Series and parallel assembly method of lithium battery pack
To use power lithium battery packs in series and in parallel, it sounds simple, but by following some simple rules, unnecessary problems can be avoided. The lithium battery pack pack contains two parts: the lithium battery and the lithium battery pack protection board circuit.
In the lithium battery pack pack, multiple lithium batteries are connected in series to obtain the required working voltage. If what is needed 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-ion 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 The milliamp-hour is increased to 4000 milliamp-hours. This kind of connection is called 'four series and two parallelThe nominal voltage of a lithium battery pack 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 there is a problem with a battery, its voltage will drop. In the end, a 'disconnected' battery may interrupt the flow of current. 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, and at the same time, its use time is also drastically 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, it will cause the output voltage of the entire battery chain to drop drastically. In a series of batteries in series, a battery with poor performance is like a plug blocking a water pipe, which will produce huge resistance and 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.
In order to get more power in parallel, you can connect two or more batteries in parallel. In addition to connecting the batteries in parallel, another solution is to use larger batteries. Due to the limitations of the available batteries, this method is not suitable for all situations. In addition, large-size batteries are not suitable for the external specifications required for special batteries. Most chemical batteries can be used in parallel, and lithium-ion batteries are most suitable for parallel use. In a battery pack formed by connecting four batteries in parallel, the voltage remains at 3.6V, while the current and running time are increased to four times. Compared with batteries in series, in battery parallel circuits, high impedance or 'open circuit' batteries have less impact. However, 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 in the short circuit, the faulty battery will quickly exhaust the power in the other batteries and cause a fire.
Use series and parallel connections. The method is very flexible in design and can use standard battery sizes to achieve the required rated voltage and current. It should be noted that the total power will not change due to different connection methods of the battery. Power is equal to voltage times current. For lithium-ion batteries, series and parallel connection methods are very common.
The most commonly used battery pack is 18650 lithium ion battery (diameter 18mm, length 650mm), which has a protection circuit, namely a lithium battery protection board, which can monitor the series connected together Each battery, therefore, its 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 using four batteries in series, there are a total of 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 the connection point is increased, 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, it will reduce the voltage of the entire string of batteries instead of increasing the voltage.
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