We need to know the common sense when purchasing the fuse holder. For example: What parameters does the fuse have and what is its performance?
First, which parameters are involved in the selection of the fuse
A number of authoritative testing and accreditation bodies, such as the UL certification of the Underwriters Laboratories of the United States, the CSA certification of the Canadian Standards Association, the MTTI certification of the Japan International and Trade Industry Department, and the ICE certification of the International Electrical Technical Committee.
The choice of fuse involves the following factors:
1. Normal operating current.
2. The applied voltage applied to the fuse.
3. An abnormal current that requires the fuse to be disconnected.
4. The shortest and longest time allowed for abnormal currents to exist.
5. The ambient temperature of the fuse.
6. Pulse, inrush current, inrush current, starting current and circuit transients.
7. Is there a special requirement that exceeds the fuse specification?
8. Size limitations of the mounting structure.
9. The required certification body.
The performance of a fuse is how quickly the fuse reacts to various current loads.
Fuses are often classified into four types: normal response, delayed disconnection, fast action, and current limit.
Harmful disconnection: often due to incomplete analysis of the designed circuit. Of all the factors involved in the fuse selection listed above, special attention must be paid to normal operating current, ambient temperature and overload.
When using, it is not possible to select the fuse based only on the normal operating current and ambient temperature, and also pay attention to other conditions of use. For example, a common cause of a harmful disconnection of a conventional power supply is that the fuse’s nominal heat of fusion is not adequately considered, and it must also meet the fuse requirements imposed by the surge current generated by the power supply smoothed input capacitor. If the fuse is to work safely and reliably, then the fuse’s melting heat should be no more than 20% of the fuse’s nominal heat of fusion.
Nominal melting heat: refers to the energy required to melt the dissolved part, expressed in i2t, read as “ampere square seconds.”
Generally, in the authoritative certification body, the melting heat test is performed: a current increment is applied to the fuse and the time at which the melting occurs is measured. If the melting does not occur in about 0.008 seconds or longer, the intensity of the pulse current is increased.
The experiment was repeated until the fuse had a fuse time of less than 0.008 seconds. The purpose of this test is to ensure that the heat generated does not have enough time to run away from the fuse components by heat transfer, that is, all of the heat is used to blow the fuse. Therefore, when selecting a fuse, in addition to considering the normal operating current, reducing the rated value, and the ambient temperature, the i2t value should also be considered. Also note that since most fuses have solder joints, special care must be taken when soldering these fuses. Because the excessive heat of the solder causes the solder in the fuse to reflow and change its rating. The fuse is similar to a semiconductor thermal sensor, so it is best to use a heat sink when soldering the fuse.
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Post time: Feb-13-2019