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DMX over dimmer wiring

Discussion in 'Lighting and Electrics' started by mrstebbings, Feb 13, 2019.

  1. mrstebbings

    mrstebbings Member

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    I know it is possible to sent digital signals over power wiring in a house to control light switches, etc.
    As an alternative to an extensive and expensive retro-fix DMX cabling for LEDs replacing old tungsten instruments i wonder if it is possible to use existing dimmer circuit power wiring to send DMX to LED instruments? What equipment additions or modifications would be necessary?
     
  2. robmerow

    robmerow Active Member

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    Do you mean disconnect the power wiring from line voltage and use it as DMX instead, or do you mean try and piggy-back a DMX signal over an in-use power line? One one would probably work just fine. The other sounds like a disaster.
     
  3. MNicolai

    MNicolai Well-Known Member Fight Leukemia

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    No.

    If you don't want to pull cable, go with wireless DMX.
     
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  4. Jeph H

    Jeph H Member

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    The biggest headache would be isolating the data from the power circuits...
    At that point it would be easier just to run cable or use wireless DMX like MNicolai already said...
     
  5. ChrisB_SanDiego

    ChrisB_SanDiego Active Member

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    I assume you are thinking something that works along the lines of power-line networking... in some of the museums I run shows where you can't change things and often can't run cabling, I have to get creative, so DMX over powerline does work.

    In a theatrical setting where you're dealing with dimmer racks, not likely. you will run into an incredible amount of headaches for each circuit, and that's if the CEM, battery backups, power conditioners even allows the DMX signal to pass through, which I would be amazed if you could get a clean signal through. I have never been able to pass signal through a powerconditioner or UPS.. Not to mention you still have to convert it to a form that the fixture can handle. It's a nice idea but the cost savings, if there even is any is not worth all additional configuration you will have to do. Of course that all doesn't even matter if your local code doesn't allow for it.

    There are a ton of wireless DMX options out there That I would highly recommend you look into. RC4 systems are incredibly reliable and I would trust them in a permanent install. Blizzard lighting makes incredibly affordable wireless solutions that I have had good experience with.

    And if you don't want to go wireless, swapping 1 power run and running a single cat cable rather than pulling all your cabling is far more cost effective than replacing all your power runs with DMX.
    ex. run cat to your electric and hang a node. vs changing all wiring on an electric. You'll still need power to your LEDs
     
    Last edited: Feb 13, 2019
  6. mrstebbings

    mrstebbings Member

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    Yes. Just using the wiring.
     
  7. Jeph H

    Jeph H Member

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    Would you be running any of the other dimmer circuits while doing this?
     
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  8. RickR

    RickR Well-Known Member

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    DMX requires twisted pair wire to reject electronic noise picked up along the run. It's conceivable that the signal could make it through if no noise was present. (There's a story of running it down a barbed wire fence.) Likely to work or practical? No way!

    Edit: Data - line!
    The transmission lines are Data+ and Data- meaning that they both contain levels, but in opposite polarity. You'd have to take a unique neutral and match it to the hot line making sure there's no other connection. You do have all separate neutrals, right?
     
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  9. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    Its hard to imagine if you can change to LED lights that running DMX is really a "extensive and expensive retro-fit". Use Category wire and/or wireless. Hard to offer best solution without knowing a lot of details.
     
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  10. porkchop

    porkchop Well-Known Member

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    The cheap and easy way would be to find a fixture that will return to it's previous levels on power up and just use the power on/off to control the lights. You would be sacrificing a lot in terms of dimming and changing levels, but it comes at a convenient price.

    Otherwise, if pulling DMX is prohibitively expensive I would look at wireless. I bet if you ask @theatrewireless nicely you can work out a demo to see how robust wireless control is in your space.
     
