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.
10A
For currents up to 10A, a number of BMS boards are commonly available.
Compact
Here is a very compact board:
Unfortunately, the compactness of the board did not leave room for markings on the front side. Instead, the markings for the soldering pads were printed on the back side:
On the other end, the board has a big soldering pad marked as B- which is accessible from both sides, and two smaller ones marked B1 and B+ on the backside whereas the solder pads are accessible on the front.
Connection
Connect the batteries like this:
- First battery string to B- (-) and B1 (+)
- Second battery string to B1 (-) and B+ (+)
The output voltage is available at B+ and C-. These two pads are accessible from both sides.
Specs
| Protection | Threshold |
|---|---|
| Over-Charge | >4.3V |
| Over-Discharge | <2.3-2.5V |
| Over-Current | 16A |
| Short Circuit | yes,resettable, 200mS delay |
| Continuous Current | 10A |
| Size | 24x11x2mm |
Charging
When charging batteries through this BMS, the charging voltage needs to be 8.4V. The BMS limits the charging current to 10A.
This board is available as 1S BMS also and looks almost the same. The 1S BMS is lacking the B1 terminal.
Regular Size
This is a regular size board:
All connections are available both from front and back and are clearly marked on both sides:
Connection
Connect the batteries like this:
- First battery string to B- (-) and BM (+)
- Second battery string to BM (-) and B+ (+)
The output voltage is available at P+ and P-.
This board often has the model specification HX-2S-JH20 printed on the back side.
Specs
| Protection | Threshold |
|---|---|
| Over-Charge | >4.3V |
| Over-Discharge | <2.5-3.0V |
| Over-Current | 20A |
| Short Circuit | yes, resettable |
| Continuous Current | 10A |
| Size | 46.7x23x3.15mm |
Charging
When charging batteries through this BMS, the charging voltage needs to be 8.4V-9.0V. The BMS limits the charging current to 10A.
A heat sink may be required with currents exceeding 8A.
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(content created Mar 26, 2024 - last updated Mar 28, 2024)