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Is connecting the Common a must for power injection with pixels?

Discussion in 'RGB Lights - Intelligent Pixels and 3-Channel RGB' started by Porsche, Jan 3, 2015.

  1. Porsche

    Porsche Full Time Elf

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    Hi all, I was playing with my blinkys as I will pulling them down today and came across something accidentally regarding power injection.
    I have 3 arches WS2811 12v. 25 pixels each arch and all connected together running Data and Common from the controller (ECG P2), and power straight to the 1st arch. But when I added + to the 3rd arch to power inject, it worked.
    I was under the impression both +V and -V had to be connected to the strip/string your injecting power into?
    Power to 1st arch and at 3rd arch were running off the same PSU.
    Just want to clarify if this is ok to do?
    Cheers
    Phil
     
  2. Benschristmaslights

    Benschristmaslights Dedicated Elf Global Moderator Generous Elf

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    yes you want to mate sure the neg is going from the psu through all the pixels you are using off that psu
     
  3. Bill Ellick

    Bill Ellick Full Time Elf

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    Information was incorrect so I deleted my response.
     
  4. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    The reason the ground is so important with pixels is because of what is called ground loops. By having the grounds tied together you are ensuring that each ground reference is at the same potential, if the ground varies then we can get current flowing where we dont want it and thus cause ground loops

    In your situation it worked with just a +V but the Ground would still be at the same potential because you still had the ground connected further back as its not the +V that causes the issue, its the ground, . The issue here is that now all the current from that +V has to go somewhere and thus will go down the path of least resistance and that is the ground futher back which now adds additional current and voltage drop to that ground wire and if your +V input cable is not the same guage as the ground cable then we run the risk of overheating the cable or suffering from voltage drop issues

    Now i must correct Beeiilll (sorry :) ) because you can have multiple power supplies connected to a long string, in fact you can have a mix of 5, 12v and 24v strings connected together as long as you tie the grounds together at the injection point and keep the +V seperate. I had one line that was made up of 5v, 12v and 24v pixels all using the 2811 chip, i just connected the grounds between the strings and injected the correct power and it worked fine.
     
  5. Bill Ellick

    Bill Ellick Full Time Elf

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    No problem Eddy! I stand corrected.

    I thought though that you should not have a case of one power supply being at one end of a pixel string and another power supply feeding the other end for power injection? I can see using multiple supplies if they are each feeding their own separate string of pixels but would you want two different supplies feeding the same string from different ends?

    I do realize that my answer was too short and misleading though in my original post and for that I should probably be flogged!
     
  6. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    With very long runs then this is desirable because with a long run the injection itself will suffer from voltage drop due to the long cable run.
    It is perfectly fine to mix power supplies on the same string as long as the ground is connected and the +V is seperated between the two.

    The Minleon mini controller and the wireless controller when used with 4 seperate 5 amp power supplies and the power-T injector can give you a 120 metre long string, now power injection wont work well over 120 metres if the string is supplied from the same power supply.

    Dont flog yourself, its all about sharing knowlege together
     
  7. Bill Ellick

    Bill Ellick Full Time Elf

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    Well it kept me awake last night so I had to jump in and make a response to this.
    I should have said that you can use multiple supplies as long as the V+ sides are not connected as FastEddy has pointed out.
    I was wrong in not taking the time to explain better (which Eddy is one of the best at explaining things so I can't compare to him anyway) which I did not and that was wrong of me.

    I was trying to make the point of this (which I took from Eddy's 101 manual presentation, page 51 http://auschristmaslighting.com/forums/index.php?topic=1889.0
    so all credit to him and the manual which should be one of the "bibles" that people who are getting into this stuff should read and carry along with them) about not connecting the V+ from one supply to another which I did not explain good enough for which I do apologize!
     

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  8. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Apology not accepted :D because there isnt anything to apoligise for. You were trying to help and for the most part you explained it well. We all need to be corrected from time to time and that includes me (more times than i wish to admit)
     

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