BMS 4S (16.8V – 30A) Lithium Battery Protection Module

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A Battery Management System (BMS) for a 4S battery pack. With this circuit you can safely make a battery pack of 4 series Li-ion/Li-Po batteries (cells). The circuit protects the battery pack against short circuits, overvoltage and undervoltage. In addition, the circuit ensures that the batteries are charged evenly (balance function). The circuit is supplied with protection connecting wires.


  • Charging voltage: 16.8V
  • Maximum charging current: 30A*
  • Maximum continuous discharge current: 30A*
  • Short circuit protection: 75 ± 5A
  • Overcharge protection voltage (per cell/battery):  4.25 ± 0.05V
  • Discharge protection voltage (per cell/battery): 2.55 ± 0.08V
  • Balance function: Yes
  • Dimensions: 56x45x8mm (without connection wires)

*Note: These are the maximum currents of the BMS circuit. Connected batteries may not be able to handle this current!

Pin description (See the images for the connection diagram):

  • B-: Min cell/battery 1
  • B1: Plus cell/battery 1, min cell/battery 2
  • B2: Plus cell/battery 2, min cell/battery 3
  • B3: Plus cell/battery 3, min cell/battery 4
  • B+: Plus cell/battery 4
  • P+: Plus output battery pack
  • P-: Min output battery pack

Use the P+ and P connections to charge and discharge the battery pack.

Caution: Making a Li-ion/Li-Po battery pack requires knowledge. Only make the package if you know what you are doing. Incorrectly connecting the batteries and the BMS can cause the batteries to catch fire, or even explode.


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