Patent Publication Number: US-9889324-B2

Title: Fire protection device for small electrical devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 13/765,967, filed Feb. 13, 2013, which claims priority to DE 20 2012 100 623.5 filed on Feb. 24, 2012, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The invention relates to a fire protection device for small electrical devices having housings. It also relates to a small electrical device with a housing that is equipped with such a fire protection device. Finally, it relates to the use of a bursting capsule as a fire protection device for small electrical devices. 
     Background Information 
     Small electrical devices for the purposes of this invention are devices with small dimensions that operate using electric power, wherein small dimensions are understood to mean edges that are a maximum of 1 m in length, typically in a range of several cm to several dm. For example, a typical small electrical device is a power adaptor as is often currently used in conjunction with laptop computers. These kinds of power adaptors have dimensions of 10 cm to 15 cm along its longest edge length and up to 10 cm along its shortest edge length. Encapsulated in a housing, they contain electrical components for the voltage conversion of a supply voltage originating from the mains voltage, for example 230V AC in Europe, into a supply voltage for the electrical device being supplied, for example a laptop, e.g. a DC voltage of 12 V. 
     These kinds of small electrical devices, for example such power adaptors, heat up during operation. If there is any damage, this kind of small electrical device, such as a power adaptor, can overheat, for example as a result of a short circuit or an overload that is not adequately absorbed by a corresponding safety device, which under unfavorable circumstances can lead to the plastic components in the small electrical device catching fire, and can thereby lead to a fire. Various house and apartment fires, or fires in office buildings, are caused by defective electrical devices that catch fire as a result of such malfunctions. 
     Although such small electrical devices are frequently equipped with electrical fuses that are tripped in the event of a defect and a resulting overcurrent, and that are supposed to cut the power supply, such fuses are not always adequate protection against a fire in this kind of small electrical device. In particular, such fuses can no longer provide effective protection if excessive overheating of the small electrical device, or of the electrical components in the small electrical device, has already occurred before the fuse is tripped. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is intended as a remedy for this by providing a reliable fire protection device for small electrical devices with a housing. 
     According to the invention, such a fire protection device consists of a bursting capsule featuring a hollow space that is completely enclosed and delimited by a vessel wall, wherein a liquid that exhibits two essential characteristics is disposed in the hollow space. This liquid breaks the vessel wall at a predetermined trigger temperature due to thermal expansion, thereby causing the bursting capsule to rupture. Furthermore, the liquid has a fire inhibiting effect and/or an extinguishing effect. 
     Thus the fire protection device according to the invention functions as follows: Based on a predetermined trigger temperature, the fire protection device monitors whether the small electrical device exceeds the maximum permitted temperature, specifically the trigger temperature, and if the small electrical device overheats, or in other words the inner temperature inside the housing in which the fire protection device is disposed exceeds the trigger temperature, the fire protection device is triggered, namely by the rupture of the bursting capsule. The liquid that escapes the bursting capsule then provides a fire inhibiting effect or an extinguishing effect. In this way, smoldering fires that have already begun inside the small electrical device can be extinguished when the trigger temperature is reached, if necessary, or in the case of a risk of smoldering fire, said fire can be prevented due to the fire-inhibiting effect of the liquid. 
     Bursting capsules, like those used for fire protection according to the invention, are known from the prior art in different variations. Particularly suited are the so-called glass vessels or glass tube sections that are sealed at both ends, such as those that are used in the release valves of sprinkler systems for example. There, corresponding glass vessels are placed between a support and an external cap on sprinkler system. They are filled with a triggering liquid, which causes the glass vessel to rupture due to thermal expansion when a trigger temperature is exceeded, wherein the bursting or rupture of the glass vessel releases the sprinkler system valve, thereby opening the sprinkler valve. In this application, the liquid functions solely as a thermal trigger, and the liquid is selected accordingly. A fire inhibiting effect and/or an extinguishing effect is not important for the triggering liquid, and known triggering liquids do not exhibit such an effect. 