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  11. KacyC

    KacyC Member

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    In addition to the points made above, I would be concerned about the topology of the system using existing circuit wire. Proper DMX wiring needs to be in a continuous run (or through opto-splitters). There are cable length requirements for signal timing, and you should have a resistance termination at the end of each line. To be in accordance with the ANSI standards for DMX-512A, you should be using a Belden or Cat5+ cable.
    I also wonder if the wire gauge of the existing wiring (likely 10-14ga?) would be an issue for the resistance along the wire, but people who are more knowledgeable about this than me can comment on that.

    Basically, in a theatrical setting, you are sending data that you want to have 1) no interference, 2) fast response, and 3) high integrity/reliability of signal. I would be leary to skimp on the control backbone.
     
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  12. rsmentele

    rsmentele Well-Known Member Premium Member Fight Leukemia

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    I would highly suggest wireless if the spectrum environment in your facility allows it.
     
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  13. theatrewireless

    theatrewireless Jim @RC4Wireless #RC4DoesThat

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  14. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    If this is for lighting positions for theatre lights, I agree wireless is very possibly your best option. I am confused but the "house" reference, but maybe not for house lighting. I have a lot of faith in wireless but probably an equal number of people say "why wireless when it can be wired?" so choose. I don't know what makes it so hard to run cable but may be in your facility.
     
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  15. Chris Pflieger

    Chris Pflieger Well-Known Member

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    If you're using old, dead ~12 ga. wires for DMX512, you'd have to create a rather complicated level shifter to devise a whole new physical layer, because DMX512's RS485 signals ain't gonna fly on that wire (reliably).

    The prospect of designing such a circuit is the stuff of electrical engineering nightmares.
     
  16. BillConnerFASTC

    BillConnerFASTC Well-Known Member

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    If you can send ethernet over barbed wire (Google that and there are lots of demonstrations) how hard can DMX on #12 THHN be?
     
  17. porkchop

    porkchop Well-Known Member

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    False.

    Shielding from 120VAC lines running through the same conduit might be an issue, but that has nothing to do with level shifting. 485 is really flexible and has been used effectively over longer length of much worse cable.
     
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  18. Chris15

    Chris15 CBMod CB Mods Premium Member

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    I don't know about North American code, but repurposing a mains cable to run data on could be non kosher.
    We are required to maintain separation and/or segregation between comms and such ELV cabling and mains wiring. If the run goes through existing structure, shared conduits, etc, it is highly unlikely that this could be achieved...

    It also is not the wisest idea long term, there is a very real potential for it to be mistaken for mains cabling at some stage in the future and connected to a mains voltage which almost certainly will let some magic smoke out of whatever DMX devices are attached - if only frying the optoisolators...
     
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  19. SteveB

    SteveB Well-Known Member

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    There are assorted home quality automated systems that send data over the primary A.C. power lines. One of the systems is known as X10. It’s been around for decades. My understanding is it sends packets at the zero crossover point in the AC sine wave. They make units that tie into single phase 2 pole as well as 3 phase systems to get the signal I jetted on a particular phase, to devices on other phases. I have a 2 pole unit on my house system as I use X10 in a number of rooms. I could see where the transmission rate is too slow for DMX while it waits for the zero crossing. There is a lag in the X10 system.

    I believe that many home automation systems essentially function the same as X10 using mains power lines as the transmission system.

    I can as well, recall that Union Connector, manufacturer of 2P&G connectors, company switches, etc.... at one point maybe 30 years ago, manufactrured a ramped up X10 type dimming and control system. The Theater Crafts advert. at the time indicated a system installed at a TV studio in Alaska. Never saw one in real life, thankfully.
     
    Last edited: Feb 15, 2019
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  20. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Amazon: 200' Cat 5e cable under $15. A set of 5pin DMX to RJ45 adapters under $30. Add an afternoon of creative work fishing cable and you have a new DMX line.

    If you can't make that work then go with the RC4 900mhz wireless setup. Yes there are cheaper options, but if you are like me, you don't want to gamble your show on cheap wireless gear. Good stuff costs, but it's worth it... and a lot cheaper than paying for a major electrical install. (Note: RC4 is a sponsor of CB and Jim and Sean are a couple of great guys, so I am a bit biased).
     
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