be OFF when the first receptacle  14  is selected. A second display mode can have the meter  20  always activated to provide voltage, current, and power measurements for the second receptacle  16 . The first display mode may consume less power, where the second display mode precludes repeated power-cycling to the AC meter and thus may extend the lifespan of the AC meter. 
     Typically, the user can make a voltage selection at side A or B, then starts to run the load at either side A or B until done, then changes side when the load is not pulling, i.e., when no current is present. This typical use does not expose the switch  18  to arcing. However, if the user changes/toggles the switch  18  while the load is pulling, i.e., when high current is present, there may be arcing at the switch because the abrupt change in current and any inductance in the wiring and/or in the load/system can generate a large voltage (V−L=L*di/dt). Arc suppression circuits may be used at the switch  18  to minimize such arcing which may damage the switch. 
     In some embodiments, an automatic version of the switch box  10  may be provided, where the manual AC switch  18  is activated automatically, either via a switch, or through other circuitry, such as power transistors, or the like. 
     In the automatic system, a microcomputer system can be included to implement the following algorithm: 
     The on-board microcomputer can continually and accurately monitor the current drawn by the first receptacle  16 A, where the electric dryer may be connected to receive power from this receptacle and whenever the dryer is deemed active, i.e., the current is more than a predetermined threshold, e.g., 0.1 ampere for a period of time, the microcomputer can de-activate the second receptacle  18 A where the EV charger is connected. 
     The microcomputer can automatically reconnect power to the second receptacle  18 A (EV charger) whenever the first receptacle  16 A (electric dryer) is safely inactive, i.e., the monitored current is less than a predetermined threshold, e.g., 0.1 ampere for more than a safe time period. 
     Activation and de-activation of power to the second receptacle  18 A can be done by power relays or transistors under microcomputer control. 
     This default selection is deliberately made to “favor” the first receptacle  16 A, where the electric dryer is expected. The reasons for this are because the dryer operation is more urgent, with clothes that need to be dried and typically takes less time (about 1 to 1.5 hours), while EV charging may take &gt;10 hours. The user can give EV charger priority by plugging it to the first receptacle  18 A, if desired. 
     Two LED indicators can be used to indicate which receptacle is on/activated. 
     The optional AC panel meter can be configured to be always on to provide voltage, current, and power measurements for the second receptacle  18 A (EV charger). 
     There may be an optional normally open momentary switch that may be configured to that when the user presses and holds this switch for longer than a specified time, e.g. 3 sec, the microcomputer will de-activate the second receptacle  18 A (EV charger, for example) for a set time, e.g., 90 seconds, so that the user can safely remove the charger cable from the EV. 
     The housing  40  for the automatic AC switch box  50  may be the same or bigger than the standard manual model, AC switch box  10 , discussed above. 
     Referring to  FIG. 4 , a schematic representation of an automatic AC switch box  50  is shown. Similar to that of  FIGS. 1 through 3 , power may be provided through lines  28 ,  30  and neutral  26 . Of course, depending on the configuration, other power, neutral and ground lines may be present. Like that described above, a cord and plug (not shown) may be used to connect the switch box  50  to an existing outlet. A similar fuse  32  and reset button  34  may be present on the housing  40  of the switch box  50 . Overcurrent protection may be provided for each receptacle  16 A,  18 A by overcurrent devices  46 ,  48 . A current monitor  42  may be configured to measure current drawn by the first receptacle  16 A. One or more displays  36 ,  38  may be provided to display voltage, current, power, or the like at one or both of the receptacles  16 A,  18 A. 
     A switch  44  may be used to disconnect power from reaching the second receptacle  18 A. The switch  44  may include power relays or transistors  52 ,  54 , as discussed in greater detail below. 
     The Automatic Version (AV) of the switch box  50  can include power relays or transistors  52 ,  54 , such as MOSFETs, connected in parallel, to switch the EV-charger port, second receptacle  18 A, for a 30 A load. This design allows the hardware to fit into the same box/housing as the manual switch box  10 , described above. 
