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BRX Relay output module

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  • BRX Relay output module

    I have a Bx-12TR relay module. I am wanting to switch 120 vac but am getting about 10 vac bleed through and it keeps my 120 vac LED indicator on my switch slightly lit. Is there a work around for this?


  • #2
    Leakage is surprising with a mechanical output. Must have an RC around the contact. Add more load.

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    • #3
      Originally posted by ControlsGuy View Post
      Leakage is surprising with a mechanical output. Must have an RC around the contact. Add more load.
      That is what I was thinking too. Thanks for the input, I'll load it up lol.

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      • #4
        There is an RC to quiet noise. It does produce a small amount of AC leakage.

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        • #5
          Originally posted by BobO View Post
          There is an RC to quiet noise. It does produce a small amount of AC leakage.
          OK, thanks, BobO

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          • #6
            I've personally decided LED indicators on AC with the BRX relay outputs is just a bad idea. "Small" leakage is relative and LEDs sure become ambiguous when one that is "off" leaves you wondering. I went back and replaced them with incandescent.

            I tried RC snubbers across the lamp and found I could get them almost "off" but it took quite a high value capacitor and low value resistor and snubbers aren't cheap. The D2-12TR doesn't use RCs and doesn't have the glowing when off problem on 120VAC.

            Just my experience.

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            • #7
              Typically, I'll drive pilot lights with DCDOs. Not sure the RDOs need snubbing, though. Never had an issue with any of the older modules that didn't have it (and I never snub the loads).

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              • #8
                Oh, when you say "noise" are you referring to the effect on logic in the PLC rather than output circuit electrical design? If so, then that would be another matter

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                • #9
                  Originally posted by ControlsGuy View Post
                  Oh, when you say "noise" are you referring to the effect on logic in the PLC rather than output circuit electrical design? If so, then that would be another matter
                  The modern world of low voltage and high speeds doesnít blend as well with inductive loads and dry contacts as slow 5v stuff of yesteryear. So yes, much of this is about us protecting us. Itís a different world now. Out on the backplane itís easier to control, but onboard the margin for failure is small. We err on the side of caution. I would rather apologize for the leaky led indicators (which ironically is also a fast/low voltage issue) than for stuff falling down.

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                  • #10
                    Originally posted by BobO View Post

                    The modern world of low voltage and high speeds doesnít blend as well with inductive loads and dry contacts as slow 5v stuff of yesteryear. So yes, much of this is about us protecting us. Itís a different world now. Out on the backplane itís easier to control, but onboard the margin for failure is small. We err on the side of caution. I would rather apologize for the leaky led indicators (which ironically is also a fast/low voltage issue) than for stuff falling down.
                    Yes, I agree with you. Thanks!

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                    • #11
                      Originally posted by BobO View Post

                      The modern world of low voltage and high speeds doesnít blend as well with inductive loads and dry contacts as slow 5v stuff of yesteryear. So yes, much of this is about us protecting us. Itís a different world now. Out on the backplane itís easier to control, but onboard the margin for failure is small. We err on the side of caution. I would rather apologize for the leaky led indicators (which ironically is also a fast/low voltage issue) than for stuff falling down.
                      Unfortunately for us, all of the BRX relay outputs including the expansion modules have the 300uA leakage on AC. It's the 120VAC LED indicators AutomationDirect sells that have an unacceptably high level of illumination with these relay RC networks even with no power applied to the card other than Line to contact to LED to Neutral. This is also a safety issue as it may be seen as an indicator that is 'ON' indicating a safe condition to an operator when it is not.

                      I do understand the reason it is there, it is just unacceptable for AC applications and that is unfortunate.

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                      • #12
                        Is it necessary to use AC for the panel indicators.

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                        • #13
                          Originally posted by BobO View Post
                          Is it necessary to use AC for the panel indicators.
                          Retrofits where existing operators and wiring are to be re-used, usually. The biggest reason to use relay outputs in the past was excessive leakage from triacs, so having to add interposing relays or some burden load to devices means more $ and more real estate and more labor and more complexity. Also interfacing to other PLC 120V inputs where output leakage is suddenly a major issue. Relay outputs are the goto for interfacing to "other's" equipment since they are versatile as long as there are no engineered-in issues.

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                          • #14
                            Originally posted by Mike Nash View Post

                            Unfortunately for us, all of the BRX relay outputs including the expansion modules have the 300uA leakage on AC. It's the 120VAC LED indicators AutomationDirect sells that have an unacceptably high level of illumination with these relay RC networks even with no power applied to the card other than Line to contact to LED to Neutral. This is also a safety issue as it may be seen as an indicator that is 'ON' indicating a safe condition to an operator when it is not.

                            I do understand the reason it is there, it is just unacceptable for AC applications and that is unfortunate.
                            I hate to sound ignorant, but do other brands not have snubbers? We've been doing it this way since we were at TI....like 30 years ago. BRX actually uses a far less aggressive circuit than what we used then.

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                            • #15
                              Some do, some don't. Some model cards do, other models don't in the same PLC system. Let's just say it makes things "interesting" in an un-fun kind of way.

                              The D2-12TR uses an MOV and an inductor. I couldn't tell you if this accomplishes the same thing as the RC for preventing interference with the processor. I can tell you it doesn't make the LED indicators glow.

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