Lead-Acid BMS

LABMSV1

My goal with this project was to create a battery management system for a lead-acid battery so that I can later use it for another project. The main feature I wanted in this BMS was a latching low-voltage cutoff so that a manual reset would be required for the load to be reconnected to the battery. This project does not use any programmable microcontrollers.

Hardware

The board has 3 battery inputs, Vsup, Vbat, and GND.

Vsup is the current-carrying input, connected to the battery via an MCB acting as the switch and as a fuse.

Vbat is connected directly to the battery and is only used for latching the circuit in the off state and for charging the battery via the barrel jack (with a Schottky diode for reverse current protection).

GND is connected directly to the negative battery terminal. All grounds on this board are electrically connected together.

The current enters the board through the Vsup input and is connected to the relay's COM pin. From the normally closed pin it is then connected to the fuse casing, and from the other side of the fuse it is connected to the output terminals.

After the current exits the fuse, it is also used to power the LM358 opamp, the REF02CP reference voltage IC, and the TSR1-2450E switching regulator. The 5V switching regulator powers the CD4001BE NOR-gate IC and the power led (bottom left).

PCB design

The BMS uses a 4-layer PCB. There is absolutely no reason why a 4 layer PCB is required. I chose to use 4 layers because the price difference was not that much and because I wanted the outer layers to be dedicated to current carrying.

Testing and validation

The 24V battery cutoff works as intended.

The 12V battery cuttoff does not work due to an oversight in the circuit design that I didn't catch during the simulations. The fix is trivial and will be included in version 2.

Unfortunately, during testing I burned the buck converter I was using so any in depth testing such as timing analysis and oscilloscope shots will have to wait.

Front side

Back side

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