🔋 Sponder

Replacing the Mia's BMS without depending on anyone — a personal project, still in development

🚧 Nothing to download, nothing to try on your car. Sponder has never been driven yet. This page tells where the project comes from and where it stands; it is neither a manual nor an invitation to reproduce it.

⚡ Why this project exists

The original BMS of the 12 kWh Mia, made by E4V, can no longer be ordered. When its electronics fail — fault code P3054 is the typical symptom — the car will not start, even though the battery pack itself is often perfectly healthy.

Configuring or unlocking it requires proprietary software that almost nobody masters. That is not a failure, it is a dependency — and this project aims not to carry it into the next ten years.

Starting point, checked on captures from several vehicles: the dialogue between the BMS and the vehicle controller (EGV) is unencrypted. Replacing the BMS is an engineering problem, not a wall.

Three layers, each in its own role

No off-the-shelf BMS can hold the dialogue the Mia expects on its own: the EGV does not merely read frames, it drives its BMS and waits for answers. Sponder is the missing layer between the two.

🚗
The Mia, unchanged
Original EGV, motor controller, charger, contactors and battery packs. Nothing is modified in the car.
🔁
Sponder, the interpreter
A dedicated controller (ESP32-P4) on a custom carrier board. It speaks Mia on one side and the BMS protocol on the other, and reproduces the behaviour of the original BMS: state machine, acknowledgements, start-up sequence, charging dialogue.
🔋
An open BMS
An unmodified Ennoid Gen 1 doing its job: measuring the 24 cells, balancing them, protecting the pack. Open hardware, configurable without paid software.

The hardware

The module running Sponder on the bench, its carrier board as it was designed, and the Ennoid BMS as it arrived. The bare carrier boards are manufactured; none is soldered yet.

Waveshare ESP32-P4-WIFI6 module plugged into a breadboard, wired to the test bench
Sponder's brain — an ESP32-P4 module (Waveshare), here on the test bench. On the right, its ESP32-C6 co-processor provides Bluetooth; the P4 itself has no radio.
3D view of the Sponder carrier board, 150 × 78 mm, with the ESP32-P4 module footprint
The carrier board, 3D view (KiCad) — 150 × 78 mm. The ESP32-P4 module plugs into the 2 × 20 socket on the right; it is not shown.
Ennoid Master-LV main board, top view, with its BAT and LOAD power lugs
Ennoid Master-LV — the main board: current measurement, pack contactor control, CAN dialogue.
Ennoid 18-channel slave board with LTC6813 chip and balancing resistors
18-channel slave (LTC6813) — measures and balances the 15 cells of the main module.
Ennoid 12-channel slave board with LTC6811 chip and balancing resistors
12-channel slave (LTC6811) — measures and balances the 9 cells of the secondary module.

Safety principles

  • Sponder never opens a contactor. If the BMS data goes silent, it progressively cuts the allowed current: the car loses power and the driver has time to pull over.
  • If Sponder fails, the BMS keeps protecting the battery. That is the whole point of the three-layer split.
  • Sponder listens to the BMS and never talks to it. It cannot change its configuration, drive its contactors or switch it off.
  • Bluetooth diagnostics are read-only. A controller handling hundreds of amps must not be influenced from a phone.

Where the project stands

Status as of 29 September 2026.

✅ On the bench: the dialogue expected by the EGV is produced and checked at start-up against more than a hundred vectors taken from real captures; the real Ennoid BMS is connected, reconfigured for the Mia's LiFePO4 cells and its 24 cells, and the state of charge read by Sponder matches frame for frame; degraded modes are exercised on every run; Bluetooth diagnostics work.

⏳ Not yet: the carrier board is not soldered, the BMS has not seen real cells, and nothing has run in a vehicle. No date is announced.

Did you find this address on a circuit board?

The address EVSpark.fr/sponder is printed on Sponder's carrier board. If you find it in a Mia, it is the board that talks to the vehicle controller in place of the original BMS. This page will later host the diagnostic tool that reads it from a phone.

⚠️ Without it, the car will not start. Do not unplug it "to see", and do not connect it to any other vehicle.

Follow the project

The origins, the choice of BMS and the progress are told in detail, in French, on the vehiculeselectriques.fr forum, where each step will be published as it happens — including the ones that fail.

Read the forum announcement

The Mia-specific work — firmware, board design, wiring — will be published, but not before the system has run in a car. Until then there is nothing to share, publicly or privately.

Disclaimer

Sponder is a personal project that commits no one but its author. It deals with the traction battery, its contactors and vehicle safety. What is described here is a field report, not a manual: the author accepts no liability if anyone tries to reproduce it, in whole or in part, and it does not work or causes damage. No support is provided for other builds.

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