Universal active Charger 4S
Universal active Charger 4S
The small Universal active Charger 4S module will be useful in building battery packs for portable devices. Because it works actively, excess energy is stored in inductance and transferred from a higher voltage cell to a lower voltage cell.
- works actively, excess energy is not lost as heat,
- adapted to work with 4 cells (optionally with 3 cells),
- balancing is performed if the voltages between cells differ by more than 100 mV,
- the maximum balancing current value is approximately 1500 mA.
The balancing process is handled by specialized ETA3000 systems (ETA Solutions). Every 2 seconds they measure the voltages of two series-connected cells of the pack (e.g. GND-CS1, CS1-CS2), if the measured voltages differ by more than 100 mV, and the sum of the voltages of the two cells is greater than the threshold of the ULVO detector = 3.75 V, the balancing process begins, i.e. transferring energy from the cell with a higher voltage to the cell with a lower voltage.
Construction and operation
The circuit diagram is shown in Figure 1. The maximum value of the balancing current is set by the resistor Rx connected to the ISET pin, in the model it is about 1500 mA. Balancing is stopped when the voltages on the cells are equalized, after which the circuit goes into the SLEEP state, drawing no more than 2 μA, which ensures low self-discharge of the pack.
Due to the internal resistance of cells and leads affecting the accuracy of voltage measurement, the maximum difference on cells after balancing does not exceed ±30 mV. Due to the principle of operation, based on detecting the voltage difference, and not a fixed threshold, the system is universal and suitable for Li-FePo4 and Li-Ion cells, provided that the voltage of the two-cell pack does not exceed 10 V. This condition is met even by modern cells with a voltage increased to 4.35 V.
To balance a larger number of cells, it is necessary to connect ETA systems in series, in which each of them is individually connected to two cells, but also includes one cell from the previous balancer, which allows the transfer of charge throughout the pack. The 4S battery is connected to one of the BAT connectors type JST PH 2 mm or BAT1 type SIP 2.54, depending on your preferences. The battery should be connected in the order of cells – i.e. first connect the ground lead, then in order the individual cells CS1, CS2, CS3, CS4.
Installation and start-up
The circuit is made on a double-sided printed circuit board, the diagram of which is shown in Figure 2. The assembly of the circuit does not require a detailed description, and the assembled module is shown in the title photo.
The system does not require start-up, the value of the components should be adjusted to the battery capacity and the set balancing current according to the ETA3000 catalog card, which is available in the additional materials to the article. The balancer can be adapted to a 3S battery by not soldering the components U1, R1, C1, C4, C7, L1 and leaving the C4S lead unconnected.