     In the fire protection device according to the invention, in addition to the liquid, a gas bubble is advantageously disposed in the hollow space. This gas bubble may be an air bubble, for example, but may also be a gas that does not promote fire such as nitrogen or carbon dioxide. Such a gas bubble can be used to precisely set the trigger temperature of the bursting capsule. 
     According to another advantageous embodiment of the invention, the boiling point of the liquid is at a temperature that falls below the trigger temperature. As a result, the liquid released after the bursting capsule ruptures immediately vaporizes or transitions to the gaseous phase. Due to of the massive expansion of the material when it transitions to the gas phase (in the case of an ideal gas, one mole of such a gas would take up a volume of approximately 22.4 liters under normal conditions), the gas formed by the liquid would quickly fill the interior of the housing of the small electrical device and can exert a preventative effect and/or extinguishing effect. This extinguishing effect or fire inhibiting effect may take the form of displacing the oxygen needed by any type of fire in the housing of the small electrical device, for example. The effect may also take the form of homogeneous inhibition. 
     Another form of extinguishing effect, for which it is not necessary to select a liquid that has a boiling point that falls below the trigger temperature, may consist of a liquid that turns into foam when it is released, thereby developing an extinguishing property. This kind of foam formation may occur as a result of a reaction with components in the atmosphere within the small device, for example, or it may occur when the liquid encounters a second liquid component, for example when these are held separately in the bursting capsule and are only combined when the vessel has ruptured. 
     Another possible extinguishing effect can arise when the liquid exhibits a high bonding affinity with oxygen and therefore bonds chemically with oxygen, even as droplets of liquid distributed in the interior of the small appliance, thus withdrawing the oxygen from the seat of the fire. In this case, liquid can exhibit the extinguishing effect even without vaporizing, and need not have a boiling point that falls below the trigger temperature. 
     Liquids that are suitable for the purpose of the protection device according to the invention include halons. Moreover, fluorinated ketones can also be used, especially a perfluorinated ethyl isopropyl ketone. 
     An additional protective function arises for the fire protection device according to the invention when an electrical conductor is routed between two contact points formed on the bursting capsule, which electrical conductor is designed in such a way that it is destroyed when the bursting capsule ruptures. In particular, such a conductor can be interconnected in the small electrical device so that it conducts the voltage supply. Thus the conductor constitutes an independent safety element since, in the event that the bursting capsule is triggered, the electrical conductor is destroyed and the power supply to the small electrical device is cut off. Thus, in addition to the fire inhibiting effect or extinguishing effect of the liquid that is released when the bursting capsule is triggered or ruptured, it is also ensured that electrical energy is no longer supplied to the small electrical device, and therefore no further heating is caused by this electrical energy, or the malfunctioning of the small electrical device, with a resulting increased risk of fire. Here, the electrical conductor can be designed in such a way that it serves as electrical overload protection, independent of the triggering of the fire protection device (the rupturing of the bursting capsule). For example, the conductor may be designed in such a way that it melts or is otherwise destroyed when the current exceeds a predetermined upper limit, thereby interrupting the power supply, even if the bursting capsule is still intact. 
     An additional aspect of the invention teaches of a small electrical device with a housing, in which electrical components are disposed and furthermore in which a fire protection device as described above is disposed. A small electrical device thus equipped is protected from a possible fire, for example a smoldering fire in the housing as a result of the effects described above. In particular, the small electrical device can be designed in such a way that its electrical supply line is connected to the contact points of the bursting capsule and routed through the conductor that is routed between these contact points. The result is the above-described additional safety effect. 
     An additional aspect of the invention relates to the use of a bursting capsule, with the various possible characteristics described above, as a fire protection device for a small electrical device, by disposing said bursting capsule in the housing of such a small electrical device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       Further advantages and characteristics of the invention will become apparent in the following description of possible embodiments with reference to the accompanying figures. These include: 
         FIG. 1  a schematic view of a possible fire protection device according to the invention; 
         FIG. 2  a view similar to that in  FIG. 1  showing an alternative embodiment of a fire protection device according to the invention; 
         FIG. 3  a view similar to that in  FIG. 1  showing another alternative embodiment of a fire protection device according to the invention; 
         FIG. 4  a schematic representation of a small electrical device equipped with a fire protection device according to the invention; here, a power adaptor; and 
         FIG. 5  an alternative embodiment of a small electrical device equipped with a fire protection device according to the invention; here again, a power adaptor. 
