4S 8A Battery Management Systems (BMS)

BMS For Four Battery Strings And 8A Max Current

BMS often ship in locked state: no output voltage is available at the output pins. Locked state is also entered whenever over-current protection was triggered. To unlock the BMS, connect it to a charger. If you did not add a dedicated charger board, apply the appropriate charging voltage to its output terminal.

When connecting batteries to your BMS, make sure to use wires with sufficient diameter for the anticipated high currents.

When designing battery packs, use batteries of same type and same state of charge only. It is recommended you fully charge all batteries before connecting. All batteries must have the same voltage (voltage difference less than 0.05V). Do not mix batteries from different vendors, types, capacity, or age.


LiIon LiPo For currents up to 8A, you can use a BMS with a square form factor. This makes it ideal for battery packs with four 18650 LiIon cells but can also be used for other lithium batteries including LiPo:

There are quite a few connectors on this board that are accessible only from the top. Make sure you connect your batteries correctly.

Connect the batteries like this:

  • First battery string to B- (-) and B1 (+)
  • Second battery string to B1 (-) and B2 (+)
  • Third battery string to B2 (-) and B3 (+)
  • Forth battery string to B3 (-) and B+ (+)

The output voltage is available at the (relatively small) P+ and P- terminals.

The terminals B1 and B3 are also available on the back side of the board:


Protection Threshold
Over-Charge >4.25V
Over-Discharge 2.3-3.0V
Over-Current 20A
Short Circuit yes,resettable
Continuous Current 8A
Size 34x34x3.2mm


When charging batteries through this BMS, the charging voltage needs to be 16.8-17.0V. The BMS limits the charging current to 6A.


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(content created Feb 27, 2024)