Battery Health Monitoring PCB
One of three on a custom KiCad board that monitors the car's low-voltage pack — voltage, charge rate, state of charge and pack health — and raises a fault to the driver when something is wrong.
- Role
- PCB design and component selection
- Organisation
- Bruin Formula Racing — Electrical Distribution
- Dates
- 2025 – present
- Status
- In development
- Tags
- KiCad · BQ76942 · I²C · Test rig design
- Monitors
- Low-voltage pack (not the accumulator)
- Tracks
- Cell voltage, charge rate, state of charge, health
- BMS front end
- TI BQ76942, 4 cells
- Tools
- KiCad
- Status
- BOM done, schematic in progress, not yet built
Why it exists
The car has a high-voltage system and a low-voltage system. This board covers the low-voltage pack — the one that runs the electronics rather than the motors — where a quiet failure is easy to miss until something stops working mid-session. The board tracks pack health, charge state and charging behaviour, and raises an error when any of them go out of range.
Requirements
Compact enough for the car's small electrical compartments. Track cell voltage, charge rate, state of charge and pack health, and detect charging faults — overvoltage, undervoltage, overcurrent, short circuit, and temperature.
My role
Board design and component selection, alongside two teammates. This is a new-member project on the Electrical Distribution System subteam.
Validation plan
A protection board is only worth what its fault behaviour is worth, and you cannot test that on a real pack without deliberately abusing a real pack. So the test rig was specified alongside the board:
- Cell emulator
- Four independent supply voltages standing in for the VC pins, steppable to drive the board into overvoltage and undervoltage, plus thermistor emulation or real thermistors on TS1/TS2.
- Programmable load
- Heatsinked discharge load, controllable from small currents up to the fault threshold, with a sense resistor for current measurement.
- Charge-side harness
- Bench supply and series resistor sourcing current into the pack to simulate overcharge and overcurrent.
- Harness and protection
- VC1–VC4, PACK+/PACK−, SRP/SRN across the sense resistor, TS1/TS2, CHG/DSG gates, ALERT, SDA/SCL — with fuse, TVS diode and gate resistors per the reference design.
- Logger
- I²C to the board under test, interrupt capture on ALERT, timestamped CSV of cell voltages, temperatures, status bits and fault events so reaction times can be computed rather than estimated.
- Test scripts
- One per fault mode — set condition, trigger, log the reaction, restore, log recovery — against written pass/fail thresholds and delays.
The obvious one: why the BQ76942 over a discrete implementation or another BMS front end? Also cell count and chemistry, and why this board is separate from the rest of the EDS rather than integrated. Two real tradeoffs will lift this page a long way.
On the car
A KiCad schematic screenshot and a 3D board render are both one export away and would round this page out.
Where it stands
Concept, BOM and the start of the KiCad schematic are done. The board has not been fabricated yet.