In the lithium battery pack, a plurality of lithium cells are connected in series and parallel to obtain the required large enough operating voltage. If you need higher capacity and greater current, you should connect the lithium cell in parallel, and the aging cabinet of the lithium battery assembly equipment can know the high voltage and high capacity standards by combining the series and parallel two methods.
1, lithium battery series parallel method
Lithium battery parallel: the voltage is unchanged, the battery capacity is added, the internal resistance is reduced, and the power supply time can be extended.
Lithium battery series: voltage addition, capacity unchanged.
Parallel connection To obtain more power, multiple batteries can be connected in parallel. An alternative to parallel batteries is to use larger batteries, as there are limited batteries that can be used and this method is not suitable for all applications. In addition, large batteries are not suitable for the form factor required for dedicated batteries. Most chemical batteries can be used in parallel, and lithium batteries are most suitable for parallel use.
For example, the battery voltage of a parallel connection of five cells is maintained at 3.6V, and the current and running time are increased by five times. A high-impedance or "open" battery has less effect on the parallel circuit of the battery than it does in series with the battery, however, a parallel battery pack can reduce load capacity and reduce operating time.
When connected in series and parallel, the design is flexible enough to reach the rated point voltage and current required for standard battery sizes. It should be noted that due to the different connection methods used to produce lithium batteries, the total power will not change. Power is equal to voltage times current, and for lithium batteries, the series-parallel connection method is common. One of the most commonly used battery packs is the 18650 lithium battery, which has a protection circuit and a lithium battery protection board. The lithium battery protection board can monitor each battery in series, so its maximum actual voltage is 4.2V. The lithium battery protection circuit (i.e., the lithium battery protection board) can also be used to monitor the status of each battery connected in series.
When using 18650 lithium batteries in series, the following basic requirements must be followed: the voltage should be consistent, the internal resistance should not exceed 5 milliohm, and the capacity difference should not exceed 10 mA. The other is to keep the battery‘s connection points clean, and each connection point has a certain resistance. If the connection point is not clean or the connection point is increased, the internal resistance may be high, which may affect the performance of the entire lithium battery pack.
2, lithium battery series parallel precautions
General lithium battery series parallel use requires lithium battery cell pairing, pairing standards: lithium battery cell voltage difference ≤3mV, lithium battery cell internal resistance difference ≤5mΩ, lithium battery cell capacity difference ≤10mA.
When batteries are connected in parallel, the same battery must be used. The voltage of different batteries is different. After the parallel connection, the battery with high voltage charges the battery with low voltage, which consumes electric energy.
The same battery should also be used when the battery is in series. Otherwise, after different capacity batteries are connected in series (such as different old and new degrees of the same battery), the battery with small capacity first emits light, and the internal resistance increases, at this time, the battery with large capacity will discharge through the internal resistance of the small-capacity battery, consume electric energy, and also reverse charge it. In this way, the voltage on the load will be greatly reduced, and it will not work, and the battery with a large capacity is only equivalent to the battery with a small capacity.
