If divided by voltage level, there are high-voltage fuses and low-voltage fuses
According to installation conditions, there are indoor and outdoor,
According to appearance , including spiral type, drop-out type, etc.
The main materials are insulating materials, usually ceramics, paper tubes (for drop-out fuses),
Conductive materials, usually copper
The melt material includes copper wire or lead-antimony alloy
The following is an introduction to fuses, not original,
Basic knowledge of fuses
What is a fuse and what is its function?
The fuse is also called a fuse, and the IEC127 standard defines it as a "fuse-link". It is an electrical component installed in a circuit to ensure the safe operation of the circuit. The function of the fuse is: when a fault or abnormality occurs in the circuit, the current will continue to increase
and the increased current may damage some important devices or valuables in the circuit
< p> parts may also burn out the circuit or even cause a fire. If the fuse is correctly placed in the circuit,then the fuse will
itself blow and cut off the current when the current abnormally rises to a certain height and at a certain time, thereby playing a role in Protect the safe operation of the circuit.
The earliest fuse was invented by Edison more than a hundred years ago. Due to the underdeveloped industrial technology at that time, incandescent lamps were very expensive, so they were originally used to protect the expensive ones. incandescent lamp.
How does a fuse work?
We all know that when current flows through a conductor, because the conductor has a certain resistance,
the conductor will generate heat. And the heat generation follows this formula: Q=0.24I2RT; where Q is the heat generation, 0.24 is a constant, I is the current flowing through the conductor, R is the resistance of the conductor, T
It is the time for the current to flow through the conductor; according to this formula, it is not difficult to see the simple working principle of the fuse
. Once the material and shape of the fuse are determined, its resistance R is relatively determined (if its temperature coefficient of resistance is not considered). When electric current flows through it, it generates heat, and the amount of heat it generates increases over time. The size of the current and resistance determines the rate of heat generation. The structure of the fuse and its installation condition determine the rate of heat dissipation. If the rate of heat generation is less than the heat consumption, The fuse will not blow when the dissipation speed is high. If the rate of
heat generation is equal to the rate of heat dissipation, it will not melt
for a long time. If the rate of heat generation is greater than the rate of heat dissipation, then more and more heat will be generated. And because it has a certain specific heat and mass, the increase in heat is reflected in the increase in temperature. When the temperature rises above the melting point of the fuse, the fuse will blow.
This is how a fuse works. From this principle, it should be known that when designing and manufacturing fuses, the physical properties of the selected materials must be carefully studied and ensure that they have consistent geometric dimensions. Because these factors play a crucial role in whether the fuse can work properly. Likewise,
When you use it, be sure to install it correctly.
How are fuses constructed? What are the functions of each? What else are you asking for?
Generally, fuses are composed of three parts: one is the melt part, which is the core of the fuse.
It plays the role of cutting off the current when fusing. The fuses of the same type and specification The melt, material
should be the same, the geometric dimensions should be the same, the resistance value should be as small as possible and consistent, and the most important thing is
the fusing characteristics should be consistent; the second is the electrode part, There are usually two. It is an important component for connecting the melt and the circuit. It must have good conductivity and should not produce obvious installation contact resistance;
The third is the bracket Parts, the melt of the fuse is generally slender and soft. The function of the bracket is to fix the melt and make the three parts into a rigid whole for easy installation and use. It must have good quality
< p>Good mechanical strength, insulation, heat resistance and flame retardancy, and should not cause breakage, deformation, burning and short circuit during use; used in power circuits and high-power equipment Fuse,not only has three parts of a general fuse, but also an arc extinguishing device, because the circuit protected by this type of fuse
not only has a large working current, but also has a high current when melting When a fuse occurs, the voltage at both ends is also very high. The melt often melts (fuses) or even vaporizes, but the current is not cut off. The reason is that At the moment of fusing, under the action of voltage and current, an arcing phenomenon occurs between the two electrodes of the fuse. This arc extinguishing device must have strong insulation and
good thermal conductivity, and be electronegative. Quartz sand is a commonly used arc extinguishing material.
