Key points of fuse selection
I believe we all have a headache in choosing fuses because there is no good guidance,
The following is a list of the factors involved in fuse selection,
You can choose the most suitable fuse according to these ideas.
1. Normal working current: the reliable working current of fuse is usually 75% of rated current at 25C to avoid failure. For example: in 25C environment, it is not recommended to use fuse with rated current of 10a to work above 7.5A.
2. Application voltage (AC or DC): the rated voltage of the fuse must be equal to or greater than the voltage of the applied circuit.
3. Ambient temperature: the higher the ambient temperature, the hotter the fuse works and the shorter the service life. On the contrary, working at a lower temperature will prolong the service life of the fuse. The fuse is also hotter when the normal operating current approaches or exceeds its rated value.
4. Overload current: it defines the current that the circuit needs to be protected in case of a fault. The fault condition can be current or current and the maximum fault time that can be sustained before damage occurs. In the matching of fuses and circuits, the time current curve should be considered, but remember that the curve is based on average data.
5. Maximum fault current: the fuse rating must meet or exceed the maximum fault current of the circuit.
6. Pulse (current mutation, surge current, start-up current and circuit transients): electrical pulse conditions may vary greatly in different applications. Different fuse configurations may not respond the same to a given pulse condition. Thermal cycling and possible mechanical fatigue caused by electrical pulses can affect the service life of fuses. The initial pulse or starting pulse is normal for some applications where the fuse is to be selected with a thermal delay design to maintain the normal start pulse and still provide protection in the event of prolonged overload. We should refer to and compare the time current curve and i2t rating of the fuse for the selection of the fuse which should respond to the starting pulse.
7. Physical size limits: refer to the manufacturer's data book for fuse length, diameter and height information.
8. Agency approval required: refer to the manufacturer's data book for information on Agency approval for a specific device, such as UL, CSA, VDE, METI, or MITI. Military requirements need special consideration.
9. Fuse characteristics: refer to the manufacturer's data book for installation type / overall dimensions, ease of disassembly, axial leads, visual indications, etc.
10. Fuse holder characteristics and reassessment: refer to the manufacturer's data book for information on clips, mounting blocks, panel mounting, PCB mounting, RFI shielding, etc.
11. Pre production application testing and validation: verify the selection by requesting samples to be tested in the actual circuit. Before evaluating the sample, make sure that the fuse has a good electrical connection and that the cable connection used is appropriate. The test shall include a life test under normal conditions and an overload test under fault conditions to ensure that the fuse works properly in the circuit. The above are the key points of fuse selection,
There are many kinds of fuses, such as protection type, application range, volume, rated voltage, breaking capacity and fusing speed,
The following is an introduction to the classification according to the type: current fuse: patch fuse, micro fuse, plug-in fuse, tubular fuse; temperature fuse: RH square type, RP resistance type, ry metal shell; self recovery fuse: plug-in, lamination, patch.
1、 Current fuse.
1. SMD fuse. There are 0805, 1206 and other specifications. Thin film technology is used to accurately control electrical characteristics. Due to its small size, it is more suitable for circuits in space limited applications to provide secondary protection, such as portable electronic devices and various instruments.
2. Tubular fuse. This is very common, especially in switching power supply and other power supply applications.
3. Insert fuse. It can be seen in automobile use occasion, sometimes also called fork bolt fuse
4. Miniature fuse.
2、 Temperature fuse.
Temperature fuse, also called thermal fuse (GB 9816.1-2013), is a temperature sensing circuit cut-off device. The temperature fuse can sense the overheat caused by abnormal operation of electrical and electronic products, and cut off the circuit to avoid the occurrence of fire. It is an irrecoverable disposable thermal protection device, including RH, RF, ry series, etc. the product has exquisite appearance structure, good sealing performance, sensitive and reliable operating temperature, small impact of current impact and vibration resistance. It is mainly used in electric fans, electric cookers, electric frying pans, disinfection cabinets, etc.
