Why Is It Said That A Good Data Line Has A Great Influence On Charging Efficiency?

I believe everyone has had such an experience, that is to use the original charger and data cable to charge the mobile phone, it may only take less than 1 hour to charge from 10% to 100%, but after switching to a third-party data cable The charging speed of the mobile phone becomes very slow, or even unable to charge at all. Obviously, this third-party data cable does not match the charging requirements of the mobile phone, which means that you need to find the original data cable or change it to one that can meet the demand. The data line is used. Many users have questions about this, isn't the structure of the current data cable uniform? Since the physical structure is the same, why is there such a compatibility problem?

In fact, this problem is not caused by the physical structure of the data line, but more caused by the material used in the data line. As everyone knows, no matter whether it is mainstream or high-end mobile phone products, the data lines they use are basically universal, and there is no real 'exclusive data line', even if it is like a OnePlus mobile phone, If you want fast charging, you must use your own data cable, which is limited to the fast charging handshake. When it is used with a common style data cable, the basic charging and data transmission functions will not be affected. Therefore, when you switch to a third-party data cable, the charging speed is obviously slower. After excluding the reason that the 'handshake fast charging protocol must use the original wire', the rest is naturally the 'data cable quality' problem that everyone often refers to.

Don’t underestimate this “data cable quality” issue. In fact, we can open the page of JD.com or Taobao. If you search for “mobile phone data cable”, we can see that the price of similar cables ranges from a few dollars to 1 There are one for hundreds of dollars. Obviously, this cannot be explained by pure 'brand premium'. The function of the data cable and the charging efficiency are the most critical factors. I believe everyone can understand the difference in function, such as the difference between USB 2.0 cable and USB 3.0/3.1 cable, the difference between ordinary USB Type-C interface and Thunderbolt 3 interface, etc. How do you understand the charging efficiency? This is the key point we are going to talk about today.
Why does the voltage drop have a significant impact on the charging efficiency?

Before starting to talk about the charging efficiency, let's first call a keyword 'voltage drop'. Voltage drop refers to the voltage difference between the two ends of the wire. For example, if a 5V power supply is connected to the input end of the wire, but only 4.8V is detected at the output end, the voltage drop of this wire is 0.2V. So how does the pressure drop occur? In fact, although the material used in our data line is a good electrical conductor, it is not a superconductor after all. There is resistance inside. Therefore, when we connect the charger and the mobile phone with the data line, it is equivalent to connecting in series in a circuit. After the charging circuit is formed, there will be current passing through the data line. With the presence of resistance and current, a voltage will naturally be generated at both ends of the wire, and the value of this voltage is the voltage drop value.

Supporting 5A current wire, the voltage drop is only 0.3V when passing 3A current, which is equivalent to 0.9W loss

So why is the voltage drop a key word for judging charging efficiency? That's because during the charging process, the input voltage of the terminal device is processed by the 'voltage drop' of the data line. To give a simple example, when the charger output voltage is 5V and the charging loop current is 2A, the voltage drop is used A data line of 0.2V means that the input voltage of the terminal device is 4.8V, and the total input power is 9.6W; while using a data line with a voltage drop of 0.4V, it means that the input power of the terminal device is only 2A*4.6V =9.2W, the wire brings an additional 0.4W loss. The lower the input power, the slower the charging speed, which is the main reason why the voltage drop of the wire can affect the charging efficiency.


The wire that supports 3A current has a voltage drop of 0.6V when passing 3A current, which is equivalent to 1.8W loss

Moreover, the above is often only a theoretical calculation. In fact, many terminal devices have minimum charging voltage requirements. For example, a certain device supports a charging voltage of 5V±5%, that is, 4.75V to 5.25V. When you use one at 2A When the voltage drop reaches 0.4V, the charging input voltage is only 4.6V, and the charging current has to be reduced to reduce the voltage drop, or even the charging will be stopped directly. It will only be possible to replace a lower voltage data line. restore. Theoretically, when a data line has a voltage drop of 0.4V at a current of 2A, and if the voltage drop is reduced to 0.25V, the current passed must drop to 1.25A. At this time, the input power of the terminal device is only equivalent to 4.75 V*1.25A≈5.94W, which is a significant drop compared to the original theoretical 5V*2A=10W.
What caused the pressure drop? Line resistance plays a decisive role in the size of the voltage drop

Since the 'voltage drop' has a significant impact on the charging efficiency of the data line, which attribute of the data line has a significant impact on the 'voltage drop'? In fact, according to the voltage drop calculation formula 'voltage=current*resistance', we can know that the resistance of the wire has a significant effect on the voltage drop. The resistance of the wire is what we often call 'wire resistance'. According to the calculation formula of 'resistance = resistivity * length/cross-sectional area', it can be known that when the material of the cable is the same, that is, the resistivity is the same. The resistance is proportional to the length and inversely proportional to the cross-sectional area. Therefore, if you want to reduce the resistance of the cable, shortening the length and increasing the cross-sectional area are the most direct methods.


