adccommunitymod (AutomationDirect) asked a question.
VFD's on RS485
Created Date: March 23,2007
Created By: DaveBartel
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I will be connecting 6 GS2 Variable Frequency Drives (VFD's) to a DL-260 via the RS-485 (port 2). The manual says I need terminating resistors but only on “Large Runs�. I don't know what they mean by a large run. Would 6 VFDs spanning a total distance of 5' (includes the PLC) be considered a large run? Also is it permissible to “Star� connect the VFD's communication ports or do they it need to be “Daisy Chain� connected (or does it matter).
Created Date: March 23,2007
Created by: Tech Guy
The RS-485 specification prohibits 'star ' type configurations. Daisy chaining is the only permissible configuration per the specification.
As far as termination goes, you can always try it and see if it works. If it doesn't, add the resistors. Usually I add them on anything over a few feet.
Created Date: March 23,2007
Created by: 72hdflh
Check this out. AD part# GS-RS485-8 (RS485 COMM BOARD 8 PORT GS SERIES AC DRIVE)I used one on a panel I am currently building controlling 3 GS2 drives, all short runs 5 ' or less, with no problems as yet in testing. It is not installed on the floor yet.
Created Date: March 23,2007
Created by: Anvilsoup
Tech Guy,
What would you call the wiring configuration of AD part# GS-RS485-8?
Created Date: March 23,2007
Created by: Tech Guy
I know. I know. It is in a sense a Star configuration, but it isn't a home run Star configuration.
Personally I have never been able to make a home run style Star configuration work.
And before this goes farther, I'm not going to argue the differences between a home run style Star vs an end node Star. Suffice it to say that they are two very different beasts with regard to wave reflection and noise.
Created Date: March 23,2007
Created by: Anvilsoup
Thank you Tech Guy,
I have used the AD part# GS-RS485-8 only four times, The first time it didn't work (also my first time using modbus in a dl06). The other times I twisted the "phone line " cord to help with interference. Did it help? I don't know but I'm not pressing my luck!
Created Date: March 25,2007
Created by: DaveBartel
Thanks everyone for your insight.
I'll be making the cables by hand so I only want to do this once, sounds like I should play it safe and Daisy Chain the connections.
Created Date: April 13,2007
Created by: daakers
We have always used CAT5 for our cables for this setup and have never had any problems.
We have used the GS-RS485-4 and GS-RS485-8, they have always worked great.
Created Date: March 23,2007
Created by: DaveBartel
I will be connecting 6 GS2 Variable Frequency Drives (VFD’s) to a DL-260 via the RS-485 (port 2). The manual says I need terminating resistors but only on “Large Runs�. I don’t know what they mean by a large run. Would 6 VFDs spanning a total distance of 5’ (includes the PLC) be considered a large run?
Also is it permissible to “Star� connect the VFD’s communication ports or do they it need to be “Daisy Chain� connected (or does it matter).