In addition, some fuses have a blow indicator device. Its function is to change the appearance of the fuse
after it operates (blows), which is easy to be discovered by maintenance personnel.
For example: glowing, changing color, pop-up solid indicator, etc.
What types of fuses are there?
According to the protection form, it can be divided into: overcurrent protection and overheating protection. The fuse used for overcurrent protection is the usual fuse (also called a current-limiting fuse). Fuses used for overheating protection are generally called "thermal fuses". Thermal fuses are divided into low melting point alloy
type, temperature sensitive trigger type, memory alloy type, etc. Thermal fuses are used to protect heating appliances or
heat-prone appliances from being overheated, such as: hair dryers, electric irons, rice cookers,
electric stoves, transformers, motors, etc. etc.; it responds to the rise in temperature of electrical appliances and does not care about the operating current of the circuit. Its working principle is different from that of "current limiting fuse".
According to the scope of use, it can be divided into: power fuses, machine tool fuses, electrical instrument fuses
Fuses (electronic fuses), automobile fuses.
According to volume, it can be divided into: large, medium, small and micro.
According to the rated voltage, it can be divided into: high-voltage fuses, low-voltage fuses and safety voltage fuses
Fuses.
According to the breaking capacity, it can be divided into: high and low breaking capacity fuses.
According to shape, they can be divided into: flat-head tubular fuses (which can also be divided into internal-welded fuses and external-welded fuses), pointed tubular fuses, guillotine-type fuses, and spiral-type fuses. Fuses, blade fuses, flat fuses, wrapped fuses, chip fuses.
According to the fusing speed, it can be divided into: extra slow fuse (generally represented by TT), slow
fuse (generally represented by T), medium speed fuse (generally used M represents), fast fuse (generally represented by F), extra fast fuse (generally represented by FF).
According to standards, they can be divided into: European fuses (VDE), American fuses (UL), and Japanese
Fuses (PSE).
What is a slow fuse?
Slow fuses are also called time-delay fuses. Its delay characteristics are reflected in the fact that the circuit remains intact when there is a non-fault pulse current
and can provide protection against long-term overloads. In some circuits, the current at the moment of opening and closing is several times greater than the normal operating current. Although the peak value of this current is very high, it appears for a very short time. We call it a pulse. Electric current is also called impact current or surge current. Ordinary fuses cannot withstand this kind of current. If you use an ordinary fuse in such a circuit, you may not be able to start it normally. If you use a larger fuse, you may not be able to start it normally. , then there is no protection when the circuit is overloaded. The melt of the time-delay fuse is specially processed.
It has the function of absorbing energy. Adjusting the amount of energy absorption can make it not only resistant to
impulse current but also resistant to impact. Provides protection against overload. Standards have regulations on delay characteristics. If the characteristics specified in the standard cannot meet the requirements, you can contact the manufacturer for a solution.
Is the rated current of the fuse the current that causes the fuse to blow?
No. It should only be regarded as a nominal specification, and the current flowing through the fuse
How large it is and when it blows are detailed in the fuse product standards. < /p>
The regulations vary depending on the standards. The fuse has a "fuse coefficient" whose value is greater than "1" (generally between 1.1 and 1.5). It is a combination of "regular non-fuse current" and "rating" current" ratio. It can be seen from this that even if the current flowing through the fuse is greater than its rated current but does not exceed the conventional non-fuse current, the fuse should not blow.
How to understand the rated voltage of the fuse?
Whether the fuse blows or not depends on the current flowing through it, and has nothing to do with the operating voltage of the circuit
The rated voltage of the fuse is proposed from the perspective of safe use of the fuse. It is the highest working voltage of the circuit where the fuse is placed in a safe working condition. This shows that the fuse can only be placed in a circuit whose operating voltage is less than or equal to the rated voltage of the fuse. Only in this way can the fuse
work safely and effectively. Otherwise, when the fuse blows, there will be continuous arcing and
voltage breakdown, which will endanger the circuit.
