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Thread: First pixel in WS2812b strip extremely hot (enough to fail)

  1. #1
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    First pixel in WS2812b strip extremely hot (enough to fail)

    The power supply is about 15' from the two strips currently exhibiting this behavior, and I've tried both 18AWG and 12AWG wire.

    Each "strip" is cut into 4 41-pixel segments. Each segment has it's +5/GND wired in parallel from the "end" of the 15' power cable:

    Click image for larger version. 

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    (sorry - basic paint programs are all I have at the moment)

    At low brightness (#161616, for example), things run beautifully. I can also run a subset of the LEDs at full brightness and leave the rest dark and all is well. However, if I run all LEDs at full brightness, the first LED gets extremely hot, to the point where it stops passing data to the rest of the strip, and in one case to the point of failing entirely. If it was the load of the strip, I would think that the second and third LED's would be warm too; more importantly, I would expect the "first" led in each 41-led segment to be hot, but it's only the first pixel of the FIRST segment.

    Also worth noting:
    - it doesn't seem to be a consistent problem for all strips. All of them have higher temps in the first LED, but not all of them get super hot.
    - Power at the start of each segment is 4.9xx volts. [edit] This turned out not to be true! 4.9 was, at the time, only at very low brightness. [/edit]

    Being a software guy, I'm still a trial and error n00b when it comes to troubleshooting circuits. Any tips or pointers for what I should try?
    Last edited by tetsuo; 12-06-2013 at 03:41 PM. Reason: fixed a bit if half-truth, potentially unrelated (marked w/ [edit] tags)

  2. #2
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    Can you temporarily rewire the strips so another LED is #1 and test again? That will tell you if the problem is in that physical pixel or something else.

  3. #3
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    Will do, potatotron. Having burnt out one LED, I was a bit gun-shy about going back to trial-end-error without posting here first. If nothing about how I'm powering them jumps out as "wrong", then I'll certainly try swapping the first pair of segments w/ the second.

    I also wonder about the quality consistency of the LEDs... this is a 4500+ LED project and I feel that the first two orders were better quality than the last 12 5m rolls I received.

  4. #4
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    I haven't had much time to look at this, but I did a quick swap and found the behavior to be the same. I've also found that I can run everything at 80% brightness and while the same "hot" LED still runs warm compared to the rest, there's no heat-induced discoloration or outright failure as seen at 100%. Will follow up once I've had the chance to experiment a bit more and perhaps take some pictures of the wiring.

  5. #5
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    Just to update for anyone else experiencing similar symptoms:

    My problem appears to have been caused by my wiring. the first 41-led segment had the factory 3-pin connector on it, and I was re-using this with it wired in such a way that a great deal of current was being drawn through that connector (164 LEDs worth). This, compounded with the meager 22AWG wire that was pre-installed vs the 18AWG on the other three segments (soldered by me) lead to the first segments' wires getting quite warm and, apparently, the first led getting VERY warm. My quick-swap test was a red herring because I happened to swap with another segment that had the original connector on it.

  6. #6
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    Glad you got it working & posted your solution for others.

    Good luck!

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