Weird PCG Communication issue

[Igotworms]

I'm trying to get a PCG to communicate on an MS/TP network with an FX70. The only way I can get this to connect to the network is if my BTVCT is connected through the front FC Bus port. As soon as I unplug the BTCVT it loses communication to the network. There are a few other 3rd party devices after the PCG but they are working fine. I also have another PCG right next to it in the same panel and that is also communication fine. I'm running PCT version 10.2.0.2600. Has anyone seen this before?

[Igotworms]

I'm thinking this has to be a hardware issue. One controller is communicating and the other is not. Both were downloaded with PCT 10.2. I'm going to replace the controller and see what happens

[Igotworms]

I've replaced the PCG controller with a brand new PCG right out of the box and still the same issue. I thought the max master setting in the bacnet trunk was screwing things up but increasing that number didn't work. If I disconnect the 3rd party ABB drives it will start to communicate. I tried changing the address to a higher number but that still didn't work. The RS-485 eol resistor is set to "on" on the last frequency drive. Does anyone have any other ideas?

[orion242]

VFDs are typically a 3 wire bacnet device, ie the 485 transceiver is not earth referenced like typical 2 wire mstp controllers. If you look at the ACH550s, there is a ref and Agnd on the comms terminal block. Ref is the common reference on the transceiver, ie the 3rd wire. That might be your hassle, mixing 2 & 3 wire devices on the same trunk. There's various ways to hack 2/3 wire devices together. The slides I put up in the MSTP section of the pro area show how to do it correctly.

http://hvac-talk.com/vbb/showthread....1#post22902231

[Igotworms]

The integration to the VFDs has been working fine all this week. I'm working with a small MS/TP network address 4-12. The max master setting in the Jace is set to 12. "Towers" PCG address 6, will not communicate once it is added to the network. This is the only controller on the network that will not communicate. PCG address 5 is right next to address 6 in the control panel and has been working fine. The only way I can get address 6 to communicate is to disconnect the drives from the MS/TP trunk. I'm not sure what PCG address 6 doesn't like on the network but I'm going to mess around with the MS/TP wiring and EOL resistor on the drives next week. Below is a link to the screenshot of the network. Thanks for the reply orion.

https://i.imgur.com/HKzQe3M.png

[Igotworms]

I also forgot to mention that the PCG controllers are also 3-wire with a shield, there is no mixing 2 and 3 wire devices together. I have + - Ref Shield terminals on all controllers. I think I'm going to hook everything back up on Monday and shut each drive off at the disconnect. If all PCGs are communicating, I'm going to turn on each drive one at a time and see what happens.

[orion242]

Ain't that then. Sounds like the point I would whip out a sniffer / scope and take a looks see.

[JCIman]

Could be EOL termination/biasing. It could be that the BTCVT is loading the trunk just right to make it work.
Check the trunk voltages, and try putting a PCG controller as the EOL for a test (turn off the EOL on the drives).
Make sure the shield is not grounded at any other points along the way.
Capturing traffic on the trunk would be fun also. You might see some header CRC errors if it is a physical bus problem.

[kontrolphreak]

As a rule of thumb I use matched EOL resistors/ terminators. Nothing but trouble using two from different manufacturers. Also max master should be only set on the highest MAC addressed controller not the lowest (router).

kontrol out

[Igotworms]

It was the EOL resistor in the last ABB drive on the network that was screwing things up. As soon as I shut the EOL off at the drive the PCG started to communicate. I don't know what the PCG didn't like about it but I'm leaving the EOL off. If there still continues to be problems on the network I'm going to use the JCI resistor MS-BACEOL-0. I've used this JCI resistor on a trunk with 3rd party devices before and never had a problem. Thanks for all the input

[orion242]

As a rule of thumb I use matched EOL resistors/ terminators.

Ditto, you have no idea what your getting otherwise. Buy a reel of 100ohm or whatever 1% resistors from digikey and call it a day. Think I had ~$50 for the reel which is 5K resistors. Set for life and then some.

[Cagey57]

Igotworms,
From past experience with FX-70's (and now FX-80's), PCG's and ABB Drives:
Always have a PCG as the EOL and only connect the + and - at the ABB Drives. Wire nut the "S" or Ref together in the VFD's.

I had a project that had about 12 ABB drives and once we disconnected the "Ref" from them everything was good. The final fix was to make a PCG the last device on a BACnet Trunk. I am sure others can explain the electrical theory but that's how we do it now.