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How to power white LEDs direct from AC line

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  • How to power white LEDs direct from AC line

    All the usual disclaimers are in the link at the bottom. If you die don't call me to complain.

    There have been quite a few threads over the last few years about using LEDs for work lights. LED lighting is something I have been playing with as well.

    I finally found information on how to properly power white LEDs from the AC line directly. Note that this method will produce 120 hertz flicker (100 hertz in those places with poor frequency regulation ).

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  • #2
    Flciker

    Hi..

    Wouldn't a capacitor reduce flicker? That would make a RC network, I still have not seen a place to purchase them cheaply.. I can buy a flashlight cheaper than I saw the LED's..

    David
    Excuse me, I farted.

    Comment


    • #3
      Yep. I just ran the reactance and it comes out about 18 ma.
      For the electronicaly challenged:
      1
      X(sub)c = ______________
      2 Pi F C

      :-) Gad trying to do a math expression in ASCII is a riot.
      Wonder how this is going to display?
      ...lew...
      (edited) FORGET IT . I gues there is no way to make it,the spaces are ignored.
      Last edited by Lew Hartswick; 05-02-2008, 11:20 AM.

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      • #4
        Originally posted by Lew Hartswick
        :-) Gad trying to do a math expression in ASCII is a riot.
        Wonder how this is going to display?
        I had the same problem when I posted the equations for the skin depth. Oddly, if you open the quote window, you can see your formula with the correct spacing, just as you intended

        By the way, there's a flood of Chinese LED-lighted consumer products at your local Sears/Walmart/Home Depot... For $20 you can buy a 20 LED work light, rip out the guts, and have an AC-power string of white LED's for far less than you could buy the parts.
        Last edited by lazlo; 05-02-2008, 11:22 AM.
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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        • #5
          White LED's have a forward voltage drop of 3.0 - 3.5 v, so when you put 12 in series you have to back out that voltage. The current is actually less than 15ma assuming impedance of 5.6k for the capacitor plus the 1k resistor.

          It is not mentioned in the schematic but it is critical to the success of these circuits that diodes be placed back to back exactly as shown. Otherwise the full line voltage will be imposed on the diode or diode string in the reverse direction and they cannot handle that kind of reverse voltage. Putting them back to back provides a voltage clamping function for the non-conducting path.

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          • #6
            Try a dollar store. I recently picked up a dozen cheezy fiber optic decorations for a buck each that contain three super high intensity leds, red, green and blue. I'm in the process of making a special effects picture frame. If it works the way I hope I'll post it. If it doesn't then I will have a full spectrum adjustable night light.
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            • #7
              Originally posted by Lew Hartswick
              Yep
              1
              X(sub)c = ______________
              2 Pi F C
              Your trying to be too fancy. Easier to state it as:

              Xc=1/(2*Pi*f*C) = 1/(2*3.14*60*0.47e-6) = 5644 ohms

              I personally think this is asking for trouble. Just throw a $5 wall wort transformer into the circuit, and it becomes easy to make without risking setting something on fire.

              Anybody every overload an LED before? It blows up in a spectacular fashion at about 30V dc... scatterring shrapnel everywhere.

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              • #8
                FORGET IT . I gues there is no way to make it,the spaces are ignored.
                Use the 'code' tag and the 'System' font.

                Code:
                 Xc = -( ___1___ )
                             2 Pi F C     
                
                Free software for calculating bolt circles and similar: Click Here

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                • #9
                  I personally think this is asking for trouble. Just throw a $5 wall wort transformer into the circuit, and it becomes easy to make without risking setting something on fire.
                  I take it you don't use LED Christmas lights either? This is a safer circuit.

                  [edit]I'm having a hard time visualizing shrapnel from something that weighs 0.4 grams, including leads...
                  Last edited by Evan; 05-02-2008, 12:32 PM.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Hm Why not have two strings one with cap to provide a phase shift and another without but with extra dropping resistance. That way you'd get "overlap" to eliminate flicker.

                    Also wouldn't some of the LED's be brighter than others? How well do they match?

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                    • #11
                      THE lil lady..

                      The lil lady across the road used to have my dad come over to plug her iron up... she had saw a spark once and it scared her so bad she never really had her house wired correctly. I can still remember seeing coal oil lamps glowing over there.

                      it had these twist electrical switches I wanted so bad.. I offered to rewire the house *labor for the electrical service in it.. a 120 volt meter base with twist switch on it. All the light switches and exposed flex.. old black wires hanging on the fixtures..

                      She was scared of electricity too. either that or she had the hots for my dad..
                      Excuse me, I farted.

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                      • #12
                        Awesome!

                        Keep tinkering fellas, when you've got the perfect circuit figured out, I want to put together one of these:



                        You just can't have too much light directly where the machine is doing its thing.

                        Best,

                        BW
                        ---------------------------------------------------

                        http://www.cnccookbook.com/index.htm
                        Try G-Wizard Machinist's Calculator for free:
                        http://www.cnccookbook.com/CCGWizard.html

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                        • #13
                          Originally posted by Evan
                          Note that this method will produce 120 hertz flicker (100 hertz in those places with poor frequency regulation ).
                          These circuits will actually produce two 60 Hz flicker sources, 180 degrees out of phase. In some situations this would be very noticible - a light rod, for example, where the LED's are not phycially interleaved.

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                          • #14
                            What does the cap do in this circuit that a 5.6k resistor wouldn't do?

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                            • #15
                              The cap doesn't act as a voltage divider.
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