Open-source 3/4/5S Lithium BMS

In this Instructable the design of the BMS345 will be explained. The design is fully open-source, the design files can be found in the GitHub link in the last step. There is also a limited supply available on Tindie.

The BMS345 is a BatteryManagementSystem that supports 3, 4 and 5 cells lithium-ion packs. If you build/buy a pack with unprotected cells, this PCB can be added to handle protection and charging. This includes:

• Under/overvoltage protection
• Overcurrent (/shortcircuit) protection
• Cell balancing
• MPPT charging

The documentation will be divided into:

1. Protection
2. Charging
3. Configuration
4. The end product

Enjoy :)

The protection is handled by the TI BQ77915.

• The input resistors are 1K, which sets balancing current to 4mA/cell
• The header is the commonly used JST-XH 4/5/6P depending on the configuration
• A NTC can be connected to header J5, but this features is disabled by default by R26
• The negative connection is switched by a dual N-channel mosfet (NVMFD5C466NL)
• The current sense resistor is 2x8m (4m equivalent) ohm, setting the current protection to 15A

The charging is handled by the TI BQ24650

• D1 shows the charging status, an external LED can be connected via J4
• R30 sets the charge current to 1A
• Temperature sensing is disabled by R13/R14/C14
• MPPT voltage is set to 17.2V by R22 and R28
• The mosfets are the same dual-package type as is used in the protection circuit
• The default charge voltage is 4.2V, which barely trips the overvoltage protection of the BQ77915. It is recommended to populate R36 with 22M to lower the charge voltage to 4.05V/cell. This avoids false over-voltage triggering.

Charging can be done from a 24V 1A supply or even a solar panel (only for 3/4S configurations).

This header can be just with jumpers to set the configuration.

You can add the PCB to a Vruzend system as seen in the picture, but it is also suited for RC lipo and regular spot-welded packs.

Link to Tindie:

https://www.tindie.com/products/zoudio/bms345-prot...

Link to github

https://github.com/ZOUDIO/BMS345

Thanks for reading.