Abstract:
A power Y-adapter provides power at a high voltage to an output end from at least two input ends to which power of a lower voltage and a phase difference is provided and includes a first polarity sensitive current isolation device, a second polarity sensitive current isolation device, a control section, and an output section. When the voltage signals supplied to the hot wire terminals of the first input connector and the second input connector sufficiently are out of phase, the Y-adapter can produce a voltage of higher magnitude between the first and the second hot wire terminals of the output connector.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This claims the benefit of U.S. Provisional Patent Application No. 61/437,473 filed Jan. 28, 2011, the disclosure of which is hereby incorporated by reference for all purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a power adapter, more particularly an adapter unit for supplying electrical power to a marine vessel from a dockside power center. 
       BACKGROUND OF THE INVENTION 
       [0003]    Power adapters are commonly used for mobile vehicles which are equipped with significant electrical and electronic equipment. A typical example is a boat or recreational vehicle which can be equipped with navigational equipment such as radio and radar, kitchen appliances such as a cooking range and refrigerator, entertainment equipment such as television and stereo, and other such electrical and electronic equipment. When a boat is moored at a dock or the like, electrical power is commonly supplied from a shore or dockside power center, such as a dockside electrical pedestal at the marina, which includes at least two electrical receptacles into which cables from the vessel can be inserted. Such a power center commonly has two or more identical receptacles each supplying 120 volts AC. If all of the equipment aboard the vessel is designed to operate at the same voltage, there is no problem. However, if the craft has 240 volt (or  208  volt) equipment, or if the power distribution system on the craft is a 240 distribution system, the operator of the craft can not simply connect a docking power connector on the craft to the pedestal. For example, equipment such as blower motors, pumps or the like are wired for 208-240 volt power, that equipment may either not operate at all or operate at a low speed and overheat because of improper voltage. 
         [0004]    Marinas usually provide separate 120 volt outlets on the pedestal wired from two phases of a two or three phase supply so that appropriate voltages are available for powering the equipment on a craft which requires a 240 volt supply. However, those two or three out-of-phase sources must be connected together in an appropriate manner before they are useful for powering the 240 volt equipment on the craft. Typically, the pedestal simply has the out-of-phase 120 volt sources brought out to separate receptacles, so that they can be used in the ordinary way for powering 120 volt equipment. It is common for a boat owner to make or buy a “Y” adapter with two male plugs at one end to make 120 volt input connections and a single 125/250 volt output connector having female contacts. The 125 volt input connectors are then inserted into the two receptacles on the pedestal and the single 125/250 volt output connector is plugged into the marine vessel ship-to-shore cable set as an input to the receptacle on the vessel. The electrical wiring for the vessel is connected to this receptacle. 
         [0005]    Although a Y-adapter can theoretically provide a desired voltage of 120V or 208-240V and current to a vessel from a receptacle, there are a few practical problems with using the Y-adapter in various situations, such as improper connection of the Y-adapter to the power source, potential problems with the wiring of the pedestal power source, problems with the phase of the power supplied to the pedestal, and the like. 
         [0006]    As an example of an improper connection of the Y-adapter, when one of the input connectors is inserted into a live socket in the pedestal, live voltage can also appear on the other input connector if precautions are not taken. If the user has his body in contact with the electrical prongs of an unconnected input connector, (s)he is subjected to the danger of receiving an electrical shock. 
         [0007]    As another example of potential problems with the pedestal power source, if the electrical sources from the two selected receptacles are not from different phases, or not of a sufficient difference, the output voltage will not be adequate to drive the equipment on the craft. As another example, although with the proper phase difference, additional problems can result if one of the voltage sources is wired with its polarity reversed. 
         [0008]    Further, overcurrent and overtemperature situations can also cause serious problems. For example, as the adapter plugs into a 50 A rated receptacle, it is a common misconception that the reverse Y-adapter is rated for 50 A. Although it may operate indefinitely at 50 A, circuit runs, wires and connectors that are rated at 30 A may overheat and have a shortened life. 
