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  • BobbyS
    started a topic BRX Relay output module

    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?

  • BobO
    replied
    Originally posted by MikeN View Post
    Maybe release a second version of the card for sale alongside the output cards we have now that specifically have no snubbers? Save cost on not including them and then sell it for the same price and make more money to cover the cost of needing to do the second line of stock. And only release it for Do-More products and dont go back to DLogic to further push people onto the new platform. Since people want to interface with LEDs or other PLC brand inputs they are mostly resistive load anyway so no real need for snubbers for voltage spikes anyway. Perhaps even put in the description that it is a "PLC interface designed card" or something like that to help customers understand.
    Our original design plan was to eliminate them, but we put sites on the board because we've always used them. When testing at 264V at rated current bad things happened, so we populated them. When we moved from the onboard to the module we kept the same circuit, but admittedly didn't test the modules without them. It is possible they aren't needed, but unknown. Wouldn't take much to test...just gotta find a free second.

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  • MikeN
    replied
    Maybe release a second version of the card for sale alongside the output cards we have now that specifically have no snubbers? Save cost on not including them and then sell it for the same price and make more money to cover the cost of needing to do the second line of stock. And only release it for Do-More products and dont go back to DLogic to further push people onto the new platform. Since people want to interface with LEDs or other PLC brand inputs they are mostly resistive load anyway so no real need for snubbers for voltage spikes anyway. Perhaps even put in the description that it is a "PLC interface designed card" or something like that to help customers understand.

    Leave a comment:


  • BobO
    replied
    Originally posted by Mike Nash View Post
    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.
    The D2-12TR actually states a leakage spec identical to BRX. Go figure.

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  • Mike Nash
    replied
    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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  • BobO
    replied
    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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  • Mike Nash
    replied
    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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  • BobO
    replied
    Is it necessary to use AC for the panel indicators.

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  • Mike Nash
    replied
    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.

    Leave a comment:


  • BobbyS
    replied
    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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  • BobO
    replied
    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.

    Leave a comment:


  • ControlsGuy
    replied
    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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  • ControlsGuy
    replied
    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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  • Mike Nash
    replied
    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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  • BobbyS
    replied
    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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