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How to correctly connect lithium batteries in series and in parallel?

15,675 Published by BSLBATT Mar 01,2019

The purpose of parallel connection of lithium batteries is to increase the capacity. Therefore, parallel charging of lithium batteries has different design characteristics compared with single-cell lithium batteries, mainly reflected in the consistency of charging current design and parallel battery.

The characteristics of the parallel lithium battery are: the voltage is constant, the battery capacity is added, the internal resistance is reduced, and the power supply time is prolonged. The core content of parallel charging is the size of the parallel current and its effect. According to the parallel theory, the main circuit current is equal to the sum of the currents of the respective branches. Therefore, the n-th parallel lithium battery that has been combined into a battery pack should achieve the same charging efficiency as the single-cell battery, and the charging current should be the sum of the n lithium battery currents. Under the formula of Ohm’s law: I=U/R, this design is reasonable. However, the internal resistance of the battery in parallel will also change. According to the parallel internal resistance formula, the total internal resistance of the two parallel lithium batteries is equal to the ratio of the sum of the internal resistance products of the two batteries and the internal resistance. The parallel resistance will follow. The number of parallel batteries increases and decreases. Therefore, the efficiency of parallel charging of lithium batteries can be achieved on the basis of the current less than the sum of the currents of n parallel lithium batteries.

Lithium battery parallel should pay attention to the consistency of the battery, because the parallel lithium battery with poor consistency will not charge or overcharge during the charging process, thereby destroying the battery structure and affecting the life of the whole battery. Therefore, when using parallel batteries, avoid mixing lithium batteries of different brands, different capacities and different old and new levels. The inherent requirements for battery consistency are: lithium battery cell voltage difference ≤ 10mV, internal resistance difference ≤ 5mΩ, capacity difference ≤ 20mA.

In fact, after the lithium battery is connected in parallel, there will be a charging protection chip to protect the lithium battery. The lithium ion battery manufacturer has fully considered the variation characteristics of the lithium battery in parallel when making the parallel lithium battery, and also designed the current according to the above requirements. The battery is selected, so the user needs to follow the instructions of the parallel lithium battery to charge step by step to avoid damage to the battery caused by incorrect charging.

The battery series voltage is equal to the sum of the battery voltages of the string, the voltage is increased, the bulbs are connected in series, and one switch can control all the bulbs connected in series on one line.

The use of the pool in series can increase the output voltage. What are the characteristics of the bulbs in series: the sum of the voltages of the two bulbs is the total voltage of the circuit.

After the batteries are connected in series, the voltages are added, and the currents are equal, which increases the voltage; the batteries are connected in parallel, and the voltage is constant (provided that the batteries with the voltages can be connected in parallel, otherwise the high voltage will charge the voltage low, if the difference is too large, There is also a danger) that the current is equal to the sum of the individual batteries, which is often considered to increase the battery capacity and provide more current.

The voltage increases and the capacity does not change.

The difference between battery series and parallel:

Battery in series:

It means that the battery is connected end to end. That is, the positive pole of the first battery is connected to the negative pole of the second battery, and the positive pole of the second battery is connected to the negative pole of the third battery, and so on;

The series voltage is equal to the sum of the battery voltages, and the current is equal to the current flowing through each battery;

A damage in one of the battery packs will cause the entire battery pack to be unusable or the voltage to drop;

Series connection can increase the total voltage.

Battery in parallel:

It means that the first head of the battery is connected and the tail is connected. That is, the positive poles of all the batteries are connected, and the negative poles of all the batteries are connected.

The shunt voltage is equal to the individual battery voltage and the current is equal to the sum of the battery currents.

Although the battery life of the battery pack is enhanced, the damage caused by the short-circuit current is more serious;

Parallel can increase the total current.

 

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