         [0009]    Although some available technology can fix some of the problems, there are still some problems. For example, it is common in currently available circuit designs for a Y-adapter to place at least one circuit element across the hot terminal of two input connectors or plugs. In this design, a single component fault can cause a shock condition. As another example, some currently available designs have a tendency to buzz at low input voltage conditions and may cause the circuit to chatter or produce intermittent output. Still other problems include a bulky size or a tendency to fail at prolonged relatively high current conditions. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention provides a Y-adapter configured to provide a reliable connection of an electrical load of one electrical characteristic to a pair of electrical sources of a different characteristic. 
         [0011]    The power Y-adapter for providing power at a high voltage to an output end from at least two input ends to which power of a lower voltage and a phase difference is provided, includes a first polarity sensitive current isolation device, a second polarity sensitive current isolation device, a control section, and an output section. 
         [0012]    The first polarity sensitive current isolation device is associated with a first input connector which is adapted to be connected to a first receptacle of a first voltage and phase. Further, the first polarity sensitive current isolation device has a first input terminal and a second input terminal. The first input terminal is connected to a hot wire terminal of the first input connector and the negative input terminal being connected to a neutral terminal of the first input connector. The second polarity sensitive current isolation device is associated with a second input connector which is adapted to be connected to a second receptacle of substantially the same voltage as the first receptacle and at a different phase than the first receptacle. The second polarity sensitive current isolation device has a first input terminal and a second input terminal. The first input terminal is connected to a neutral terminal at the second input connector and the second input terminal is connected to a hot wire terminal at the second input connector. Each of the first and the second polarity sensitive current isolation devices have a first output node and a second output node in series. The control section is in series with the output nodes of the first and the second polarity sensitive current isolation devices. The output section has an output connector with a first hot wire terminal and a second hot wire terminal controlled by the control section. When the voltage signals supplied to the hot wire terminals of the first input connector and the second input connector are out of phase, the Y-adapter can produce a voltage of higher magnitude between the first and the second hot wire terminals of the output connector. 
         [0013]    The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a circuit diagram showing a first embodiment of a Y-adapter that is configured to supply electrical power from a pair of power sources to a single receptacle, in accordance with the present invention; 
           [0015]      FIG. 2  is a diagram showing another embodiment of a Y-adapter that is configured to supply electrical power from a pair of power sources to a single receptacle, in accordance with the present invention; 
           [0016]      FIG. 3  is a diagram showing another embodiment of a Y-adapter that is configured to supply an electrical power from a pair of power sources to a single receptacle, in accordance with the present invention; 
           [0017]      FIG. 4  is a diagram showing another embodiment of a Y-adapter that is configured to supply electrical power from a pair of power sources to a single receptacle, in accordance with the present invention; and 
           [0018]      FIG. 5  is a diagram showing another embodiment of a Y-adapter that is configured to supply electrical power from a pair of power sources to a single receptacle, in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a circuit diagram showing one embodiment of a Y-adapter  10  that is configured to supply electrical power from a pair of power sources to a single receptacle. The Y-adapter  10  includes a first input connector  101 , a second input connector  102 , an output connector  103 , a control section  104 , a power supply unit  105 , a first polarity sensitive current isolation device  140 , and a second polarity sensitive current isolation device  150 . 
         [0020]    More specifically, as shown in  FIG. 1 , the first input connector  101  includes a hot wire terminal  112  and a neutral terminal  114 , and the second connector  102  includes a hot wire terminal  122  and a neutral terminal  124 . The output connector  103  includes a first hot wire terminal  134 , a second hot wire terminal  132 , and a neutral terminal  136 . The hot wire terminal  112  of the first connector  101  is connected to the first hot terminal  134  of the output connector through the first polarity sensitive current isolation device  140  and the control section  104 . The hot wire terminal  122  of the second connector  102  is connected to the second terminal  132  of the output connector  103  through the second polarity sensitive current isolation device and the control section  104 . 
