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-   -   Multidrop RJ45 RS485 connectors (http://www.plctalk.net/qanda/showthread.php?t=114573)

AustralIan March 8th, 2018 09:49 AM

Multidrop RJ45 RS485 connectors
 
What do you guys use for connecting several Modbus RS485 devices with a single RJ45 port in the one panel? and terminating resistors?

kolyur March 8th, 2018 12:04 PM

I've used these in the past:
http://www.redlion.net/accessory/rj4...llel-connector

If you download the datasheet they have a similar product that has a RJ45 breakout terminal block, looks like a nice way to add a terminating resistor.

geniusintraining March 8th, 2018 12:32 PM

I use a lot of Winford products.... great quality, prices are better than anyone else in the market, great supply of different **** that we need and they normally ship the same day or the next

https://www.winford.com/products/brk8p8csj4b.php

swimmy67 March 8th, 2018 02:44 PM

I have used these type of connectors. They work good for RS485 Modbus RTU.

https://www.amazon.com/C2G-Single-37...70_&dpSrc=srch

BITS N BYTES March 8th, 2018 03:15 PM

Quote:

Originally Posted by geniusintraining (Post 771232)
I use a lot of Winford products.... great quality, prices are better than anyone else in the market, great supply of different **** that we need and they normally ship the same day or the next

https://www.winford.com/products/brk8p8csj4b.php

+1 for Winford Engineering. Great resource, good quality and reasonably priced.:beerchug:

danw March 8th, 2018 05:31 PM

I would have concerns about either module creating a standing wave which reflects energy back that creates false bits because I see either as more of a star topology where each RJ connector is the beginning of 'stub' exiting from a common point.

https://s9.postimg.org/9ytt6uuhb/How...ar_network.jpg

Yes, the connectors are physically separated by mm or inches of tracing, but daisy chaining puts devices in parallel. each of which is at some distance from each other, there is a clear end on each end, unlike a star that does not have two ends.

One of the 'rules' of RS-485 is to limit stub or star wiring.

It might be that reflections are not a problem at internal-to-the-panel distances. But it goes against conventional wisdom in 485 networking.

lfe March 8th, 2018 06:01 PM

+1 danw

What makes RS-485 more resistant to noise is to work by current, circulating an appreciable intensity through the cable, and this is only fulfilled with a daisy chain connection and the resistors at the ends.

Geoff White March 8th, 2018 08:20 PM

I'm totally going to try the red lion product on DSI multidrop if I am ever forced to use it again. The Powerflex 523/525 rj45 connectors are utter garbage to try and terminate as a daisy chain.


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