DMX or DALI for LED's

Discussion in 'C-Bus Wired Hardware' started by znelbok, May 17, 2013.

  1. znelbok

    znelbok

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    Trying to work out what is the best option here

    If I have say 50 non RGB lights I want to dim and I use a DMX controller I would need 5 gateways. If I used DALI instead I would I only need one DALI gateway?

    Assuming that because they are not RGB, that only a single slot is required, then only a single group address is required in C-bus. That would mean 12 lights per DMX gateway ?

    If I use a DALI gateway, then I only need one (plus a pair of power supplies) as the DALI Gateway handles up to 64 DALI devices.

    What makes the DMX gateway a better option?

    Are there any caveats to either? I was reading about MMI's not having DALI values, but I think that was that the DALI network was not persistent and that the gateway could not "poll" the DALI network to get the current values of the devices, but I suspect that if there is no external control (i.e. all C-bus only) then this wont matter as the groups in C-Bus will hold the current value of the DALI device and the MMI will reflect the groups address value.

    Which is the best way to go - is there something else I should consider?

    Mick
     
    znelbok, May 17, 2013
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  2. znelbok

    ashleigh Moderator

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    It's much of a muchness.

    Neither gateway will be able to determine the lamp states and populate the MMI but as you say, the C-Bus side will know state in input units - its just that things that use MMI discovery won't get that right.

    DMX tends to be more specialised because its major use is theatrical lighting. There's DMX gear out there, some good some bad, the good stuff is fairly expensive.

    In terms of DALI, and 50 lamps, it really sounds like you are just using a DALI broadcast to control them all at the same time. If that's all you want to do, and all you would ever need in future, then it seems like DALI is going to be a cheaper way to do, because you need less other fluff in the mix.

    When it comes to LAMPS WITH DALI, there are a few to choose from. If choosing LED, watch the bottom end of the dimming range.

    Remember a few years ago with Fluoro DALI ballasts there was a big stink because the 1% and 3% ballasts were not readily identifiable. The effect was that some lamps would not dim as low as others. This became "ooh ooh ohh bad C-Bus, you gateway is crap it won't dim lamps properly". Which was in fact using 3% ballasts (so called because they only go down to 3%) mixed on a line with 1% ballasts.

    In DALI land, the difference in DALI level between 3% and 1% is *rather a lot*. [Look up the DALI dimming curve to see why - its a loss of about 1/2 the dynamic range.]

    Now the trouble in LED land is that there a lot of LED control gear out there which is WORSE. Minimum levels on DALI LED of only 10% are common. Frankly - thats complete crap, but people are selling it.

    So try and find a LED control gear that can do a bottom end of around 1% in order to ensure decent low end dimming performance.

    [Bear in mind that the DALI dimming range is actually 0.1% to 100%, so pretty much everything loses the very low end.]

    I suspect you will find the same performance issues in DMX, its just that they may not be so clearly spelled out or characterised.
     
    ashleigh, May 18, 2013
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  3. znelbok

    samluo

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    Minimum levels at 25 in DALI means min output <0.5%.
     
    samluo, May 18, 2013
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  4. znelbok

    znelbok

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    Just to clarify, the 50 lights would equate to 50 light groups in C-bus i.e. 50 lights to be all controlled separately.

    I have just realized that it is more than 50 physical fittings so that would mean I need two DALI gateways. There are strings on small LED fittings in some locations.

    Am I assuming correctly that DALI is a bus notwork that will allow you to send a message to one ballast to go to 100% (at address x) and then a second ballast or group of ballasts to 75% (all at address y)?

    What about turning off the light? does a value of 0 equate to off or do I need to use relays similar to a 1-10V system?
     
    znelbok, May 18, 2013
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  5. znelbok

    samluo

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    "Am I assuming correctly that DALI is a bus notwork that will allow you to send a message to one ballast to go to 100% (at address x) and then a second ballast or group of ballasts to 75% (all at address y)?"
    YES set different levels in scene, and call the scene the ballasts will go to different levels wanted .

    "What about turning off the light? does a value of 0 equate to off or do I need to use relays similar to a 1-10V system?"

    0 mean OFF, relay not need.
     
    samluo, May 19, 2013
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  6. znelbok

    DarylMc

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    Hello Mykel

    If you are looking at the 5502DAL CBus DALI interface, it has 2 DALI networks each with 64 ballast addresses so 128 in total.
     
    DarylMc, May 20, 2013
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