Why is it so slow to charge the lithium-ion battery of a mobile phone with USB?

There are two ways to charge the phone: seat charging and direct charging. Dock charging is to take out the battery to charge the charger, and the corresponding is direct charging, that is, the charger is directly connected to the mobile phone to charge. USB charging refers to the use of electronic devices with USB interfaces to charge mobile phones, and currently refers to PCs and laptops. Generally speaking, USB charging takes longer than a charger. In order to explain the difference between USB charging and DC charging, it is important to understand the charging principle of lithium-ion batteries. The charging method of lithium-ion batteries is voltage-limiting and constant-current charging, which generally passes through three charging stages: (1) pre-charging, the charging voltage is less than 3V; (2) constant-current charging. When the voltage reaches 3V, it enters the fast charging phase. At this time, the current is relatively large, and constant current charging continues until the voltage rises to 4.2v; (3) Constant voltage charging. When the voltage rises to 4.2v, it becomes a small current charging, and the voltage remains unchanged at 4.2v. Usually, the current at this point is 1/10 of the constant current phase. Seat charging and direct charging will have a certain impact on lithium-ion batteries and mobile phones, and will cause a certain degree of damage in the long run. However, the output current of USB is smaller than the above two types, which is why the charging time of USB is longer than these two types. This kind of small ammeter is in the constant current and constant voltage stage. The purpose of constant voltage charging is to supplement the capacity loss caused by the self-discharge of the lithium-ion battery after it is fully charged. At present, the USB output voltage of the computer is 5V, the output current is 500mA, and the charging current of the charger is 1000mA. Since the USB output current is very small, the current in its constant voltage phase is smaller. Therefore, the USB charging time is longer, and more importantly, the time in the constant voltage stage is longer. If you can't wait to complete the process of charging your phone with USB as soon as possible, because there is still a part of the charging power that is not fully charged, it looks a little insufficient. This is indeed a current issue, not leakage and other issues that consumers worry about. However, the problem of incomplete charging has almost no impact. Even if there is no constant voltage charging process, the battery has at least 90% capacity at this time. Lithium-ion batteries, as long as they are not charged, can be charged at any time. This is it and Ni-MH batteries. The difference between USB car charger: also commonly known as USB car charger. It takes advantage of the versatility of USB and is widely used in various charging ports. Combined with vehicle applications, the vehicle 12V DC and 24V DC are converted into universal USB DC 5V voltage and all charging appliances. This leads to the use of the car's standard power supply and USB port to charge DC5V electrical appliances. Such as: mobile phones, MP3s, navigators, game consoles and all 5V DC electrical appliances. Some cars now have only one USB interface in the car. This interface is only used for data transmission and cannot be charged. With this interface, you can only plug in your smart phone or MP3 player to listen to music. Due to this type of port, it can only transmit data and cannot provide any type of charging method. The USB standard specifies configurations from 1 to 4 terminals. Terminals 1 and 4 transmit power, and terminals 2 and 3 transmit data. Most USB data cables simply connect the terminal at one end of the cable to the terminal at the other end, allowing the cable to transmit data and power. Only the data line completely omits 1, 4 terminals, and only the data line completely omits 2, 3 terminals. However, the actual situation is a bit more complicated than this. In order for the computer or infotainment system to supply higher charging current, you cannot plug in the charging cable. The computer must be given a specific reminder to supply a higher amperage, and the reminder varies according to the equipment involved. The USB specification requires that the charging cable short-circuit the data line or terminals 2 and 3 to the device end. Therefore, to convert a normal USB cable to a charging cable, terminals 2 and 3 of the cable device end may be short-circuited. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: How to calculate the power of lithium ion battery charger?