         [0021]    The first polarity sensitive current isolation device  140 , such as an optocoupler, opto-isolator, photocoupler, or optical isolator, has a first input terminal  142 , a second input terminal  144 , a first output terminal  146 , and a second output terminal  148 . The first input terminal  142  of the first polarity sensitive current isolation device  140  is connected to the hot wire terminal  112  of the first input connector  101  through a second resistor  192 . The second input terminal  144  of the first polarity sensitive current isolation device  140  is connected to the neutral terminal  114  of the first connector  101  through a third resistor  193 . A second rectifier  292 , such as a diode, is connected to the first polarity sensitive current isolation device  140  with a positive terminal connected to the first input terminal  144  and a negative terminal connected to the second input terminal  142 . 
         [0022]    The second polarity sensitive current isolation  150 , such as an optocoupler, opto-isolator, photocoupler, or optical isolator, has a first input terminal  152 , a second input terminal  154 , a first output terminal  156 , a second output terminal  158 . The first input terminal  152  of the second polarity sensitive current isolation device  150  is connected to the neutral terminal  124  of the second input terminal  102  through a fourth resistor  194 . The second input terminal  154  of the second polarity sensitive device is connected to the hot wire terminal  124  of the second connector  102  through a fifth resistor  195 . A third rectifier  293 , such as a diode, is connected to the second polarity sensitive current isolation device  150  with a positive terminal connected to the second input terminal  154  and a negative terminal connected to the first input terminal  152 . 
         [0023]    The power supply unit  105  includes a transformer  160 , a bridge rectifier  170 , a power output  182 , a first voltage output  184 , and a second voltage output  186 . The transformer  160  has a first input terminal  162  and a second input terminal  164  connected to the hot wire terminal  122  and the neutral terminal  124  of the first input connector, respectively. A first output terminal  166  and a second output terminal  168  of the transformer are connected to a first input terminal  172  and a second input terminal  174  of the bridge rectifier  170 . A positive output terminal  176  of the bridge rectifier is connected to the power output  182 , and a negative output terminal  178  of the bridge rectifier is connected to a ground  109 . The first voltage output  184  is connected to the positive output terminal  176  of the bridge rectifier  170  through a first resistor  191 . The second voltage output  186  is connected to the positive output terminal of the bridge rectifier through a resistor  198 . The power output  182  is connected to the ground  109  through a capacitor  262 . The first voltage output  184  is connected to a cathode node  274  of a first voltage reference zener diode  270 . An anode node  272  of the first voltage reference zener diode  270  is connected to the ground  109 . The second voltage output is connected to a cathode node  282  of a zener diode  280 . An anode node  284  of the zener diode  280  is connected to the ground  109 . 
         [0024]    The control section  104  essentially includes a third polarity sensitive current isolation device  210 , a comparator  220 , a transistor  230 , a first relay  240 , and a second relay  250 . The third polarity sensitive current isolation device  210  is series connected with the first polarity sensitive current isolation device  140  and the second polarity sensitive current isolation device  150 . A first input terminal  212  of the third polarity sensitive current isolation device  210  is connected to the second output terminal  148  of the first polarity sensitive current isolation device  140 . A second input terminal  214  connected to the first input terminal  156  of the second polarity sensitive current isolation device  150 ; a first output terminal of the third polarity sensitive current isolation device  210  is connected to the second voltage output  186 . The comparator  220  having a non-inverting input terminal  221  connected to the second output terminal  218  of the third polarity sensitive current isolation device  210 , an inverting input terminal  222  connected to the ground  109  through a capacitor and to the power supply output  184 , a positive power supply terminal  223  connected to the second voltage output  186  of the power supply unit  105 , a negative power supply  224  connected to the ground  109 , and an output terminal  225  connected to the second output terminal  218  of the third polarity sensitive current isolation device  210  through a ninth resistor  199  and a capacitor. The transistor  230  has a gate terminal  232  connected to the output terminal  225  of the comparator  220 , a source terminal  234  is connected to the ground  109 , and a drain terminal  236 . 
