New Multiplus II 48V goes in to Fault Condition with Battery Low Voltage Warning when > 50V

Q&A and troubleshooting
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1

I am experiencing a recurring “Low Battery Voltage” fault on my Victron MultiPlus-II 48/3000/35-32 inverter/charger, which causes the unit to enter a fault condition and stop inverting. This happens even when the battery voltage is well above the configured low voltage thresholds. I have tried several troubleshooting steps based on community advice and documentation, but the issue persists. Below is a detailed description of my system, the problem, and what I’ve done so far. I’d appreciate any guidance or next steps to resolve this.

System Description

  • Inverter/Charger: MultiPlus-II GX 48/3000/35-32 (firmware version: 3.67)

  • Solar Charger: SmartSolar MPPT (150/20)

  • Battery Monitor: SmartShunt 500A (connected via VE.Direct to USB on MultiPlus GX)

  • Battery: 48V lithium battery bank

  • Setup: 100% off-grid, no AC input. System powers a pump during daylight hours via solar. MPPT charges battery; inverter only runs when solar is sufficient (automated via Home Assistant).

  • Connections: MPPT and SmartShunt integrated with MultiPlus GX. DVCC enabled with Shared Voltage Sense (SVS).

  • Monitoring: Via VictronConnect app, VRM portal, and Home Assistant (MQTT integration).

  • Load: Primarily the pump, 1200-350W

Problem Description

  • The MultiPlus-II triggers a “Low Battery Voltage” alarm and enters fault mode, shutting down the inverter, with no load so no voltage sag

  • This occurs despite the SmartShunt reporting battery voltage above 49V.

  • Configured thresholds in VEConfigure (Inverter tab):

    • DC input low shut-down: 37.20V

    • DC input low restart: 43.60V

    • DC input low pre-alarm: 43.60V

  • No ESS or other assistants enabled (off-grid mode).

  • The fault happens under no load or idle.

  • No other alarms (e.g., overload, temperature) are present.

Troubleshooting Steps Taken

  1. Voltage Drop Check: Measured voltage at battery terminals vs. MultiPlus DC terminals – no drop.

  2. DVCC Configuration: Enabled SVS in GX settings to use SmartShunt’s voltage reading for the MultiPlus – fault still occurs.

  3. Firmware Updates: Updated all devices (MultiPlus, GX, MPPT, SmartShunt) to latest via VictronConnect.

  4. System Test: Disconnected load (pump), restarted MultiPlus – fault clears temporarily but returns.

  5. Community Advice: Followed Victron Community threads on similar “false low voltage” faults (e.g., wiring drops, ripple) – no resolution yet.

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2

Is there any dust/moisture ir corrosion inside the unit?

Is the inverter reading its own terminal voltage correctly?
(If you use ve config or victron connect for stats with a dmm on the terminals)

It looks like it does on the gx screen.

The other suggestion i have is maybe run through the pre rma.

3

Out of the box, it was reading ~2.4V higher than the SmartShunt (in HA). It did have some dust on it, but nothing I would call problematic.

My MPPT was connected to the battery terminals of the MultiPlus-II, so if the battery was acting up, the MPPT might have just been powering the MultiPlus-II directly. There’s no record anywhere of the voltage dropping below 48.8V.

I’ll do a pre-RMA check: disconnect everything, power it with just a PSU, and monitor the results.

4

Interesting how with a higher reading it is still cutting off early when inverting. Keen to hear your findings with the bench test.

5

A bench test with no load was successful, so I reinstalled the unit and re-verified all cabling, which appears to be in good condition.

My theory: The BMS was disconnecting the battery due to over-current protection. During these events, I was likely reading the MPPT voltage. Once the battery was disconnected from the load, the BMS reset, and the battery voltage appeared normal again. Consequently, the MultiPlus attempted to draw power directly from the MPPT, causing the DC voltage to become highly unstable.
I think the Multiplus was more sensitive to any logging so voltage always looked fine. Also transient current spikes may also have contributed. But honestly I have no idea, but since I’ve limited the inverter to 1600W ~35A it has not shutdown. I now have another problem though, grid disconnects :frowning: