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Too much current with 5v, how to handle or resize?!

Discussion in 'General Electronics Discussion' started by sladaar, Oct 31, 2017.

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  1. sladaar


    Oct 31, 2017
    Hello you all,
    first of all thank you in advance for reading me and sorry for my english!

    I'm going to install in the ceiling some leds, 15m of ws2812, but i'm a little afraid about the size of the cables that the calculator suggests because the leds amperage are high, specs say 3,6A/m @full load, which is 54A for the whole length (15m) and i need 8m cables long (putting the power supply in the middle of the track); the calculator outputs 5awg (18mm2), which is really too much, specially compared to my goal which is 2,5mm2 (13awg)

    So I thought how to resize them and researching on the internet i found two main solutions, but i really appreciate if you would please help me!

    First idea was to split the strips, 1m (18w) short so they need less current and the cables could be thinner , but also this way it seems they have to be too big.
    Second idea was to use higher voltage dc power supply, like 24v, to cover the area of the ceiling and lowering the voltage @ 5v just for the strip, but even this way seems to be hard to do (i should split every strip in 2 parts, which results in 6 dc-dc stepdown, too much money).

    Fyi, the measured voltage drop per 1m seems to be 0.30V, and to be honest the measured amperage seems to be 1.5A/m @full load, not the declared 3.6.

    Do I miss something? Am i wrong about all that stuff?
    And other noob questions..if i use downsized cables, what is the risk? Just too much voltage drop (so yellowish leds) or too burn something?

    Many thanks in advice!!
  2. Bluejets


    Oct 5, 2014
    Can you show the LED strip specs.
    Seems rather high at 3.6A/m.
  3. sladaar


    Oct 31, 2017
    of course, and thank you for the reply!
    I don't really know if i can post the link, i bought them from the most know chinese shop, ali***, ws2812b with usual 5050 Epistar chipled.
    Here are the specs:

    Input voltage:.............DC5v;
    .......................60leds/m----18watt/meter -----------this one
    LED resource:.............WS2812B led(5050 SMD RGB LED with built-in improved version of ws2811 ic)
    LED: ...............each LED is separately controlled
    IC Type: .....................improved version ws2812 IC(built inside the 5050 smd rgb led)
    of IC: ..................(1 IC drives 1 led chip);
    Pixels:......... 30/60/144/meter;
    Pitch: .........................16.6mm(1000/64);
    Grey scale: ................256;
    Bits/color: ...................8-bits/color;
    FPC size: ....................Width: 10mm, High: 2.5mm;
    FPC color: ......... BLACK/White
    Protection rate...... IP30/ IP65 /IP67
    Colors: ........................Full color RGB, dream color changing;
    Cuttable:......................every LED is cuttable;
    Package: anti-static bag,with 3M adhensive tape on the back(Except the Waterproof in SiliconTube)
    Lighting angle: 120degree
    Life time: 50,000hours
    Certification: CE & ROSH
    Warranty: 3years

    And even on the package obviously it's written the same, even 3.6A/m.
    I can understand they declare more than the real, but i want to be safe!
  4. Bluejets


    Oct 5, 2014
    Yes, well I looked into this a bit more on Sparkfun and it is some serious current requirement.
    Also it will have to be some serious power supply to regulate at 5v and assuming all LEDs are full on to maintain this level at the 50 odd amps.
    Problem with low voltage (5V) almost any cable you use is going to have to be massive to withstand the obvious voltage drop you will encounter even by using large cabling.
    It might be more advantageous to use gangs of voltage regulated power supplies fed by a higher voltage to drive smaller sections of LED strip.
    All assuming this is going to be driving all of them at full on at any given time.

    Perhaps a bit more on how you intend to use this system may allow some suggestion for a better setup.
  5. kellys_eye


    Jun 25, 2010
    The current consumption assumes worst case (RGB all driven 100%) and I don't think the driver chip is capable of dissipating that kind of power anyway..... so some attention to HOW you're driving them will make considerable differences to the power consumption.

    You can also power them from both ends of the cable - effectively halving the individual current requirement (whatever that turns out to be).
  6. sladaar


    Oct 31, 2017
    Many thanks to both of you.

    So, and forgive me for the noobish question, if i "inject" power the cables could be thinner? I mean, maybe every meter! Do the cable size somehow become the sum of them all? Extra novice alert here!
    Yes I already thought to power them from both beginning and end, but thanks anyway!

    I'm starting to think to get rid of these 5v strip and use them in other projects and buy something different for the ceiling. Sadly!
  7. kellys_eye


    Jun 25, 2010
    The cable you link to is serially programmable for total individual-pixel colour control which is fine if your lighting requirement extends to multi-phasic alternating patterns!

    If all you want is fixed, colour-changing lighting then even the likes of Ikea do such - or you can fit the Phillips range of LED globe lights with remote control of colour.

    Many, many ways to skin that particular cat.
  8. sladaar


    Oct 31, 2017
    That's why i like them so much! I love lights and making effects! The core is an esp8266, which connects to the data pin and controls the led, they are in serial between each strip so the led count is linear.

    I was just worried about the power supply and how to resize those giants cables, but thanks for the reply!
  9. BobK


    Jan 5, 2010
    You can split the power any way you want, and each cable is required only to carry the current it might be supplying. I presume you will have some arrangement of multiple stripes, each several meters long. I would use one cable to each end of each stripe.

    With 15 meters, you are talking about 900 LEDs. The bit rate for WS2812B is 800K b/s, at 24 bits per LED that means 37 updates per second if you using only one data stream. This would cause noticeable flickering.

  10. sladaar


    Oct 31, 2017
    Thanks BobK for the reply!

    Good to hear! So is it correct to think that, if 5meters strip absorbs (needs) 18A, powering it from each end both pair of cables would carry, roughly, 9A?

    I thought it too but to be honest it is not, at least to me. I tried some effects on my bench and the results are pretty acceptable!
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