         [0025]    A first terminal  242  of the first relay  240  and a first terminal  252  of the second relay  250  are connected to the drain terminal  236  of the transistor  230 . A second terminal  244  of the first relay  240  and the second terminal  254  of the second relay  250  are connected to the power output  182  of the power supply unit  105 , the third terminal  246  of the first relay  240  is connected to the first hot wire terminal  134  of the output connector  103 , the third terminal  256  of the second relay  250  is connected to the second hot wire terminal  132  of the output connector  103 , the fourth terminal  248  of the first relay  240  is connected to the hot wire terminal  112  of the first input connector  101 , and the fourth terminal  258  of the second relay  250  is connected to the hot wire terminal  122  of the second input connector  102 . A neutral terminal  136  of the output connector  103  is connected to the neutral terminal  124  of the second input connector  102 . 
         [0026]    In  FIG. 1 , the reverse Y-adapter  10  is configured to connect two 30 A, 125V receptacles through the first connector  101  and the second connector  102  to provide an equivalent to 50 A, 125V/250V shore power through the output connector  103 . The combined power supplied has two phases of 120V with a voltage of 208-240V between them. The supply current is limited to 30 A as the reverse Y-adapter will not boost current to 50 A. 
         [0027]    The reverse Y-adapter  10  uses the first polarity sensitive current isolation device  101  and the second polarity sensitive current isolation device  102  to isolate and sense the incoming voltage levels and phase. It then provides a filtered voltage level to the comparator  220 , which determines if conditions are correct for turn-on. Adding delay and hysteresis, the comparator  220  drives the transistor  230  which then turns on both the first relay  240  and the second relay  250  simultaneously. 
         [0028]    More particularly, the second resistor  192  and third resistor  193  limit the incoming 120V AC current to approximately 1 mA for the first polarity sensitive current isolation device  101 . The second rectifier  292  works as a reverse bias protector for the first polarity sensitive current isolation device  101 . Similarly, the fourth resistor  194  and the fifth resistor  195  limit the incoming 120V AC current for the second polarity sensitive current isolation device  102 . The second rectifier  293  works as a reverse bias protector for the second polarity sensitive current isolation device  102 . The first isolation device  101  and the second isolation  102  provide substantial isolation between the input voltage and sensing circuitry as well as complete isolation of the hot wire terminal  112  of the first connector  101  and the hot wire terminal  122  of the second connector  102 . 
         [0029]    The power supply unit  105  for the circuit is a traditional full wave bridge providing two regulated and one unregulated voltages, a first voltage, for example 3.0V, through the first voltage output  184  and a second voltage, for example 7.5V, through the second voltage output  186  and a third voltage, for example 12V. The first voltage is used as a voltage reference for the comparator  220 , the second voltage is used to power everything except for the first relay  240  and the second relay  250 , and the third voltage powers the relays  240  and  250 . 
         [0030]    The first isolation device  140 , the second isolation  150 , and the third isolation device  160  work as part of the circuit that is configured to make the phase decisions. In general, when positive voltage is supplied to the isolation device between the positive input terminal and the negative input terminal, the isolation device is in a connected state; otherwise the isolation device is in an isolated state. More particularly, by the first isolation device  140  and the second isolation device  150  unidirectionally, relative phase information is preserved. The first isolation device  140  and the third isolation device  210  are both in a connected state during a positive cycle of a first input AC signal from the first connector  101  and in an isolated state during a negative cycle. Further, since the second isolation device  150  is phase reverse connected, where the positive input terminal  162  is connected to the neutral terminal  124  and the negative input terminal  164  is connected to the hot wire terminal  122 , the second isolation  160  is in a connected state during a negative cycle of a second input AC signal from the second connector  102 . 
         [0031]    Further the third isolation device  210  also works as a power source which drives the control section  104 . When the third isolation device  210  is in a connected state, the current through it drives the control section. When the third isolation device is in an isolated state, the control section  104  is turned off and the first isolation device  140  and the second isolation device  150  are isolated from each other, which results in the first connector  101  and the second connector  102  being isolated from the output connector  103 . 
         [0032]    In the case of the first input AC signal from the first connector  101  and the second input AC signal from the second connector  102  having the same phase, due to the phase reversed connection of the second isolation device  150 , the first isolation device  140  and the second isolation device  150  are never simultaneously in the connected state. Since the first isolation device  140 , the second isolation device  150  are connected in series, the third isolation device  210  is provided no input current in this situation. Therefore, in this case, the first connector  101  and the second connector  102  are isolated from each other, and are also isolated from the output connector  103 . 
