RGB LED Wiring: Strip burned in the same place twice.

Discussion in 'Computers & Technology' started by AOS-, Jan 25, 2020.

  1. AOS-

    AOS- Premium

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    I thought maybe just that one segment of the strip was bad, but I'm starting to think it isn't. Anyway, I'm going to be transparent with this as I am not the most experienced at soldering, and I like to think the product isn't at fault here. I want to know if I'm making any common mistakes because I really would like this thing to work out without burning down my stuff.

    Basically, I'm hoping someone can help here.

    Context:

    So... Bookcase. Setting up a series of 5050 LED strips to cover only two shelves at the moment. Three ~70cm RGB 4-wire strips. Provided AC Adapter produces 12V, 2A (product used: amazon link). Used 5050 4-wire ribbon to join each strip (link). I'm using 3 strips per shelf (including this so it's clear in the diagrams below).


    I went with this layout originally:

    [​IMG]

    Plug it in. Problem I found here was that the colours were gradually less blue after the first strip. If I put the lights on 100% red, it looks fine. 100% green: fine. 100% blue: cuts off halfway into the 2nd strip. I unplug the 4-pin connector that connects to the driver. I was thinking conductivity for the blue end wasn't done well enough... maybe the wire wasn't making the best contact with the copper contacts on the strip. Undid and resoldered. Plugged it back in at the 4-pin connection, noticed the lights blipped on/off (should I be worried?). Took the included remote, hit the power button and everything lights up more evenly. Unplug.

    At this point I rearranged the 2nd set of wires in hopes of allowing more current to travel to the 2nd set of strips in a shorter path with a daisy-chain layout:

    [​IMG]

    Tested this. Thing lights up without issue. No dimming seen further down the line. So now I cover the wire connections with hot glue to seal in the connections and to help reduce oxidization. Plug it back in. LEDs blip again on and off. Light does not come back on. This time we get smoke in the 12V line here:

    [​IMG]

    It happens on the last segment of the strip, the 12V side is black. Not sure why though. It wasn't burning before.

    Okay, maybe it was faulty I thought. I cut off that segment, attach a new one in place, and wire it up. Tested it. Successful. Everything lights up all the way to the end without issue. Wonderful. Project is complete. Seal it in with the hot glue, and need to mount it now to the bookcase. I do just that, plug it all in, hit the power button. No lights, smoke appears... in the same spot.

    [​IMG]

    [​IMG]

    So I'm at a bit of a loss here. I know people have used hot glue in the past. Is this malpractice?
    If I had a messy solder job where I actually joined the 12V and the Green together, shouldn't that have caused an issue during testing?
    Is unplugging/replugging the 4-pin connector while there is power a bad thing to do? Should I be doing the power connect/disconnecting at the barrel plug only?
     
  2. Grayfox

    Grayfox

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    The width of the traces should be able to handle 2A

    Things may not fail during testing as the joints may not get hot enough.
     
  3. neema_t

    neema_t Premium

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    First of all, yes, the colours become redder as the strips get longer because the voltage drop from putting them in series increases as you go along, red LEDs have a lower forward voltage than blue or green so the blue and green get weaker and red stays the same.

    Secondly, what you've done is put one strip in series with the power supply then loads in parallel. In series circuits the current is the same throughout while the voltage decreases whereas in parallel the voltage is the same while current decreases (which is a huge oversimplification) - so you've got the total current to all the parallel strips going through a single strip which is why it's burning, they're designed to be used in series.

    What you're supposed to do is power the strip at intervals. This means you'd end up with parallel groups of strips in series, that way the power supply is the component taking the load so as long as you're not overloading the power supply, you won't burn any strips as they'll only see the current required for the entire length of their own series strip, if that makes sense?

    How many LEDs you can put in series before the colour changes significantly is dependent on the LED, it's probably OK to use the Adafruit Neopixel "uberguide" as a base though.

    In other words, you just need to cut the link between the top three and bottom three strips in your first drawing, then add wires from the power supply to power the top three strips.
     
    Rallywagon likes this.
  4. AOS-

    AOS- Premium

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    I'm thinking it was destined to eventually burn based on neema's explanation, so I'll definitely run them for at least a minute next time. :lol:

    The roll begins with the strip already attached to a 4-pin connection which is then neatly packaged up in a rubber coating:

    [​IMG]

    I'm guessing these products are meant to stay as is only if I run the full 5m strip without all the splitting? And to confirm, splitting the connection where I'm pointing should take the load off the first strip? And lastly, I should be able to now run the first 3 strips in a series?
     
  5. AOS-

    AOS- Premium

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    Update:

    I still haven't split the cable that comes attached to the one end of the strip, so I have done this instead to see if it works:

    [​IMG]

    Using the contacts where the white cable is already soldered to, this works. No overheating, no burning, no fire. Now that this works, I'm wiring in the lines from the second strip to the third:

    [​IMG]

    Got the discolouring like before. 3rd strip goes from white to green to red..... also detected the heat build-up before anything started burning this time. Although I doubted it, I was thinking maybe the daisy-chaining shouldn't be done at the contacts, so I soldered the wires together outside of that:

    [​IMG]

    Same results. Still the discolouring and heating up in the same place... :banghead:




    [​IMG]

    Is this how I have to go about wiring this up?


    @neema_t
     
  6. neema_t

    neema_t Premium

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    @AOS- if you're wiring them in parallel like that then as long as your PSU can output enough current to power all the LEDs you've got you shouldn't see discolouration. If it can't source the current required then the voltage will start to drop and you should see all the strips go reddish and dim. Can you test that top strip that's exhibiting the discolouration in isolation to see if it still happens? Could be a bad strip, maybe.

    Also do you know what the actual LEDs are (as in the code for the LEDs - should be something like WS2812B or whatever) and how many LEDs you have (or how many LEDs per metre and how many metres of strip you've got)? Or does the strip tell you how many watts per metre you need? We can try to determine if you're overworking your PSU with those details.