RS485 communication issue

Thread Starter

ajitnayak

Joined Feb 22, 2013
49
I have Setup like this for my application. I have Transformer which gives out 12V 1A & 5V 500mA output.I have used isolated ADM2483 design where power galvanized isolated. Primary side 5v &gnd taken from 7805 regulator where 12v input comes from transformer. same ground used by MCU/ADM2483 side

Where as secondary 5V/ground ADM2483 taken from 5V/500mA source. this way I have total isolation in primary side.

My unit working well with Aux 85-270vAC/Dc &12V DC standby upto 10 device without any disturbance using lap cable for 1000 meter.

By seeing circuit it understood that communication works only when Aux 85-270VAC supply is given. since 12Vdc Supply from battery given. product wise it will it work on 12v dc not communication.

Issue:

  1. 1) i have introduce battery charging unit and it stop communication. if remove battery charging unit it start working.
2)i have tried grounding Communication ground and secondary side of ADM2483 ground common. In this case also it not communicating.

  1. 3) I have used terminator resistor 100E but it didn't solved issue.
  2. 4) I have same product which having non isolated rs485 trans receiver, where it work on all prospect battery, aux supply, battery charging unit where i used same transformer but it non -isolated design. When i bring isolated design in daisy chain with non-isolated design without battery charging unit. it stopped communication.here i made ground common for communication/isolated/non-isolated ground.
5) If i want to use industrial RS485 transreceiver , if i want to run communication with 12 v and aux fail condition in hardware what i need to make change
in current design transformer gives 12V/1A & 5V,500mA output . if my aux fails primary of ADM2483 get supply but not for secondary side. due to which communication fails.
we cant short primary & secondary ground of ADM 2483 . since it galvanized isolation. How can i make it work on my application.
 

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Delta prime

Joined Nov 15, 2019
814
) i have introduce battery charging unit and it stop communication. if remove battery charging unit it start working
Hello there
:) battery charger connection Why?
.ADM2483 Vdd2 will consume up to 290 mW when powered at 5 V (at maximum bus loading).
So if you are using 5x ADM2483 devices, then you will need > 1W of isolated power.
My unit working well with Aux 85-270vAC/Dc &12V DC standby upto 10 device without any disturbance
Please show pin for pin connection of your application.
Thank you.:)
 

Thread Starter

ajitnayak

Joined Feb 22, 2013
49
My application demand battery charging unit. in case auxiliary failed . my product will be working on 12 v battery supply. battery has to remain charge at high voltage potential so that it can supply when power failed.
My secondary transformer supply 5V ,500mA which delicately used for ADM Secondary. primary it uses from converter output from 7805 where transformer can source 12V 1A. i showed block diagram of wiring in thread 1

I have attached working ADM2483 CKT shown in figure,
 

Lo_volt

Joined Apr 3, 2014
149
Are you connecting the ground between the nodes in your cable? I see you have A and B connected together from one node to the next. Do you have a ground connected between nodes? This should be the isolated ground that is GND2 in your schematic.

If you don't have a ground reference between the nodes, it is likely that one node may drift outside the measureable common mode voltage range of the receiving nodes. If this happens, the receiving nodes will not be able to detect a signal. Your cable between nodes should have three conductors: A, B and GND2.
 

Thread Starter

ajitnayak

Joined Feb 22, 2013
49
In figure i haven't showed. but seeing forum i have realized it should be connected as soon as i connected ground. my all device stop working.

with Aux/12vDc/BCU/ non-isolated version device / making ground common its working well

WIth AUX/12VDC/isolated version device / making ground common its working well

with Aux /12VDC/BCU/isolated version device / making ground common stop communication.

with combining isolated & non isolated design together with above setup whole communication stop working]
 

Lo_volt

Joined Apr 3, 2014
149
It really seems like a misplaced ground connection between the combined isolated and non-isolated systems. Double check your grounds to be sure GND and GND2 are separated from each other. Also check to be sure all GND2 connections between units are connected.

Do you have an oscilloscope that you can use to view your inputs to your transceivers? I'd suggest looking at the A and B signals while under each of the power conditions to see if there is any difference when powered by one source vs another.
 
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