There are questions and answers: why is the mobile data cable almost not 3 meters long?

Generally, the standard data cable of mobile phones is about 1 m to 1.5 m in length, and the third-party data cable will be slightly more selected. The length from 0.5 m to 2 m is relatively common, but we rarely see mass production data cables with a length of more than 2 m, let alone reaching the level of 3 m. In addition to the low market demand, the long data cable will lead to a significant drop in voltage, and the sharp drop in charging efficiency is also a very important reason.

The cables in the data cable of mobile phone can be divided into two groups, one is for data transmission, the other is for power transmission. Generally speaking, the power transmission cable will be thicker than the data transmission cable, because it has to bear more current than the data transmission cable. So why should the cable with high current be thicker? To reduce the pressure drop. Nowadays, most of the data cables are made of copper cables. Although copper is second only to silver conductor, it is not superconductor after all, and there is resistance. Therefore, when you connect the data cable between your mobile phone and charger, it is equivalent to connecting a resistance in series in the circuit. When the charging circuit is formed, there will be current in the cable, and there will be resistance and current, There will be a voltage difference between the two ends of the cable, which is often called voltage drop.

iPhone Charger Cable

Generating voltage drop means that there will be power loss. In the case of the same current, the greater the voltage drop, the more energy will be lost, and the charging efficiency of the mobile phone will be low. For example, when the output voltage of the charger is 5V and the current of the charging circuit is 2a, the resistance of one line is 100m Ω "2A * 0.1" Ω= The voltage drop of "0.2V" means that the input voltage of the mobile terminal is 4.8V and the total input power is 9.6w; The line resistance can reach 200m Ω Under the same environment, the voltage drop will reach "2A * 0.2" Ω= 4V ", which means that the total power of the mobile phone is only 2A * 4.6V = 9.2w, and the wire brings additional 0.4W loss.

iPhone 12 charger cable

So what determines the wire resistance of wire rod? According to the calculation formula of "resistance = resistivity * length / cross-sectional area", we can know that when the cable material is the same, that is, the resistance of the wire is directly proportional to the length and inversely proportional to the cross-sectional area. Therefore, to reduce the resistance of the cable, shortening the length and increasing the cross-sectional area are the most direct methods. It's just that increasing the cross-sectional area of wire rod will lead to a substantial increase in the cost of wire rod, which will naturally lead to a higher price. At the same time, it will also make the wire rod harder and not easy to bend. This is obviously not a good choice for consumers. In contrast, controlling the length of wire rod is an acceptable solution in all aspects, Therefore, the length of most data cables will be controlled within 2 meters, which can not only meet the needs of most users on the length of the cable, but also meet the voltage and current needs of the equipment on the power supply.

 

Of course, directly changing the material with lower resistivity to make wire can also effectively reduce the line resistance. For example, silver is the metal with the best conductivity at present, and its ductility is also very good. The larger the cross-sectional area does not affect its softness. Therefore, silver is also used in high-end customized data cables. It's just that silver is a precious metal, and the cost is much higher than copper. It's obvious that the sales volume of products used for mass production will be affected by the price. Therefore, silver line basically only appears in a small range of customized products, and will not become a mass production and sales product. This kind of data cable made of silver material has good electrical performance in the length of more than 2 meters or even more than 3 meters, but do you really need such an expensive and long data cable