Dali Quirks

Discussion in 'C-Bus Wired Hardware' started by Ks04, Apr 11, 2020.

  1. Ks04

    Ks04

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    Hey Guys,

    I've recently installed a number of DALI LED drivers (OSRAM OTI) and have connected to my C-Bus network through the Dali Gateway.

    A few things I've noticed I'm wondering if anyone has any experience on:
    1. When I dim the lights they fade down smoothly, however when releasing the button, they snap to a different level (E.g fading lights up, on release, they'll snap to 20% brighter; the reverse is true for dimming). I have sync'd the ramp times in the Dali Gateway settings.
    2. The fade curve coming from C-Bus seems to reach around 10% of the light output at around 50% and below. I.e. the lights don't fade any dimmer until off from 50% to 0%. Whereas when I dim the lights \directly from the Dali software this behavior isn't experienced
    Any ideas how I might be able to improve these situations?
     
    Ks04, Apr 11, 2020
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  2. Ks04

    Wonkey

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    Have you ticked the match ramp rate on the C-Bus to Dali map tab of the unit.
    Colin
     
    Wonkey, Apr 11, 2020
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  3. Ks04

    jboer

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    Hi Ks04,

    So welcome to the world of DALI!

    With point 1, this is unfortunately something that has been around for ever and cant really be fixed. Having 2 command based protocols trying to talk to each other and with DALI being quite slow you get things like the jumps when 'live' dimming. What happens is that when you press a C-Bus button it actually sends a command out on DALI saying - Fade to 100% over 12 seconds (or something close) to the DALI it then tries to keep track of where the light would be up to internally, then when you pull your finger off the button it sends another command saying - Go to (level it thinks it should be) in 0 seconds. Effectively stopping the fade and setting the light level. Now there are propagation delays with this and also because the curves are different its estimated level over actual level are different. Unfortunately it is what it is and all installs suffer from this.

    Point 2: Depending on what software you are using I would definitely look at what curves you can change in the driver and see if it helps. You should be able to at least do logarithmic or linear. I would say you have it set to log...

    https://www.osram.com/ds/app-guides/3_dali_dimming_curves.jsp
     
    jboer, Apr 11, 2020
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    greig likes this.
  4. Ks04

    ashleigh Moderator

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    Stick to C-Bus ramp rates that closely match the DALI. The gateway does a conversion. Try using the 4 second ramp rate only.
     
    ashleigh, Apr 11, 2020
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  5. Ks04

    greig

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    Ouch. I wish I'd seen this post 2 weeks ago. I could have saved myself several hundred $$ and what's now looking to be a mistake I'll be living with for a while. I feel your pain Ks04!

    I have just installed a MeanWell DALI LED power supply for a new light I built here at home and surprise surprise I'm having Ks04's issue with the intensity snapping to a noticeably different value when I END RAMP after an UP/DOWN KEY journey.

    RAMP 1 is already set to 4s and "Match Ramp Rates" is checked in the DALI .

    Are there any other tweaks that might improve this, or is this my kitchen's "new normal"?
     
    greig, Apr 30, 2020
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  6. Ks04

    Ks04

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    So I've been messing around with this for a while. The issue seems to be with the delay that's caused by setting the fade rate prior to starting to dim so then the fade times are out of sync.

    My current configuration is to have C-bus not set the ramp rate (in the Dali gateway options) and I have hard set the fade time on the Dali side to 4 seconds and the c-bus side to match - the fade times are now in sync. The downside is that my lights all fade on over 4 seconds when i just want to snap them up which is a bit naff... but I find it more livable then the alternative.

    It's a shame, this could be a neat integration, but it seems c-bus isn't using all the Dali commands (Eg. Fade rate seems to be ignored, and only fade time is used).
     
    Ks04, May 3, 2020
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  7. Ks04

    ashleigh Moderator

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    DALI Fade rate is pretty much useless. Reason being you need to bash out DALI fade commands within 200 ms, over and over, in order to achieve the RATE. This turns out to be very difficult to do, especially if you have more than one THING that needs to be set on DALI at the same time, as the bus runs out of bandwidth between commands. Considering each DALI command takes around 30 ms (and in DALI2, quite a bit more). You are basically limited to about 5 to 8 DALI commands per permitted 200ms interval (and you HAVE to get in during that time our the fade rate is toast).

    So... you see why it is how it is.
     
    ashleigh, May 8, 2020
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  8. Ks04

    Ks04

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    Really interesting to know! Thanks Ashleigh.

    It's a shame there isn't a C-Bus compatible LED Driver - that would get around having to use 3P protocols such as DALI or DMX - neither of which seem to be perfectly integrated/integratable.
     
    Ks04, May 10, 2020
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  9. Ks04

    jboer

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    Yeah, there has always been a lot of discussion regarding that. The issue being that drivers really need to be matched to the LED arrays well to really work flawlessly.

    I try and use DMX as much as I can these days with Dimming LED and especially if you want live dimming. It is a much faster streaming protocol and therefore suffers a lot less with the visible rate differences. (Just try going DMX to DALI if you ever want to see first hand the differences... it is and always will be horrendous if you want live dimming)
     
    jboer, May 10, 2020
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  10. Ks04

    ashleigh Moderator

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    DMX to DALI, like DMX to C-Bus can be done. But unless the designer of the equipment to do this job uses a Kalman filter tracker, the results will be horrible.

    The number of engineers in the lighting space who know about this kind of technology is vanishingly small.

    Going from high data content, low information (DMX) to low data content, high information (DALI or C-Bus) is a VERY vexing problem. It is solvable with acceptable (but never good) results. but only if you know what the heck you are doing.

    Most people who try such things don't know what they are doing.

    And if you do know what you are doing, its difficult, slow, expensive, and bean counters won't approve the R&D project for it. Because you will sell 6 of them in the whole world.
     
    ashleigh, May 11, 2020
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  11. Ks04

    jboer

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    Hence the always will be ;-)
     
    jboer, May 12, 2020
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