         [0033]    In the case of one of the connectors not being connected or plugged with a power source, the first input AC or the second input AC signal is missing or both are missing, the corresponding isolation device turns out to be in the isolated state. Therefore the third isolation device can not get input current. Therefore, in this case, the first connector  101  and the second connector  102  are isolated from each other, and also isolated from the output connector  103 . 
         [0034]    In the case of the first input AC signal from the first connector  101  and the second input AC signal from the second connector  102  being 180 degrees out of phase, the first isolation device  140  and the second isolation device  150  are in a connected state simultaneously every positive cycle of the first input AC signal, and the third isolation device can get an input current with an approximate 50% duty cycle. Therefore, in this case, the third isolation device  210  drives the control section  104 . 
         [0035]    In the case of the first input AC signal from the first connector  101  and the second input AC signal from the second connector  102  being 120 degrees out of phase, the first isolation device  140  and the second isolation device  150  are in a connected state together only part of the positive cycle of the first input AC signal. Therefore the third isolation device  210  can get an approximate 33% duty cycle to drive the control section  104 . 
         [0036]    In the case of the first input AC signal from the first connector  101  and the second input AC signal from the second connector  102  being 60 degrees out of phase, the third isolation device  210  is energized with an approximate 16% duty cycle to drive the control section. 
         [0037]    When the third isolation device  210  is in a connected state, the current going through the third isolation device  210  can supply current to the seventh resistor  197  and voltage to the non-inverting input terminal  221  of the comparator  220 . The comparator  220  compares the voltage at its non-inverting input terminal  221  to the reference voltage provided by the first voltage output  184  on its inverting input terminal  222 . If the voltage at its non-inverting input terminal  221  is greater than the reference voltage, the output terminal  225  outputs a voltage signal. Otherwise, the output state terminal  225  stays low. Further, the fourth capacitor  264  and the ninth resistor  194  provide filtering, delay and hysteresis. The fourth capacitor  264  reduces the ripple from the duty cycle of the third isolation device  210  current and provides an approximate 100 ms delay by its charging time. 
         [0038]    When the output voltage between the first output terminal  216  and the second output terminal  218  of the third isolation device  210  goes high, the fourth capacitor can send a charge back into the seventh resistor and hold the input high momentarily, thus preventing chatter. The ninth resistor  199  provides actual hysteresis by providing high state voltage back to the non-inverting input terminal  221  of the comparator  220 . This makes the voltage of the non-inverting input terminal  221  harder to get below the threshold, for example 3V, in the high state than in the output terminal  225  low state, therefore the output terminal  225  can stay high even as the voltage of the seventh resistor  197  varies around the threshold level. The first capacitor  261  and the third capacitor  263  are noise bypass capacitors. 
         [0039]    The transistor  230  is driven by the output terminal  225  of the comparator  220  and is in a conducting state when the voltage at the gate terminal  232  is in a high state. When in the conducting state, the first relay  240  and the second relay  250  are energized which turn on the connection between the hot wire terminal  112  of the first connector  101  with the first hot wire terminal  134  of the output connector  102  and the connection between the hot wire terminal  122  of the second connector  102  and the second hot wire terminal  132  of the output connector  102 . As a supplement to the transistor  236 , the diode  295  and the diode  296 , which are snubber diodes, can suppress the spikes created when the relays turn off. 
         [0040]    Further, the reverse Y-adapter has circuitry to determine if the two 30 A shore power sources have adequate voltage and correct phasing to provide 208-240 VAC to the connected boat or other load. Each of the two power sources are independently monitored and no electrical device such as a circuit including a capacitor, or another circuit element that is subject to being shorted in the case of a fire or overheating, is connected between the two supplies. Because of this, no leakage current can be measured between the sources and thus, there is no hazard of electrical shock when one source is plugged in and the other is not (independent of whether the boat is plugged in). The independence causes some operational abnormalities, which are described in the following table along with normal conditions. 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Supply Voltage 
                 Phasing 
                   
