Modifying 120vac LED string lights to run on 10 volts AC or DC

Discussion in '101 Display Basics' started by aussteve, Aug 30, 2016.

  1. aussteve

    aussteve New Elf

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    I have some LED light strings (Walmart brand) that have 60 LEDs (3 strings of 20 each) which are controlled by a 16 function MFC. They are designed to run off of household 120vac. I would like to run them off of a 8-20vac input or e a 5v -12v DC input instead of the 120vac the circuit is designed for.
    Here are some pictures of the controller circuit board

    Frontside http://s86.photobucket.com/user/aussteve/media/IMG_20160829_160159715-a-25-60_zpsmgoc4ehj.png.html?sort=3&o=0

    Backside http://s86.photobucket.com/user/aussteve/media/IMG_20160829_160436592-a-25-60_zpsxu55sths.png.html?sort=3&o=1

    Schematic http://s86.photobucket.com/user/aussteve/media/IMG_20160829_162409823_zps4ygf0wfo.jpg.html?sort=3&o=2


    Any ideas on what I can modify in the circuit to lower the input voltage and still get the circuit to function
    as it does on the 120vac source?
     
  2. David_AVD

    David_AVD Good news, everyone!

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    No easy way without completely rewiring them as multiple shorter sections.
     
  3. OP
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    aussteve

    aussteve New Elf

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    My main focus was to try and make use of that 16 function controller which I assume is on the vertical pcb (that is soldered into the main board). I would like to run 8 - 10 leds off of each output which currently runs 20 leds each. I can supply the 8 - 18 vac or I would prefer to supply a clean regulated 5.0 vdc to the board. I just can't figure out how to get this board to work and use the 16 lighting functions at a lower voltage. I was hoping someone had done this before or could give me some hints at things to try.
     
  4. David_AVD

    David_AVD Good news, everyone!

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    The board needs to see the AC (currently via the 2.7M resistor) to do the timing for the phase control.

    I guess you could try changing R1 to around 2.2K and R2 to 220K and see how that goes.

    For 8 LEDs, you'd need about 20VAC while 10 LEDs would require about 24VAC.

    Each LED string will also need a current limiting resistor; maybe 470 Ohms at a pure guess?

    You could start higher on that and decrease the value for increase the brightness.
     
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    aussteve

    aussteve New Elf

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    Thanks very much for your help. I will try that and report back.
     

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