     The MOSFET power transistor switch is shown in the schematic diagram of  FIG. 5 . Two N-channel MOSFETs were connected in series at the source (S) terminal. When the gate (G) is set HI (from about 3 V DE up to about 15 V DC), the switch is closed and AC current can pass. When the gate (G) is set LO (about 0 V DC), the switch is open and AC current cannot pass. Up to 12 such parallel MOSFET-pairs, for example, can be used in the automatic version of the AC switch box to switch one active AC line (L1 or L2) and handle the generated heat. By using parallel MOSFETs, the power per MOSFET transistor can be lowered. In some embodiments, the switch box may allow breaking both L1 and L2 lines while keeping the same form factor/housing. 
     Because the MOSFETs are small and flat, this power transistor design approach enables the fitting of the automatic version AC switch hardware in a smaller/thinner or the smallest/thinnest box. Conversely, a design without power transistors will require a larger/thicker box/housing. 
     The Automatic Version (AV) of the switch box  50  can include one or two mini LCD displays, similar to the displays described above, that are used to display current or/and voltage at one or both receptacles from built-in and proprietary circuitries with various specifications, such as ±1 to ±2% accuracy for current measurements, ±1% to ±2% accuracy for voltage measurements. 
     The current monitor  42  may be done by a current transformer (CT) circuit. One primary task in the automatic switch box  50  is to accurately measure/monitor AC current at the dryer side, receptacle  16 A. This may be achieved by the design at current levels from about 0.1-0.2 A to at least 3 A or up to 4 A. Typical response time for this measurement can be within 1 to 1.5 seconds, as with a 30 A fuse and about a 25 A EV load at the second receptacle  18 A, the hardware needs to know when the first receptacle  16 A gets to about 5 A or less as soon as possible to dis-engage second receptacle  18 A. 
     The current transformer and its associated operational amplifier circuit can be used to obtain a voltage that linearly relates to the magnetic field generated by an AC current and therefore to the AC current itself. This voltage can then be converted into a digital format by an Analog-to-Digital Converter (ADC) with sufficient resolution and accuracy to yield +/−1% to +/−2% current measurements. The ADC can be physically inside the microcomputer within the housing of the power switch. 
     The microcomputer can continually make the current measurements at the favored outlet and, depending on the detected current load, the microcomputer can automatically perform the switching to connect or remove AC power at the non-favored outlet. 
     Software techniques can be used to sample and filter the measurement data to preclude false readings. 
     The Automatic AC Switch Box can include two current monitor circuits and is thus capable of monitoring and reporting AC currents at both receptacles independently. Optionally, it can also monitor the system AC input voltage (240 VAC). 
     Other current monitoring technologies may be used within the scope of the present invention. For example, in some embodiments, a Hall Effect (HE) sensor can be used to monitor/measure AC and DC currents. The Hall Effect monitor can measure both AC and DC currents. In other embodiments, a shunt/series resistor can also be used to measure current. Each of these technologies, or other known methods, may be used to measure current drawn by at least one of the first and second receptacles. 
     All the features disclosed in this specification, including any accompanying abstract and drawings, may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. 
     Claim elements and steps herein may have been numbered and/or lettered solely as an aid in readability and understanding. Any such numbering and lettering in itself is not intended to and should not be taken to indicate the ordering of elements and/or steps in the claims. 
     Many alterations and modifications may be made by those having ordinary skill in the art without departing from the spirit and scope of the invention. Therefore, it must be understood that the illustrated embodiments have been set forth only for the purposes of examples and that they should not be taken as limiting the invention as defined by the following claims. For example, notwithstanding the fact that the elements of a claim are set forth below in a certain combination, it must be expressly understood that the invention includes other combinations of fewer, more or different ones of the disclosed elements. 
     The words used in this specification to describe the invention and its various embodiments are to be understood not only in the sense of their commonly defined meanings, but to include by special definition in this specification the generic structure, material or acts of which they represent a single species. 
     The definitions of the words or elements of the following claims are, therefore, defined in this specification to not only include the combination of elements which are literally set forth. In this sense it is therefore contemplated that an equivalent substitution of two or more elements may be made for any one of the elements in the claims below or that a single element may be substituted for two or more elements in a claim. Although elements may be described above as acting in certain combinations and even initially claimed as such, it is to be expressly understood that one or more elements from a claimed combination can in some cases be excised from the combination and that the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements. 
     The claims are thus to be understood to include what is specifically illustrated and described above, what is conceptually equivalent, what can be obviously substituted and also what incorporates the essential idea of the invention.