Question

I'm trying to read energy meter using Gurux. I have tried connected by serial using 3onedata gateway and succesful to read the meter with Gurux software. Now im trying to ready the meter using RS485 connection over IP with RUT955.

Im using 2 wire connection and notice the port 6 of rs485 is power input. Is it necessary to supply 6-30v to the port 6 rs485?

Answer 1

No need to supply power to the RS485 connector.

We use 3-wire RS485 with just the 485+ connected to D_P and R_P, the 485- connected to D_N and R_N.

I had the ground connected when I was bench testing, but I don't have it on my drawing. I haven't checked if DC- is bonded to the RS485 Ground.

We are using the Modem as a Modbus Gateway and just send Modbus TCP/IP request to the modem IP address, with the modem communicating Modbus RTU over RS485 to our end device.

Comments

Is it possible to read without connecting the ground?

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Hello,

It is not necessary. For reference on connecting RS485, please check a couple of links below:

• https://community.teltonika-networks.com/54909/trb145-photo-of-rs484-half-duplex
• https://wiki.teltonika-networks.com/view/RUT955_RS485

Best regards,

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I just checked the GND pin against DC- on a RUT955 on the bench beside me. They are bonded (though no confirmation of whether there are fuses in the middle), so as long as the remote device is on the same ground reference (or close enough), then you can safely leave the ground disconnected and only run the RS485 A and RS485 B.
This is one of those things where in 98% of cases, you can safely only even run it as 2-wire RS485, but the other 2% of cases you end up blowing an RS485 transceiver at one end or the other if the ground references are able to deviate by as little as a few volts.