1. RH square temperature fuse. The appearance is a plastic square shell shape, block type temperature fuse, generally low melting point alloy type
2. Ry metal case temperature fuse. It adopts metal shell and organic chemical material as heat sensing body. It has sensitive induction, accurate action and reliable performance. For rice cooker, hair dryer, motor, etc
3. RP resistance type temperature fuse, generally low melting point alloy type
3、 Self recovery fuse.
This is a kind of fuse which can recover automatically when the current is too high. It belongs to multiple use type and is suitable for overload protection circuit.
1. Plug in self recovery fuse
2. SMD self recovery fuse
3. Laminated self recovery fuse
The use of electric heating system is more and more families, how to save energy has become a concern of many people, in addition to do a good job in building insulation, temperature control is one of the key to energy saving. Some users who have installed electric heating always turn on the thermostat when they need it and turn it off when they go out, thinking that this will save electricity. In fact, it will not only save energy but also consume more energy. So how to use the thermostat to achieve real energy saving? Now let's make up of Longde electric appliance to take you to study.
1. Meeting energy saving?
Turn on the thermostat when necessary and turn it off when going out, which will consume energy. The electric heating system is a low-temperature operation system with good heat storage type. It takes a certain time to make the room temperature reach the set temperature after the system is turned on. However, the indoor temperature will not drop rapidly after the system is closed. When the system is turned on again, it also takes a long time to make the temperature rise again. Frequent switching not only can not save energy, but also increase the operating cost of heating system.
In a room that is not commonly used, the temperature can be lowered by a few degrees by the temperature controller. When leaving the room for a long time, the temperature of the temperature controller can be reduced by a few degrees. In the case of long-term absence of people or leaving for a long time, the system can be turned off. However, it should be noted that if there is equipment in the room that is afraid of freezing damage, it is also necessary to open it to a certain temperature to prevent the equipment or pipeline from freezing and cracking.
2. Temperature controller set high temperature, fast temperature rise?
Some users feel that the room temperature is low and they need to heat up quickly to set the temperature of the thermostat to the highest. This practice is also wrong. The heating time of room temperature depends on the indoor and outdoor temperature difference and the installed power per unit area of the room. When the installation power and the indoor and outdoor temperature difference are fixed, no matter how many degrees are set, the time for the room to rise to the temperature you need is the same. If the room is now 16 degrees and you want to make the room temperature rise to 18 degrees, in this case, setting the room temperature to 18 degrees or 20 degrees, 25 degrees is the same as heating to 18 degrees.
Set as many degrees as you need, or use an intelligent thermostat, which can automatically calculate the opening time of the thermostat in advance.
The control methods are generally divided into two types: one is controlled by the temperature change of the object to be cooled, and the other is controlled by the temperature difference of the object to be cooled, and the electronic temperature controller is used. The thermostat is divided into:
Mechanical type is divided into: steam pressure type temperature controller, liquid expansion type temperature controller, gas adsorption type temperature controller, metal expansion type temperature controller.
Among them, the steam pressure type temperature controller can be divided into: inflatable type, liquid gas mixing type and liquid filling type. This kind of thermostat is mainly used in mechanical type of household air conditioner.
Electronic type is divided into resistance type temperature controller and thermocouple type temperature controller.
Many friends are very interested in what kind of temperature control switch is used to sense temperature! Since it is a jump type temperature control switch, it must have its own temperature sensing system. If there is no good temperature sensing system, there is no way to predict the temperature, which comes from the ground breaking or contact. The principle of the temperature controller is very simple. It is composed of bimetallic pieces. When the temperature reaches a certain height, it will be disconnected or contacted freely. This is also the most basic temperature sensing setting of the temperature control switch. Temperature setting is also the most important point in the whole process. No matter what kind of electric heating equipment is, it needs good temperature sensing. If it can not be well sensed, it indicates that it is a quality problem, which will have a great impact on our normal use.