In the design of automotive electrical systems, people often only pay attention to the design of various electrical functions, and ignore the protection of electrical appliances. For the protection of electrical appliances in automobiles, fuses are generally used. The fuse is actually a fuse that we are all familiar with. Let's take a more in-depth understanding and research on automotive fuses in the form of question and answer.
Q: What is a car fuse?
Answer: The fuse is also called a fuse or fuse box. It is called an automobile fuse for automobiles. It is generally composed of two parts: 1. The seat that fixes the fuse tube or fuse has a lead wire or a connecting wire Used bolts. 2. Fuse or fuse tube or fuse is also called melt.
Question: What form of melt is often used in automotive fuses?
Answer: The rated fuse current is below 50A. The old-fashioned design mostly uses the fuse tube type, most of which is a glass tube type. The two ends are metal sleeves, with copper wires or tinned copper wires in the middle. Commonly used sizes are Φ6 & TImes; 30, Φ5 & TImes; 20, etc., and most of the rated currents above 50A are flat.
At present, there are mainly insert type and flat type.
1. Plug-in type: the melt structure made of metal is embedded in the protection body of engineering plastics (commonly used PC). The melt is generally made of Zn or Cu, with 2 pins, and it can be connected to the circuit after insertion. Type fuse can be divided into Japanese type, European type, Eastern European type, American (national) type, and Japanese type commonly used in China according to the size of the size. The general rated working current of the insert type is 2A-40A.
2. Flat type: composed of base, upper cover and fuse. The base is usually pressed with phenolic resin (bakelite), and the upper cover is usually made of transparent PC. Those with rated current less than 80A can also be made with ABS. Fuses are generally made of Zn or Cu. Advanced fuses are made of Cu plated gold to reduce contact resistance and prevent oxidation, and a protective body made of thick bakelite or ceramics is added to the work area.
Flat-plate rated working current is generally 10A-500A.
Q: What is the color mark of the rated operating current of the plug-in fuse?
Answer: The working current specifications of the top of the protective fuse of the plug-in type fuse, and the overall color signs are as follows: 2A gray, 3A purple, 4A pink, 5A orange, 7.5A coffee, 10A red, 15A blue, 20A yellow, 25A Colorless and transparent, 30A green and 40A deep orange are different depending on the manufacturer. May be adjusted slightly.
Q: What is the role of the fuse insert with cue light? working principle?
Answer: The fuse insert with indicator light is a new product that has appeared in recent years. Its function is that the indicator light does not light when the fuse insert is not blown. After the fuse, the indicator light is lit for easy maintenance and replacement.
The principle is as follows: a special small electric ball is connected in parallel between the two sections of the fuse insert. When the fuse insert works normally, that is, when the fuse is not blown, it is equivalent to the short circuit current of the electric bead passing through the melt. The small electric bead will not have a current through and will not light. When the melt is blown, the small electric bead is connected in series with the load. When a small current flows through a small electric bead, the load will light.
There is also a kind of light-emitting diode instead of small electric beads. When inserting the insert, pay attention to the polarity cannot be reversed, because the light-emitting diode has polarity.
Question: What is the relationship between the rated operating current of an automobile fuse and the actual fusing current?
Answer: The load characteristics of car fuses are generally electric salty box resistive, circuit breakers, motors (including wipers, electric doors and windows, electric seats, starter motors, etc.) are electric salty load car lamps with filaments, heating The device is a resistive load. The starting characteristics of the above 2 types of loads are: the starting instantaneous current is 3-10 times the rated working current, so the requirements for automotive fuses can withstand short-term (generally several milliseconds) inrush current Not to blow. In addition, we know that the voltage generated by the car generator is high when the engine speed is high, and the voltage is low when the engine speed is low. Although there is a voltage adjustment port, the voltage emitted by the highest speed box at the lowest speed will differ by 20%. According to the international QC / T420-1999 "Automobile Fuse" stipulates that the continuous load-bearing performance of the chip fuse is that when the load current is 110% of the rated current, it should be able to carry continuously for not less than 100 hours.
a. When the load current is 135% of the rated current, the fusing time should be no less than 0.75 seconds and no more than 30 minutes
b. When the load current is 200% of the rated current, the fusing time should be no less than 0.15 seconds and no more than 5 seconds.
c. When the load current is 350% of the rated current, the fusing time is not less than 0.08 seconds.
The load performance of the flat panel fuse and the wire fuse is: continuous load for 4 hours, and the fuse performance: when the load current is 200% of the rated current, the fusing time should not exceed 30 seconds.
It can be seen from this that many people think that when the load current exceeds the fusing rated current, the concept that the car fuse blows immediately is wrong.
Q: How to choose the rated working current of an automobile fuse ?
Answer: It depends on which circuit you use. Let ’s talk about the nominal voltage of the generator and battery on the car according to the provisions of Articles 3 and 9 of the National Standard QC / T413-1999 "Basic Technical Conditions of Automotive Electrical Equipment": the nominal voltage of the product is stipulated as 3 types: 6, 12 , 24V. When the voltage range is 5.5 ～ 7.5V, 11 ～ 15V, 22 ～ 30V respectively, the products with three nominal voltages should be able to work. In recent years, more and more electronic devices on automobiles are used to reduce energy consumption and line consumption. There is a generator and battery with a nominal 3DV voltage, and the voltage range is roughly between 28V and 39V. Because the generator is driven by the engine, the engine speed changes according to the working state of the car, so when the engine speed is high The speed of the generator is also high. Although the voltage regulation is disconnected, there is still a great change. In other words, if the voltage emitted by the generator is within the above range, the car's electrical appliances should be able to work normally, which creates a problem. We know Ohm's law: current (A) = voltage (V) resistance (R). So we can see that when When the actual voltage of the generator is greater than the nominal voltage, the actual current of various automotive electrical appliances is also greater than the rated working current. Therefore, the automotive fuse in the single-circuit electrical circuit protection is generally selected to be 1.20 to 1.30 times the rated current of the electrical appliance in the line as the rated operating current of the automotive fuse, and the rated operating current of the fuse in multi-channel protection and total power protection For the selection, considering that all kinds of appliances do not need to be turned on at the same time, or if A appliances are turned on, and B appliances do not need to be turned on, their rated working current is generally selected to be 80% of the sum of the rated working current of various appliances ~ 100% to enhance safety. Therefore, the specifications of various fuses selected by automobile manufacturers at the factory cannot be changed arbitrarily, nor can they be replaced by large ones or small ones, otherwise there will be endless troubles.
Q: How to choose car fuses?
Answer: Choose the fuse produced by the regular manufacturer! Automobile fuses on the market are mixed, some people use lighter AL instead of Zn to make fuses and inserts, and do not fuse when short-circuited; some flat-type fuse bases do not use phenolic resin, but are replaced by common plastics As a result, the high temperature of the melt at the time of fusing causes the plastic to burn, causing a safety accident and so on. Therefore, we must choose the products of regular manufacturers.
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