What does the voltage drop across the fuse indicate?
The voltage drop of the fuse is the voltage drop across the fuse under rated current conditions.
It reflects the internal resistance of the fuse, and its value should not be too large. If a
fuse with too large internal resistance (voltage drop) is installed in the circuit, it will affect the system parameters of the circuit and cause the circuit to not work properly
. The standard not only stipulates the upper limit of the voltage drop value, but also stipulates its consistency.
What is the significance of studying the temperature rise of fuses?
The temperature rise of the fuse refers to the temperature rise value of the fuse when 1.1 times (110%) of the rated current flows through the fuse.
The temperature rise of the fuse is the measured temperature minus the ambient temperature. . The UL standard sets the upper limit at 75°C. Because the melt of the fuse is relatively sensitive to temperature, its melting point and impedance will change under the influence of a certain high temperature
for a long time, and this change will affect the fuse
Fuse accuracy. This is commonly referred to as fuse aging. Aging fuses are very dangerous when used in electrical circuits. Therefore, when making and using fuses, we should pay attention to the temperature rise of the fuses. In the same way, we should also note that even if the fuse has not been blown after a long period of use, it may have aged, and it is best to replace it at this time.
What does the breaking capacity of a fuse mean?
When a current between the conventional non-fuse current and the rated breaking capacity (current) specified in relevant standards is applied to the fuse, the fuse should be able to operate satisfactorily. And it won't
endanger the surrounding environment. The expected fault current of the circuit where the fuse is placed must be less than the rated breaking capacity current specified in the standard. Otherwise, when a fault occurs and the fuse blows, continuous arcing and ignition will occur. , the fuse is burned out, the contacts are melted together, the fuse mark cannot be read
and so on. Of course, the breaking capacity of inferior fuses cannot meet the requirements of the standards, and the above hazards will also occur when used.
Selection of fuses
In order to facilitate users to select appropriate fuse tubes for the components, circuits or equipment that need to be protected,
this guide is specially formulated. The selection of fuse tubes can be based on the following process:
Factors need to be considered to determine the safety certification of the fuse tube based on the safety certification required for the complete machine. Here
the fuse tube can be initially determined to be IEC specifications or UL specifications.
1. Space limitations in the circuit during design.
2. Installation method.
The rated voltage should be greater than or equal to the effective circuit voltage, and the breaking capacity should be greater than the
maximum fault current in the circuit. Check whether there is starting current in the circuit when the whole machine is switched on and off. The starting current is normal in some circuits. In this case, delay type and medium delay type fuse tubes should be used.
The current and duration that the fuse tube must cut off (these conditions are determined by the designer based on the specific
protection needs of the circuit). Refer to the I-T curve of the corresponding model and take the maximum rated current that meets the requirements as the upper limit value A1.
1. Stable current through the fuse tube (depending on the specific circuit).
2. For details on the difference in rated current of fuses based on IEC specifications and UL specifications, see "Stabilizing Current".
3. For details on the impact of ambient temperature on the load-bearing capacity of the fuse tube, see "Ambient Temperature".
4. For the impact of pulses (impulse current, surge current, starting current and current transient value) on the life of the fuse
tube, see "Pulse" for details.
5. Compare the starting current and duration with the I-T curve of the corresponding model.
After comprehensively considering the above five factors, select the minimum rated current that meets the requirements as the lower limit
A2.
After comprehensively considering the above factors, select the most suitable model and rated current.
When A1>A2, select the corresponding model fuse tube with rated current A2.
When A1≤A2, select the corresponding model fuse tube with rated current A1.
The sample should be tested in the actual circuit
Fuse selection process:
Start→Safety certification→Shape and size→Rated voltage→Breaking capacity→Preliminary selection< /p>
Model → Determine the upper limit of rated current A1 → Determine the lower limit of rated current A2 → Specific model and
Current → Test → End.
