Parameter selection and application of the hottest

Parameter selection and application of fuse

in many electronic devices, fuse is indispensable. Since Edison invented the first plug-in fuse that sealed the thin wire in the lamp holder in the 1990s, the types of fuses have become more and more widely used. This article introduces the parameters, selection and application of fuses, hoping that you can benefit

the rated values and performance indexes of fuses are determined according to laboratory conditions and acceptance specifications. There are many authoritative testing and identification institutions in the world, such as UL certification of Underwriters Laboratories in the United States, CSA certification of Canadian Standards Association, MTTI certification of the Ministry of international trade and industry of Japan and IEC certification of sensors of the International Electrotechnical Commission

the selection of fuse involves the following factors:

1 normal working current

2 ﹐ the applied voltage applied to the fuse

3 ﹐ abnormal current required to disconnect the fuse

4 ﹐ the shortest and longest time allowed for abnormal current

5 ambient temperature of fuse

6 pulse, impulse current, surge current, starting current and circuit transient value

7 whether there are special requirements beyond the fuse specification

8 ﹐ size limitation of installation structure

9 ﹐ required institutional certification

10. Fuse base parts: fuse clip, mounting box, panel installation, etc

the following describes the common parameters in fuse selection and the new requirements of the corresponding test bench and experimental machine equipment manufacturers

1. When the normal working current operates at 25 ℃, the current rating of the fuse is usually reduced by 25% to avoid harmful fusing. Most traditional fuses use materials with low melting temperatures. Therefore, this kind of fuse is sensitive to the change of ambient temperature. For example, a fuse with a current rating of 10A is generally not recommended to operate at a current greater than 7 5A at an ambient temperature of 25 ℃

2. Voltage rating the voltage rating of the fuse must be equal to or greater than the effective circuit voltage. The general standard voltage rating series are 32V, 125V, 250V and 600V

3. The resistance of the resistance fuse is not important in the whole circuit. Since the fuse resistance with amperage less than 1 is only a few ohms, this problem should be considered when using fuses in low-voltage circuits. Most fuses are made of materials with positive temperature coefficient. Therefore, there are cold resistance and thermal resistance

4. The current carrying capacity of the ambient temperature fuse is tested at an ambient temperature of 25 ℃, which is affected by the change of ambient temperature. The higher the ambient temperature, the higher the working temperature of the fuse and the shorter its service life. On the contrary, operating at a lower temperature will prolong the life of the fuse

5. Rated fusing capacity is also called breaking capacity. The rated fusing capacity is the maximum allowable current that the fuse can indeed fuse under the rated voltage. In case of short circuit, the instantaneous overload current greater than the normal working current will pass through the fuse for many times. Safe operation requires the fuse to remain in a complete state (without bursting or breakage) and eliminate short circuits

6. Fuse performance the performance of fuse design refers to the speed with which the fuse reacts to various negative current data. Fuses are often divided into four main types according to their performance: normal response, delayed disconnection, fast action and current limitation

7. Harmful open circuit is often caused by incomplete analysis of the designed circuit. Among all the factors involved in fuse selection listed above, special attention must be paid to normal operating current, ambient temperature and overload increment (item 6). When using, the fuse should not be selected only according to the normal working current and ambient temperature, but also pay attention to other service conditions. For example, a common reason for the harmful open circuit of the conventional power supply is that the nominal melting of the fuse is not fully considered. The friction and wear testing machine of Jinan new era Gold Testing Instrument Co., Ltd. converts the rated value of heat energy based on the principle of time production of the manufacturer. It must also meet the requirements of various surge currents generated by the input capacitor of the smooth filter of the power supply for the fuse. If you want a fuse to be safe and reliable and have a long service life, you should make the melting heat energy of the selected fuse not greater than 20% of the nominal melting heat energy rating of the fuse

8. The nominal melting heat energy is the energy required to melt the fused parts, expressed in i2t and read as "ampere square second". Generally, in authoritative certification bodies, the nominal melting heat energy should be tested: apply a current increment to the fuse and measure the melting time. If the melting does not occur within about 0 008 seconds or even less, then increase the intensity of the pulse current. Repeat this experiment until the melting of the fuse is limited to about 0 008 seconds. The purpose of this test is to ensure that the generated heat energy does not have enough time to escape from the fuse components through heat conduction, that is, all the heat energy is used for melting

therefore, when selecting fuses, in addition to the normal working current, reduced rating and ambient temperature mentioned above, i2t value should also be considered. In addition, we should pay attention to one thing: when welding, because most fuses have welded joints, we should be very careful when installing these fuses by welding. Excessive welding heat will make the solder in the fuse reflow and change its rating. Fuse is a thermal element similar to semiconductor, so it is best to use heat absorbing device when welding fuse. (end)