LED Light Array Failed

Discussion in 'General Electronics Chat' started by luis84, Jun 8, 2011.

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  1. luis84

    Thread Starter New Member

    Jun 8, 2011
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    Hello all,

    I am new here... and I am a computer tech. I have an LED emergency light that I really like. I haven't been able to order a new one since I am in Central America now so I decided to just fix it. It's chinese so of course I can't find any schematic, etc.

    The light has 4 batteries connected in a series. It has two switch (a high-low-off switch) and then a pull string power switch. It also has an input from a wall socket.

    It stopped working and made a funny smell. I pulled it apart and noticed 2 resistors are burnt, they are to the point where I can't identify their color bands. The burnt ones appear to be the ones that go between the electrical input (wall socket) and the pull string switch. It says never to charge in the on position....... I assume my wife did just that. Best I can tell. The rest of the components seem to be okay.

    It's 60 LED lights.

    So what are my options here? Any way to guess the value of the resistors? Can I bypass the functionality and somehow route the elctricity directly to LED's? No because it needs to be controlled and filtered right?

    Replacing the resistors would fix it but I have no idea WHICH value they are.

    Any input or ideas?

    [​IMG]

    [​IMG]
     
  2. tom66

    Senior Member

    May 9, 2009
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    Unfortunately, you may be out of luck. From what I am seeing, it does not use a transformer. It looks like a capacitive power supply. I must stress that working on such a power supply is dangerous, as there is no isolation between you, and 115V/230V. It's a cheap design. I have used a capacitive power supply in past projects (but never production - that would be a nightmare!), but I have made sure to make the projects completely sealed with no exposed contacts as they could cause a lethal shock, and printed suitable warnings on the PCB, and on the casing. I believe it is prohibited under the TOS here, too, but that is not your only worry.

    For now if you bypass the charging circuit you could get away with running it off the batteries. But if they were NiMH or something you would need a NiMH charger for the type of cells it uses. I would presume with 60 LEDs at 20mA each, they are running two in series and so the array draws 600mA, which would deplete good 5000mAh NiMH D-cells in about 8 hours.
     
  3. luis84

    Thread Starter New Member

    Jun 8, 2011
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    Right, this device was opened by me. It is normally closed... and not exposed. It is a transformeless, 2 prong .... capactive supply.

    I figured if I could identify the resistor values, I could resolder new resistors, reseal the device (as it was) and it will function normally again.

    Is that not an option?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That is not the case. For one transformerless power is not something we can discuss -
    The other is that the burned resistors are almost a byproduct of a lager failure, and trying to find that just might prove fatal. These things are quite cheap as they are not designed to be repaired.
     
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