Steady-state current
There are different conditions between practical applications and laboratories, such as:
A. Sometimes a fuse box is used;
B. Cross-sectional area of ??wires in the circuit;
C. Contact resistance of fuse clamp, etc.
Considering the above factors, the fuse tube selected under 25℃ should meet the following conditions
to ensure that the fuse tube continues to work reliably:
< p>IEC specification: Rated current of fuse tube In=steady-state current/0.9UL specification: Rated current of fuse tube In=steady-state current/0.75
Ambient temperature
p>The current carrying capacity test of the fuse tube is carried out at an ambient temperature of 25°C.
The current carrying capacity of the fuse tube is affected by the ambient temperature. The higher the ambient temperature, the lower the fuse capacity.
The shorter the life of the fuse tube, the lower the load-bearing capacity. Therefore, when selecting a fuse tube, the ambient temperature around the fuse tube should be considered. The impact of ambient temperature on the carrying capacity of various fuse tubes is as shown in the figure below:
(II) Indicates the effect of ambient temperature on the load carrying capacity and 5In fusing time of fast-acting and wire-wound fuse tubes
Pulse
The pulse creates thermal cycling, which produces mechanical fatigue that affects fuse tube life.
The design should make the pulse I2T much smaller than the nominal melting heat energy I2T of the fuse tube. The relationship between the fuse tube life (the number of pulse cycles that can be tolerated) and U (U = the ratio of the pulse I2T value to the fuse tube I2T value) is shown in Table 1. The melting heat energy I2T of fuse tubes of various specifications provided in this catalog are for reference. Table 2 provides the approximate calculation formula of the I2T value of various typical pulse waveforms:
Can withstand pulses Number of times U (ratio)
100,000 times 20%
10,000 times 30%
1,000 times 40%
Note: Pulse interval time It must be long enough to allow the heat generated by the previous pulse to dissipate.
Common knowledge about resettable fuses
What is the working principle of polymer resettable fuses?
Polymer resettable fuses are composed of a polymer matrix and carbon black particles that make it conductive. Since the polymer resettable fuse is a conductor, current will flow through it. When an overcurrent passes through a polymer
resettable fuse, the heat generated (which is I2R) will cause it to expand. As a result, the carbon black particles will
separate and the resistance of the polymer resettable fuse will increase. This will cause the polymer resettable fuse to generate heat faster and expand more, further increasing the resistance. When the temperature reaches 125°C
the resistance changes significantly, causing the current to decrease significantly. At this time, the small current flowing through the polymer resettable wire is enough to keep it at this temperature and in a high resistance state. When the fault is cleared
the polymer resettable fuse shrinks to its original shape and reconnects the carbon black particles,
thus reducing the resistance to a level with a specified holding current. The above process can be cycled multiple times
.
What is the difference between Rmin, Rmax and R1max?
Rmin is the minimum resistance specified for the polymer resettable fuse provided by ANDU Company. This resistance determines the lowest operating current of the polymer resettable fuse. Rmax is the maximum specified resistance of the polymer resettable fuse provided by ANDU Company
. R1max is the maximum resistance that the polymer resettable fuse should reach after it is activated. Its resistance determines the maximum holding current of the polymer resettable fuse. When the polymer resettable fuse operates, the resistance of the resistor provided by ANDU (greater than or equal to Rmin and less than or equal to Rmax) will rise to less than or equal to R1max.
How much voltage drop will there be on a polymer resettable fuse?
This depends on the specific circuit. Generally speaking, if the resistance and equilibrium current are known, the voltage drop can be calculated.
