RS485 "selector switch?"

I have an application where a 485 connection needs to go from a genset to either computer A or computer B. I had a relay in use (A on NC contacts) (B on NO contacts) that was energized by a 2pos selector switch. Well as many of you much smarter than I can guess, 485 through a set of relay contacts does not work very well.
So what i need is a 485 "switch or relay" that will connect C to either A or B. Ideally this would be something that has can be switched via 24vdc input signal.
Does this exist?

Perhaps something like this...

https://www.blackbox.com/en-us/stor...atching-remote-controlled-Dry-Contact/SW1047A

So you want two masters (computers A and B) talking to the same slave (genset "C")? First question would be is there a second free port available on the genset so you could have two independent networks? If no, maybe you could make one PC a master that reads from the genset and subsequently writes the data to the second computer as RS485 is multidrop. Only problem there is if the master goes down the second PC will stop getting data written to it, so there is no redundancy.

For this type of signal a sealed relay with gold plated contacts may work reasonably well. Low voltage and low current signals don't always travel well across standard relay alloys when there is the slightest resistance due to wear or dust.

Thanks for help.
1 computers can't talk to each other.
2 I need to investigate if set controller will allow multiple masters to talk at same time. This is not modbus protocol, and I don't believe there is anything with regards to sender/receiver addresses. I can try and ask though.
3. The comms worked "slightly" through the relay but dropped constantly. I will check my box for gold contacts.

Read only or do the computers talk back?
IF read only, Could use a splitter instead and not fuss w/ switching contacts..

Both and I believe the reads are queried

I'm doing the same thing with a relay between to control stations for a camera. It is running flawlessly at 2400 baud. Have you (can you) lower the baud rate?

I agree with OkiePC, but I would suggest adding bifurcated contacts to that list.

rootboy said:

I agree with OkiePC, but I would suggest adding bifurcated contacts to that list.

Click to expand...

Yes. That too.

In a former life, we had a bunch of machines with servo drives that were designed with plug-in relays that had gold plated bifurcated contacts used to switch the enable signal and when disabled, the speed reference was shorted. (I didn't design it). The thing was, these relays they stocked in our parts room did not have indicators.

The maintenance guys would swap them for cheap relays with ten amp contacts and indicator LEDs for troubleshooting. within a week or two, we would have real trouble to shoot and scrap product when the enable signal got flaky in the middle of a machine cycle.

The special relays were expensive and only had 3 amp contacts, so the cheap relays with 10 amp contacts MUST be an upgrade, right? wrong...

I must have put a hundred relays in 20 machines three times before I finally convinced all the floor techs to leave them alone. I tried to get them to switch our "good" gold relay to one with an indicator but at about $25/ea after using so many of them I think it never happened.

The remote switchable black box looks best.


Next wild question. Does anyone know of a 232 to 485 converter that is switchable? Ie. Sometimes i need to convert to 485 and sometimes not? Got to love finding such things out on site....