Modbus Cerbo GX and Siemens S7 PLC

Dear Community,

I am currently working on a project to intergrate an Siemens 1214C PLC into my Victron system.
I have a Siemens S7 1214C (FM V3) PLC and a Cerbo of 2022.

I have a few questions about doing this. As my current attempt failed.

  1. First of all can is the cerbo a client or a modbus server?
    I tried connecting with the cerbo as a modbusclient but the PLC was not seen by the cerbo.

  2. Can I send commands from the cerbo to the PLC via modbus?
    I would like to have the PLC monitor and control multiple espects of my home. The modbus connection with the Cerbo is prefered as I would like to display some of the data of the PLC and send a few basic commands to the PLC from the control panel.

  3. How does the cerbo display or store the recieved data? Where from can I acces this to use in node red?
    As I would like to display the data on the screen I would like to use the node red dashboard to do so. But where will de read data of the PLC be stored in the cerbo? I can find a custon node with a modbus option. Is this correct?

  4. Is there a better way of doing this?
    As I would only like to display 4 intergers and send 4 boolians I was thinking of using the relay as an digital signal for now and was thinking of a way to send the information to the analog inputs.
    But as the PLC can only send 0-10V or 0-20mA (or in between) I have no way of doing this I think.

I hope you all can help me out! Thanks a lot


Hi Manus,
My system is similar to yours. Cerbo GX via Modbus on a Siemens PLC S7-1214C (FW V4.6) and TIA Portal V18. I read all device data from Cerbo with Modbus. Pytes battery, 2x Victron Smartsolar 150/35 charge controllers, Selly 3EMPro and Hoymiles inverters with OpenDTU.
Modbus works very quickly and reliably.
I load the forecast data from the VRM portal into the PLC via Node-Red. Writing to the Cerbo (e.g. relays) is best done via Node- Red.
It’s a bit of work when you first create it, but it works very well.
Your Modbus FB looks a little different, I suspect it is an older version.
Which TIA Portal version are you using?


1 Like

Hello! If you are using an S7 you can use this node. It has a direct communication with the DB blocks in the S7. See the documentation in order to configure it, but here are some heads up:

  • You will need to enable access with PUT/GET communication in the PLC configuration (PLC Configuration β†’ Protection And Security β†’ Connection Mechanisms)
  • You will need to disable the optimized access in the DB (DB Config β†’ Attributes).
  • You will need to reference each variable you need to access from the node-red project in the S7 Config Node.

Thank you very much. I will try to implement this.
I have FW3.0 and therefore use TIA 15.1.

What are you adress settings in siemens? Could you also share a screenshot of DB100?
What node do you use for the modbus? The same that I tried?
Do I understand correctly that the Cerbo ID is alway 100?

I will for sure try this! This looks like a simple solution if it works on my older PLC.

Yes, the ID of the Cerbo is always 100. All device IDs are listed under Modbus TCP services.

The communication parameters for each Modbus device are entered in DB100.

Since I query several Modbus participants, I assign the corresponding ID before calling the Modbus_Client FB. Once in my DB100 and in the respective instance data block of the Modbus FB.

The read data is written to the databuffer. The data block is structured according to the Victron Modbus-TCP register list.

If you only want to read in a small amount of data, querying via Node Red is of course easier.
If you want all the data from the Cerbo, I would prefer the Modbus variant.