For polymer resettable fuses, the maximum voltage drop is calculated using the resistance value
R1max; the typical voltage drop can be calculated using the resistance value Rmax or, if Rmax is not provided
Rmin and The average value of R1max. If Iop is the normal operating current and Rps is the resistance of the polymer resettable fuse (R1max, (Rmax or (Rmin + R1max)
/2)), then the polymerization in the circuit The voltage drop on a physical resettable fuse is: Vdrop = Iop x Rps
Can polymer resettable fuses be connected in series?
This has no practical significance. Because there is always one that will act first, and the others will not protect the circuit.
How to calculate the resistance of a polymer resettable fuse in the operating state?
The resistance of the polymer resettable fuse in the operating state depends on the specific type and the voltage
and power on it. The following formula can be used to calculate: Rt = V2/Pd?
How many times can the polymer resettable fuse operate under the maximum voltage and inrush current?
Each polymer resettable fuse has a specific operating voltage and can withstand a specific surge current
Current. UL stipulates that polymer resettable fuses must still exhibit the PTC effect after 6,000 operations. For SN/SF polymer resettable fuses used in communication equipment, it is stipulated that under the maximum voltage, its various performance parameters will still be within the original range after at least a dozen or up to hundreds of operations.
Within. Designers should realize this: Polymer resettable fuses are used for protection, not for situations where their constant movement is regarded as normal working conditions.
How quickly can a polymer resettable fuse be restored after operation?
The time it takes for a polymer resettable fuse to return to its low resistance state after action is affected by the following factors:
The type of polymer resettable fuse; how it is mounted or fixed; Ambient temperature;
The internal cause and duration of the action. Generally speaking, most polymer resettable fuses will reset within a few minutes, although many will reset within a few seconds.
How long can a polymer resettable fuse stay in the operating state without being damaged?
UL stipulates that polymer resettable fuses must stay at the maximum voltage for 1000 hours without losing their PTC characteristics.
Organization: Electronic Standard Network/
Its PTC characteristics. The longer the polymer resettable fuse is in the operating state, the more likely it is that its resistance value will not be restored and therefore may not meet its original definition. The amount of time each polymer can remain in a resettable fuse varies with the event and type of failure.
Can polymer resettable fuses be classified according to resistance value?
Some of our polymer resettable fuses are classified according to resistance value and then provided to users.
Polymer resettable fuses mainly used in the communication field, such as SF250, SD250 and
SF600.
What are the implications of encapsulating polymer resettable fuses?
Generally speaking, although some users have successfully encapsulated polymer resettable fuses,
it is not recommended. When packaging, you must pay attention to the selection of materials and the method of bending the packaging. If
the encapsulation material is too hard it will not allow the polymer resettable fuse to expand as designed, thus
making it unable to work as designed. Even if the packaging material is soft, the heat transfer characteristics of the polymer resettable fuse will be affected, causing the polymer resettable fuse to behave differently from the design requirements.
What is the effect of pressure on polymer resettable fuses?
Pressure affects the electrical properties of polymer resettable fuses.
If the pressure during operation is too high
restricting the expansion of the polymer resettable fuse, the polymer resettable fuse will not operate as specified
.
How to determine the type of polymer resettable fuse based on the appearance of a sample?
Most polymer resettable fuses will be printed with a trademark logo and model number. Various standard polymer resettable fuse product models are listed in the product data sheet.
What is the maximum ambient temperature for polymer resettable fuses to operate?
The polymer resettable fuse in working condition depends on the product type. For most of our
products this range is up to 85°C, some up to 125°C (e.g. SN/SF),
also as low as 70°C of (LP-CW). Polymer resettable fuses in the non-operating state
Some are able to withstand shorter reflow temperatures (LP-SM, LP-MSM, SD).
Can polymer resettable fuses reset themselves? How to recover? How fast?
