Short, bright pulses on dimmed loads

Discussion in 'C-Bus Wired Hardware' started by Marc, Jun 3, 2008.

  1. Marc

    Marc

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    I have seen this phenomenon once myself but had put it down to a once-off situation but now i have a customer who is experiencing the problem.
    I searched the forum and could find anything helpful, I was hoping someone here can shed some light on this problem.

    Pasted from user email:
    "...the lights in the kids bedrooms and in our dining room regularly flash very brightly and quickly when they are dimmed..."

    Its really just a short, bright burst of light, just a fraction of a second or so long, that may happen when the load is load is at a higher dimming level, but is only obvious when heavily dimmed.
    One load consists of 2x LV halogen downlights connected to an L5508D1A, and the other is a feature light (600W of incandescent lamps) connected to an L5104D5 pro dimmer and the installation is at the Gold Coast if that is of any relevance.

    Cheers
    Marc.
     
    Last edited by a moderator: Jun 3, 2008
    Marc, Jun 3, 2008
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  2. Marc

    froop

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    Hi Marc,

    Sorry can't help you fix your problem, but I can put my hand up to say I see the same thing. Not on all my dimmer channels, but have noticed it on a couple, and one in particular.

    At the bottom of the stairs I have a 2-key keypad. One key is a dimmer for the upstairs passage, the other for downstairs. Can't remember if they are set to toggle or memory. It usually when the light is on, and I hold the button to dim it. When I release at the desired brightness (dimness?), on occasion the light jumps back brighter, then dims down again, but not quite to the same level as it was when I released the key.

    My dimmer is a 8-ch DIN. Upstairs load is 2x60w 240v R63 downlights, downstairs is 1.
     
    Last edited by a moderator: Jun 3, 2008
    froop, Jun 3, 2008
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  3. Marc

    CC&C

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    I've previously experienced this problem and it turned out to be a loose neutral connection between the light and the dimmer unit. I'm no technical expert on dimming but I assume it's related to the dimmer suddenly seeing "no current" and the voltage goes to 240V (100%). Once the load reconnects the 240V (100%) is present and hence the flash and as the load is redetected the dimmer quickly ramps back down again. The flash only ever occurred at dimmed levels because as you pointed out, it wasn't visible at higher brightnesses.

    I hope this helps. Cheers, cc&c.
     
    CC&C, Jun 3, 2008
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  4. Marc

    Darpa

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    I'm not sure how relevant my information is to your situation, as I haven't had the following happen on a C-Bus dimmer, only on a cheap HPM one.

    In certain areas, when the data pulses are transmitted by the power companies at night to turn on hot water service meters, and then back off again in the morning, I have seen the loads (both incandescent and LV halogen) connected to dimmers, as well as CFL's not running through a dimmer, flicker in the manner you've described.

    This was always at a certain time of the night, dependant on area, and the same dimmers did not do the same thing at different premises.

    I have no idea if this same issue can possibly affect C-Bus dimmers, or if they have filtering of some kind built-in to prevent this from happening, but I just thought I'd share the thought in case it is of any help.

    Darpa
     
    Darpa, Jun 3, 2008
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  5. Marc

    Ingo

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    I have seen this. It happens, like you said, around the same time at night. It is fairly faint but noticable especially if you have dimmed a LV lamp to say 25%

    I did have a ClickOn dimmer that filtered these out completely but not all their products filter as good. The CBus Dimmer also filter most of the stuff out but not all - I suspect that they send the data at a too high level (amplitude) but that is just a guess. If I can find a filter that removes this alltogether I would be very happy.
     
    Ingo, Jun 4, 2008
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  6. Marc

    ashleigh Moderator

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    There are several possible causes:

    1/ Under some circumstances with SOME electronic transformers, the capacitance in the transformers can add up sufficient that in the off-portion of the 1/2 wave and excess voltage builds up and causes false triggering of the TRIAC. This causes a flash.

    2/ The power utiility may be injecting a control signal onto the mains. These control signals are usually somewhere in the region of 400Hz to 1000Hz superimposed onto the mains. Filtering this is difficult, some products do it better than others. Most Clipsal dimmers are not too bad but it depends on the signal and the utility, and sometimes the filtering does not as well as we would all like.

    CURES

    For case (1), there are two possible solutions.

    1A/ Change ONE electronic transformer to an iron-core type. This will prevent (by damping out) the excess voltage on the off-portion of the 1/2 cycle and the flashes / flickers will go away.

    1B/ Reduce the load on the dimmer.

    For case (2), there is not much you can do.

    IF CASE (2) is happening, the flashes / flicker should be occurring at roughly the same time each day (or on a repeating cycle), and the flash / flicker should be lasting a few seconds, no more than a minute.

    Because you mention in one case 600W of incandescent, I'm inclined to suspect case (2). More information about frequency of occurence (every day, some days, time of day) is needed to confirm.
     
    ashleigh, Jun 4, 2008
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  7. Marc

    damian.flynn

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    Interesting;

    I have also seen this on a single LV [12 Lamps] circuit - it was happening for about a week while I was running the initial tests and configuration on the 2A dimmer pack, but i have not observed the issue since.

    -d
     
    damian.flynn, Jun 4, 2008
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  8. Marc

    Marc

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    Thank to everyone for their responses...

    I have a few things to check now, but i'm fairly confident that it's not due to ripple control signals on the mains.

    I've seen this sort of interference before and it's a much less subtle effect and also usually several seconds in duration.

    What we've got is a single bright flash, possibly up to 100% of the lamp intensity level but only for an instant...and only every so often (say once, then not again for 10 mins, and then not again for hours)

    It's something we've witnessed here at our office on a rare occaision too. But it has never seemed to happen at a regular time of day...

    Any further thoughts would be apreciated.

    Cheers
    Marc.
     
    Marc, Jun 10, 2008
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