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colin-jones avatar image
colin-jones asked

Cerbo Modbus TCP Unit ID didnt change when I swapped ports?

I have a monitoring program reading from the Cerbo via modbus TCP.

It has been working happily for several weeks.

I had a BlueSolar Charger connected VE.Direct to USB, as well as a SmartSolar Charger on VE.Direct port 1.

In order to connect a meter to the USB port, I swapped the BlueSolar Charger to a straight VE.Direct cable to VE.Direct port 2. In dbus-spy it changed to tty6 as I expected, so I looked up the modbus spreadsheet and changed the UnitID to 224. All I got back was zeros from all of the registers.

Thinking I had got the wrong number from the spreadsheet I read some posts on here and saw one that said to check the VRM instance and cross reference that. It was still 288 (VE.Direct via USB) so I put the UnitID back to 239 and it is working again.

So the questions are will it change in the future, after code upgrade or similar event ?

Also what address will I get if I plug something else into USB0 ? (I actually plugged the meter into USB1)

Confused

Modbus TCP
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1 Answer
mvader (Victron Energy) avatar image
mvader (Victron Energy) answered ·

Hi Colin, since a while, the VE.Direct producs get their instance (used for VRM as well as ModbusTCP) assigned and tied to their serial number.


If you would have started with plugging the charger into the VE.Direct port, then it would have ad 288 or similar. Since the software still defaults to those. But now, since it already had another one assigned, it stayed like that even though you changed the cabling.

So, no those numbers won't change if you rearrange the cabling in the future. And if you add another device, then best is to just check the instance number in the Settings -> Services -> ModbusTCP menu. It lists all devices and their unit id.

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Related Resources

Modbus TCP Basics