Control/Dimming LED Decoders stops working until turned off and on again. We're all stumped.

Discussion in 'Lighting and Electrics' started by Stages Electrics, Jun 14, 2019.

  1. Stages Electrics

    Stages Electrics Member

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    Hi everyone,

    We are using some LTech DMX512 24 Channel decoders (http://www.ltechonline.com/html/en/LED-Controller/DMX-RDM-Controller/DMX-PWM-CV-type/LT-880.html) in one of our shows and we're having a strange problem with them. Every so often (but way too often) we need to turn them off and on again. We've had this issue when they turn on for the first time in a show and halfway through the show and we can't figure out what is going on with them. Our lightboxes are made up of SMD5050 LED modules, each channel using fewer watts than the output of the decoder.

    We've narrowed it down to the decoders and specifically a power issue on the decoders.

    Things we've found interesting but still puzzling
    • DMX is still going from decoder to decoder.
    • We've swapped decoders out for brand new decoders of the same type and experienced the same issues.
    • These decoders have been used in previous shows in a similar application and have never had this issue before. Plenty of other issues, but never THIS issue.
    • Each decoder is only running 12 of the possible 24 channels except for one. Problems persist with both.
    • We had no issues like this until we experienced a brownout in one leg before everything was connected to line conditioners. We changed bad decoders and bad power supplies out. Since then we've continued to change out decoders before we realized that they needed to cycle power.
    • This show is kind of hard on them. They turn on and off, change color rapidly, and cycle through rainbow colors.

    Issues we've eliminated
    • DMX, see above reasons
    • Overheating
    • Power surges and brownouts (line conditioners)
    • Bad LEDs (they're still kicking someway somehow)
    If anyone has any idea what is going wrong, need more information, have questions or possible fixes I'd love to hear them. Thank you!
     
    RonHebbard likes this.
  2. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @Stages Electrics What happens if you power your devices from utility duplex receptacles, specifically NOT from power from dimmers or solid state non-dims. Non-dims switched via mechanical (often referred to as "air gap") relays could also be utilized. Dimmers, regardless of what level they're parked at and / or non-dims switched via solid state devices (dual SCR's, TRIAC's, etcetera) require an amount of turn on time clipping a minute amount from the rise of each half of the positive and negative sine waves. This clipping of the waves' rise often plays havoc with many power supplies receiving their primary power from such sources.
    @Ron Foley Would you care to comment?
    Toodleoo!
    Ron Hebbard
     
    FMEng likes this.
  3. JD

    JD Well-Known Member

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    Line filters are not going to replace the missing waveform. As Ron said, power them off a regular old wall outlet, or an "air gap" non-dim module. Another issue is that the idle current may be too low. When using electronic equipment on any dimmer, even parked, you open up a can of worms. Throwing a 100 watt incandescent lamp on the circuit as a ghost load may make them behave better, but your best solution is to go with real utility power that doesn't have a dimmer in series with it.
     
    RonHebbard likes this.
  4. Amiers

    Amiers Renting to Corporate One Fixture at a Time.

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    I also vote the decoders on the dimmer are messing with the rest of them.

    Easy test take the dimmer decoders out of the dmx run and see if they still act up.
     
    RonHebbard likes this.
  5. EdSavoie

    EdSavoie Well-Known Member

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    As a side note, DMX should pass through unit to unit regardless of if they are powered on as you've noticed, the DMX in is wired directly to the DMX out, as devices "tap" the bus
     
    RonHebbard likes this.
  6. BlackoutGo

    BlackoutGo Member

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    Sounds like you are pulling too much power on the led tape. You have reached the limit of the output of the controller, which is 72A, or 3A a channel. The controller can handle a maximum of 864 watts at 12v. You should be capping this at 80% of the maximum output.
    You do have a 1000w power supply, which is adequate for one controller. Do the voltage drop calculations on the lines going from the controller to the power supply, or simply measure it.
    I do suggest you look at how much power your LEDs are using. Needing a hard reset usually is usually a sign of incorrect wiring or overdrawing power.
    As others have suggested, get them off of dimmers, as it’s cutting the curve of the power, just a good practice to help extend the life of the components.
    Best of luck. Troubleshooting LEDs, especially with cheaper controllers is a pain.
     
    RonHebbard likes this.
  7. Stages Electrics

    Stages Electrics Member

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    Thank you all for your responses. It took running power from the adjacent building to get everything off of dimmers (we've exceeded the capabilities of our theater by quite a bit) but we've had our shows go well so far. I'll update again at the end of the week if we've totally solved this one. Thank you all so much for your help, I really do appreciate it.
     
    RonHebbard likes this.
  8. Stages Electrics

    Stages Electrics Member

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    We have decoders that are incapable of sending data through unless they have power. I don't know why they were manufactured that way, but needless to say we try not to use that type unless we're in a bind.
     
  9. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    @Stages Electrics Exceeding capabilities is O.K. as long as you've still got space for paying patrons. (Know when you're being teased mercilessly.)
    Toodleoo!
    Ron Hebbard
     
  10. JD

    JD Well-Known Member

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    MOST pass the DMX through... but not all. In addition, some devices use input protection that prevents input voltages from exceeding the chip's 5 volt supply rail. In some cases, when power is removed, this protection ends up clamping down to the new rail voltage of 0 volts! (actually, not quite 0 as there is diod voltage drop.) Usually, this will take the whole chain down as compared to only fixtures after it.
     
    EdSavoie and RonHebbard like this.
  11. Chris Pflieger

    Chris Pflieger Well-Known Member

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    DMX should always pasthrough as it's a direct electrical connection.


    When they lock up, can you measure the output of the power supply without interrupting it?



    And it probably goes without saying, but stuff like this is par for the course with cheap Chinese stuff.
     

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