Yes, once the fault event has been cleared and the polymer resettable fuse has had a chance to cool, it will
reset. Cooling causes the carbon black particles to contact and reconnect, reducing resistance. Typically, the method for cooling a polymer resettable fuse is to cut off the energy supply to the device being protected, cutting off the overcurrent and allowing the polymer resettable fuse to cool. Polymer resettable fuses should be distinguished from bimetallic devices that are also resettable. Even if the fault event is not cleared, a typical bimetallic device will reset itself, switching between the fault event and a protected state that may damage the device. Polymer resettable fuses remain in a high resistance state until the fault event is cleared. The time it takes for a polymer resettable fuse to reset to a low-resistance state depends on a large number of factors: type of polymer resettable fuse; how it is mounted or fixed; ambient temperature; action
Internal causes and duration. Generally speaking, most polymer resettable fuses will reset within a few minutes, although many will reset within a few seconds.
p>
Can polymer resettable fuses undergo state transitions? How can I keep the state unchanged?
When the fault event is not eliminated, the polymer resettable fuse will not
transition between the normal and operating states. When the polymer resettable fuse operates, its resistance changes from low to high. In the high resistance state, a trace amount of fault current still exists. This small fault current is enough to keep it in a high resistance state. When the fault is cleared, the polymer resettable fuse can be cooled back to its low resistance state.
What is the difference between IH and IT? Why is it different?
IH is the highest current that does not trigger resistance jump in still air (the temperature can range from
20°C to 25°C depending on the product), that is, the highest working temperature at room temperature. current. IT is the minimum current when the polymer resettable fuse operates in still air (the temperature can range from 20°C to
25°C depending on the product), that is, at room temperature Minimum fault current. For most of our products, the ratio of IT to IH is 2:1, but for some products it can be as low as 1.7:1, and for others it can be higher
Up to 3:1. Differences in materials and production methods as well as changes in resistance after action will determine this
ratio.
Under what circumstances does a polymer resettable fuse reset?
Polymer resettable fuse reset is a function of current, voltage and temperature.
Polymer resettable fuses often begin to reset when the temperature drops below 90°C (so to speak, below 80°C).
Polymer resettable fuses have (self-resetting)
What is the difference between polymer resettable fuses and ordinary fuses and other circuit protection devices
? How do polymer resettable fuses protect circuits together with overvoltage-bearing devices?
The most obvious difference between polymer resettable fuses and ordinary fuses is their resettable characteristics.
Although both can provide overcurrent protection, polymer resettable fuses can provide overcurrent protection many times
While regular fuses, once they blow, must be replaced for the circuit to function properly. . The performance of polymer resettable fuses is somewhat similar to time delay fuses. Both need to take their own heat dissipation into consideration, but polymer resettable fuses are not like time delay fuses. Dissipate heat according to I2t
because the polymer resettable fuse does not work initially. The difference between a polymer resettable fuse and a bimetallic fuse is not in its resettability. The bimetallic fuse can reset itself when the fault
still exists. When it operates, it generates a large voltage and may damage the equipment.
Reconnect. Polymer resettable fuses remain in a high resistance state until the fault is eliminated
. The difference between polymer resettable fuses and ceramic resettable fuses is their initial resistance,
reaction time to faults and size. Both are resettable, but compared with ceramic resettable fuses with the same holding current, polymer resettable fuses operate more efficiently due to their smaller size. quick. Polymer resettable fuses are commonly used in the communications field when used in combination with overvoltage-bearing devices. For many fault events, overvoltage-carrying devices such as thyristors, gas discharge tubes or diodes can provide protection. Polymer resettable fuses can protect these overvoltage protection devices in certain fault events, and of course polymer resettable fuses can also provide overcurrent protection.
Polymer resettable fuses expand when they operate. Will they return to their original state when they reset?
The polymer resettable fuse in the activated state will expand and return to its original
size and shape after cooling and reset. Although its resistance value will not return to its original value, it will return to a value that conforms to its definition.
What is the maximum temperature that a polymer resettable fuse can reach?
The maximum surface temperature of polymer resettable fuses can reach 150°C, but the typical surface temperature is
110°C.
