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Wiring LED Lights

Discussion in 'LEDs and Optoelectronics' started by Aidan Carrigan, Dec 27, 2016.

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  1. Aidan Carrigan

    Aidan Carrigan

    Nov 14, 2016
    I recently purchased red/green twinkling leds off of eBay and wanted to assemble them into a Christmas light string.They have a forward voltage of 3.0-3.5 and a max current of 30 MA. I had figured 120 v / 3.5 = about 35 bulbs. So I wired them together in series and plugged them in, killing them all almost instantly :(. Would putting a resistor on each bulb allow them to work off of 120v ac? Or maybe a large resistor inline? If so how would I go about finding which resistors to use? I did make a short string running off of 12 volts with groups of 4 bulbs wired in parallel however I really dislike having to use a power supply for the lights and they are not able to be dimmed when using a power supply. Thanks
  2. BobK


    Jan 5, 2010
    The first problem is that 120VAC peaks at 170V. And you don't want to be running them off the line anyway -- too dangerous.

    The next problem is that you cannot put flickering LEDs in series. When any one is off, all would be off.

    You need a low voltage supply, like a 5V USB charger, and resistor for each LED. Then wire all the resistor / LED pairs in parallel.

  3. Aidan Carrigan

    Aidan Carrigan

    Nov 14, 2016
    They aren't the traditional flickering bulbs, they simply change color between red and green without interrupting the power flow, I did wire them in series with a 12v supply and they work great, just can't use them as I would like with a power supply. How do they wire the store bought light strings off of mains safely?
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Go to our resource section and read the one about driving LEDs.
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