I bought 2 x BMS JK-PB2A16S-15P for my two batteries and I wanted to connect them to my Voltronic Axpert VMIII 3kW-24V inverter. I found that in the menu in item 05 I only have 3 items, namely AGM, FLD and USE, there is no Pylontech and nothing else. I have the inverter connected via RPi4 to Solar Assistant, where in the settings I can change the type of battery connected to the inverter, but I don't think anything will change in the inverter, because there are no similar settings in its menu. I have attached the label on the inverter, with U1 being 20.58, U2 being 01.12 and U3 being 00.21. Can anyone recommend an update for my inverter so that I can connect it to the mentioned JK BMS?

https://photos.app.goo.gl/bz2Q8q94P77jfWuC7

https://photos.app.goo.gl/C8E65WNL3RqG9xjJ7

Did you try to set it with official watchpower sw?

Interestingly, the WatchPower mobile app also has a "Pylon" option, which can be saved, but when viewing via the removable panel, there is no such option and "User" is still set.

So I decided to contact Voltronic in Thailand. To my surprise, they wrote back the next day that they needed the inverter serial number, which I provided and also listed the current firmware versions in the inverter (U1 - 20.58, U2 - 01.12 and U3 - 00.21). Three days later I received an email with links to Voltronic's ftp, where they created a directory for me and saved the firmware U1 DSP 41.18 and U2 REMOTE PANEL 02.89 in it, along with instructions for updating.

1. Do you think it will be safe to update the firmware?

2. What should I update first, the DSP or remote panel?

3. Is it possible to download the DSP 20.58 and remote panel 01.12 firmware somewhere (the original one, if it doesn't work) and where, or can I back up the firmware from the inverter, if so, how?

4. Do I need a 1k resistor in the RS232 cable on the white wire?

Edited October 30, 2025Oct 30 by blaskoi

If it helps anyone, here is my communication with Voltronic:

My question:

I am preparing to update the firmware on my off-grid inverter and require clarification on the correct procedure to ensure a safe update of the Remote Panel (MCU/U2).

Inverter Details:

·       Model: Axpert VMIII

·       Power: 3kW / 24V

·       Current DSP Firmware (U1): 20.58

·       Current MCU Firmware (U2): 01.12

·       New Firmware Version for DSP (U1): 41.18

·       New Firmware Version for Remote Panel (U2): 02.89

·       Serial Number (S/N): XXXXXXXXXX

My Question is highly specific to the U2 (Remote Panel) update procedure via the RS-232 port:

Based on my inverter's hardware revision (identified by the S/N above), is it mandatory to use an RS-232 cable with an added current-limiting resistor (typically 1kohm or 3 kohm inserted on the TX/White wire (Pin 2, or TX line from the PC to the inverter) when flashing the Remote Panel (U2) to version 02.89? I am aware that for some VMIII revisions, this resistor is critical to prevent communication failure and potential bricking of the display panel during the flash process. Please provide a definitive "Yes" or "No" regarding the 1 kohm resistor requirement for this specific U2 update (02.89) on my unit. Thank you very much for your immediate assistance and clarification on this critical safety point.

Reply from Voltronic (Tommy Wu):

Only Regarding SN is during  2021/11~2022/6,you must use reworked communication cable to update FW. Therefore, please make sure follow attached SOP to rework communication cable first. If you cannot rework communication cable,it's not recommended directly update. because it will fail and original FW will be erased. Your unit is 2018

Edited November 3, 2025Nov 3 by blaskoi

I have the same device do you talk and recognize the lithium battery

23 hours ago, hmid said:

I have the same device do you talk and recognize the lithium battery

Yes, the menu will change and items for LiFEPO4 will be added.