b2500-pico-bridge

A tiny MicroPython bridge that lets a Marstek B2500 balcony battery storage system talk to a Shelly 3EM Gen3 (or any other Shelly EM that the B2500 doesn't natively support yet).

Runs on a Raspberry Pi Pico W / Pico 2 W powered from any USB port — e.g. a router USB port that's already on 24/7. No Linux, no SD card, no extra power supply, no Docker.

Why this exists

The Marstek B2500 firmware only accepts smart meters whose RPC src field starts with one of the prefixes it has whitelisted (e.g. shellypro3em-…, shellyemg3-…, shellyproem50-…). The newer Shelly 3EM Gen3 identifies itself as shelly3em63g3-… and is therefore rejected by the B2500 even though it speaks the same JSON‑RPC over UDP and returns the exact same data fields.

This bridge sits between the B2500 and the Shelly:

B2500 ──UDP──▶ Pico W ──HTTP──▶ Shelly 3EM Gen3
        ◀──UDP──        ◀──HTTP──
        (rewritten src)

It listens for the B2500's EM.GetStatus requests, fetches the actual power data from the Shelly via HTTP RPC, and replies pretending to be a Shelly Pro 3EM by setting src to a shellypro3em-… value the B2500 accepts.

Hardware

Item	Cost	Notes
Raspberry Pi Pico W or Pico 2 W	~7–8 €	2.4 GHz WiFi required
Micro‑USB‑B cable, ~30 cm	~3 €	data + power, not charge‑only
USB power source	0 €	any 5 V port: router, wall plug, TV, NAS

The Pico draws ~50–150 mA, well under any USB 2.0 spec. Powering it from the Vodafone Station USB port works (data is locked, power is not) — see docs/setup.md for details.

Quick start

1. Flash MicroPython onto the Pico — see docs/setup.md.
2. Copy src/config.py.example to src/config.py and fill in your WiFi, Shelly IP, and a fake src value.
3. Upload src/boot.py, src/main.py, and src/config.py to the Pico via Thonny.
4. Unplug from your computer, plug into the router's USB port. Done.
5. In the Marstek app: Bluetooth disconnect, switch the B2500 to Self‑Adaptation. After ~30 s the meter shows up.

Status

Confirmed working with:

• Marstek B2500 firmware V110.9 (HMJ) — original target hardware
• Marstek Venus A — confirmed by @werner-thomas in #1
• Shelly 3EM Gen3, model S3EM-003CXCEU63, firmware 1.7.5
• Raspberry Pi Pico 2 W, MicroPython 1.x

If you confirm it works on a different combo, please open an issue or PR — happy to grow the compatibility table.

Optional: monitoring dashboard

The bridge can also report a heartbeat to Supabase every 5 minutes so a companion dashboard knows it's alive — see bjolo-de/b2500-dashboard. Two extra fields in config.py (both default empty = disabled), no change to the bridge's primary function.

Related projects

• tomquist/AstraMeter — the full‑featured Python emulator that supports many smart meter sources and runs on Linux/Docker/Home Assistant. This bridge is the minimal‑hardware counterpart, focused on a single use case.
• tomquist/hm2mqtt and tomquist/hame-relay — the upstream MQTT integrations the dashboard builds on top of.

License

MIT — see LICENSE.