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Confirm Understanding of Power Injection

Discussion in 'Power Supplies' started by Danno, Feb 19, 2019.

  1. Danno

    Danno New Elf

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    Hi there, I am assembling my layout now and just want to confirm my understanding of power injection. I am going to run 5V, so I will need to power inject every 50 pixels, however, given I won't run at 100% it will be a few more than that, but that's irrelevant for these questions as my questions really relate to the approach.

    I have a diagram below of a few example props and how they're hooked up from my controller, with power injection from an F8 distro board.

    2019-02-18 21_16_02-Window.png

    Can anyone confirm the following:
    1. Between props, I will power inject even if the props don't have a full 50 pixel spacing between injections. This won't matter as long as there are some pixels [resistance] between power injection points.

    2. My window outline will require an injection mid prop, so I will run an injection from an F8 somewhere in the middle of the prop.

    3. My tree prop will draw up to 5.04A and will require 4 injections (on top of the injection at the start and end of the prop - which would reduce the number of Amps needed via power injection). I would run a single power injection cable from my F8, and inject multiple times from the same wire into the prop. I understand this is OK because the current draw would be less than the fuses & wire (5A).

    4. My 'Big Prop' would draw 8.79A, so I would need at least two runs from an F8 distro to stay below the amperage threshold on each fuse & wire (5A). So using the same approach as the tree prop above, I would inject mid prop, however, in this case, there would be two runs from the F8.


    I know there are other considerations with regards to cable length and voltage drop etc which need to be considered, and the Spiker Lights calculators have helped with that, however, I really just want to confirm my thinking around 3 and 4 above.

    I've been using the Miller Christmas Lights 'Controller and Power Distribution 2.0 (TEMPLATE)' which has proven very helpful with calculating amperage by power supply, however when I took a look at my proposed overall display, I would need 135 Power Injection points, which is a lot of F8 distros and cable if I can't consolidate leads from the Power Supply to the prop.


    Cheers

    Dan
     
  2. scamper

    scamper Senior Elf

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    Biggest thing here is don't over complicate things.
    Inject where it is easy to do so. when running your pixels at reduced brightness you can get away with a lot more, and at the end of the day, the lights will only draw what power they require.
    What you have above is fine, but look at the real world scenario. Meaning if your "big prop" has pixels that are accessible at every 75, then use that.
    I for one have a mega tree that is 5v and has 75 pixels up and then 75 down. All of the strings are injected at the bottom only. I have 18 strings and I have 2 power runs that loop through 9 strings each. I don't get any yellowing on full white, which tells me there is no significant voltage drop. but I rarely use white anyway and if I do, it is snow flakes which means it would be lucky if there were 20% lit at any given time.
    Your window for example could have power at either both ends if the power was not returned, or in the middle and at the start.
    Think of it like a water pipe that has three points of entry, start middle and end.
    If you pour water in at the start, it will run in one direction. toward the end. If you pour it in at the end, it will want to go toward the start. If you pour it in at the middle, it will try and go both ways.
    So if you wanted to get the water in the quickest, it would be wise to go from both ends as they will both go in and meet in the middle and fill and equalise.
    If you attempted to go in the start and middle, the middle one would try and go both ways but fight against the start one and would eventually equalise, but be less efficient. That is what the power is doing. It will just balance out just like water, but be less effective.
    That is the theory, but in the real world, as long as you have enough power and limit the voltage drop as best you can, K.I.S.S. keep it simple :)
     
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  3. MrX

    MrX New Elf

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    Yea fully agree with keeping it simple and looking for convenient places. I have a 550 node element which essentially outlines a deck facade including poles, floor line, handrail, and roof line. Basically 3 parallel horizontal runs and 4 parallel vertical ones which intersect the horizontal ones to form a large grid. I power inject at 4 points, the places where the middle horizontal run intersects the verticals. Power is connected there in all directions as well as at the tops and bottoms. I think there is no pixel further than 45 away from fresh power.
     
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  4. lithgowlights

    lithgowlights Senior Elf Generous Elf

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    where did you get the calculations for the currents from? For instance 419 pixels at 100% brightness, draws 25A, not 8A. I'm not a fan of designing props, and power injection systems, based on reduced brightness values as a failure of the data line has the potential to turn your lights on to a random value which includes 100% white
     
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  5. MrX

    MrX New Elf

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    Not ideal but in that setup if a bunch of pixels run amok and draw too much fuses should just pop
     
  6. OP
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    Danno

    Danno New Elf

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    You're right, I've just gone and checked my data and discovered that I used 0.03 amps per pixel, and 0.03 was the wattage, not the amperage. Whoops! My new figure is 0.06A, which for 419 pixels at full brightness is 25A. My general calcs right now are to operate at 70% brightness, but I do acknowledge what you're saying and I think I will change to build for 100%... So even more power injection now!
     
  7. OP
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    Danno

    Danno New Elf

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    So after doing some reading a bit about my 18AWG wire, at face value, it would appear that I can run 7.5 amps on those cables to be able to do more injections from each wire (and have less runs).

    When I bought my f16v3 and my f8 distros they all came with 5a fuses. Am I right in believing that I can just replace the 5A fuses with 7.5A fuses? Is there something with those devices that would be causing the limitation to be 5A, or is 5A just a "common" limit that people tend to set?


    Cheers

    Dan
     

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