I am currently have a bit of an issue connecting to a Love 2600 temperature controller via RS485 full duplex with a Grid Connect NET485 Modbus RTU to TCP ethernet bridge.

I first hooked up the temperature controller to a run of the mill RS485 to USB converter and it worked great. Polling was effortless and easy.

Now when I try to connect to the NET485 module I receive nothing but timeouts. I double checked all my settings and my wiring to no avail.

Lastly, thinking that perhaps I had a faulty gateway, I hooked up the RS485 to USB converter to the NET485 and used a Modbus slave simulator to replicate the temperature controller as my computer. Polling worked great there as well. Talk about frustrating!

The manufacturer of the ethernet bridge did say their device drives a 3.5V RS485 signal that maybe too weak for the Temperature controller to receive properly. I also have no signal ground as the temperature controller has no spot for it. Has anyone else ran into a issue similar to this one?

 

Do make sure the slave address is correct. For example, if the Modbus/TCP client/master is putting a zero or 255 as the unit-id, how is that being output on RS-485 Modbus/RTU?

Also, check how your 3rd signal ground is handled. You probably need to confirm both the GridConnect and Love device share a common ground reference.

decades of RS485 experience tells me it is likely one of the above (or the A/B/+/- lines need to be swapped).

3vdc is NOT low for RS-485, which (by definition) only requires a 0.2v differential. Any device with can't handle 3v, thinking that as being too low probably doesn't work with anything!

 

Are both Love and the RTU side of the bridge 4 wire, full duplex? If one side is 2 wire half duplex then a couple of jumper wires are needed.

If jumpered, is it jumpered (+) to (+), (-) to (-)?