Introduction：
The core issue in battery repair and lithium battery pack expansion applications is whether two or more sets of lithium battery packs can be directly connected in series or parallel. Incorrect connection methods can not only lead to a decrease in battery performance, but also potentially cause safety hazards such as short circuits and overheating. Next, we will analyze in detail the correct methods and precautions for connecting lithium battery packs from both parallel and series perspectives. Next, we will analyze in detail the correct methods and precautions for connecting lithium battery packs from both parallel and series perspectives, combined with the use of battery test and repair instruments.
Parallel connection of lithium battery pack: equal emphasis on conditions and protection
The parallel connection of lithium battery packs can be divided into two situations, the core of which lies in whether the battery pack parameters are consistent and whether necessary protective measures have been taken. When judging the parameters of the battery pack, the lithium battery tester can accurately measure data such as voltage and internal resistance, providing scientific basis for the connection scheme.
（1） Direct parallel connection when parameters are consistent
When the voltage, capacity, internal resistance, cell model and other specifications of two sets of lithium battery packs are exactly the same, parallel operation can be directly carried out. For example, using a lithium battery tester to detect two sets of lithium battery packs with the same 4-series structure and a nominal voltage of 12V, when fully charged and with the same voltage, connect their total positive pole to the total positive pole and total negative pole to complete parallel connection. It should be emphasized that each battery pack must be equipped with an independent protection board to ensure the overcharge, overdischarge, and short-circuit protection functions of the battery. In addition, after the connection is completed, it is necessary to use a lithium battery tester to recheck the overall parameters to ensure the stable performance of the parallel connected battery pack.
（2） Parallel scheme when parameters are inconsistent
In the actual repair process, it is common to encounter battery packs composed of different batches of cells, even if the nominal voltage is the same (such as 12V), there are differences in capacity (50Ah and 60Ah) and internal resistance. In this case, direct parallel connection will bring huge risks - when the voltages of the two battery groups are different (such as 14V and 12V), the high-voltage battery group will quickly charge the low-voltage battery group. According to Ohm's Law, if the internal resistance of a low-voltage battery pack is 2 Ω, the instantaneous mutual charging current can reach 1000A, which can easily cause the battery to heat up, bulge, or even catch fire.
To cope with this situation, parallel protection devices must be added:
Choose a protection board with built-in current limiting function: Some high-end protection boards have parallel current limiting characteristics, which can automatically limit the mutual charging current within a safe range. When selecting a protective board, a lithium battery repair device can be used to check if its function is normal.
Installing an external parallel current limiting module: If the protection board does not have this function, an additional professional current limiting module can be configured to control the current at a reasonable level and ensure safe connection. After installing the current limiting module, it is necessary to use a lithium battery tester to monitor the current changes and verify the effectiveness of the module.
Series connection of lithium battery pack: high requirements and customization
Compared to parallel connection, the series connection of lithium battery packs requires more stringent consistency requirements for the battery pack. When connected in series, it can be likened to the assembly process of internal battery cells in a battery pack, which requires highly consistent parameters such as voltage, capacity, internal resistance, and self discharge rate between the two battery packs. Otherwise, uneven voltage distribution may occur, accelerating the aging of poorly performing battery packs. When selecting suitable battery packs, lithium battery testers can quickly and accurately detect various parameters, improving screening efficiency.
In addition, the total voltage after series connection is the sum of the voltage of a single group (such as two sets of 12V batteries connected in series for 24V), which puts higher requirements on the withstand voltage value of the Mos tube in the protection board. Ordinary protection boards are usually only suitable for single voltage groups. When used in series, it is often necessary to customize high-voltage protection boards or choose professional battery management systems (BMS) that support multiple strings to ensure the safety and stability of the series connected battery pack during charging and discharging. The lithium battery maintenance device can perform functional debugging and troubleshooting on customized protection boards and BMS to ensure their normal operation.
Safety Tips and Practical Suggestions
Random series parallel connection is strictly prohibited: Lithium battery packs of different brands and batches are not allowed to be directly connected without treatment due to differences in battery cell chemical characteristics and processes.
Regular inspection and maintenance: The parallel system needs to check the battery pack voltage every month, and if the difference exceeds 0.3V, it needs to be charged separately for balancing; It is recommended to actively balance the series system through BMS every quarter.
Select high-quality accessories: It is necessary to use protection boards and BMS certified by UN38.3, CE, etc. The connecting wire should be selected with the appropriate wire diameter according to the current load to avoid heating caused by wire loss.
The series parallel operation of lithium battery packs should be based on safety, strictly controlling the consistency of battery pack parameters, and cooperating with professional protection devices. Mastering these key points can not only improve the efficiency of battery repair, but also ensure the long-term stable operation of lithium battery packs.
Request for Quotation:
Jacqueline: jacqueline@heltec-bms.com / +86 185 8375 6538
Nancy: nancy@heltec-bms.com / +86 184 8223 7713
Post time: May-23-2025