question

Hi Sasha

Because of talking each other that morning over an other Forum here my already given answer to complete that request. Connecting with a longer cable normale requires the termination of Modbus with 120 Ohm. The venus attached Rj45 "Canbus" Terminator is "not" the correct Terminator for the Rj45 connection on the ET340. For termination direktly on the ET you can bridge the internal restistor with a bridge between A- to T directly on the ET340

@mvader (Victron Energy Staff) may you can add a generell info concerning termination of Modbus with extended cables to https://www.victronenergy.com/live/energy-meters:et340 because thats an often asked question of installers

Let me first address the claims regarding termination.

The rule of thumb is: If the propagation delay of the data line is much less than one bit (pulse) width, termination is not needed.

On a 100 meter cable (round trip of 200m), assuming 300 000 km/sec speed of light and propagation time of around 67% (so 200 000km/sec), propagation delay on the line is 1µs. The pulse with at 9600 baud (which is what is used in this application) is 100µs. So termination should not be required for any of the cables Victron sells. Also see here.

Also, as @WKirby points out, it is already terminated on the one end.

Inside the USB plug there are two LEDs, a red one and a green one. Whenever there is outgoing data (a request to read a register) the red LED will flash, and when there is a response the green one will flash. This can help you to figure out what is going on. You should see the two LEDs flash alternately. If you only see the red one flashing and no green (or intermittent green), then there is a break or disturbance in the communication somewhere. I would start here, and if comms appear to be fine on this level, then have someone from tech support look on the Venus device if the device is detected and working properly.

I've had quite a few cases in the past where the device is in fact detected but the connection is so poor that 90% of the data fails a CRC test and it never manages to complete acquisition of the meter.

I had some issues connecting my Venus GX to the ET340 Carlo Gavazzi energy meter using a USB-RS485 adaptor with a non-FTDI chipset.

While I was able to connect the ET340's to my Windows 10 computer using the non-FTDI chipset and operate the Carlo Gavazzi configuration software, and set the second ET340 energy meter to address "2", when I then connected to the Venus GX nothing would communicate. It was only when I managed to purchase a Victron USB-RS485 which uses the FTDI chipset did everything work. To get the windows 10 computer and the Carlo Gavazzi configuration software to talk to each other I also needed to get a driver for the Victron Energy USB-RS485 converter (you need an internet connection).

The ET340 manual (extract 4. below) states you will need two USB-RS485 adaptors to connect more than one ET340. This is not the case if you use the Carlo Gavazzi software to change the default address 1 to 2 and then connect the second ET340 energy meter to the same RS485 bus. This saves the added cost of the RS485 adaptor and frees up the second (or remaining USB port). The added advantage of connecting your Windows 10 PC is that the correct operation of the energy meters can be check before connecting the RS485 bus to the Victron Venus GX or similar.

"4. Multiple Energy Meters in one system

Re RS485 line terminations, while in theory, a 120ohm termination should do no harm on the RS484 bus even for a short cable length, I experienced communications issues with the USB RS485 adaptor when the cable was terminated. When all terminations were removed everything worked well. This termination issue only seemed to apply to my non-FTDI chipset adaptor.

Hello

I had problems with connections too. I removed the Termination and everything goes fine.

Andreas