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SketchUp SMT Led Project

Discussion in 'Modding' started by Narinik, 11 Jul 2009.

  1. Narinik

    Narinik What's a Dremel?

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    So i've been a long long time lurker here and finally decided to actually post. Cause I've got a mod question and completely blanked on asking here ::facepalm::

    So I've got a smt(surface mount) led project that I would like to drive off of a USB 5v line.
    I'm using (atm) 10 Kingbright smt super bright green leds, part no KP-3216SGC, not sure if that matters but I'm including anyway. The specs on the leds are 2.2v fv @ 20mA. and ofc the source is 5v so I need 33 ohm resistors on a series of two ill post the schematic from "http://led.linear1.org/led.wiz" at the end.

    So my question is, the wizard suggests 1/4w resistors but I want to use surface mount resistors. I did a quick search, and from what I can tell surface mount resistors are rated at 1/10w and the wizard says each one dissipates 13.2mW, 3.2mW over what im taking as the rating for the smt resistors.

    Will this setup burn out the resistors? I am planning to eventually sink them into a channel and then fill the channel with water clear silicone, I'm thinking that might act as a heat sink as well but id rather not burn resistors while I'm testing and fitting. Any ideas/suggestions/experience?

    Thanks in advance!

    Solution 0: 2 x 5 array uses 10 LEDs exactly
    +----|>|----|>|---/\/\/----+ R = 33 ohms
    +----|>|----|>|---/\/\/----+ R = 33 ohms
    +----|>|----|>|---/\/\/----+ R = 33 ohms
    +----|>|----|>|---/\/\/----+ R = 33 ohms
    +----|>|----|>|---/\/\/----+ R = 33 ohms

    The wizard says: In solution 0:
    each 33 ohm resistor dissipates 13.2 mW
    the wizard thinks ¼W resistors are fine for your application
    together, all resistors dissipate 66 mW
    together, the diodes dissipate 440 mW
    total power dissipated by the array is 506 mW
    the array draws current of 100 mA from the source.
     
  2. r4tch3t

    r4tch3t hmmmm....

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    They might get a bit warm if your over powering them, you could always use 2 smaller resistors to cover the power. Another way is have all the resistors connected to a bit of metal wire to act as a heatsink.
     
    mvagusta likes this.
  3. Narinik

    Narinik What's a Dremel?

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    well with 5v and only two leds inline with a single resistor, should i be concerned at all? im not sure what the 1/10th watt rating on the resistors are then.
     
  4. r4tch3t

    r4tch3t hmmmm....

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    The 1/10th Watt rating is the amount of power the resistor can dissipate. Because it is so close to the power rating it will probably be fine. I would say build the circuit and leave it on for a bit and see how warm the resistors get.
     
  5. Narinik

    Narinik What's a Dremel?

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    I just realized, isn't 1/10 watt = 100mW? since 1 watt = 1000mW? so the resistors would be able to handle the load a few times over?
     
  6. r4tch3t

    r4tch3t hmmmm....

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    Heh, indeed that is true. The simplest things always pass us by.
     

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