I'm new to community and it's my first question, so please forgive me for mistakes I could do referring to adding pictures and descriptions.
I plan to use 100 devices and connect them via RS-485 in half duplex manner as it can be seen in below picture. Each node will need max 150 mA and I plan to use 12V 20A power supply connected to 220V AC main. Termination resistors will be added to ends.
I searched for problems I might end up with RS-485 communication and saw that ground loops might be problematic. In that sense, implementing specific ground for communication and isolation is offered as it can be seen below picture;
However all of examples I could find related to ground loop problems in RS-485 mentions about ground differences according to different power supplies connected to building mains which are far away and might have different potentials although power supply reference is earth. Connecting grounds might create ground loops and interfere with communication signals. Large current might created in ground loop and might damage the circuit. If grounds are not connected, than ground potentials might be a lot different and transceiver could not handle ground potential gap.
In my case I will use single supply and connect all devices in daisy chain. And in worst case total of 15A will be used and I am afraid this might also create ground differences between devices. Would this will create ground loop like in the case with different power supply? I have no experience about transmission line but in my PCB designs I try to seperate digital grounds and analog grounds and also seperate high current grounds and connect them at one point to avoid ground loops. By the way, total distance (device 1 to 100) will be no more than 200 meters and baud rate is low (9600). I know isolation is the best way but from cost perspective this setup is my preferred one if there will be no problems.
Also I would like to ask about fail-safe pull up and pull down resistors connected to A and B lines. Having them only at the master device is enough or should I have them at every device?
Thanks for replies,