Hi everyone,

I need your help. My Voltronic VM III 5000-48 was running on original Main CPU 91.19 and Secondary 102.70.

I mistakenly flashed Main CPU 41.63 (found on a distributor website). The flash was successful, but now the inverter is stuck on Error F51 (Inverter Over Current) immediately at startup, even with no loads connected.

I understand this is a "false positive" due to firmware/hardware mismatch between branch 91.xx and 41.xx. I am looking for the firmware VM III 91.17 (or 91.19/91.20) to perform a rollback and fix the sensors' calibration.

Does anyone have the .hex file for the 91.xx series for VM III?

Thank you so much in advance!

On 2026/04/14 at 8:12 PM, stefanoch said:

I mistakenly flashed Main CPU 41.63 (found on a distributor website). The flash was successful, but now the inverter is stuck on Error F51 (Inverter Over Current) immediately at startup, even with no loads connected.

I understand this is a "false positive" due to firmware/hardware mismatch between branch 91.xx and 41.xx.

I'm a little surprised by that incompatibility, though it does reinforce the "same major firmware number (series) is best" adage. But VM III firmwares are so chaotic that it's often hard to follow that logic.

I have version 91.19 but also a later (2021) 91.25 that has similar ratings and is also for the older VM III models. Neither of these seems to be published, so I'll add them below.

Edit: Removed confusion about 91.17.

Edited April 15Apr 15 by Coulomb

This is main (U1) factory firmware version 91.19 for the Axpert VM III (older models) 1500/3000/3200/5000/5200W PF1 '28062 non-Twin. Do not use with any other model or version; not even models that come with main firmware version 41.xx (see first post of this thread).

Use at your own risk. The hex file is dated 18/Aug/2020.

Firmware upload instructions for models with a removable display.

This firmware does NOT process the QDOP command, so with suitably recent display firmware, it will not support SoC% for settings 12,13, and 29 when connected to a suitable battery's BMS.

The file name mentions "slower fan for low load".

VMIII_Ver91.19_Slower fan for low load.7z

This is main (U1) factory firmware version 91.25 for the Axpert VM III (older models) 1500/3000/3200/5000/5200W PF1 '28062 non-Twin. Do not use with any other model or version; not even models that come with main firmware version 41.xx (see first post of this thread).

NOTE WELL: ALL models are 48V, including the 3200W, 3000W, and even 1500W models! Usually these are 24V. CHECK YOUR INVERTER'S VOLTAGE!!

Use at your own risk. The hex file is dated 08/Mar/2021.

Firmware upload instructions for models with a removable display.

This firmware does NOT process the QDOP command, so with suitably recent display firmware, it will not support SoC% for settings 12,13, and 29 when connected to a suitable battery's BMS.

91.25 FW reflash.7z

Edited April 30Apr 30 by Coulomb
Added warning about 48V for every model.