Abstract:
A power extension cable with a loading indication and warning system. The power extension cable uses the loading indication and warning system to detect size of loading current passing through the extension cable. When the loading current passing though the extension cable exceeds a preset warning level, a warning message is issued so that a user may redistribute the loads before overloading the power extension cable to the breaking point.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the priority benefit of Taiwan application serial no. 91209234, filed Jun. 20, 2002. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    1. Field of Invention  
           [0003]    The present invention relates to a power extension cable. More particularly, the present invention relates to a power extension cable with loading indication and warning.  
           [0004]    2. Description of Related Art  
           [0005]    Ever since the discovery of usefulness of electricity, electric power has been used almost everywhere. Electricity is often the main source of power for lighting fixtures and many of our electronic appliances. The convenience and operational efficiency is unmatched by other sources of power. Equipment that uses electricity is all around us. Inside households, for example, televisions, hi-fi and video equipments, electric fans, air conditioners, microwaves and electric ovens all use electricity. To supply necessary electricity to the household equipment, a sufficient number of power sockets must be installed. Sometimes, however, the number of power sockets is smaller than the number of electrical appliances requiring electric power or the location of the appliances is too far away from the fixed outlet socket. In this case, an extension cable is often used to provide the number of extra sockets necessary for plugging the electrical appliances.  
           [0006]    Following rapid economic improvement, most families have more than a few electronic products at home. To support all these electrical appliances, a variable number of power sockets are often provided through an extension cable. Yet, a conventional power extension does not have any loading indication and warning. The only safety feature available to a power extension cable is a cut-off fuse that trips when there is a current overload. Although the electrical appliance plugged to the extension cable is protected, a user has no way of assessing the current loading situation.  
         SUMMARY OF INVENTION  
         [0007]    Accordingly, one object of the present invention is to provide a power extension cable with loading indication and warning so that a warning signal is emitted when the loading current exceeds a preset warning level. Hence, a user may assess the degree of overloading and determine if the loading needs to be distributed.  
           [0008]    To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a power extension cable with loading indication and warning that includes a conventional power extension cable and a loading indication warning system. The conventional power extension cable has at least a power socket for providing a current to an electrical appliance. The loading indication and warning system detects size of current flowing to the load. When the detected loading current exceeds a preset warning level, an alarm signal is triggered warning the user.  
           [0009]    In one embodiment of this invention, the loading indication and warning system further includes a current detector, a current/voltage converter, a comparator and an alarm unit. The current detector gauges the size of the loading current and outputs a monitor current. The current/voltage converter is coupled to the current detector for receiving the monitor current and converting the monitor current into a monitor voltage. The comparator is coupled to the current/voltage converter for comparing the monitor voltage with a preset warning voltage and outputting a warning signal. The alarm unit is coupled to the comparator for receiving the warning signal and generating a warning message.  
           [0010]    The current detector is preferably made up of a primary electric coil on one side of an iron core and a secondary electric coil on the other side of the iron core. Moreover, the number of turns in the primary electric coil connected to the power extension cable is smaller than the number of turns in the secondary electric coil.  
           [0011]    The warning message is preferably a visual message provided by a light-emitting diode or an acoustic message provided by a buzzer. Alternatively, the preset warning level is divided into a few sections so that each section is indicated by the appearance of a warning message from a light-emitting diode in that section. When the loading current reaches the highest preset warning level, the buzzer also emits a sound to alarm the user about this condition.  
           [0012]    In brief, this invention provides a power extension cable with loading indication and warning capable of issuing a warning message when the loading current exceeds a pre-determined warning level. Hence, a user may determine if some electrical loads should be plugged elsewhere to relieve the loading in the extension cable. Ultimately, the user is able to plug up electrical appliances more safely.  
           [0013]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]    The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
         [0015]    [0015]FIG. 1 is a sketch of a power extension cable with a loading indication and warning system thereon according to one preferred embodiment of this invention; and  
         [0016]    [0016]FIG. 2 is a block diagram of the loading indication and warning system according to this invention.  
     
    
     DETAILED DESCRIPTION  
       [0017]    Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
         [0018]    [0018]FIG. 1 is a sketch of a power extension cable with a loading indication and warning system thereon according to one preferred embodiment of this invention. FIG. 2 is a block diagram of the loading indication and warning system according to this invention. The power extension cable  100  includes a conventional power extension cable and a loading indication and warning system  200 . The loading indication and warning system  200  detects size of loading current and emits a warning message such as a visual message or an acoustic message when the loading current exceeds a preset warning level.  
         [0019]    As shown in FIG. 1, the conventional power extension cable  100  has a plug  110 , a power cable  120  and a plurality of power sockets  130 ,  132  and  134 . The plug  110  plugs into a power outlet (not shown) and the power cable  120  channels the power from the power outlet to various power sockets  130 ,  132  and  134  so that each of the sockets may supply a necessary loading current to a plugged electrical appliance. In addition, the range of loading current is divided into three sections whose limits are decided by a set of preset warning levels. According to the size of the loading current, the loading indication and warning system  200  determines which of the three sections the loading current belongs in and lights up light-emitting diodes LED 1 , LED 2  and LED 3  to indicate the loading level of the power extension cable  100 . If the loading current is in the highest section marked out by the preset warning level, a buzzer will emit an alarm to inform a user so that the user may act accordingly. The preset warning values used for setting up various sections may be a ratio of the fixed loading current that can be supported by the power extension cable. For example, if the power extension cable  100  is able to support a maximum loading current of 12 amperes, the first light-emitting diode LED 1  will light up when the loading current reaches 1 ampere. When the loading current reaches 5 amperes, the second light-emitting diode LED 2  will light up. Finally, when the loading current reaches 10 amperes, the third light-emitting diode LED 3  will light up and the buzzer will emit a buzzing sound at the same time. The operating principle of the loading indication and warning system  200  is further explained with reference to FIG. 2.  
         [0020]    As shown in FIG. 2, the loading indication and warning system  200  further includes a current detector  210 , a current/voltage converter  220 , a comparator  230  and an alarm unit  240 . The current detector  210  is made up of a primary electric coil  214  around one side of a circular iron core  212  and a secondary electric coil  216  around the other side of the circular iron core  212 . The primary electric coil preferably is an extension of the power cable  120  and the number of turns in the primary electric coil  214  is smaller than the number of turns in the secondary electric coil  216 . Hence, the loading current I L  provided by the voltage source V S  is converted to a monitor current I D  according to a ratio without affecting electrical loading L of the electrical appliances intended to be monitored. The power voltage Vs can be a 110V alternating current or a 220V alternating current depending on the type of power source the power extension cable  100  is plugged into. In general, the turn ratio of the current detector  210  is mainly determined by the required circuit design.  
         [0021]    The current/voltage converter  220  is coupled to the current detector  210  for converting the monitor current I D  into a monitor voltage V D . The comparator  230  is coupled to the current/voltage converter  220  for comparing the monitor voltage V D  with respective reference warning voltages V ref1 , V ref2  and V ref3 . Here, the loading current I L  belongs to one of three sections partitioned according to preset warning levels of 1 ampere, 5 amperes and 10 amperes. Hence, the reference voltages V ref1 , V ref2  and V ref3  represent a monitor voltage V D  under a loading current I L  of 1 ampere, 5 amperes and 10 amperes respectively. When the loading current I L  is greater than 1 ampere, the monitor voltage V D  is greater than the reference voltage V  ref1 . Hence, the comparator  230  outputs a warning signal S 1  to light up the light-emitting diode LED 1  in the alarm unit  240 . When the loading current I L  is greater than 5 amperes, the monitor voltage V D  is greater than the reference voltage V ref2 . Hence, the comparator  230  outputs a warning signal S 2  to light up the light-emitting diode LED 2  in the alarm unit  240 . Finally, when the loading current I L  is greater than 10 amperes, the monitor voltage V D  is greater than the reference voltage V ref3 . Hence, the comparator  230  outputs a warning signal S 3  to light up the light-emitting diode LED 3  in the alarm unit  240  and the buzzer in the alarm unit  240  emits a sound to alarm the user at the same time.  
         [0022]    Although three preset warning levels at 1 ampere, 5 amperes and 10 amperes are chosen for the loading current IL, actual values of the current partitioning up the sections may vary according to design. In addition, the number of preset warning levels does not have to be three. One may design an indication and warning system having the highest section at a loading current of 10 amperes so that only the third light-emitting diode LED 3  lights up and/or the buzzer emits a sound.  
         [0023]    In conclusion, major advantages of this invention include:  
         [0024]    1. Current loading condition of the power extension cable is provided to the user at all times so that the plugging of too many electrical loads is prevented.  
         [0025]    2. Since the current loading status of the power extension cable is always provided, users of the power extension cable may plug in electrical appliances without exceeding the operating limit. Hence, the user rarely has to reset the fuse.  
         [0026]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.