What are the precautions for 18650 lithium batteries in series and parallel

In the lithium battery pack, multiple lithium batteries are connected in series to obtain the desired operating voltage. If what is required is higher capacity and higher current, then lithium batteries should be connected in parallel. There are also some battery packs that combine the two methods of series and parallel. The battery of a laptop computer may be connected in series with four 3.6V lithium batteries, the total voltage reaches 14.4V; then, two groups of batteries connected in series are connected in parallel, so that the total power of the battery pack can be from 2000 milliliters. The ampere hour is increased to 4000 mAh. This kind of connection is called four-series two-parallel, which means: connect two sets of battery packs connected in series with four batteries in parallel. The nominal voltage is 3.6V. Using lithium ion polymer and other types of lithium batteries, its rated voltage is generally 3.7V. If you want to get an unusual voltage like 11.1V, you have to connect three such batteries in series. Portable devices that require high power in series are generally powered by a battery pack with two or more batteries connected in series. Another problem brought by the use of high-voltage battery packs is that one of the batteries in the battery pack may fail. This is like a chain, the more batteries connected in series, the higher the chance of this happening. As long as a battery has a problem, its voltage will drop. In the end, a disconnected battery may interrupt the current delivery. It is not easy to replace a bad battery, because the old and new batteries do not match each other. Generally speaking, the capacity of new batteries is much higher than that of old batteries. As the working voltage drops, it reaches the critical point of the end of discharge faster than a normal battery pack. At the same time, its use time is also sharply shortened. Once the device cuts off the power supply due to low voltage, the remaining battery cells are still intact and cannot send out the stored power. At this time, the broken battery battery still presents a large internal resistance. If there is a load at this time, the output voltage of the entire battery chain will be greatly reduced. A battery with poor performance in a series of batteries is like a plug blocking a water pipe, and there will be huge resistance to prevent current from flowing through. Other batteries will also be short-circuited, which will reduce the terminal voltage to 3.6V or disconnect the battery pack link and cut off the current. The performance of a battery pack depends on the performance of the worst battery in the battery pack. To get more power, you can connect two or more batteries in parallel. In addition to connecting batteries in parallel, another method is to use larger batteries. Due to the limitations of the available batteries, this method is not suitable for all situations. In addition, large-sized batteries are not suitable for the external specifications required for special batteries. Most chemical batteries can be used in parallel, and lithium batteries are most suitable for parallel use. A battery pack made up of four batteries in parallel maintains a voltage of 3.6V, while the current and running time are quadrupled. Compared with batteries in series, in battery parallel circuits, high impedance or open-circuit batteries have less impact, but parallel battery packs will reduce the load capacity and shorten the running time. This is like an engine with only three cylinders activated. The damage caused by the short circuit of the circuit will be greater. This is because the battery that fails in the short circuit will quickly exhaust the power in other batteries and cause a fire. When using the series-parallel connection method, the design is very flexible. Standard battery sizes can be used to achieve the required rated voltage and current. It should be noted that the total power will not change due to different battery connection methods. Power is equal to voltage times current. For lithium batteries, series and parallel connections are very common. The most commonly used battery pack is 18650 (diameter is 18mm, length is 650m.), it has a protection circuit that is a lithium battery protection board. The lithium battery protection board can monitor each battery connected in series. Therefore, its The maximum actual voltage is 14.4V. This lithium battery protection circuit (ie, lithium battery protection board) can also be used to monitor the status of each battery connected in series. When connecting several batteries in series, the following basic requirements must be followed: Keep the connection points of the batteries clean. When four batteries are connected in series, there are eight connection points (the connection point from the battery to the battery compartment, and the connection point from the battery compartment to the next battery). Each connection point has a certain resistance. If a connection point is added, the performance of the entire battery pack may be affected. Do not mix batteries, choose batteries with consistent performance. When the battery power is low, replace all the batteries. When using in series, use the same type of battery. Pay attention to the polarity of the battery. If the polarity of one battery is reversed, the voltage of the entire string of batteries will be reduced instead of increasing. 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 article: How to guard against battery explosion?