                   
                 Output 
                 Light 
               
               
                 Condition 
                 source 1 
                 source 2 
                 Result 
                 Voltage 
                 State 
               
               
                   
               
             
             
               
                 normal 240 V 
                 0 deg 
                 180 deg 
                 Turn-on 
                  240 V 
                 On 
               
               
                 normal 208 V 
                 0 deg 
                 120 deg 
                 Turn-on 
                  208 V 
                 On 
               
               
                 normal 120 V 
                 0 deg 
                  0 deg 
                 Stay off 
                 na 
                 Off 
               
               
                 1 plug disconnected 
                 any 
                 any 
                 Stay off 
                 na 
                 Off 
               
               
                 1 phase reversed 120 V 
                 0 deg 
                 180 deg 
                 Turn-on 
                   0 V 
                 Off 
               
               
                 1 phase reversed 240 V 
                 0 deg 
                  0 deg 
                 Stay off 
                 na 
                 Off 
               
               
                 1 phase reversed 208 V 
                 0 deg 
                  60 deg 
                 Turn-on 
                  120 V 
                 On 
               
               
                   
                   
                   
                 Stay off 
                 na 
                 Off 
               
               
                 Voltage under 90 V 
                 any 
                 any 
                 Cycle 
                 &lt;180 V 
                 On/Off 
               
               
                   
                   
                   
                 Turn-on* 
                  &lt;90 V 
                 Off 
               
               
                   
                   
                   
                 Turn-on  
                 &lt;180 V 
                 On 
               
               
                 Temperature above 
                 any 
                 any 
                 Cycle 
                 na 
                 On/Off 
               
               
                 100 C. 
                   
                   
                   
                   
                   
               
               
                 Load over 30A 
                 any 
                 any 
                 Cycle 
                 na 
                 On/Off 
               
               
                   
               
               
                 *only 1-phase will be connected 
               
             
          
         
       
     
         [0041]    The operation abnormalities described above with respect to the phase reversed conditions help diagnose the existence of these conditions. 
         [0042]      FIG. 2  is a diagram showing another embodiment of the Y-adapter  20  that is configured to safely supply an electrical power from a pair of power sources, in accordance with the present invention. The overall structure, functions and operations of the Y-adapter  20  in  FIG. 2  are essentially the same as those in  FIG. 1 , and a description thereof of similar components and function will be omitted. 
         [0043]    The difference between the Y-adapter  130  shown in  FIG. 1  and the Y-adapter in  FIG. 2  lies in a resistor  270  is added in the Y-adapter  20  between the first output terminal  216  of the third isolation device  210 . 
         [0044]    As shown in  FIG. 2 , when the third isolation device  210  is in a connected state, an associated voltage can be developed by the seventh resistor  197  and the ninth resistor  199  and the tenth resistor  270 . In this embodiment, the voltage of the non-inverting terminal  221  can be configured by using a particular resistance value to the seventh resistor  197 , the ninth resistor  199 , and the tenth resistor  270  to discriminate input AC signal with an improper phase relation, such as 60 degree out of phase. 
         [0045]    For example, the first voltage provided by the first voltage output  184  is 3.0V, the second voltage provided by the second voltage output  186  is 7.5V, the resistance value of the ninth resistor  199  is 165 kΩ, the resistance value of the seventh resistor  197  is 82.5 kΩ, and the resistance value of the tenth resistor  270  is 20 kΩ. When the first AC input signal and the second AC input signal are 180 degree out of phase, the voltage of the non-inverting terminal  221  of the comparator is 4.4V, which is greater than the voltage of the inverting input terminal  222  of the comparator  220 , 3.0V. Therefore the comparator is turned on and outputs a voltage signal, which turns on the connection between the input connectors and the output connector through the transistor and the relays. Similarly, when they are 120 degree out of phase, the voltage of the non-inverting terminal  221  of the comparator is 3.6V, which is greater than 3.0V, therefore the connections between the input connectors and the output connectors are turned on. However, when they are 60 degrees out of phase, the voltage of the non-inverting terminal  221  of the comparator is 2.4V, which is less than 3.0V; therefore the connections between the input connectors and the output connectors stay off. Hence, the improper phase relation of 60 degrees is treated as a no input condition. Therefore, the following condition chart applies to the circuit of  FIG. 2 : 
         [0000]    
       