Intuitively, the wire with larger current (top) will be thicker than the wire with smaller current (bottom)

This is why some longer data lines are often thicker, because it needs to increase the cross-sectional area to compensate for the line resistance caused by the length, but this approach will often greatly increase the cost of the wire. Therefore, these longer and thicker data lines tend to sell more expensively. However, some products do not change the cross-sectional area of ​​the wire while increasing the length. The longer the length of such data lines, the more obvious the voltage drop. Of course, we are not saying that such data lines cannot be used, but the charging efficiency of such wires is indeed It will be lower.

In addition, if the length and cross-sectional area are equal, the wire resistance may not necessarily be the same. The material used for the wire is also a key factor. At present, copper wires are generally used in data cables. Some high-end products may use silver-plated wires or even pure silver wires to reduce wire resistance. However, some low-end wires are made of aluminum, which has good conductivity. But it is much lower than copper. It may have little effect on data cables with a short length, such as products with a length of only 10-15cm, but for cables with a length of 1 meter, 1.5 meters or even 2 meters or more, the line resistance caused by aluminum material is not affected. Ignored.

Calculated by pure copper and pure aluminum, the resistivity of the latter is 1.6 times that of the latter, which means that under the same length and the same cross-sectional area, the pressure drop caused by the latter will be 1.6 times that of the former. We have previously measured the charging data cable that comes standard with Apple's MacBook Pro 16. Its line resistance is 0.125Ω, and the voltage drop generated when passing a 4.7A current is about 0.6V, which is equivalent to a loss of 2.82W of energy. If this line is changed from copper to aluminum, theoretically its line resistance will become 0.200Ω, and the voltage drop under 4.7A current will become 0.94V, which is equivalent to a loss of 4.42W of energy.


Different output power will have different output voltage, and the current will be limited in a reasonable range to reduce the energy loss on the wire.

It is worth mentioning that the 'high voltage and low current', which is still in the mainstream fast charging mode, was developed to solve the problem of reduced charging efficiency caused by the voltage drop of the wire. The charger also outputs 18W power, which is equivalent in a 5V environment. For a current of 3.6A, the voltage drop is 0.36V on a wire with a wire resistance of 0.1Ω, which exceeds the requirement of ±5%, and the energy loss is as high as 1.3W; for a 9V environment, it is 2A. The voltage drop is only 0.2V, which is equivalent to a power loss of 0.4W. The power loss of the latter is less than one-third of the former. Therefore, whether it is the current mainstream 'high voltage and low current' mode or the gradual trend toward a unified PD charging protocol, as the charging power increases, the voltage increase will often be greater than the current increase, which can reduce the power loss on the wire. At the same time, it can also prevent the wire from becoming too thick in order to pass large currents, which is inconvenient for users to use.

Of course, the data cable can be used not only for charging, but also for data transmission. But compared to the line used for charging, the line used to transmit data can be said to have quite low requirements on the wire, because the current passing through it is very small, and it is more often used to express the level. Therefore, when we cut a data line, we will see that the cable of the power supply line is obviously thicker than the cable of the data line. It is precisely because of this that, for the wire that transmits data, whether the connection is firm is more important than whether the wire is thick enough and the resistance is low enough. Because of this, most third-party data cables now emphasize the current passing capacity of their own products, and the data transmission capacity is more expressed in terms of whether it supports USB 3.0/3.1 or Thunderbolt 3.
How to choose a useful data line?

So how do we choose a useful data line? For users, the original cable should be the first choice, because even if the original cable is not as good as the third-party cable in terms of theoretical electrical performance, it will definitely not have compatibility issues when used with their own equipment. Quick charge handshake, data Transmission and charging efficiency will be better guaranteed, because these have been tested and verified by the original factory; and for third-party cables, high specifications and large brands are still a relatively safe choice. 'You get what you pay for' can also be regarded as an eternal 'truth'. After all, a '5A high-current USB 3.1 Type-C' cable with a price of only 9.9 yuan does not look like a normal existence.

The hard-core players can use some simple equipment on the market to measure the data line. For example, two USB ammeters can quickly measure the voltage drop and current of the data line, and then calculate the line resistance of the cable. By calculating its voltage drop under different currents, it can be judged whether this data line is suitable for a high-current environment. Of course, if you just want to quickly choose a suitable data cable, you may wish to buy it according to the 5 points of '45W minimum 3A, 65W or above minimum 5A, big brand, suitable length, and suitable price'. Of course, if you are really not bad money, you can choose a thick enough silver wire to customize a long enough data cable, but do you really need such a data cable?

 

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