Wiring diagram 123-Off-Grid

After the introduction of affordable Lithium-Ferro-Phosphate batteries, off-grid solutions became feasible. It is vital that such batteries are charged very carefully. In other words, they can easily be over-charged, or over-discharged. Cell-temperature and current are also very important, in order to guarantee a long life.

The 123electric Battery Management System (or: BMS) is primarily intended for prismatic LiFePO4-cells, but can also be adapted by the end-user for other cells like Li-Ion and LiPo, provided the cell-voltage is in the range of 2V to 5V.

The diagram shown on  the right, gives a nice overview of a wired system consisting of a single pack of batteries with BMS-boards, the relay block, the current-sensor and in the middle the circuit-board of the 123electric BMS-controller.


For a single pack of say 16 batteries, the system would consist of:

1 BMS-'IN'-board

1 BMS-'OUT'-board

14 ordinary BMS-boards

1 BMS-Controller (Including: 100 Ampere current sensor and relay block)

 (Important: for sub-divided battery-packs, each sub-pack will have to be equipped with its own BMS-'IN' and BMS-'OUT' -board!)  


The BMS-boards are interconnected with a soldered single-wire, which makes mounting less time-consuming, and very reliable. The 'IN'- and 'OUT'- boards connect via a twisted-pair to the BMS-controller. (or, in case of sub-divided battery-packs, to the next-in-line)

To measure current during charging and dis-charging, the current sensor should be connected in the position indicated. This is important, as this sensor is used for the so-called Coulomb-counting software, with which the BMS-controller calculates the remaining battery-capacity.

The Relay block is directly controlled from the BMS-controller.  These two high current relays (60 Ampère) will control the charge and discharge current. This results in an optimum balanced and protected battery pack.


 In the settings-area of the PC-software, one can customise practically anything:

- Voltmeterscale: 10-60V; 40-140V; 100-200V; 150-300V & 250-500V

- Current sensor: 100A

- Cell-capacity: 10 - 999 Ah

- Cell-voltages (Vmax, Vmin, Vbypass & V-recharge)

- Cell-temperature (Tmax, Tmin in degrees Celsius)