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5K Fresnel on 2.4 k dimmers

Discussion in 'Lighting and Electrics' started by pudgeo2, Jan 15, 2008.

  1. pudgeo2

    pudgeo2 Member

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    So, I'm ME on this show, and the LD wants to use a 5k Fresnel, the only problem is I only have 2.4k dimmers. I don't really have the budget to rent 5k dimmers. I thought that I once heard that you can combine dimmers. Has anyone else ever heard of this, and if so how do I do this? P.S. I know that 2.4 + 2.4 is only 4.8, and that still isn't enough.
     
  2. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    No, you cannot combine dimmers to accept a single load larger than 20A.

    You have two solutions:
    1) Rent a single 6Kw dimmer
    or
    2) Use a maximum 2Kw Fresnel.
     
  3. Charc

    Charc Well-Known Member

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    Can I cut my 5kW in half, and power that off one dimmer, if I scale the dimmer to not go above 95%?

    (pudgeo, not poking fun at you, just Derek.)
     
  4. JD

    JD Well-Known Member

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    Dimmers work by chopping the waveform, but no two dimmers are going to be aligned that closely. One will always be getting hit first as they cut in. That's only the first reason not to! Small resistances in things like plugs and part tolerances will also lop-side the load, and heaven forbid you end up trying to parallel two dimmers on different phase legs! About the only time you can get more than 2.4k on a 20 amp dimmer is if the dimmer is designed to run on 220v, and you are operating a 220 volt lamp. (Not too common over here in the states.)

    One other note, the current curve on a lamp is not liner to the voltage curve, so a 5k lamp will already be drawing over 20 amps at 25%. (That is if the breaker holds past the preheat inrush!)
     
  5. zac850

    zac850 Well-Known Member

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    As was said, you have two choices: get 2k fresnels, or rent a 5k dimmer.

    Its not only the dimmer that your issue is, you also need rated cable to get from the dimmer to the fixture. Most theatrical cable is only rated for 25A, you'd be looking to pull around 41A through it.

    As was said, you can't use two dimmers for one fixture, and because of the way SCRs work, you can't just keep the fixture dim. (and even if you could, that defeats the point of using a 5k fresnel in the first place).

    Tell your designer to find the money to rent a dimmer and cable, or to come up with another solution to the problem.
     
  6. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    How about a 2K lamp in a 5K fixture? Provided LCL is the same of course. Would still need a 20A-60A adapter.
     
    Last edited: Jan 16, 2008
  7. icewolf08

    icewolf08 CBMod CB Mods

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    Well, assuming that sine the OP does not have 6K dimmers he probably doesn't own 5k fresnels. So, no reason to change lamps and use adapters when you could just rent 2K units.
     
    Last edited by a moderator: Jan 16, 2008

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