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Led color control

Discussion in 'LEDs and Optoelectronics' started by Tha fios agaibh, Jul 1, 2020.

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  1. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    My Daughter bought some led strip lights for her room.
    Problem is, they came with a controller that has two plugs designed to independently feed each of the 2 spools of strip lights.
    She wasn't happy she couldn't have a long continuous strip of lights so I spliced the 2nd spool into the first.

    It does work, except the colors of the added length doesn't always match the first.
    Blue is the same, some colors only slightly mismatched, but red doesn't work at all.

    I was under the impression the strip was just parallel R,G,B leds with limiting resistors and color were derived by a pwm stream that fired the leds?

    Why isn't the color pattern matching?

    I imagine it's because the additional load. But even if it was overloading the power supply I'd still expect the same colors along the entire length.
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    That is the typical way it is done. Usually recognizable from a labeling like RGB.
    The other method is by using addressabel LEDs (e.g. WS2812b), but that is much more expensive and only required if you want individually manageable colors for each ELD. Usually recognizable by a labeling including Din, Dout and/or an arrow to indicate data flow direction. It is not waht you have, I'm quite sure.

    Do they match when used separately on the 2 ports of the driver? If not, the two strips have badly matched LEDs.
    Did you try the combined strip on the second port of the driver?

    There may be a reason for this:
    If the strips match when used separately, the voltage drop along the first strip may simply be too much so the second strip receives not enough power. Remedy: instead if jumpering from strip 1 to strip 2, use appropriate thick wire to feed strip 2 from the input of strip 1 (r from the second connector present on the driver). You can easily hide these additional wires behind the first strip.
    Also the transistors within the controller may not be up to driving a long (combined) strip from one output. There could be two sets of transistors, one for each driver output to distribute the load. You can only tell by looking at the PCB.

    Check your wiring. Possibly a broken trace at the end of the 1st strip?
    Tha fios agaibh likes this.
  3. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Thanks Harald.
    I know Its spliced fine at the transition.
    Strip only has 4 traces labeled +12, R, B, G
    to match it I had to cut the factory plug and flip orientation but I may have created an open end at the far end?
    I'll have to investigate farther.

    I initially tested before installing and all lit up an even blue.

    No chance of fiddling with it now (adding wires or plugging into second port) as they are adhesive tapped to her ceiling.

    If the end looks ok, I might try paralleling the two color control ports together to see if aditional current would drive them evenly?
  4. bertus

    bertus Moderator

    Nov 8, 2019

    Led strips can be cut, but the cuts must be made at cetrain places.


    When cutting at the wrong places, some leds may not work.

  5. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    That is probably not going to work. If it were an overloaded driver, the LEDs should all dim, not only on the 2nd strip.
    But give it a try, there's only a negligible risk of damage (these are open drain outputs, so no risk of short circuiting anything).
    Maybe you broke a connection during installation?
  6. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    Edit, I though it was spliced correctly.

    I did cut ribbon squarely and cleanly like Bertus picture shows and evenly inserted ends into connector before closing.

    I set color mode to red and squeezed connector with my fingers and it started to light up. Obviously connection wasn't tight.

    After fiddling with it all colors seem to work except some vary in intensity and hue.

    Not perfect but, I'm happy as long as my girl is.

    Thanks for your help.
  7. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    I took a peek inside color control box and the two output ports are parallel connected.

    So the set is designed to feed each string to overcome voltage drop.
    Not ideal to have to hook it up in the center of the light string.

    Live and learn.
    Last edited: Jul 6, 2020
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