Multiplus IIgx+external current sensor–delayed inverter response after AC restore until reset VE.BUS

Q&A and troubleshooting
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Multiplus II GX with external current sensor – delayed inverter reaction after AC input restore (ESS: Optimized without BatteryLife) until VE.Bus reset is performed

Issue description:
An external current sensor is connected to the Multiplus II GX 48/3000. Please disregard the battery voltage, as an LTO battery is used (Absorption voltage: 61 V, Float voltage: 58.4 V). The system is being tested with a load connected between the current sensor and the inverter input. ESS is configured in the mode: Optimized without BatteryLife. Initially, everything works as expected. A video was recorded to demonstrate the behavior.

Key moments in the video:

0:35 – A resistive load (heater) is turned on; the system initially responds correctly.

0:50 – The AC input breaker of the inverter is switched off. The load remains connected because the main grid was not interrupted.

1:00 – The AC input breaker is switched back on.

2:15 – The system still detects active load, but the battery is not discharging.

3:05 – Grid load information appears on the dashboard, although the load has been active the entire time between the current sensor and the inverter input. At this point, the inverter very slowly starts compensating for the heater’s consumption: grid power draw gradually decreases, and battery discharge increases, but with noticeable delay.

5:02 – The heater is turned off, but the system response is still slow. It continues feeding energy into the grid, and this export stops only 2 minutes and 25 seconds later.

7:30 – Grid feed-in finally stops.

7:40 – The heater is switched on again. Once again, the inverter’s reaction to the load change is very slow.

8:40 – Even after a full minute, the system still does not fully compensate the load.

8:50 – A “VE.Bus reset” is executed via the Remote Console.

10:09 – The system starts working correctly again, reacting promptly.

11:15 – My wife turned on a hot water tap, activating the flow-through water heater. While this nearly disrupted the experiment, the inverter still reacted quickly and correctly.

Core issue summary:
After switching the AC input breaker off and then back on, the system enters a state where its reaction to load changes becomes abnormally slow. The inverter does not compensate the load from the battery properly until a manual “VE.Bus reset” is performed.

Firmware version used:

Device: MultiPlus-II 48/3000/35-32
Serial number: HQ23202хххх
Firmware (GX): v3.55
VE.Bus firmware: v556
Firmware status: Up to date (20.04.2025)

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After observing no change in behavior when switching to the internal current sensor and unchecking the related option in VE.Configure, I also tried removing all Assistants except ESS — but the issue persisted.

Since I cannot allow any grid feed-in in my setup, I’ve implemented a temporary workaround using Node-RED (see flow above). It monitors AC input voltage, and if it drops below 100 V (nominal ≈230 V), a 10-second trigger is started. However, as long as the voltage remains low, the delay is automatically extended. Once the AC voltage is restored and stable for 10 seconds, the flow sends a signal to trigger a VE.Bus reset.

:warning: Important note: This solution comes with a major drawback — it reinitializes the input relay check and causes the AC output to briefly drop, which is unacceptable for critical loads. Nevertheless, it ensures proper ESS behavior is resumed after the grid returns.

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Clarification regarding the “Power rate 100% per [X] s” parameter and its effect on ESS behavior

According to EN 50549-1:2019, section 4.10.2, the Power rate 100% per [X] s setting is intended to limit the ramp-up of active power after automatic reconnection following a disconnection (e.g., due to voltage or frequency deviations). This is to avoid a sudden injection of power into the grid.

“After reconnection, the active power generated by the generating plant shall not exceed a specified gradient…”

:white_check_mark: This logic is valid only after reconnection.

However, in practice, I observed that this power ramp limitation only affects the system during the first 600 seconds after grid reconnection (based on the default setting). So at first glance, the behavior seems to align with the standard.

But the issue is that even during this 600-second ramp-up period, ESS should still respond instantly to sudden changes in local load, especially when large loads are turned off.

:warning: In my case, when a large load was suddenly disconnected during this period, the inverter continued generating power at the limited ramp-down rate — instead of immediately reducing output — which resulted in:

  • Unwanted feed-in to the grid (problematic in systems with non-bidirectional meters),
  • Voltage spikes or disturbances on the grid due to delayed power reduction.

Expected behavior: Even during ramp-up after reconnection, the inverter should immediately reduce output to match actual load consumption, thus avoiding grid injection and electrical disturbances.

While waiting for your feedback and comments, I have temporarily changed the “Power rate 100% per 0 s” (instead of the default 600 s in the “Reconnection after trip” section). As a result, no feed-in to the grid occurs after a sudden disconnection of a large load. This is a temporary workaround!

Can you confirm whether this is the intended behavior, or should this be considered for firmware adjustment?