General power supply connecting questions

Discussion in 'Power Supplies' started by aplant92, Dec 18, 2016.

  1. aplant92

    aplant92 New Elf

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    Hi all,


    Long time lurker first time poster here. I'm trying to get organised for next year with LED strips. I understand for the most part how everything works, but have a couple of questions around the actual connecting of the DC power supplies.


    First of all, are the negative terminals on the PSU already connected to ground? If not, is the best way to ground each output to have a jumper going from ground to negative? If this is the case, wouldn't the ground terminal end up getting pretty "full" with all the jumpers coming out?


    Secondly, when people mention injecting power into each strip, they're referring to running another lot of cables from separate terminals at the power supply to another point on the strips, yes? If true, this is why I'm assuming negative needs to have a jumper to ground on the power supply (strips have a 5V and GND connection, which I'm assuming is the positive and negative output from a power supply), so no extra pad just for ground.


    FINALLY, how do people tidy the connections coming out of the power supply? Are fork connectors the easiest way?


    I know there's a lot of questions here, so hopefully someone can help!


    Thanks!
     
  2. scamper

    scamper Senior Elf

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    Firstly, Welcome the the hobby that will absorb your life 8)


    You should ground your enclosure if it is metal, but not necessarily your negative wires.


    As far as power injection, it is not always that you need to run another cable all the way from the power supply itself, so long as you use a cable with high enough rating to handle the current flow, you can loop from one string to the next
    power injection.jpg

    The photo is a bit hard to see, but I have waterproof plugs at the end of every string and there is a cable that has spurs coming out to plug into every string. I connect to 8 strings then another cable to the other 8.
    Some people choose to use 'T' connectors but I cannot afford that, so make up dedicated cables for each prop.
    And to tidy connections. Many people do different things, do what works best. Some box's are going to get messy
    tree sm.jpg

    But i do have a dedicated power supply box for injection only and I have a bunch of waterproof glands on the bottom of it. The big issue depending on where you are after keeping water out, is keeping it cool and then keeping the bugs out.[/attach]
     
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    aplant92

    aplant92 New Elf

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    Thanks for the reply and the pictures!

    With the grounding though, doesn't each strip need to have some connection to ground? Or is the term ground being used to refer to the return side of the circuit back into the power supply? My understanding was that each injection point had to have some sort of connection back to the physical ground (through the plug connected to the PSU), so what is the best way to do this? Multiple jumpers? Or am I misunderstanding the required grounding?
     
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    aplant92

    aplant92 New Elf

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    To clarify, this is what I'm going off:


    [​IMG]


    Annoyingly though it seems ground is used interchangeably for different things, so I might be misinterpreting what the diagram is saying.
     
  5. JPB

    JPB Full Time Elf

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    Any metal enclosures with mains connected power supplies in them should be connected to earth or ground.

    When using multiple power supplies connected to the same controller (and this is where power injection can come into.play) the negative terminals of each power supply need to be connected, but not the positives.

    Sent from my GT-I9505 using Tapatalk
     
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    aplant92

    aplant92 New Elf

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    Ok I think that makes sense. So multiple power supplies require any outgoing negative terminal to be wired to any other connected power supplies? Or does only one between them need to be connected?
     
  7. scamper

    scamper Senior Elf

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    The issue here is the diagram is showing the negative DC terminal as ground.
    In a power supply, sometimes the negative output can be tied to ground but not always.
    The grounding I refer to in regards the enclosure is the AC side. This is for safety just in case of a problem on the AC side, which is lethal.
    On the DC side, the negative is loosely referred to as ground also, however this is the only side that needs to have the negative wires tied together.
    This is because if you use different supplies over your display that are tied back to one controller, the negative terminal has not got a reference and therefore could 'float' meaning potentially the positive could be higher or lower with reference to another supply which could cause any number of problems.
     
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    aplant92

    aplant92 New Elf

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    Yep that makes sense to me! So negatives from each power supply should be connected together correct? Should this be terminal to terminal? Or just a split wire?
     
  9. i13

    i13 Senior Elf

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    You can do it from terminal to terminal or through the string of pixels as in the diagram. The negative wire is continuous along the string of pixels so therefore the negatives of the multiple supplies are connected together in the diagram.
     
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    aplant92

    aplant92 New Elf

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    Ahhh ok the way they phrased it made it sound like you had to this separately (I assumed the negative would flow through, but was worried I was missing something extra).


    Thanks for your help!! That's cleared it all up for me!
     
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    aplant92

    aplant92 New Elf

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    Just out of curiosity, what would happen if the positives were connected? Obviously current would try to flow both ways, but what's the physical result of this?
     
  12. JPB

    JPB Full Time Elf

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    One power supply could start feeding 12v back into another one as they are generally not designed to load share or balance.

    There are power supplies that allow this but they are specifically designed to include this feature and not normally within the budget.
     
  13. tooms

    tooms Apprentice Elf

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  14. OzAz

    OzAz Full Time Elf

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    tooms - that's a reasonable price, and I'm with you on not using it on lighting equipment.


    Have used 'stacked/parrallel' power supplies in industrial equipment in the past. However 200A, even at low voltage, can be quite dangerous to you and equipment
     

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