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Thread: Shed Led

  1. #1

    Default Shed Led

    Hey guys, I need some help.

    I am planning on getting some leds from quickar.com and am in need of a little help with putting my plan together.

    I plan on using six Hex Shaped 3W "UFO" LEDs, each with a voltage requirement of 4 volts, so I would wire three in a series to get 12 volts and use four of those in parallel to make 12. This is what the 3 channel PWM controller on their site can power.

    Here is what they wrote to me-
    "strings of 3 in series will equal approx 12vdc at 1 amp draw

    and then say 3 more in parallel with the first string of 3

    so 4 strings of 3 each - for a total of 12 white 3 watt luxeon stars

    is 4 amps at 12 volts needed - or remember volts x amps= watts? so its
    then 48 watts"

    What I am trying to get at is, What if I don't want to use 12 leds, how can I run only 6 without frying them?

    My last question is does anybody know about PWM supplies, is there a difference between say a luxeon driver supply, for example I know they can dim the lights.

    I hope you got some of that

    Trafton

  2. #2
    Flashaholic* Timson's Avatar
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    Default Re: Shed Led

    Quote Originally Posted by trafton
    What I am trying to get at is, What if I don't want to use 12 leds, how can I run only 6 without frying them?
    Your formula seems designed for direct driving of the emitters.

    Not sure what the PWM thing does. My understanding was that these were used to regulate output by high frequency on/off cycles, thereby allowing varying brightness levels.....Suffice to say - I can't really advise on this as I don't know enough about it.

    As far as direct driving the emitters from a 12V power source...If you want to use 6 emitters.....
    Just hook up 2 strings of 3.......The 3 LED's in series gets your Vf about right.

    As long as your power source is up to it - The emitters will be driven at around spec, regardless of whether you connect 1 string of 3 LED's or all 4 strings.

    For varying output, you could still use 12 emitter as stated but have switches interupting the parallel connection between each string - allowing you to switch on strips of 3 individually for 12/24/36/48 W.

    Direct drive is never the best option though....If your emitters Vf is less than 4v and your power supply is more than 12v you're in danger of overdriving them or worse.
    If you're going to splash out money on expensive LED's then best advice would be to get a current regulating circuit.

    Dont forget to allow for good heatsinking!!!


    Tim.
    M3-CB, C3-HAIII, A2-RD, Fenix L1P, Fenix P1D-CE, Tri-Star Phaser, Inova T3, Mag85, SNII Clone, DD LuxIII Mag,

    Trilobike
    , Hot-Diver

  3. #3

    Default Re: Shed Led

    Quote Originally Posted by trafton
    My last question is does anybody know about PWM supplies, is there a difference between say a luxeon driver supply, for example I know they can dim the lights.
    Timson is correct. A Pulse Width Modulation unit is basically a little tiny strobe that runs really fast. If you have a 12 volt PWM unit and you examined what was coming out of it closely, you'd see that it went back and forth from 12 volts to zero volts many times a second. This means the light is actually flickering, but when it flickers fast enough you really don't see it, it looks like it's on steadily.

    During the points when it is putting out zero volts you are getting zero (or not many) lumens. A PWM unit dims lights by increasing the amount of time they spend turned off, even though each bit of time is so small you don't quite see it individually. You just see that there is less total light.

    If you use a rheostat or a resistor instead, you are dimming them by sending them less voltage, but you send it steadily and they are constantly on, but at a lower brightness.

    I don't know what technique is being used in the Luxeon driver you are looking at, I don't know which one it is.

  4. #4

    Default Re: Shed Led

    Thanks for the information.

    If I get a buck puck 1000ma driver with ac input. Could I use an ac transformer to step the power down into its 5-32 volts input range, correct?

    Thanks again.

  5. #5
    Flashaholic* Timson's Avatar
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    Default Re: Shed Led

    Quote Originally Posted by trafton
    Thanks for the information.

    If I get a buck puck 1000ma driver with ac input. Could I use an ac transformer to step the power down into its 5-32 volts input range, correct?

    Thanks again.

    Don't see any reason why not.....

    Out of interest....I presume you're working from mains voltage.
    If so - wouldnt it be easier and cheaper to just fit an ordinary household bulb?....Or is that not the point!

    I completely understand the challenge of doing something different - just for the sake of it.

    As before don't forget to heatsink those stars properly if you're going to run at 1 amp.

    Do you plan on using any kind of optics / reflectors / backlighting set-up, or are you just gonna let em run al-fresco for general flood illumination.

    Don't forget to do pictures and and write up once you're done.


    Tim.
    M3-CB, C3-HAIII, A2-RD, Fenix L1P, Fenix P1D-CE, Tri-Star Phaser, Inova T3, Mag85, SNII Clone, DD LuxIII Mag,

    Trilobike
    , Hot-Diver

  6. #6

    Default Re: Shed Led





    By the pictures it is hard to tell, but the light is really even and a very nice light for lighting the workbench. The optics don't fit perfectly onto a k2 star, so I just used a little foam tape to put it on there nice. I used these pieces of metal I got from the grocery store for 50 cents as a heat sink.

    Also the power supply was a 1000ma buck puck dc with a power supply all from ledsupply.com. The Pentonmeter is used to dim the lights

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