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.
8A
LiIon
LiPo
This is a cost-effective and simple BMS that claims to sustain continuous currents of 8A, however in this case make sure you add heat sinks. I use this BMS for smaller loads up to 3A without heat sink.
Note that this BMS is not balancing the cells. It only provides the typical protections (i.e. over-discharge, short-circuit):
- assemble your battery pack with fully charged cells of equal size, type, manufacturer, and age (to ensure they charge and discharge equally) -or-
- add a passive (or better yet, active) balancer board
The BMS monitors each cell individually which is why you connect your battery pack 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:
Specs
| 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 |
Charging
You can charge your battery pack directly through this BMS by applying 16.8-17.0V to p- and P+, however this would result in relatively high charging currents of 6A, and you may not typically have 16.8-17.0V at hand.
A much better way is to add a dedicated 4S USB Charger Board, for example the LIFC2-N module. This way, you can charge your 4S battery from any USB power supply.
Example
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(content created Feb 27, 2024 - last updated Oct 27, 2025)