The main advantage of a modern battery is accompanied by disadvantages that need to be compensated. We are talking about recharge and deep discharge. The battery will not tolerate such treatment and will react with a failure. BMS (Battery Management System) board, a device that monitors battery parameters, controls charging and switches the load.
Preparing The LifePO4 Battery For Installing The BMS Board
Before connecting the BMS board, it is important to correctly connect (assemble) the LifePO4 battery cells into the battery pack.
Between the battery cells during sequential assembly, it is MANDATORY to put insulating gaskets, the best option for insulating gaskets is fiberglass with a thickness of 0.5 millimeters.
Switching Types:
- Parallel connection of battery cells.
When connecting battery cells in parallel, we increase the battery capacity, for example: we have 4 batteries 3.2V 25Ah, by connecting these batteries in parallel we get 3.2V 100Ah. When batteries are connected in parallel, insulating gaskets between them can be omitted.
- Serial connection of battery cells.
When connecting battery cells in series, we increase the voltage (voltage) of the battery, for example: we have 4 batteries 3.2V 25Ah, by connecting these batteries in series we get 12V 25Ah. When connecting batteries in series, it is MANDATORY to install insulating gaskets between them.
- Parallel-serial connection of battery cells.
With this assembly method, the cells are first connected in parallel, then the parallel assemblies are connected in series. For a BMS board, a parallel assembly counts as one single battery cell.
Instructions For Connecting A Symmetrical BMS Board
When connecting the BMS board, you must follow the sequence of operations:
The first step is to connect a balancing cable, for this, we take a black thin wire connecting the “B-” of the balancing cable, connect to the negative “-” terminal of the first cell of the battery assembly, then take the next thin wire (indicated in red in the diagram) of the balancing cable and connect to the positive “+” terminal of the first cell.
Next, in strict sequence, connect the remaining wires (indicated in red in the diagram) of the balancing loop to the positive terminals of each cell of the battery assembly. It is very IMPORTANT to connect the cable in strict sequence from the black wire to the last red wire, before installing the cable into the socket, check the sequence of connecting the wires of the balancing cable.
After connecting the balancing cable to the battery cells, do not rush to install the connector in the BMS board. Check the voltage at the connector terminals (multimeter minus on the black wire of the balancing cable, plus on the red one).
After checking the connection sequence and voltage on the balancing cable, install the connector in the BMS socket of the board.
Connect the power wire “B-” to the negative terminal of the first cell (the black wire of the balancing loop is installed on this cell terminal). The black power wire “P-” goes to the consumer and the charger, which is the minus of the battery.
The positive pole of the battery must be connected to the positive terminal of the last cell of the battery assembly and let it go directly to the consumer and the charger.
After the connection of the BMS board is completed, it is necessary to check the battery voltage at the terminals, the extreme minus “-” and the extreme plus “+” of the cell assembly, then the voltage through the BMS, the wire “P-” and the extreme plus “+” of the assembly. If the voltage is different, check the connection sequence.
After assembling the battery, you need to test it in operation.
The first step is to fully charge the battery and at the end of the charge, check the cutoff voltage of the BMS board at the upper voltage threshold for each cell, i.e. BMS should turn off the charger as soon as the voltage on one of the cells reaches the upper threshold, then, after a short period time to turn it back on. This check must be done on all cells of the battery assembly, until the battery is fully balanced.
The second step is to fully discharge the battery under control and check the cut-off voltage at the lower threshold of the BMS board.
At this stage, the assembly of the battery and connecting the BMS board can be considered complete and, if no additional equipment is required, the battery assembly can be packed in a protective case. If the battery case is metal, it is first necessary to isolate the battery, for example, cover it with sheets of fiberglass.
