External Control / DynamicEss Node-RED mode accepteert setpoints, maar batterij reageert er niet op

Has anyone managed to get Node-RED setpoints to actually do anything with a Victron ESS setup?

I've been experimenting with the External Control / DynamicESS mode on my Cerbo GX (Venus OS v3.x) and I can see the setpoints being accepted in the Node-RED dashboard — the values land correctly on the MQTT topics — but the MultiPlus-II doesn't seem to care. Battery just does whatever it likes regardless.

My setup:

• MultiPlus-II 48/5000 (firmware 502)
• Cerbo GX
• Fogstar Drift 48V LiFePO4 with CAN-bus BMS
• ESS enabled, normally runs fine via VRM

What I think is happening is the CAN-bus BMS might be overriding the charge/discharge commands, essentially taking priority over whatever Node-RED is pushing. The BMS has final say and it seems to be ignoring the ESS setpoints entirely.

A few things I'm wondering:

1. Does the BMS communication mode need to be set to a specific option before External Control works properly?
2. Is there a known conflict between CAN-bus managed batteries and Node-RED ESS control?
3. Should I be writing to com.victronenergy.battery paths rather than the ESS assistant paths?

My main use case is emergency backup management — I want to programmatically hold the battery above a certain SOC threshold during grid outages rather than relying on the VRM scheduler, which feels a bit fragile for critical stuff.

Anyone cracked this, or hit the same wall? Particularly interested if you're running a CAN-bus BMS rather than a simple voltage-based setup.

Watching this thread closely — I've hit the same wall on my boat conversion with a Cerbo GX and a couple of Fogstar Drift 100Ah batteries.

One thing I noticed: are you confirming the ESS mode is actually switching to External Control in the DVCC settings, not just appearing to accept it? On mine, the setpoint looked like it was being written via Node-RED but the MultiPlus was completely ignoring it until I realised the DVCC charge current limit was overriding everything upstream.

Also worth checking — what Venus OS build specifically? There were some known issues around v3.10-3.20 where the com.victronenergy.system setpoint path wasn't being honoured correctly.

What path are you writing to in Node-RED? The /Hub4/L1/AcPowerSetpoint vs /Ac/In/... distinction caught me out badly.

@SunnyNomad yes, been down this rabbit hole with my motorhome setup. The thing that caught me out was that External Control mode requires the ESS assistant to actually be installed on the inverter/charger — not just configured on the Cerbo. Sounds obvious in hindsight, but the Cerbo happily accepts setpoints either way without complaint.

Also worth checking: the setpoint path needs to be /Hub4/Setpoint via MQTT or dbus, not just writing to a random grid setpoint path — the naming confused me for ages.

One more gotcha — there's a 30-second watchdog. If your Node-RED flow doesn't refresh the setpoint within that window, the system falls back to normal ESS behaviour silently. Tripped me up repeatedly before I added a simple inject node on a timer loop.

@DownsDweller the Fogstar Drift BMS communication layer shouldn't affect this particular issue — it's upstream of that.

Good thread. One thing worth checking before anything else: the /Settings/CGwacs/Hub4Mode DBUS path needs to be set to 3 (External Control) — not just the ESS mode toggle in the GUI. They're separate settings and the GUI alone won't get you there.

Once that's confirmed, verify your setpoints are landing on /com.victronenergy.hub4/Ac/Control/ChargePower or the relevant path using dbus-spy directly on the Cerbo. I've caught Node-RED flows silently failing to write because the service name had a subtle typo.

Also worth noting: the MultiPlus-II needs a moment after mode switch before it responds to setpoints — I found a 10–15 second delay in my flow resolved what looked like the battery ignoring commands entirely in my shepherd's hut setup.

@CaddyCamper — curious what your Hub4Mode value was when you hit issues?

Really useful thread this — I had the exact same headache with my motorhome emergency backup setup last year.

One thing nobody's mentioned yet: even with Hub4Mode set correctly and External Control active, the MultiPlus needs to be in the right inverter mode via DBUS (/Mode path). If it's sitting in Charger Only it'll flat-out ignore ESS setpoints regardless of what Node-RED throws at it.

Also worth checking: are your setpoints within the min/max power limits configured in the ESS assistant? Out-of-range values get silently discarded — no error, nothing in the logs, battery just sits there doing nowt. Drove me absolutely mad before I spotted it.

@CaddyCamper did you find the AcPowerSetpoint write needed to happen on a regular heartbeat interval, or was a single write sufficient on your setup?

Good points all round here. One thing I'd add that hasn't been mentioned yet — check your /Settings/CGwacs/AcPowerSetPoint is actually being written with the right data type. Node-RED can be fussy about this; it needs to be an integer, not a float or string. I spent an embarrassing amount of time staring at my flows before realising I was pushing "0" instead of 0.

Also worth verifying your Node-RED MQTT broker is actually authenticated properly to the Cerbo — silent failures are common if the credentials are slightly off. Chuck a debug node after your write and confirm the broker is acknowledging the message. @SunnyNomad what does your current flow look like? Might help narrow it down quicker if you can share a screenshot.