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LED lighting for a camper with 12dcV power

Discussion in 'LEDs and Optoelectronics' started by Kamper Dave, Apr 16, 2012.

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  1. Kamper Dave

    Kamper Dave

    2
    0
    Mar 29, 2012
    LED lighting for a camper with 12dcV power:
    Please, tell me if what I ended up doing will work. Do I need high wattage resistors?
    We ordered two styles of 12dcV LED arrays from China for use in our camper. The first batch were basic 24 LED arrays with one 4 legged chip on the board. Reversing the 12 volt supply makes no difference, it lights either way. The problem is that they are very bright until the LED’s become hot enough to melt solder. I wired two in series but they are not bright enough that way. Since they were small and we needed more light, I wired two arrays in parallel and placed a 100 ohm resister in series to them both. They are bright enough and warm not hot. The resistor is very warm but holding at 140ºF. I measure 8.5dcV volts down from 12dcV. Without the resister in the supply line we draw 0.85dcA with the resistor 0.1dcA.
    The second set of 12dcV LED arrays that we purchased contained 48 LED per array no other components on the circuit board. They came with adaptors to convert standard automotive light fixtures to these LED arrays as well as being backed with 3M double sided tape for easy installation. We installed one array and after one hour the array was still working but the double sided tape had shrunk and curled up and the back of the LEDs black where the adhesive burnt. So, I went back to the bench and wired a 100 ohm resistor in line same as above and with the same results as above.
    Will this cobbling job work? Should I be using power resistors vs. carbon?
    Thank you in advance for your help.
    Kamper Dave
     
  2. davenn

    davenn Moderator

    13,386
    1,785
    Sep 5, 2009
    hi kamper Dave

    welcome to Electronics Point :)

    Have a lookie here for info on driving LED's and resistors needed etc
    Hopefully that will get you out of trouble :)

    cheers
    Dave
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,258
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    Jan 21, 2010
    Perhaps you can give us a link to where you purchased these things and we can figure out the best way to drive them.

    Unless of course you have some specs on them?

    I'm sure we had a very recent question almost exactly along these lines, but I can't find it.
     
  4. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    Save yourself a headache and avoid cheap Chinese LED lights. Even if you use a current regulated supply, the LEDs will generate lots of heat. They build enough resistance into the LEDs to allow them to get away with placing large numbers of LEDs in parallel; something that's normally considered bad design practice.

    If you like the form factor or design of the housing, gut it and build a real LED light in it using real LEDs from a reputable manufacturer. You may be able to re-use the circuit board after you've stripped the junk parts off it but it's usually less work to build your own board considering all the desoldering and trace cuts you'd have on your hands.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    There's not a lot wrong with cheap Chinese products aside from the fact that they may not work as advertised.

    In the case of LED lights, you may have to operate them at a lower than specified power, and provide additional current limiting.

    You've essentially done this with the 100 ohm resistors. If the resistors are getting that hot then its time to get a higher powered resistor (say go from 1/2 watt to 2 watt. (A factor of 4 seems appropriate).
     
  6. Kamper Dave

    Kamper Dave

    2
    0
    Mar 29, 2012
    Thank you all.
    Kamper Dave
     
  7. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    I agree... A vast majority of the 'cheap' LEDs are simply manufacturing lots that had higher failure rates per million, inconsistent color, didn't perform up to the clients requirements, over runs or simply the factory using idle manufacturing time to turn a profit vs making nothing... Just because they are cheap doesn't necessarily mean they are bad...
     
  8. KJ6EAD

    KJ6EAD

    1,114
    157
    Aug 13, 2011
    Try running one of those Ningbo lights with a panel of 24 LEDs wired in parallel at 480mA and tell me what happens. Hint: you'll need an oven mitt.
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,258
    2,705
    Jan 21, 2010
    True. A lot of bargains to be had if you're technically minded enough to perform some slight re-engineering in some cases.

    Maybe a world of pain if you're not though...

    You've got to remember that many of these devices are designed to be sold without any warranty other than "not DOA". If you consider what that means you will understand why you need to be cautious.
     
  10. selanac

    selanac

    22
    0
    Apr 15, 2012
    If anything, you'll reduce your heating bill.
     
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