Domoticz

Conclusions: HomeWizard P1 multiplexer + Domoticz + Ratio Solar
1. HomeWizard P1 splitter is not a true multiplexer
Despite the name, the HomeWizard P1 splitter does not actively buffer or independently replicate the DSMR data stream.
What it does instead:
Passes through the single serial P1 data stream
Relies on well-behaved listeners
Has no arbitration, no buffering, no timing isolation
This is fine only if all connected devices behave passively and politely.

2. Ratio Solar EV charger works reliably on the P1 splitter
Your observation confirms this:
Ratio charger (via wireless sensor box)
Reads P1 data read-only
Does not request data, does not reset the port
Has predictable, low-impact timing

Result: stable operation, correct solar charging behavior

This is exactly the kind of device the HomeWizard splitter can handle well.

3. Domoticz P1 integration is the destabilizing factor
As soon as Domoticz P1 is connected:
Short time later → P1 communication failure
Ratio / HomeWizard chain becomes unstable
Sometimes works for hours or days, then fails
This strongly indicates that Domoticz:
Actively opens/closes the serial connection
Possibly toggles DTR / RTS
Parses DSMR aggressively
May not fully respect DSMR timing or voltage constraints

The splitter cannot isolate Domoticz’s behavior from the other device.

4. Why it sometimes works “for a week”
This is important — and misleading if you don’t know why.
Likely explanation:
Timing coincidentally lines up
No reconnects/restarts
No CRC or framing errors during that period
But:
The setup is marginal
One reconnect, Domoticz restart, or timing hiccup is enough
Failure is inevitable, not accidental

A week of uptime does not mean the setup is sound.

5. Root cause (summary)
The real issue is:
Two active P1 consumers on one passive splitter
Specifically:
Ratio = passive listener → OK
Domoticz = active serial client → NOT OK
HomeWizard splitter = no isolation → conflict
Final verdict
HomeWizard P1 splitter + Domoticz + Ratio Solar

Structurally unreliable

HomeWizard P1 splitter + Ratio Solar only
Stable and supported
HomeWizard P1 splitter + Domoticz only
Usually works, but still depends on meter and cable quality

Recommended solutions (ranked)
Best solution
One real P1 master → distribute data in software
Use Home Assistant / ESP / P1 reader as single P1 master
Forward data via:
MQTT
HTTP
Modbus TCP
Let Domoticz & Ratio consume derived data

Hardware-safe option
Active P1 buffer / isolator
ESP32 with optocoupler
Commercial buffered P1 splitters (rare, but real)
Not recommended
More passive splitters
USB-TTL Y-cables
Hoping Domoticz “behaves nicer”

If everything else fails and you can't find a solution, you could try to replace the current wired Domoticz P1 with a Homewizard P1 that can be read by Domoticz via Wifi.

For years domoticz is stable running.

FireWizard wrote: Wednesday 04 February 2026 14:18 Hello @BartSr

@willemd said:

If everything else fails and you can't find a solution, you could try to replace the current wired Domoticz P1 with a Homewizard P1 that can be read by Domoticz via Wifi.

But how do you intend to connect your EV sensorboxes?

The P1 splitter is the probable root cause.