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Looking for help with a repair please to be able to advise a capacitor rating.

I have a 13.5V 5W 21 x led strip. Each LED 70ma 2.2 forward voltage. Apart from that 1pc SOD 2pcs 1k resisitor and 47r x 21

Hopefully someone with more knowledge than could fit on a postage stamp (me) can offer a helping hand to work out suitable uF for this head scratcher Tried 16V 47uf and it shorted a LED at end of circuit. I feel old cap is breaking down as leds behind it in middle of board have shorted out more than once and are getting a slightly higher fv reading It's also pulling more current the longer it's illuminated enter image description hereenter image description here

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    \$\begingroup\$ How exactly do the capacitor(s) relate to the LEDs in terms of circuit connection? What did the original part look.like? \$\endgroup\$
    – Chris Stratton
    Commented Oct 7, 2020 at 20:42
  • \$\begingroup\$ Hi Chris I've tried to upload a pic \$\endgroup\$
    – DrNick
    Commented Oct 7, 2020 at 20:52
  • \$\begingroup\$ IS this for a vehicle? What is the supply Vmax? You don't need a cap yet \$\endgroup\$
    – Tony Stewart EE75
    Commented Oct 7, 2020 at 21:06
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    \$\begingroup\$ It's not clear what you are wanting to understand or how someone can help. \$\endgroup\$
    – Andy aka
    Commented Oct 7, 2020 at 21:14
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    \$\begingroup\$ It is not clear to me what the capacitor is required for or where you intend to put it. \$\endgroup\$
    – DKNguyen
    Commented Oct 7, 2020 at 21:16

1 Answer 1

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LED's have been fried from an overvoltage source, so current will rise as the LEDs get much hotter as the Vf of LEDs drops with rising temp.

The key evidence is the burning of the green epoxy FR4.

example

If this is rated for 13.5V max and you are using 14.5V from a vehicle, you would need to add a voltage drop 1V power resistor 5W/13.5V = 370 mA thus 1V/0.37 = 2.7 Ohms and Pd = 1W so use a 5W for 125'C/5 = 25'C rise

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  • \$\begingroup\$ All leds replaced it was the boiling flux that caused the dark spotting to epoxy \$\endgroup\$
    – DrNick
    Commented Oct 7, 2020 at 21:32
  • \$\begingroup\$ How did that happen? Where are the design details? \$\endgroup\$
    – Tony Stewart EE75
    Commented Oct 7, 2020 at 21:44
  • \$\begingroup\$ Supply v reads 11.6 part stares 13.5max 5w \$\endgroup\$
    – DrNick
    Commented Oct 7, 2020 at 21:44
  • \$\begingroup\$ Where are the design details? \$\endgroup\$
    – Tony Stewart EE75
    Commented Oct 7, 2020 at 21:46
  • \$\begingroup\$ I don't have design details I've added a couple of images to show components \$\endgroup\$
    – DrNick
    Commented Oct 7, 2020 at 21:56

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