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Wiring LED Lights

Aidan Carrigan

Nov 14, 2016
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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
 

BobK

Jan 5, 2010
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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.


Bob
 

Aidan Carrigan

Nov 14, 2016
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Nov 14, 2016
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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?
 

(*steve*)

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