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Thread: Power injecting led strip?

  1. #1
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    Default Power injecting led strip?

    So, despite working with pixels for 3 seasons now, i've only every worked with bullet nodes in the 12v and 5v, ws2811. I've never worked with led string before. I was considering integrating some this season, and something dawned on me. It may be a ridiculous question, I don't know, but how exactly would you power inject led strip? With strings, you can splice in to the appropriate wire where needed. But with strips, i'm not even sure how that would work? I can't imagine trying to splice power wires in the middle of a strip, but remember, haven't worked with them before

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    Default Re: Power injecting led strip?

    For long strips (5M) you inject at both ends from the SAME PSU. That way each injection point services one half of the string. For short strips (1M) you inject at either end of the strip. Both ends with same PSU are not needed (but would not hurt).

    NOTE: Injecting into a single strip using multiple PSUs is not recommended without a special circuit that prevents the PSUs from trying to power each other.


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  3. #3
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    Default Re: Power injecting led strip?

    Quote Originally Posted by MartinMueller2003 View Post
    For long strips (5M) you inject at both ends from the SAME PSU. That way each injection point services one half of the string. For short strips (1M) you inject at either end of the strip. Both ends with same PSU are not needed (but would not hurt).

    NOTE: Injecting into a single strip using multiple PSUs is not recommended without a special circuit that prevents the PSUs from trying to power each other.

    The reason I'm wondering about that, is let's say 5v pixel nodes bullets...I'll usually have to power inject every 50 or less. With the led strips, let's say I have 60 led/1m....and a 5m strip or even a 2m strip.. But 5m x60=300 pixels....Unless i'm missing something, how would power injecting from both ends of that 5m not have issues? Is it because they are so close that the voltage doesn't drop too far?

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    Default Re: Power injecting led strip?

    Power consumption is a little different between Nodes and Strips. On a light Strip 3 lights count and act as one Pixel. I use 12v 30/meter strips, which comes out to be 150 lights, but only 50 pixels, again, every 3 count/at as one. Each strip uses 3A and 36W, roughly. The strips I have use a 3 pin connector and a separate set of wires for power injection. I can connect 2 strips together and inject at both ends and don't have any issues. I don't know how different it would be with 5v, but the best way to tell is to hook them up and test them. For me the quickest way to see if you need to inject power is when they are all on, making white, and you start to see some pinkish at the end.
    You can cut strips every 3 lights at the copper "cut" points, and solder some wires on the power leads to inject on custom lengths if needed.

  5. #5
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    Default Re: Power injecting led strip?

    Voltage drop occurs at each LED, not at each control chip. The power specification for a number of 12v WS2812B pixels is .24watts per LED, so 150 LEDs using 36w total is right in spec. We talk so much about power injecting “pixels” that it’s easy to lose sight of the fact that the voltage drop is a feature of the diode itself rather than the IC.

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    Default Re: Power injecting led strip?

    The reason we power inject is because the wires between the pixels all have a resistance per foot of length. When you pass current through the wire you get a voltage drop across the length of the wire.

    Here are a few statements that gang up to give you issues
    • The longer the wire the greater the voltage drop at a given current level
    • The higher the current level the greater the the voltage drop on the wire
    • The thicker the wire the lower the resistance/foot of the wire.
    • The cheaper strings of pixels tend to have thinner (higher resistance / foot) wire.
    • The more current the individual pixels draw, the more total current passes through the wire.
    • Strips of pixels acknowledge the physics of wire resistance and use the equivalent of thicker wire between the pixels.
    • The total effective wire length of a strip is smaller than that in a bullet string (this is the important one).


    This means that a strip has less wire at a greater effective gauge than your bullet nodes and therefore there are more pixels between 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

  7. #7
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    Default Re: Power injecting led strip?

    Quote Originally Posted by MartinMueller2003 View Post
    The reason we power inject is because the wires between the pixels all have a resistance per foot of length. When you pass current through the wire you get a voltage drop across the length of the wire.

    Here are a few statements that gang up to give you issues
    • The longer the wire the greater the voltage drop at a given current level
    • The higher the current level the greater the the voltage drop on the wire
    • The thicker the wire the lower the resistance/foot of the wire.
    • The cheaper strings of pixels tend to have thinner (higher resistance / foot) wire.
    • The more current the individual pixels draw, the more total current passes through the wire.
    • Strips of pixels acknowledge the physics of wire resistance and use the equivalent of thicker wire between the pixels.
    • The total effective wire length of a strip is smaller than that in a bullet string (this is the important one).


    This means that a strip has less wire at a greater effective gauge than your bullet nodes and therefore there are more pixels between injection points.
    That was incredibly thorough and sensical, thanks. That settles it

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