Error 11 and Loss of VE.Bus Power in a 3-Phase MultiPlus-II 48/5000 System After a Short Circuit on

Q&A and troubleshooting
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System Background and Configuration

The system consists of three MultiPlus-II 48/5000/70-50 inverters configured in a 3-phase setup, along with a Cerbo GX.

The installation had been operating stably and successfully for about one year.

The problem started after a short circuit occurred in one of the sockets on the load side.

Following this event, the inverters stopped functioning correctly in backup mode.

Problem Description and Current Symptoms

After attempting to update the configuration and restart the system, the inverters began entering a cyclic error state.

They operate normally for approximately 3–4 minutes, after which they drop AC Out for about one minute, and then resume operation again.

Currently, the system does not start properly, and the LED indicators show Error #11 (Relay Test Failure).

The main difficulty is that in a three-phase configuration it is not possible to determine which of the three inverters is generating the relay error.

Diagnostic Steps Already Taken

We physically disconnected the VE.Bus cables from the Cerbo GX and also disconnected the VE.Bus connections between the inverters, in order to test each inverter individually as a single-phase unit.

The master inverter (L1), when connected alone, shows no signs of life and is not detected at all via the MK3-USB interface.

We were only able to revive the L1 inverter by connecting the VE.Bus cable from the second inverter (L2).

Apparently, after receiving port power from the neighboring device, L1 powered up and we were even able to update its firmware.

Note: When we tried installing a brand-new inverter directly on phase L1, the firmware update process also failed with EEPROM / Bootloader errors.

Questions to the Community

  1. How can we accurately determine which specific inverter (out of the three) has the damaged or stuck relay causing Error 11?

  2. Is it possible that the AC short circuit damaged the power supply circuit for the VE.Bus communication ports on the L1 inverter?

  3. Why does the new inverter installed on phase L1 not operate when the VE.Bus bus is disconnected?

  4. What is the correct step-by-step procedure to follow in this situation in order to restore the system to normal operation?

Please HELP :slightly_smiling_face: