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Is it acceptable to put 4x S4s on a dimmer?

Discussion in 'Question of the Day' started by derekleffew, Oct 5, 2008.

  1. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    20A (2400W) dimmer. Four fixtures with HPL575/115 lamps. Discuss.
     
  2. Sean

    Sean Active Member

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    Yes.

    --Sean
     
  3. waynehoskins

    waynehoskins Active Member

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    My opinion = yes.
     
  4. seanandkate

    seanandkate Well-Known Member Fight Leukemia

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    Barring obnoxiously long cable runs, yes.
     
  5. len

    len Well-Known Member

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    Theoretically, yes.

    Real world, probably not.
     
  6. clbarker

    clbarker Member

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    Works for me everytime! So, yes!
     
  7. soundlight

    soundlight Well-Known Member

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    Done it multiple times, and it hasn't tripped a breaker yet.
     
  8. propmonkey

    propmonkey Well-Known Member

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    isnt that way they made the lamps 575w?
     
  9. David Ashton

    David Ashton Active Member

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    Yes and no, while 4 certainly can run off a dimmer if you blow a lamp it will almost certainly take out the breaker and you lose 4 lights out of your rig,-black hole.If you can split them it's safer.
     
  10. Pip

    Pip Active Member

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    Well, it's possible, but I wouldn't say it's advisable.

    Consider the almighty power equation:
    Watts equals Volts times Amps:
    W = V * A

    You have 4 instruments, 575W each, for a total of 2,300W (2.3kW):
    4 * 575W = 2300 W
    That's cutting it fairly close if you're on a 2.4kW dimmer. Let's look at that in terms of current (Amperage)

    Going back to our power equation...
    2300W = 120V * A
    A = 2300 / 120 = 19.17A

    :)
     
  11. David Ashton

    David Ashton Active Member

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    Bear in mind that 2.4k is a conservative rating, there is a built in tolerance so that it is quite safe to run at that output.Your output devices are normally 40A and the breaker will not trip unless there is a prolonged or severe overload.
     
  12. Pip

    Pip Active Member

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    Yes, but that is a built in safety feature. By saying that and going about business in that manner, you're circumventing one of the ways these things are designed to keep you (and your audiences, your facilities, etc) safe.

    It's not just about the inconvenience of popping the breaker - it's about actual safety when dealing with dangerous electrical equipment.
     
  13. David Ashton

    David Ashton Active Member

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    What I said is that it is safe to run 2.4k on a 2.4k dimmer because there is a safety factor built in, unlike others who were saying that you should further de-rate it to be on the safe side, I am sure no-one would ever consider pushing them a bit further even though you could possibly get away with it.
     
  14. Chris15

    Chris15 CBMod CB Mods Premium Member

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    And the average mains supply voltage is?
     
  15. David Ashton

    David Ashton Active Member

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    I think we have to assume that we are talking 115 or 120v with the appropriate lamp, in Australia or UK the above discussion would revolve around 10A 240v dimmers, also 2.4kw.
     
  16. Chris15

    Chris15 CBMod CB Mods Premium Member

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    I was taking that voltage range as a given, but at 120V, 115V 575W lamps draw more that 575W... Rather my sums put it at about 626W, 5.2A. 4 times that and you are into the range where a fuse will trip in time but a breaker may not...

    Put a voltage spike on that and I think you'll find breakers going tripsies.

    Can you do it? Yes. Should you do it? perhaps not...
     
  17. David Ashton

    David Ashton Active Member

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    If you don't use the correct voltage lamp you're very likely to blow it as the life reduces dramatically, but in answering questions like this it is fair to assume that a 575 lamp is using 575w.If you look at fuse ratings you will see that they run at a slight overload for a long time, certainly up to an hour.Over-running a lamp is not a linear increase as the resistance is very non linear with temperature so a simple calculation is inaccurate.
     
  18. STEVETERRY

    STEVETERRY Well-Known Member

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    ETC Sensor dimmers are Listed for 100% loading, 100% duty-cycle operation. Four x 575W is no problem.

    Some dimmers with thermal breakers can only be loaded to 80%, or 1920W on a 2400W dimmer.

    You need to determine the rating of your dimmer to answer this question.

    ST
     
  19. David Ashton

    David Ashton Active Member

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    Steve, could we have some examples of 2.4k dimmers which only take 1.9k as I've never come across any in Australia?.
     
  20. Chris15

    Chris15 CBMod CB Mods Premium Member

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    Err I thought it was a not uncommon practice for our American brothers to use a 115V lamp on a 120V supply to get some extra brightness. Someone wanting brownie points can go back into the archives and find Ship's percentages for lamp life change, colour temperature change, output change etc with over or under voltaging a lamp.

    I looked at a breaker curve a while back and from memory, you could run indefinitely at 127%... Fuses are normally a little more sensitive.

    Yes the resistance is very non linear, a 500w flood lamp is only a few ohms cold at DC... I suspect current draw will still go up, though it won't be linear and hence my number will be out...
     

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