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I need to connect 3 rows of "fairy" LED (3V) lights connected in parallel from the same power source of 12V to different grounds that work as dimmers, using a Magic Home RGBW Wifi Controller to regulate the intensity of each row using the RGB ground.

What resistance do I need to add to the circuit to avoid burning the LED taking in consideration they should not go over 5V.

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    \$\begingroup\$ please draw a diagram of what you are thinking \$\endgroup\$
    – jsotola
    Jun 2, 2021 at 19:09

2 Answers 2

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Typical small LEDs will consume max 20mA. Target 10mA to be sure you dont burn them out.

R= (12 - 3) / ( # of LEDs x 0.010)

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  • \$\begingroup\$ Hi, thank you for the reply, the # of LEDs is per row or in total ? thank you \$\endgroup\$
    – VOV
    Jun 3, 2021 at 1:52
  • \$\begingroup\$ That would be per row \$\endgroup\$
    – Kyle B
    Jun 3, 2021 at 4:40
  • \$\begingroup\$ So I would need to add a 60ohm resistance per row in series with the power that goes to each row ? thank you for the help. \$\endgroup\$
    – VOV
    Jun 3, 2021 at 10:43
  • \$\begingroup\$ I don't know. You haven't said how many LED's there are in each string! \$\endgroup\$
    – Kyle B
    Jun 4, 2021 at 4:21
  • \$\begingroup\$ Sorry, you are right, there are 30 LEDs per row. thank you for the help \$\endgroup\$
    – VOV
    Jun 4, 2021 at 18:59
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3 from 12 is 9.

You need 9V worth of resistance, Find the current the strings need and use Ohm's law.

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  • \$\begingroup\$ Thank you for the reply, the issue is that I want to use a Magic Home RGBW Wifi Controller to control each row of "fairy" light intensity. This controller have a common power but different ground for each color. So do I need 3 bucks ? or better just to use resistance in serie? \$\endgroup\$
    – VOV
    Jun 3, 2021 at 2:00
  • \$\begingroup\$ it's probably best to use the resistor in that case, buck converters have capacitors which will mess up your light show,. \$\endgroup\$ Jun 3, 2021 at 5:24
  • \$\begingroup\$ thank you very much for the help. \$\endgroup\$
    – VOV
    Jun 3, 2021 at 10:44

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