     
    
    
     The figures show possible schematic representations of embodiments of the invention. The figures are not at all drawn to scale and do not show all details; rather, these are schematic diagrams intended to illustrate the essential features of the invention in conjunction with the following description of the embodiments. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram of a bursting capsule  1 , which is an essential component of a fire protection device according to the invention. The interior of this bursting capsule  1 , which here is a so-called glass vessel formed from a glass tube, features a hollow space  2  that is completely enclosed by the vessel wall. The bursting capsule  1  is essentially cylindrical in shape with two thickened ends  3 ,  4 . The bursting capsule  1  is disposed and is held between two supports  5 ,  6  at the ends  3 ,  4 . A liquid is disposed in the hollow space  2  (not shown here), which, together with a small gas bubble, nearly fills the volume of the hollow space  2 . On the one hand, this liquid is selected such that it causes the bursting capsule  1  to rupture at a predetermined trigger temperature due to thermal expansion, for example 50° C., 60° C., 65° C., 70° C. or 90° C., and on the other hand, such that it exhibits a fire inhibiting effect and/or an extinguishing effect. In this way, when the trigger temperature is reached or exceeded, the liquid in the bursting capsule is released when the vessel ruptures, and can achieve the desired fire inhibiting effect or extinguishing effect inside the housing of a small electrical device. 
     The liquid here is selected in an advantageous manner so that its boiling point is at a temperature that falls below the trigger temperature, or in other words that abruptly enters the gas phase when it is released upon reaching or exceeding the trigger temperature and therefore takes up a greater volume than the volume of the hollow space  2 . Thus a comparatively small quantity of liquid can fill a comparatively large volume within the housing of a small electrical device with the corresponding gas, which arises from the liquid and therefore can achieve the fire inhibiting effect or extinguishing effect there. 
     A halon may be considered as a possible liquid in the hollow space  2 . A fluorinated ketone is also suitable however, wherein in this embodiment, a perfluorinated ethyl isopropyl ketone according to the following structural formula 
                         
is preferable.
 
       FIG. 2  shows an alternative embodiment of such a bursting capsule  1  as a fire protection device. The primary components are essentially the same as those in the bursting capsule  1  in  FIG. 1 , and it simply includes an additional electrical conductor  7 , which runs along the longitudinal axis of the bursting capsule  1 , through the hollow space  2  and passes out through the respective ends  3  and  4 . When this bursting capsule is used, this electrical conductor can be used as a fire protection device, for example, in order to conduct a supply voltage for the small electrical device. In so doing, the thickness of the electrical conductor  7  is selected in such a way that the electrical conductor  7  breaks, and is destroyed when the bursting capsule  1  ruptures as a result of the trigger temperature being exceeded. The result is that, in the event of triggering, not only is the fire inhibiting effect or extinguishing effect of the liquid contained in the hollow space  2  triggered or achieved, but at the same time the power supply to the electrical device is also cut off. Otherwise, the structure of the bursting capsule shown in  FIG. 2  is the same as that in  FIG. 1  and the functioning is identical as well. 
