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Control/Dimming Is this possible: Lamp failure breaks a dimmer?

Discussion in 'Lighting and Electrics' started by slimrocktwo, Feb 10, 2009.

  1. slimrocktwo

    slimrocktwo Member

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    I was geling lights for a Battle of the Bands that's coming up, and i noticed an ellipsoidal was burned out in the catwalk. I changed out the bulb, plugged it back in, and nothing. So i tried connecting it to a different circuit that was powered, and it fired right up. I tried a another light on the troubled circuit, and got nothing from it. Our system is double patched, so I tried the same method on the other plug and got nothing as well. I checked the dimming rack and found none of the dimmers had a tripped breaker.

    Is it possible that when the bulb burned up that it took the dimmer with it? Prior to the bulb going out, both circuits of that dimmer worked fine.

    Thanks in advance
  2. mrb

    mrb Active Member

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    what kind of dimmers? I have seem lamps develop a short circuit when they fail but it usually trips the breaker or burns itself out before damaging the dimmer.
  3. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Yes, it's possible, but rare.
    First, are you sure all the breakers on the dimmers were un-tripped? On some, it's difficult to tell just by a visual inspection. On almost all, the handle must be switched fully to OFF then to ON, to reset the circuit breaker.
    Second, are you absolutely certain the console was telling the circuit/dimmer to be on?
    Third, IF you are qualified and IF you have modular dimmers, assuming this to be a DPC installation, swap the suspect dimmer with a known-good module. If the problem follows the module, it's likely a bad SSR--a relatively easy and inexpensive repair, depending on the make/model of the dimmer. If a "good" module doesn't work in the "bad" slot, and the "bad" dimmer works in another slot, it's a wiring or control issue. Very rare, but again, possible.

    Here's the link for the User's Manual for your dimmer rack, in case you don't have it: EDI Mark VII DimmerBank.pdf. (via Google)
    Last edited: Feb 10, 2009
  4. slimrocktwo

    slimrocktwo Member

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    The dimming rack is a Mark VII Dimming Bank, made by Electronics Diversified Inc. It was installed in '96, when the High school/ Auditorium was built.

    I'm pretty sure i flipped it on & off, but i'll gve it another try tomorow.

    Yes, because I after I moved the light to a working dimmer, I changed the channel from the troubled dimmer to the working dimmer.

    I'll try this tomorow as well.

    Thanks
    Last edited: Feb 10, 2009
  5. gafftapegreenia

    gafftapegreenia CBMod CB Mods Premium Member

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    And then there is always the chance the circuit itself has died.
  6. Clifford

    Clifford Member

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    We have the same rack a similar problem with two circuits. Please post if you find the problem.
  7. icewolf08

    icewolf08 CBMod CB Mods

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    I like how people jump to the rack/dimmers as the problem. Have you opened up the female connector to make sure that the wiring is good inside? I would do that before I assumed that there was a dimming issue. This is especially pertinent if you don't have flush-mount female connectors (i.e. you have pigtails). One step at a time folks.
  8. photoatdv

    photoatdv Active Member

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    Yeah, the connectors are often the culprit. We have had SO MANY of those go recently. My favorite was the once that was getting so hot it melted both plugs together. By the time we got the plugs off they were in multiple pieces. And yes the breaker was off when we did this.
  9. slimrocktwo

    slimrocktwo Member

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    We have flush mount connectors in the catwalk, so I didn't test that. I don't think it's an connector issue though, because the troubled dimmer is double patched, and neither circuit/plug is working.
  10. gafftapegreenia

    gafftapegreenia CBMod CB Mods Premium Member

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    How old is your venue? Sometimes wiring goes bad.
  11. slimrocktwo

    slimrocktwo Member

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    Our auditorium is about 12 years old.

    While on the topic of wiring, how is a double patch system generally wired? Is the two sets of wires coming from each dimmer? Or is there one set that comes from the dimmer, and the second channel ties into it down the line?

    Thanks for everybody's suggestions
    Last edited: Feb 10, 2009
  12. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Good point, Alex. However, in this case, the impetus was a lamp failure. And both outlets on the same circuit were non-functional. Also since, prior to opening a female connector, one must first http://www.controlbooth.com/forums/glossary/7283-lock-out-tag-out.html the dimmer rack, (NFPA 70E) I'd do the module swap first, (after checking the circuit breaker) because I had to go to the rack anyway. It's sort of a philosophical discussion, that I think I raised before: When trouble-shooting, do you go for the most likely, or the easiest to diagnose, symptom first?

    It could be either, but the more cost-effective method would be to run one set of wires from the dimmer to the connector strip, and then gang the outlets at the terminal block. I doubt your school would have paid for more labor and materials than necessary, to meet the minimum specifications.
    Last edited: Feb 10, 2009
  13. JChenault

    JChenault Well-Known Member

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    If by double patch you mean two female receptacles per dimmer - and both females are in the same wiring strip, then there is usually a single run from the dimmer to a terminator strip in the raceway. At the terminator strip, the circuit is split into two lines to the receptacles.

    IE when plug strip is constructed, the manufacturer runs the females in the plug strip to a wiring block. If you have 6 circuits and 12 ( or 18 or 24) plugs, you will have 6 circuits running from the dimmers to the plug strip. Assuming three phase power, this usually means 8 wires in a permanent installation. ( you could have some spares in the run as well).

    Copper is spendy. Electricians to run more wire than needed is spendy.
  14. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    See this document [edit: also attached] regarding the use of shared neutrals. As per 2008 NEC Section 210.4(B) the minimum number of wires required for six branch circuits in a dimming system would be thirteen.

    Years ago, I worked with a dimmer installation that was commissioned, and then warranty-repair denied, by another manufacturer, due to the use of common neutrals. (Sidenote: Expressions aren't happy about 120V coming in through the DMX line, but it rebooted just fine. I think we had to reload the show from disk, however.)

    Attached Files:

    Last edited: Feb 12, 2009
  15. church

    church Active Member

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    yes a lamp failure can result in a TRIAC failure - this is usually a "feature" of the lower cost dimmers. As already mentioned when a lamp fails it often produces a large current transient dIcom/dt. If the rate of change of the commutating current exceeds the TRIAC capability then TRIAC failure results.

    This is usually limited by including an inductor in series with the TRIAC. Dimmers that include an inductor for noise filtering purposes are ahead of the game here. Unfortunately inductors that can handle the currents found in dimmers without saturating are usually found on large torroidal cores or large E cores similar to a transformer. These are of course large, heavy and expensive. Note another cause of this problem is a motor load, the voltage and current waveforms are out of phase which can cause large values of dIcom/dt.

    Do not confuse this with the snubber circuit which is used with non-snubberless TRIACs, this is used to limit the rate of change of OFF state voltage dVD/dt. A HIGH COM TRIAC can also be used to avoid this problem.

    All of these are design choices made by the design engineer.
  16. slimrocktwo

    slimrocktwo Member

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    Alright, so when I had a free moment, I tried flipping the breaker on and off a few times, but that didn't help. I tried swapping the dimming module, and it didn't work at first. I tried flipping the breaker a few times, and it started working. I put the module back into its original place, and every thing is working smoothly now. Thanks for everyone’s help!
  17. gafftaper

    gafftaper Senior Team Senior Team

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    :confused: Um... That's weird. Is the rack full of dust bunnies and needs a good cleaning?
  18. mrtrudeau23

    mrtrudeau23 Member

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    also, you might try opening the male plug end of the instrument itself. one of the wires may be loose...
  19. slimrocktwo

    slimrocktwo Member

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    The rack is about due for it's annual cleaning
  20. gordonmcleod

    gordonmcleod Member

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    Sounds like it was possibly the connector on the module was corroded and most likely it was the low voltage control connector that had an issue
    On the issue of triacs over the years I have found that shorts still kill them even with large torroid or E and H style chokes that are rate to prevent saturation
    On thought that an engineer at Teccor told me was that the inductor was the culprit when the fuse or the breaker tripped the collapsing magnetic field in the inductor produced a high voltage spike that even the snubber could not absorb
    So I tried a very high voltage rated triac with a set of GMovs across it and it didn't fail after 3 dead shorts being applied but the losses in the choke also prevented the dimmer from reaching line output and the snubbing caused it to missfire

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