HELP... led heats up,while using mobile battery(3.7V,1000mA)

Discussion in 'The Projects Forum' started by skilkhan, Jun 16, 2013.

  1. skilkhan

    Thread Starter New Member

    Nov 8, 2011
    9
    0
    I made a small pocket size torch using mobile battery 3.7V,1000mA,
    i use 4 gboss led(named by electronics shop who gave me this shown in pic)
    i connect 4 leds in series as shown in diagram atched
    6 diodes are connected in serirs to drop 0.7v each(since i m using 6v dc nokia mobile charger for charging) and final voltage reaching battery is about 3.7V
    no problem is that leds became very hot after few min.
    can anyone please tell me how to reduce current with out reducing brightness of leds
    any thing small(like diode is used to reduce voltage)
    tnx in advance
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,345
    Hello,

    What are the specifications of the used led?
    Power leds like the one showed, need a heatsink.
    Leds are current regulated components.
    When you are using a fixed voltage to power the led, you can end up in a thermal runaway.

    Bertus
     
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,997
    3,754
    You need a big chunk of aluminum as a heat sink. Preferably something designed for the star plate your LED is already mounted to. There are no tricks to reducing heat, it is just part of making lights from LEDs. They are less hot than an incandescent of similar brightness but an incandescent can accept hit conditions, LEDs cannot.

    Unfortunately, heat sinks cost nearly the same as the LED.
    http://www.mouser.com/search/refine.aspx?Ntk=P_MarCom&Ntt=165930543
     
  4. skilkhan

    Thread Starter New Member

    Nov 8, 2011
    9
    0
    @GopherT n @bertus
    tnx for reply
    i think a small sink is already connected with these led but may be this not enough for it,,
    i will try with a bit larger sink and will post result later,,(after my exam)
    once again TNX for ur time
     
  5. skilkhan

    Thread Starter New Member

    Nov 8, 2011
    9
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    these are pics of led sink,
    led is soldered on small sink provided with each led
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,769
    969
    That is NOT a heat sink. Its a "metal clad circuit board". The aluminum there is more of a "heat spreader" and is NOT nearly sufficient to dissipate the heat of the LED.

    You also have the LED's in parallel with no form of current limiting/mirroring. You will more than likely end up with a dead torch (flashlight for the rest of the world) fairly quickly. Thermal runaway might own you.

    And you cannot reduce current without changing the brightness.. Both go hand in hand.. Brightness is directly related to the amount of current you run through it.
     
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    As mentioned, it would really help to know the LED forward voltage and current.
     
  8. skilkhan

    Thread Starter New Member

    Nov 8, 2011
    9
    0
    I have tried using 460ohm and 2watt resistor in series and is know working fine for me.
    thx to all for response. I am inserting images
     
  9. skilkhan

    Thread Starter New Member

    Nov 8, 2011
    9
    0
    thx again to all who took interest
     
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