CellKeeper

CellKeeper BMS — v1.1

KiCad PCB design for the CellKeeper Battery Management System, a replacement BMS controller for battery packs using the isoSPI protocol. The main board fits the Tesla battery's penthouse: the pack's original harness, HV sense, shunt and BMB connectors plug into it, and it mounts on the original brackets.

Each ordered revision has a release with its Gerbers, JLCPCB BOM and CPL, schematic PDF, board PDF (3D views and 1:1 prints) and the enclosure print files. Rev 1.1 was ordered on 2026-10-28; work towards rev 1.2 is on the rev1.2 branch.

Overview

• MCUs: two Raspberry Pi RP2354B (dual Cortex-M33, 2 MB in-package flash): the main BMS controller and an independent supervisor, linked by UART. The supervisor also sees the isoSPI receive line and the E-stop input, and it alone enables the contactor drivers.
• Current sensing: TI INA228 (20-bit) on a galvanically isolated domain (ISO1540 I2C isolator, isolated 5 V DC-DC), also reading the shunt's temperature.
• HV sensing: 6 sense points (BAT±, LINK±, FC±) through 501:1 dividers into two ADS1115 ADCs: pack, link and output voltage, and the voltage across each contactor.
• BMB communication: transformer-isolated isoSPI master (SP3485 driver, AM26LV32 receiver, HM2113 transformer), Manchester-encoded by the RP2354's PIO.
• CAN: two ISO1050 interfaces: inverter CAN, isolated with its own DC-DC, on an RJ45 shared with the E-stop and aux lines; and inter-BMS CAN2 on a pass-through RJ45 pair (not isolated).
• Contactors: four low-side drivers (FC+, FC-, Link+, Link-): BSC0805LS MOSFETs and UCC27524 gate drivers, PWM'd by the firmware to economise the hold current. The contactor supply is sensed.
• Supply: 13–16 V logic and contactor inputs (separate, both sensed), TPS5430 5 V buck and 3.3 V LDO; chassis ground terminal.
• HV battery: 400 V nominal.
• USB-C ×3: BMS, supervisor, and HMI link. The HMI link is not for a computer: it powers an external ESP32 display (5 V 1 A) and carries its serial.
• I/O: E-stop input (optocoupler; jumper JP37 disables it), an extra opto input and two extra outputs, fast-charge contactor aux-contact inputs for weld detection, SX serial interface, and experimental PCS signals on jumpers.
• Board revision strap on GPIO47 (ADC7).

Repository Contents

Three boards, each its own KiCad project. They share no copper: the hat and the precharge board connect to the rest of the system by wires and lugs.

Enclosure

A two-part printed case (base tray and lid) for the main board, generated by enclosure/cellkeeper_case.py. It mounts in the penthouse on the original HVC brackets. The lid carries the logo and connector labels, which can be printed as a contrasting-colour inlay, with open tunnels over the LEDs. Ready-to-print STEP and STL files are attached to each release; running the script writes them to enclosure/output/print/. The board shows the case in KiCad's 3D viewer through the ENC1 footprint.

Safety

⚠️ This board interfaces with 400 V battery packs that can deliver lethal current. Only qualified personnel should work on high-voltage systems. This is a v1.1 development design — untested, no warranty, use at your own risk.

Acknowledgments

• Damien Maguire & Tom de Bree — Original BATMan BMS software

License

GPL-3.0 — see LICENSE.