         
               
               
               
               
               
               
             
           
               
                   
               
               
                 Supply Voltage 
                 Phasing 
                   
                   
                 Output 
                 Light 
               
               
                 Condition 
                 source 1 
                 source 2 
                 Result 
                 Voltage 
                 State 
               
               
                   
               
             
             
               
                 normal 240 V 
                 0 deg 
                 180 deg 
                 Turn-on 
                  240 V 
                 On 
               
               
                 normal 208 V 
                 0 deg 
                 120 deg 
                 Turn-on 
                  208 V 
                 On 
               
               
                 normal 120 V 
                 0 deg 
                  0 deg 
                 Stay off 
                 na 
                 Off 
               
               
                 1 plug disconnected 
                 any 
                 any 
                 Stay off  
                 na 
                 Off 
               
               
                 1 phase reversed 120 V 
                 0 deg 
                 180 deg 
                 Turn-on 
                   0 V 
                 Off 
               
               
                 1 phase reversed 240 V 
                 0 deg 
                  0 deg 
                 Stay off 
                 na 
                 Off 
               
               
                 1 phase reversed 208 V 
                 0 deg 
                  60 deg 
                 Stay off  
                 na 
                 Off 
               
               
                 Voltage under 90 V 
                 any 
                 any 
                 Cycle 
                 &lt;180 V 
                 On/Off 
               
               
                   
                   
                   
                 Turn-on*  
                  &lt;90 V 
                 Off 
               
               
                   
                   
                   
                 Turn-on  
                 &lt;180 V 
                 On 
               
               
                 Temperature above  
                 any 
                 any 
                 Cycle 
                 na 
                 On/Off 
               
               
                 100 C. 
                   
                   
                   
                   
                   
               
               
                 Load over 30A 
                 any 
                 any 
                 Cycle 
                 na 
                 On/Off 
               
               
                   
               
               
                 *only 1-phase will be connected 
               
             
          
         
       
