Self-recovery fuse is an overcurrent electronic protection element. If it is used improperly, spontaneous combustion may occur under specific conditions. How to avoid spontaneous combustion? Let's analyze the structure of self-recovery fuse and the cause of self-ignition of self-recovery fuse.
The melting part of self-recovery fuse is mainly made of polyethylene mixed carbon black, in which carbon black plays a conductive role, while polyethylene itself is non-conductive. After the mixed carbon black reaches a certain proportion, carbon black particles contact and conduct with each other in polyethylene, which is temporarily called fuse melt. Polyethylene (poyethylne) is a thermoplastic resin made by polymerization of ethylene, which has the remarkable characteristics of large thermal expansion coefficient and volume expansion after heating.
When the current flowing through the melt is too large, polyethylene will expand due to heating. At this time, the distance between carbon black particles in polyethylene is widened, the resistance becomes larger, and the heating amount increases sharply. When all the carbon black particles can't form a path, the conductive path is cut off and the current can't pass, thus playing the role of fuse breaking circuit. Because there is no current flowing through the melt, the heating factor of the mixture disappears, the polyethylene begins to cool down, the volume begins to shrink, the resistance gradually decreases, and the electrification gradually recovers. This is the working principle of self-recovery fuse.
From the above principle, it can be seen that when the fuse passes current, polyethylene will undergo thermal expansion. Whether the circuit is broken depends on whether the thermal expansion can open the distance between carbon black particles. If polyethylene is heated for a long time, its molecular structure will change or its properties will change, which may affect the distance between carbon black particles. In fact, the most common problem is the uneven distribution of carbon black particles, which easily causes local high temperature. With the increase of fluidity in high temperature zone, carbon black accumulates, which further leads to uneven carbon black. When this vicious circle goes on for a certain time, the fuse will open, and then it will burn out.
Generally speaking, people who design circuits know the working principle of self-recovery fuses, so as to identify the possible hidden dangers of fuses and take countermeasures. Of course, some circuits are careless in design and easy to forget to take corresponding countermeasures. What are the countermeasures? A more suitable method is to connect a conventional fuse in series with the self-recovery fuse. When the self-recovery fuse fails, the conventional fuse is blown to prevent the self-recovery fuse from catching fire and causing greater damage.
