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Modbus TCP

Modbus Register for Relay 3,4,5&6 for Raspberry pi

Where might I find the Modbus registers for the Extra relays the Raspberry pi has? I have looked in the Excel Modbus-TCP register list, but can only find Relay 1 and 2.

I used the RpiGPioSetup add-on to assign the extra relays. I can see and control the extra relays using Remote Console.

I currently have NodeRed running on external device controlling Relay 1 and 2. I am looking to control the other relays (3-6). NodeRed is also pulling data from my BMV-712 / other Victron items.

mrorange asked

0 Answers

Ignore AC input over modbus / dbus?

I am looking for a way to just ignore the AC input.

I have modbus tcp and access to the dbus thru nodered, but I dont see how i would change that setting.

Currenlty i overwrite the settings manually every day with VEConfigure, but that is pretty painfull. :)

How can I achieve this and make some nice flows in nodered?

betz asked
jacola answered ·

3 Answers

VenusGX + Node-RED - Modbus TCP Communication Issues


I have installed the recent VenusGX v2.42 FW build with integrated Node-RED from

I am trying to communicate with an external device via Modbus TCP (a My PV AC Thor - which is a modulated AC heater power control unit) and control it via logic developed within Node-RED.

I have successfully installed the additional contrib node 'node-red-contrib-modbustcp' and am able to communicate with the unit.

However I'm unable to setup a flow to BOTH write to the unit (with a power request) at regular intervals AND read from any registers (such as temperature) at regular intervals.

For example;

Write only - connects/works fine


Write & Read - no connection



Write & Read after a few minutes - write connects/works but read doesn't


Read only (write node deleted) - connects/works fine


I do know that a Modbus TCP read and write event can't occur exactly simultaneously (and it doesn't need to), but I'm not sure how to sequence the read/write requests or what I can change to get this working with the Modbus TCP node-set that I'm currently using...

My next step was to attempt installing a different / mode advanced Modbus contrib node 'node-red-contrib-modbus' (I have seen examples of write and read nodes successfully coexisting with this node-set) but unfortunately I get a bunch of installation errors - see below;


I have also tried to install manually via Putty using the npm install command (including the suggested variations) but still get the similar errors.


My programming/Linux skills are very limited, so troubleshooting this myself is a bit beyond me.

If anyone is able to offer some advice on how I can possibly get write and read communication working with the current Modbus node-set I'm using ( or how to get the more advanced Modbus node-set ( successfully installed on the VenusGX it would be greatly appreciated.

PS. I do know that my other option is to run node-red externally to the VenusGX unit (such as on a RPi), but I want to leave this as a last option for now.

Thanks in advance, Mark.

Mark asked
shaun commented ·

1 Answer

Get data from my Victron Venus to my Node-Red ...

Hi all,

I would really like to get any kind of data from my Venus GX into my RPi Node-Red Installation.

What I tried so far:

Modbus ... unfortunately it is not possible to read data from Node-Red using the Modbus Nodes like that:



Although the reference guide tells me: Address 800 - length 6 --> Serial number

Second I tried to use the existing Victron Nodes - I added the Environment line as explained in the instructions:

  1. Environment="NODE_RED_DBUS_ADDRESS="

But still the Victron-Nodes are empty ... no connection to my Venus seem to be possible:



and thats a pitty, because I really would like to see at least ANYTHING :( :( :(

Please help me ...



gawan asked

0 Answers

Controlling TriStar diversion controller over Modbus


I'm planning my off-grid system. The main issue I have is the AC coupled wind inverter which doesn't support frequency shifting.


In order to protect the batteries from overcharging my plan is to use Morningstar Tristar PWM in diversion mode.

Unfortunately it doesn't support communication with BYD's BMU. I hope it's possible to use Modbus communication and send to it charging parameters from the Venus OS (node-red).

It will allow TriStar to dynamically divert excess power and keep the batteries happy ;)

Do you think it's possible?

Thanks for your help ;)

dyju711 asked
dyju711 answered ·

1 Answer

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