     
         [0046]      FIG. 3  is a diagram showing another embodiment of the Y-adapter that is configured to safely supply an electrical power from a pair of power sources, in accordance with the present invention. The overall structure, functions and operations of the Y-adapter  30  in  FIG. 3  are essentially the same as those in  FIG. 1 , and a description thereof of similar components and function will be omitted. Further, additional features of the Y-adapter  30  can also be applied to the second embodiment Y-adapter  20  of the present invention. 
         [0047]    The difference between the Y-adapter  30  shown in  FIG. 3  and the Y-adapter  10  shown in  FIG. 1  lies in the Y-adapter  30  has an overtemperature sensing unit  301 . 
         [0048]    The overtemperature sensing unit  301  includes a second comparator  310 , an overcurrent protector  324 , such as a PTC thermistor, a resistor  321 , a resistor  322 , a resistor  323 , an overtemperature indicator  333 , such as a light emitting diode, and a reverse current connecting device  334 , such as a diode. 
         [0049]    As shown in  FIG. 3 , a non-inverting input terminal  312  of the second comparator  310  is connected to an output terminal  316  through the resistor  321 . The overcurrent protector  324  is connected between the second voltage output  186  and the non-inverting input terminal  312 . The non-inverting input terminal  312  is connected to the ground  109  through the resistor  323 . An inverting input terminal  314  of the second comparator  310  is connected to the first voltage output  184 . The overtemperature indicator  333  has a cathode terminal connected to the output terminal  316  of the second comparator  310  and an anode terminal connected to the power supply terminal  182  through the resistor  322 . The reverse current connecting device  334  has a cathode terminal connected to the output terminal  316  and an anode terminal connected to the non-inverting input terminal  221  of the comparator  220 . 
         [0050]    The overcurrent protector  324  can protect the circuit by changing from a low-resistance to a high-resistance state in response to an overtemperature caused by an overcurrent. The overcurrent protector  324  in  FIG. 3  can work with the amplifier  220  and the diode  334  to provide a low voltage at the non-inverting input terminal  221  of the comparator  220  when the temperature is above a threshold, such as to cut down the connections between the input connectors and the output connector. More particularly, when the temperature is lower than the temperature threshold, the overcurrent protector  324  has a relatively low resistance value. In this situation, the non-inverting input terminal  312  gets a relatively high voltage which results in a high voltage state at the output terminal  316  of the second comparator  310 . Therefore there would not be any current to go through the overtemperature indicator  333 . When the temperature goes up to the temperature threshold and the resistance value of the overcurrent protector  324  is high enough to make the voltage of the non-inverting input terminal  312  lower than the inverting input terminal  314 , the output terminal  316  is at a low voltage state. In this situation, there will be a current driven by the power supply terminal  182  that goes through the overtemperature indicator  333  and turn on the light of the indicator  333 . Further, diode  334  is turned on and the non-inverting input terminal  221  of the comparator  220  is connected to the output terminal  316  of the second comparator  310 , which results in the non-inverting input terminal  221  being connected to a low voltage state. Therefore the voltage of the non-inverting input terminal  221  is reduced significantly and the connection between the input connectors and the output connectors is opened. 
         [0051]      FIG. 4  is a diagram showing another embodiment of the Y-adapter  40  that is configured to safely supply an electrical power from a pair of power sources, in accordance with the present invention. The overall structure, functions and operations of the Y-adapter  40  in  FIG. 4  are essentially the same as those in  FIG. 1 , and a description thereof of similar components and function will be omitted. Further, additional features of the Y-adapter  40  can also be applied to the second embodiment Y-adapter  20  of the present invention. 
         [0052]    As shown in  FIG. 4 , a thermal switch  410  can also be used as a substitute of the overtemperature sensing unit  301  in  FIG. 3 . The thermal switch  410  can be parallel connected to the seventh resistor  197 . When the temperature is above a threshold, the switch  340  will be closed, and therefore the non-inverting input terminal  221  of the comparator  220  is connected to the ground  109 . Hence the connection between the input connectors and the output connectors is opened. 
         [0053]      FIG. 5  is a diagram showing another embodiment of the Y-adapter  50  that is configured to safely supply an electrical power from a pair of power sources, in accordance with the present invention. The overall structure, functions and operations of the Y-adapter  50  in  FIG. 5  are essentially the same as those in  FIG. 1 , and a description thereof of similar components and function will be omitted. Further, additional features of the Y-adapter  50  can also be applied to the second embodiment Y-adapter  20  of the present invention. 
         [0054]    As shown in  FIG. 5 , the Y-adapter  50  includes a phase presence indication unit  501  and  502  for the first connector  101  and the second connector  102  respectively. The phase presence indication unit  501  includes a LED  510  and a resistor  512  in series connected between the hot wire terminal  112  and the neutral terminal  114  of the first connector  101 . Similarly, the phase presence indication unit  502  includes a LED  520  and a resistor  522  in series connected between the hot wire terminal  122  and the neutral terminal  114  of the second connector  102 . 
         [0055]    In  FIG. 5 , the LED  510  and LED  520  on each of the two input connectors can aid phase troubleshooting by indicating that one or both phases are energized. If both lights are on and no output occurs, then phase relations are improper. If one or both do not light, then that input is absent. If all LEDs light, the conditions are correct and the relays are on. 
         [0056]    Detailed description is provided above for a power adapter provided by the present invention. Embodiments are used herein to describe the principles and modes of carrying out the present invention, the above description of embodiments is only to help understand the methods and core thinking of the present invention; at the same time, those skilled in the art may modify modes of carrying out and application scope of the present invention according to the spirit thereof. In summary, the contents of the specification may not be construed as restrictive to the present invention.