Getting the right power supply

Discussion in 'Power Supplies' started by Pransta_79, Feb 3, 2014.

  1. Pransta_79

    Pransta_79 New Elf

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    Hello Fellow members,

    This will be my first year in animate lights. Thanks for an awesome site and all the good people for the great info. I need some help figuring out the right power supply. I have many 250 LED multi-colour string lights (from Kmart) which I plan to run from a MEGA60 and power supply. The plug pack on the lights are 24-36V (I assume AC).

    The voltage variance has kind of thrown me off and reading all the info in this site says 24VAC, you need 30VDC.


    Attached a pic for reference. If anyone out there can help me figure this out it would be great.

    Keep up the good work.

    Thanks
    Pran
     

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  2. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Welcome to ACL. The reason why it is 24VAC but we run the LEDs at 27 to 31VDC is because of the LEDs only conduct current one way, meaning that they are DC current devices. When we use 24VAC to drive the string we have to take into account the difference between AC and DC voltage. AC is a sine wave so the voltage peaks are actually around the 31VAC range and the mean voltage is 24VAC. The LEDs strings usually have a DC rectifier inside the controller that convert the AC to a DC signal. Without the rectifier you will see flickering of the lights as the current flows back and forth at the 50hz that our electrical AC supply runs at.

    So when we remove the controller we remove the DC rectifier and we run the lights directly through a DC light controller being supplied by a DC power supply and because we are using DC we then can run the lights at a higher voltage because the DC signal is a flat line and thus there is no peak or mean voltage to consider.
     
  3. Eastwood16G

    Eastwood16G Full Time Elf

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    I think you should read Eddy's 101 guide several times - and another time after you think you got it. Like you I've tried to understand how BigW/KMart and Hong Kong lights are wired. I have a degree in electronics - makes my brain hurt. You'll want to cut up your strings into circuits. Use about 3v per LED as a working approximation. You'll find 30V strings have 10-12 LEDs and 24v strings have 8-10 LEDs.

    You can run LEDs at a bit more or less voltage and they will work fine, maybe reduce life but it depends on duty cycle.

    I don't think it really matters much whether your strings were designed for AC, the DC controllers worth buying use a pulsing signal to get the best out of the LED.

    The natural colour of LED relates to the reverse voltage of the LED which can vary from 2V to 3V ish. There's a bit more science for precision, but I think there's a big scope to play with for our purposes, so get stuck in.

    Let me know how you go. I've a mate here trying to do what you are doing.

    Richard
     
  4. greg58

    greg58 Full Time Elf

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    Welcome to ACL
     
  5. firebug

    firebug Senior Elf

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    Welcome to ACL... 8)
     

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