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Thread: pixel wiring and grounds

  1. #1
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    Default pixel wiring and grounds

    I have wired my pixel tree and star like the drawing below without the red arrows. The ground is currently not connected down each of the strings but the PS is the same for each (at least for the moment). The PS and controller in the pic are the same ones for both sets of strings. I have watched a bunch of videos on the power injection. As it sits now with the 50 pixel star (at the end of the middle string) the first 4 strings of the second set flicker. I am guessing it is either not enough power or a ground problem. If I unplug the star it appears to work. Solid colors are OK, its the white that flickers. I am using the test page of FPP. the controller is a BBB with a F32-B cape.
    Questions: should the ground be connected along the strings (red arrows) even if the PS is the same? If I add a second PS for the second string does the ground have to be connected through or can I connect them at the power supplies themselves? Or can I just bus the power supplies together in parallel? I have at least 200 more pixels to add to the controller as well that will require a separate PS I am sure so what happens when I want data off the controller but no power? Does the controller PS ground and the ground for the new PS need to be connected? It all seemed to work until I added the 50px star. The star works fine by itself. Thanks.
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  2. #2
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    Default Re: pixel wiring and grounds

    How many pixels per string? How many strings? What size power supply? Sounds like a power issue.


    Sent from my iPhone using Tapatalk

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    Default Re: pixel wiring and grounds

    Quote Originally Posted by TSL View Post
    How many pixels per string? How many strings? What size power supply? Sounds like a power issue.


    Sent from my iPhone using Tapatalk
    Hard to see in the drawing. Each circle is 46 pixels except the second one in the middle is 50. the power supply is 360 watts, 12 volts, the strings are shown complete, there are only the three. 832 pixels total. I think it's power, I am just not really sure how to connect more supplies (of which I have plenty). The controller says 720 max or something like that so I put as many as I could per string but maybe that isn't the best plan.

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    Default Re: pixel wiring and grounds

    That data line is "With respect to ground at the source of the data signal". This is a critical statement. Wherever a data line leaves a pixel and enters another pixel, the V- line on those two pixels should travel parallel to the data line. V+ can be broken as needed, but V- needs to follow that rule.

    Next, your issue sounds like you are getting more voltage drop than you are expecting. Are the last pixels that seem to be working / stable a bit pink instead of white? If so you have too much drop between the PSU and the pixels going pink. If not then your problem may be caused by the missing V- lines causing the data reference to be off and introducing noise. NOTE: Tying the V- lines together at the PSU is not a good idea. The data reference is then different to that experienced by the last and first pixel over the gap (effective reference is much longer than the data run).

    You can use as many PSUs as you want as long as the V- and data lines run together. The V+ lines from each PSU must be kept apart (Break the V+ line between PSU connection points).

    Lastly, I almost never power a prop from my controllers. I could remove the fuses but that is too much work. I power inject at the props / elements and yes I have lots of PSUs on a given prop (aka I use buck converters at the injection points).


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

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    Default Re: pixel wiring and grounds

    Quote Originally Posted by MartinMueller2003 View Post

    You can use as many PSUs as you want as long as the V- and data lines run together. The V+ lines from each PSU must be kept apart (Break the V+ line between PSU connection points).

    Lastly, I almost never power a prop from my controllers. I could remove the fuses but that is too much work. I power inject at the props / elements and yes I have lots of PSUs on a given prop (aka I use buck converters at the injection points).
    Martin - So when I add another supply or two the grounds connect to the "ground string" but the V+ does not connect to the string, it essentially starts a new partial string on the V+ side? Thanks. Oh and do you connect the ground from the controller but not the V+ when you are not powering them from the controller?
    Last edited by Starsman20; 10-07-2019 at 01:59 PM.

  6. #6
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    Default Re: pixel wiring and grounds

    My mega tree is 32 strings 96 pixels per string. I use 4 300 watt power supplies. I inject at 50 pixels. All grounds are connected. The positives are all separate. I use 5v pixels at 65% intensity.

    A good website for power needs: spikerlights.com/calcpower.aspx


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    Default Re: pixel wiring and grounds

    Quote Originally Posted by Starsman20 View Post
    Martin - So when I add another supply or two the grounds connect to the "ground string" but the V+ does not connect to the string, it essentially starts a new partial string on the V+ side? Thanks. Oh and do you connect the ground from the controller but not the V+ when you are not powering them from the controller?

    • My controller has a dedicated PSU that powers only the controller (and sometimes a local FPP).
    • V- plus Data leaves my controller and arrives at my prop where it is joined by V+ and V- from the prop PSU.
    • V- from the PSU plus V- from the controller plus V- to the first pixel all get tied together.
    • V+ from the PSU plus V+ to the first pixel get tied together.
    • Data from the controller plus data to the first pixel get tied together.


    For props with local PSUs: I tend to run 14 AWG landscape wire (I call it a feeder wire) along with the pixel string and use it to inject power every 25 (not 50) pixels. At this point I am considered to be over engineered and I am happy with it. If the string goes above 10A load at full white then I will put in another run from the PSU. If the run gets to be more than 50' I tend to add another PSU to feed the run. I cut the V+ between the two PSUs.

    My newer props are being set up to be fed by 12v and 24v PSUs with buck converters dropping the voltage to 5v. I tend to inject in the middle of 30 pixel sets (15 on each side of the injection point) and keep the V+ from each buck converter isolated.


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
    https://www.youtube.com/channel/UCyX...ttrsZNARkUce0Q

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    Default Re: pixel wiring and grounds

    By only injecting the + on your pixel strings, you are forcing all the return current down the pixel string ground. Whatever gauge that wire is is limiting current flow. Unplugging the star is probably allowing the supply voltage to increase slightly and above the problem threshold. Simple answer, add the minus injection to each string and I am sure your problem will go away.

  9. #9
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    Default Re: pixel wiring and grounds

    +1 on this answer.
    Great point that the Ground injection wire is often ignored.
    Quote Originally Posted by aknflyer View Post
    By only injecting the + on your pixel strings, you are forcing all the return current down the pixel string ground. Whatever gauge that wire is is limiting current flow. Unplugging the star is probably allowing the supply voltage to increase slightly and above the problem threshold. Simple answer, add the minus injection to each string and I am sure your problem will go away.

  10. #10
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    Default Re: pixel wiring and grounds

    Quote Originally Posted by aknflyer View Post
    By only injecting the + on your pixel strings, you are forcing all the return current down the pixel string ground. Whatever gauge that wire is is limiting current flow. Unplugging the star is probably allowing the supply voltage to increase slightly and above the problem threshold. Simple answer, add the minus injection to each string and I am sure your problem will go away.
    The way it is currently is I am connecting both the pos and neg at the injection point, I am not however continuing the V+ nor V- through the injection point. It is more like 4 strings that are separate except for the data line. In the picture it is wired like the drawing without any of the red. I am going to connect a V- through along with the data and I am guessing that will solve it.

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