The selection of fuses involves the following factors :
1. Normal operating current.
2. The external voltage applied to the fuse.
3. Abnormal current requiring the fuse to be opened.
4. The minimum and maximum time allowed for abnormal current to exist.
5. Ambient temperature of the fuse.
6. Pulse, impact current, surge current, starting current and circuit transient value.
7. Are there any special requirements beyond the fuse specifications?
8. Dimensional limitations of the installation structure.
9. Required certification body.
10. Fuse holder: fuse clip, installation box, panel installation, etc.
The following explains some common parameters and terminology in fuse selection.
Normal operating current: When operating at 25°C, the current rating of the fuse is usually reduced by
25% to avoid harmful blowing. Most conventional fuses are made of materials with relatively low melting temperatures. Therefore, this type of fuse is sensitive to changes in ambient temperature. For example
A fuse with a current rating of 10A generally cannot operate at a current greater than
7.5A at an ambient temperature of 25°C.
Voltage Rating: The voltage rating of the fuse must be equal to or greater than the effective circuit voltage
Voltage.
The general standard voltage rating series are 32V, 125V, 250V, and 600V.
Resistance: The resistance of the fuse is not very important in the overall circuit. But for fuses with an amperage less than 1, the resistance will be several ohms, so this issue should be considered when using fuses in low-voltage circuits. Most fuses are made of positive temperature coefficient materials, so they are also divided into cold resistance and hot resistance.
Ambient temperature: the current carrying capacity of the fuse. The experiment was conducted at an ambient temperature of 25°C.
This experiment is affected by changes in ambient temperature. The higher the ambient temperature, the higher the working temperature of the fuse, the lower the current carrying capacity of the fuse, and the shorter the life span. Conversely, allowing at lower temperatures will extend the life of the fuse.
Rated fuse capacity: also called breaking capacity. The rated breaking capacity is the maximum allowable current that the fuse can reliably blow under the rated voltage. During a short circuit, an instantaneous overload current greater than the normal operating current will pass through the fuse multiple times. Safe operation requires the fuse to remain intact (not bursting or breaking).
Fuse performance: Fuse performance refers to how quickly the fuse reacts
to various current loads. Fuses are often divided into four types according to their performance: normal response, delayed opening, fast action and current limitation.
Harmful circuit breaks: often caused by incomplete analysis of the designed circuit. Of all the factors involved in fuse selection listed above, special attention must be paid to normal operating current, ambient temperature, and overload. When using, you cannot select a fuse based only on the normal operating current and ambient temperature. You must also pay attention to other usage conditions. For example, a common cause of harmful open circuits in conventional power supplies is failure to adequately consider the nominal melting heat energy rating of the fuse, which must also meet the input capacitor smoothing filtered by the power supply. The demand placed on the fuse by the generated surge current
current. If you want a fuse to work safely and reliably, you should choose a fuse whose melting heat energy is not greater than 20% of the nominal melting heat energy rating of the fuse.
Nominal melting heat energy: refers to the energy required to melt and break components, expressed in I2 t, read
as "ampere square seconds". Generally, in authoritative certification agencies, a melting heat energy test is performed:
Apply a current increment to the fuse and measure the time for melting to occur. If it is about 0.008
seconds or longer If melting does not occur within a certain period of time, increase the intensity of the pulse current. Repeat the experiment until the fuse blowing time is within 0.008 seconds. The purpose of this test is to ensure that
the heat energy generated does not have enough time to escape from the fuse component through thermal conduction, that is,
that all the heat energy is used to blow the fuse.
Therefore, when selecting a fuse, in addition to considering the normal operating current, reduction
rating value, and ambient temperature mentioned above, the I2 t value must also be considered. Also note: Since most
fuses have solder joints, be especially careful when soldering these fuses. Because soldering
excessive heat can reflow the solder in the fuse and change its rating. Fuses are similar to
heat-sensitive components of semiconductors, so it is best to use a heat absorber when soldering fuses.
If you feel dissatisfied, you can check the electrician’s manual