       FIG. 3  shows a further alternative of a bursting capsule  1 , which in turn is essentially designed and functions as described in  FIG. 1 . In deviating from the embodiment shown in  FIG. 1 , in the case of the bursting capsule  1  according to  FIG. 3 , an electrically conductive coating  8  has been applied to a section of the exterior of the bursting capsule, which extends from one end  3  of the bursting capsule  1  to the other end  4 . Contact can be established with this electrically conductive coating  8  via the supports  5  and  6 , which come into contact with the coating  8  as shown, thereby forming an electrical conductor that runs along the longitudinal axis of the bursting capsule  1  and can be routed through an electrical supply of the small electrical device, for example. Here again, the rupture of the bursting capsule  1  as a result of pressure due to the thermal expansion of the liquid in the hollow space  2  when it exceeds the trigger temperature, which pressure the wall of the bursting capsule  1  cannot withstand at or above the trigger temperature, results in a break in the conductor formed by the electrically conductive coating  8  and therefore to an interruption in the current or voltage supply of the small electrical device equipped with this fire protection device. Otherwise, the structure and functioning of the bursting capsule shown in  FIG. 3  is the same as that in  FIG. 1 , so that again, reference can be made to the description of this figure. 
       FIG. 4  shows a schematic representation of a power adaptor  10  as an example of a small electrical device according to the invention. The power adaptor  10  features a housing  11 , in which the various components are disposed. A power cable  12  runs into the housing for connecting to the mains power supply. A unit cable  13  runs from the housing, which acts as a voltage-adapted power supply for the device. A voltage converter  14  and additional electrical components  15 ,  16  on a printed circuit board  17  are disposed within the housing  11 . The voltage converter  14  is connected with the power cable  12  on the input side with both wires, and on the output side, the voltage converter  14  supplies the unit cable  13 . A bursting capsule  1  according to  FIG. 1  is disposed as a fire protection device within the housing  11  between supports  5  and  6 . If overheating that exceeds trigger temperature of the bursting capsule  1  now occurs in the power adaptor  10  as a result of a malfunction, the liquid disposed in the hollow space of the bursting capsule  1  causes the bursting capsule to rupture and thus develops its fire inhibiting effect or extinguishing effect. 
       FIG. 5  shows an alternative embodiment of a small electrical device according to the invention in the form of a power adaptor  10 . Here again, the power adaptor  10  is enclosed by a housing  11 , into which a power cable  12  extends that is connected to the mains voltage on the input side, from which the unit cable  13  extends with the device voltage adapted to the conditions for the electrical device being supplied. Again the voltage converter  14  and additional electrical components  15 ,  16  are disposed on a printed circuit board  17 . In contrast to the preceding embodiment, both wires of the power cable  12  are no longer directly connected to the voltage converter  14 , but rather, one wire  18  is routed to the bursting capsule  1 , which here is designed in accordance with the embodiment in  FIG. 2 , and connected to the electrical conductor  7  formed there in this embodiment. Connected on the opposite side to the electrical conductor  7  is an additional wire  19  from a connection cable, which then runs to the input of voltage converter  14 . This design, which varies from the embodiment in  FIG. 4 , ensures that in the event that the bursting capsule  1  is triggered, the electric conductor  7  will break, thereby interrupting the supply voltage to the power adaptor  10  from the power cable  12 . Here, in addition to the fire inhibiting effect or extinguishing effect from the liquid disposed in the bursting capsule  1 , it is also guaranteed that the power is also interrupted in the manner of a fuse. Naturally an embodiment of the bursting capsule  1  according to  FIG. 2  could be replaced with the design in  FIG. 3  in the embodiment according to  FIG. 5  with the same effect. 
     In particular, it is to be understood here that the volume ratios between the volume of the hollow space of the bursting capsule to the total volume of the housing shown in  FIGS. 4 and 5  are not to scale. Here, the bursting capsule  1  has been enlarged for better illustration. In so doing, the volume capacity of the bursting capsule  1  has been designed in such a way that upon triggering and the vaporizing of the liquid form of the chemical substance contained therein, said liquid, which is then in a gaseous state, will reliably fill the internal volume of the housing  11 . 
     LIST OF REFERENCE DRAWINGS 
     
         
           1  bursting capsule 
           2  hollow space 
           3  end 
           4  end 
           5  support 
           6  support 
           7  electrical conductor 
           8  electrically conductive coating 
           10  power adaptor 
           11  housing 
           12  power cable 
           13  unit cable 
           14  voltage converter 
           15  electrical component 
           16  electrical component 
           17  printed circuit board 
           18  wire 
           19  wire