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vanlifer007 avatar image
vanlifer007 asked

Modbus TCP unit ID keep on changing without reboot.

Hi Guys and Girls,

I would very much appreciate the help of this great community.

I am running Venus OS v2.66. I have Modbus TCP enabled and I am running Home Assistant to automate my campervan. I am able to read and write to registers and perform task suck as turning on and off the Multiplus (via MK3) based on certain conditions; SOC, Solar power etc.

I have been always having issues with the Multiplus Modbus TCP unit ID's changing without reboot. So I don't really know how it happens nor how to reproduce this. It always switches between ID 238 and 237. So this mess with my automation and therefore I am unable to control the Multiplus unless I change the register in Home Assistant to the corresponding ID shown in Venus. And when I change it it switches back again to the the original value. This can happen once every 2 days or twice a day... It is very random.


Is there a way to force the Multiplus to take one ID only like other devices? The smartshunt seems to always take 237 and the MPPT always on 239.


If it is not possible is there anyway ( for those with Home Assistant know-how) to programmatically read the Unit IDs and change them accordingly or a different approach to read and write Modbus registers?


Is Node-Red the cure here?


Many thanks guys and Girls ..;)


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Modbus TCPhome assistant
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2 Answers
wkirby avatar image
wkirby answered ·

That's wierd. It shouldn't be changing the unit ID or the related VRM instance number at all, obviously.
The only thing that I can think of is that the USB is disconnecting and reconnecting as a different device which would then cause the ID to change.

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vanlifer007 avatar image vanlifer007 commented ·
Thanks. I thought it was strange too.. the vrm instance changes sometime. I don't know what caused this.. all genuine cables.
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mvader (Victron Energy) avatar image mvader (Victron Energy) ♦♦ vanlifer007 commented ·

Hi, sounds like you're using a raspberrypi? Probably indeed usb disconnects/reconnects as wkirby. And (unlike vedirect connected devices) our software driver taking care of communications to the Multi has no special handling to prevent ID number changes.


We have not scheduled any software improvements soon for this. So the only thing I can advice you from Victron side is to get yourself a real GX device. There the modbus id numbers won't change.


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trenton avatar image trenton mvader (Victron Energy) ♦♦ commented ·
I am running a real GX device and the Modbus ID number do change is there anyway to change the numbers in the device back to their previous numbers
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vanlifer007 avatar image
vanlifer007 answered ·

This didnt happen again since I last posted about it, Maybe my campervan was stationary all this time, but I am curruious to find a cure. can anyone help please?

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Modbus TCP Basics

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