Fuses protect the vehicle's electrical circuits from overloads and short circuits. If a malfunction occurs in the electrical circuit or an excessive number of energy consumers, a short circuit occurs, it is overloaded. The wire and winding of the generator overheat, the electrolyte in the battery may boil. It is for protection against this that fuses are used that interrupt the flow of current if its strength exceeds a certain permissible value.
There can be several reasons for a blown fuse: First, damage to any electrical unit or wiring element, as well as the wiring itself as a whole, due to which a short circuit occurs. As a result of this damage, the current flows along a shorter path with a significantly lower resistance. According to Ohm's law, a decrease in the resistance of a section of a circuit leads to a proportional increase in the current strength. As a result, the fuse in the fuse burns out, the electrical circuit is opened and a short circuit is prevented. The second is a current surge (overload). Occurs when a part that is driven by an electric motor is jammed. In this case, an increased current load appears inside the electric motor itself, which the fuse takes over and burns out, protecting the electrical circuit. The third is the installation of a fuse taken without a proper margin. In this case, the current that burns out the fuse (the melting current of its shell) only slightly exceeds the normal current for a given electrical circuit. In this case, a small increase in voltage relative to the nominal is enough for the fuse to blow. Fourth, poor contact between the block and the fuse. In this case, the fuse not only burns out, but its body is melted together with the block. This often occurs when using low-quality fuses that do not burn out, but melt, causing the contacts to burn out and melt the plastic of the fuse box. This is a very serious defect, as it can destroy the entire fuse box. Fifth, the loss of the available supply by the fuse. This happens over time, when the fusible part of the fuse forms areas with a smaller cross-section and can be the result of heating, vibration, shock loads, as a result of which the cross-section of the fusible part is so reduced that it cannot withstand and blows out with a slight increase in current. burn out most often not during operation, but at the moment the electrical circuit is turned on. This is explained by the fact that the metal threads of the electrical wiring increase their resistance when heated. At the moment of switching on, the threads are not heated, therefore their resistance is small, and the flowing current exceeds normal. As it warms up, the resistance increases and the current decreases. It is obvious that at the moment of switching on, an inrush current occurs, in magnitude higher than the current consumed in normal mode. In rare cases, the fuses can also blow when the circuit is turned off. This happens because at the moment of shutdown, extra currents develop, which burn out the fuse. This phenomenon is more typical for those sections of the circuit in which there are semiconductor elements.