How to use Adapter for safe usage?

Discussion in 'General Electronics Chat' started by shreeram, Jul 30, 2015.

  1. shreeram

    Thread Starter New Member

    Nov 29, 2012
    29
    1
    I have a 12v,2A adapter I wanted to use this for a metallic PCB leds.
    My need is to glow
    1)3 pieces of 3watt LED .ie:9W totally (As shown in picture) .
    other one is
    2)18 pieces of 1/3W LED.ie:6W totally.
    Now these two connections are connected in parallel.
    During my first test with 12V,2.5A adapter worked for15mins but adapter started heating up and finally its transformer burnt .
    also when checked with my another 12v,2A adopter for once my LEDS are fine .
    so I continued testing,
    later I bought 12v,1A adopter now its working for about 1hour,same as before adopter is heating very much but my adapter is not burnt.
    Now can anyone please say me what I need to do for proper and safe working of SMD LED's and Adapter.
     
    Last edited: Jul 30, 2015
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,771
    971
    Adapter.. not adopter

    LEDs like that require a constant current power supply..
    A typical ac/dc adapter is constant voltage.

    LEDs also should NOT be wired in parallel without current limiting for each string as they do not "share" current equally.

    You need to provide specs on the LEDs (forward voltage rating and current rating) and show how you intend to wire them with a schematic or line drawing.
     
  3. shreeram

    Thread Starter New Member

    Nov 29, 2012
    29
    1
    Please say me for proper working of SMD led's and Adaptor what are the possible ways i can do?
    I want to switch this on for 14 hours/day.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
    3,250
    626
    Firstly, please decrease the resolution of your images; they're unnecessarily large.

    Secondly, read post #2. You need to use current limiting resistors; even when you're not connecting them in parallel.

    You're referring to your LED loads by wattage when you should be referring to them by their forward voltages and currents. As connected, LED current will be limited by the resistance of the LEDs; which is small when they're biased much past the knee of the curve. You're lucky you haven't burned out more adapters; unless the LEDs are less expensive...

    If you design your circuit properly, it should be able to operate continuously without excessive component heating.
     
  5. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    We need the forward voltage rating and current rating of the LEDs you are using.

    The picture you show looks more like 10W LEDs... Typically 3W LEDs are mounted to star circuit boards not their own backing plate.
     
  6. shreeram

    Thread Starter New Member

    Nov 29, 2012
    29
    1
    I am sure its a 3W LED ,can you please help me for designing the safe functioning of the circuit?
    If you could please elaborate me to design for the same.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Not until you answer the questions that have been asked of you...
    Forward voltage rating and current rating of each LED..
     
  8. shreeram

    Thread Starter New Member

    Nov 29, 2012
    29
    1
    Sorry, my local Shop guy said its a 3W LED ,after some research I came to know that its a 10W LED.
    Forward Voltage : 12V
    Forward Current: 900mA
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    So 3 in series would require a "constant current" power supply with a DC output rating of 3x12=36V or higher and a current rating of 900mA or less.
    Would you like the ability to dim the LEDs?

    I'd recommend using a Meanwell LPF-40D-48 LED driver. (Rated 28.8 to 48V DC output and 840mA)
    http://www.meanwell.com/mw_search/lpf-40d/LPF-40D-SPEC.PDF
     
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