18650 Lithium Battery Connection

2020-09-28 01:37

In the actual use of batteries, high voltage and large current are often required, which need to connect several single batteries in series or parallel (or both), we call it battery pack. The 18650 lithium battery pack needs a certain standard.

18650 battery in series: When multiple 18650 lithium batteries are connected in series, the battery pack voltage is the total of all battery voltage, but the capacity remains unchanged.

Schematic Diagram of 18650-4S Connection

18650 battery in parallel: If you connect multiple 18650 lithium batteries in parallel, you can get more power. The parallel connection of lithium battery keeps the voltage constant, while the capacity increases. The total capacity is the sum of the total capacity of all single lithium batteries.

Schematic Diagram of 18650-4P Connection

Series and parallel connection of 18650 battery: the method of series and the parallel connection is to connect several lithium batteries in series and then connect the battery packs in parallel. It not only improves the output voltage, but also the capacity.

18650-2S2P Connection Diagram

  • Series and parallel connection of lithium batteries need battery cell matching.
    Lithium battery matching standards: voltage≤10mV resistance ≤5mΩ capacity≤20 mA
  • Battery with the same voltage
  • Different batteries have different voltages. After being connected in parallel, the high-voltage battery charges the low-voltage battery, which consumes the power and may lead to accidents.
  • Battery with the same capacity
  • Connect batteries with different capacities in series. For examples, same battery may be different from the aging degree. Batteries with small capacity will fully discharge first, then the internal resistance will increase. You also need to use the same battery if connect in series. Otherwise, after connecting batteries with different capacities in series (for example, same battery may be different in the aging degree), the batteries with small capacity will fully discharge first, then the internal resistance will increase.
  • At this moment, the batteries with large capacity will discharge through the internal resistance of the batteries with small capacity, and then reverse charge. In this way, the voltage on the load will be greatly reduced, the battery will be unable to work, and the large capacity battery is only equivalent to the small capacity battery. Long-term use may cause accidents.
  • The battery pack requires a high degree of consistency (capacity, internal impedance, voltage, discharge curve, cycle life).
  • The cycle life of the battery pack is lower than that of a single battery.
  • Different batteries have different voltages. After being connected in parallel, the high-voltage battery charges the low-voltage battery, which consumes the power and may lead to accidents.
  • It needs to be used under limited conditions (including charging, discharging current, charging mode, temperature, etc.)
  • After the lithium battery pack is formed, the battery voltage and capacity will be greatly increased, so it must be protected. It also needs charging balance, temperature, voltage and overcurrent monitoring.
  • The battery pack needs to meet the design requirements of voltage and capacity.

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