Internet PLC Forum

U-485 has some biasing on the RS485 port. Nano-10 does not supply the biasing voltage. This might makes a difference to the drive?

You can try to add in a 1K resistor to RS485+ to pull up to +5V and another 1K resistor connect to RS485(-) terminal to pull-down to 0V and see if it would improve communication.

Ed,

I have not used the ABB drive but I have worked with Hitachi and TECO.

The RS485 interface for both the Hitachi and TECO VFDs is electrically isolated (floating). On these drives you must add a 3rd wire to tie the VFD signal ground to the 0Volt input to the Nano-10 PLC.

The documentation for the ABB Ach550 rs485 indicates the the RS485 interface is electrically isolated. If you do not add this 3rd wire between signal ground on the ABB unit and the this Nano-10 then Rs485 communications will not work reliably.

The ABB Ach550 signal ground is named "AGND" and it is on the X1 connector, terminal #31.

If you have already done this, then kindly ignore my meddling.

Gary D*ickinson

Thank You Both for the input! The network is already setup as you guys mentioned, the shielded wire on each drive is connected to the AGND terminal and at the Nano is connected to the 0V. All but Drive2 is not communicating at all, with UART Errors.

My next step is to enable to built in bias terminator in the last drive (Drive4) to see if that works, if it doesn't work I will disable it and then add the 1K by the Nano and try again as you mentioned.

[---------------RS 485 Network--25' max-------------]
 ====\/=======\/======\/======\/
      [Drive1]     [Drive2]     [Drive3]     [Drive4]

I have also reached out to ABB to see if there's anything else I can do, so far still waiting....

My very last attempt to fix this id everything else doesn't work, I will try to use the Auto485 and connect it to the drive via RS232 back on the network with via 485 , I haven't try this yet... Keep you all posted.


Thanks,
Ed

Thank You!
I'm leaning more to bullet #4, but the drive worked when connected to the laptop with the U-485. Comm settings are all the same for all drives.

ABB just sent me some troubleshooting documents but nothing that I haven't tried. I was thinking on using the Auto485 but I can't because the com port on the drive is used by the keypad.

Thanks!!
Ed

The wiring is correct there's not much to it, is working on the other drives on the daisy chain. ABB suggest to check the impendence across the + and - terminal. Measurement needs to be 164ohms with +/- 5%. They also asked me to remove the shielded from the ground, and turn on the bus terminator on the drive.

I will be at the plant on Monday working on this, I will keep everyone posted.

Thanks Gary!!
Ed

Hi, just to update everyone. After testing the impendence on the drive it was well above 164Ohms (34K) the transceiver was deemed blown by ABB. Next step is to change the entire board, or just use the built-in AO to read the desired analog signal. However, just because it works with the laptop, I'm researching on using an RS485 extender ie. RS485 to RS485 just to interface with the VFD to see if it works.  

Any ideas will be greatly appreciated...
Ed