Victron ESS Mode 2/3 through MK3?

[fafrd]

For any of you advanced Victron users out there, I’m trying to understand my options to control a Multiplus II on ESS modes 2 or 3 from my Modbus-RTU-based PLC.

From this document: https://www.victronenergy.com/live/ess:ess_mode_2_and_3?do=export_pdf

Dynamic control of Grid Power Setpoint - Modbus TCP Register 2700 in ESS Mode 2 is the simplest way to achieve the control I’m aiming for, so I’m trying to understand the easiest and cheapest way to do this from my PLC, ideally from Modbus RTU communication.

In particular, I’m trying to understand whether an MK3 can be used to control Grid Power Setpoint on a dynamic control loop (every ~5-10 seconds).

If it can, that should mean I could hook up a PC to change Grid Power Setpoint through it’s USB port whenever the PLC requests a change another USB port.

Or I could build an RPi-based VenusGX controller that could communicate with both my PLC through Modbus-RTU and with the Multiplus II through VE.Bus using an MK3 connected to it’s USB port.

But both of those are wasteful and I’d probably of just getting a Cerbo GX and having my PLC communucate with it through Modbus TCP.

So I’m first interested to understand whether any of you advanced Victron users knows whether:

PLC_Modbus_RTU -> USB -> MK3 -> VEBus might be a viable way to control Multiplus II registers from Modbus RTU communication?

And if not, second, if there is any easier / cheaper way to achieve this control loop using and MK3 adapter or other interface adapter from Modbus RTU or Modbus TCP over WiFi?

 

[fafrd]

A bit more detail on what I am considering if the MK3 is able to control the Grid Power Setpoint register:

The MK3 ends on a USB male connector: https://www.victronenergy.com/accessories/interface-mk3-usb

My Modbus RTU to USB adapter also ends in a USB male connector: https://www.amazon.com/gp/aw/d/B07C...d2lkZ2V0TmFtZT1zcF9waG9uZV9kZXRhaWwp13NParams

I’m thinking of connecting the Modbus RTU USB to the MK3 USB using a USB female to USB female connector like this: https://www.victronenergy.com/live/ess:ess_mode_2_and_3?do=export_pdf

Appreciate any inputs on whether this has any chance of successfully controlling register values on a Multiplus II or not…

 

[fafrd]

I think I’ve figured out for myself that was I was hoping might work will almost certainly be fruitless.

Venus OS takes care of mapping Modbus register commands (read / write) to whatever proprietary format is required for VE.bus, and it needs to be running somewhere.

The MKE merely takes VE.bus commands sent out of USB and adapts them to VE.bus physical protocol.

So attempting to take Modbus RTU commands and directly adapt them to VE.bus physical protocol using an MKE is not going to work (will not be recognized as valid VE.bus commands).

So getting a Cerbo GX and having my PLC send it Modbus TCP commands through the built-in WiFi looks like the the only practical option (short of building an RPi-based controller running Venus OS, which seems like more trouble than it is worth).

Just though I’d close out this bone-headed mistake of a thread in case any other members searching the same subject stumble into it…

 

[ricardocello]

@fafrd Sorry I missed your thread when you posted.

I know embedded firmware, and considered what you were proposing a while ago, because it seemed like the direct approach.
While Victron gives you lots of opportunities to do this sort of thing, I really recommend you go with a Cerbo.
In fact, I had a Mode 2 loop running that continually adjusted inverter output power to match solar for quite some time.
I don't do that anymore, simpler is better.

It is so much easier to write some Python and write some MQTT or Modbus TCP code to do what you need.
It can run on a rasp pi, or even on the Cerbo itself if you figure out the Venus OS architecture.

Definitely not a bone-headed thread at all, just not the easy road.