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Clarification on voltage drop for pixels

Discussion in 'RGB Lights - Intelligent Pixels and 3-Channel RGB' started by aplant92, Oct 24, 2017.

  1. aplant92

    aplant92 Apprentice Elf

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    Hi all,

    Still a bit of a newbie when it comes to calculating drops for LED strips so hoping I can get some clarification here.

    Everything I've read about voltage drop seems to talk about the wire leading to the LEDs, but not about any voltage drop during the strip. Is this because the strip is all connected in parallel so voltage will remain the same for all, and current becomes the issue?

    In which case, could you theoretically have a cable that was large enough (with a low enough resistance) to avoid voltage drop in a long strip without power injecting?

    Just trying to get my head around what is required from a power injection and cable running view!

    Hopefully what I've said above makes sense, but feel free to tell me I'm an idiot if I've completely misunderstood something ;)
     
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    aplant92

    aplant92 Apprentice Elf

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    Just thinking about it now, surely the strip itself has some sort of resistance also though? Is that noted anywhere?

    Just seems like I can't find any information as to the characteristics of the strip itself!
     
  3. fasteddy

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

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    Power injection is determined by 3 main factors
    1: Voltage used (lower voltages means higher current for the same wattage output, so lower voltage = more % voltage drop for the same wattage)
    2: Current going through that circuit (more current = more voltage drop)
    3: Resistance of the circuit (more resistance ie, longer cable/smaller cable = more voltage drop)

    So in strip you still get voltage drop because the strip +v track and ground track have resistance and current so you get voltage drop within the strip even though each section is connected in parallel. So with strip, the length of cable between the power supply and lights is determined by the type of strip used, is it 5vdc or 12vdc and how many LEDs per metre and how many LEDs per section all go into how much voltage drop occurs. The lower the resistance per meter the longer the cable can be between the lights and power supply.

    Generally with strip you can run 5 to 8 metres of strip together before injection, you can also run 10 to 14 metres if you inject power between the strips so you back feed the first strip and forward feed the second strip, but you must ensure your cable is thick enough for the current needed or you will have too much voltage drop

    So you will always need power injection when running multiple strips but there are ways to minimise the amount of injection needed
     
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    aplant92

    aplant92 Apprentice Elf

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    Thanks Eddy, that was what I was starting to believe was the case!

    Is there any solid information on the resistance of the strip tracks anywhere? If someone wanted to calculate exactly (or at least more accurately) the voltage drop across the strip?
     
  5. fasteddy

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

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    This would vary depending on manufacturers, the best way is to take a resistance measurement of the +V track on the strip by using a multimeter and seeing the resistance between the +V going in to the strip and the +V going out at the end of the strip, generally this resistance is fairly low but remember its not like a cable because you have current added to the circuit for each LED section of the strip, so this can make it difficult to actually calculate the voltage drop correctly within the strip, because its just not based on resistance but also current.
     
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    aplant92

    aplant92 Apprentice Elf

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    Ok that's great, clarification was what I was after and that's what I got!

    Part of my confusion was forgetting the LEDs run in parallel, but you've helped clear everything else up.

    Thanks again!
     
  7. lithgowlights

    lithgowlights Senior Elf

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    Also dont forget that as the temperature rises, so does resistance, and the LED's often use the tracks as a sort of heatsink, so this also has an effect on the overall voltage drop
     
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    aplant92

    aplant92 Apprentice Elf

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    Thanks for the heads up on heat!
     

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