led diy light panel please need help

Discussion in 'The Projects Forum' started by fatalexit1, Aug 27, 2011.

  1. fatalexit1

    Thread Starter New Member

    Aug 26, 2011
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    so ive been attempting to make a light panel with 200 5mm leds. here (http://www.ebay.com/itm/390221414004?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649) 110 red,60 blue and 15 amber, uv. im a novice when it comes to this to say the least lol. i want to use this as a starting point to make a much bigger array. id like to go upto 800 or so. i realize this will be alot of work but totaly worth every minute the power supply i want to use is a pc psu i managed to find for dirt cheap. so my question is how should i wire them in series or par.? will this power supply work for my needs now and in up and coming months? any help would be awesome. :D
     
  2. bertus

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  3. iONic

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    Nov 16, 2007
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    The Power supply will work, but you will need 66 parallel branches each with 3 LED's and an LED is series given the power supply is only 12V
     
  4. fatalexit1

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    Aug 26, 2011
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    the psu output is 5v/18A. or 12v/at 4.6. how come it saying its a 150watt dc output? which do i use and what type of resistor should i use? im not sure what the Ma on the leds so im not sure what the total amps would be on 200-800 leds
     
  5. iONic

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    Nov 16, 2007
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    If you use the 5V you will need 200 - 800 Resistors, one for every LED.
    800 x .02A = 16A. That's at least $25 just for the resistors.

    If you go with 12V then every 3 LED's need a resistor. Thus 200 - 800/3 will require 67 - 267 LED's. 267x .02A = 5.3A, more than the supply can handle.
     
  6. fatalexit1

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    Aug 26, 2011
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    then why does it say its 150 watts? could i run both at the same time? im kind confused
     
  7. wayneh

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    Sep 9, 2010
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    Yes, the wattage rating is the sum of what you can draw from both the 12V and the 5V supplies. You could choose a different PSU with a higher 12V current rating. If you look for used equipment, you can probably find one for free.
     
  8. SgtWookie

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    Jul 17, 2007
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    You mention UV after amber, but no count? 15 of those, too?
    You start off saying 200 LEDs, but 110+60+15= 185, so is it safe to assume 15 UV's?

    Series is the way to go, using the 12v supply.

    For the best efficiency:
    Use five red and/or amber per string with a 75 Ohm resistor in series,
    - OR -
    (Two of red and/or amber LEDs) AND (two blue and/or UV LEDs) with a 62 Ohm resistor in series.

    You'll need to have 30 strings with 2 blue LEDs and 2 red ones; that will take care of all 60 blues and 60 of the reds.

    You'll wind up with about 47 strings in the array. You won't come out quite even with your LEDs, but better to go for efficiency rather than exact LED count. Each string will draw ~20mA current, so 940mA total.


    You could go up to 800 LEDs with that 150W supply.
     
  9. fatalexit1

    Thread Starter New Member

    Aug 26, 2011
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    yes there are 15 of the uv. im thinking of getting another 100 red or uv but if i go uv id go for some of the stronger mcds. now am i going to need a heat sink or a fan for the resistor im assuming?
    do i need a zener diode or do i not have to worrie about spikes
     
    Last edited: Aug 28, 2011
  10. SgtWookie

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    No, the resistors won't be dissipating much power. 1/10 Watt resistors would be more than enough power rating to use.
     
  11. fatalexit1

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    Aug 26, 2011
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    can i use my multi-meter to figure out which harness is what? theres 7 of them. if so how :confused:
     
  12. SgtWookie

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    Wait a minute - I thought that you were going to buy these LEDs?

    Are you saying that you already have something that has been assembled into a harness, and you want to re-use the LEDs that you have?
     
  13. fatalexit1

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    Aug 26, 2011
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    the wiring harness from the pc psu. i just received the leds from hong kong.
     
  14. SgtWookie

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  15. fatalexit1

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    Aug 26, 2011
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    Last edited: Aug 28, 2011
  16. fatalexit1

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    Aug 26, 2011
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    so a 62 or 75 ohm resistor is what i need? what does the 1/4 watt and 1/8 watt mean? can i use any size? i have some of both for now until my order goes out. and is the tolrence important?
    whats the importance with metal film or carbon comp?
     
  17. SgtWookie

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    Well, they have a Vf of somewhere between 1.8v and 2v with an 18mA current through them. Figure the typical Vf will be around 1.9v @ 18mA.

    you want to operate them from 5v. So, 5v / 1.9v = 2.63157... truncate the number to an integer; 2.

    2 x 1.9 = 3.8v for two of those LEDs in series.
    5v - 3.8v = 1.2v.
    So, how much resistance do we need to drop 1.2v when current is 18mA?
    R = E/I = 1.2/18mA = 66.666.. Ohms. That's not a standard value of resistance, but 68 Ohms is a standard value.

    1.2v/68 Ohms = 17.65mA; close enough.

    Power dissipation rating; you will need 1.2v * 18mA * 1.6 = 34.56mW; very small amount of power wasted. 1/10 Watt resistors would be fine.
     
  18. SgtWookie

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    Jul 17, 2007
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    Yes, that's what I said. Which resistor you need depends on which LEDs you wire in series.

    That is the power rating of the resistors. Generally speaking, the higher the wattage rating, the larger the physical size of the resistor.

    Any size that has greater than or equal to the wattage required; the general formula is voltage x current x 1.6. The 1.6 is a safety factor so that you are not operating the resistor at the maximum current capacity.

    You probably have 5% resistors. 4 bands, the 4th band is gold, right? That's 5%. 5% is close enough.

    Carbon composition resistors are not stable; they can change quite a bit over time and temperature.
    Carbon film resistors are OK, however if you overheat them while soldering, you will change their resistance.
    Metal film resistors are very stable and very low-noise. You can still ruin them if you overheat them.
     
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  19. fatalexit1

    Thread Starter New Member

    Aug 26, 2011
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    would 1/4w with 1% tolorence be better than 5%?
     
  20. SgtWookie

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    1% tolerance resistors are E96 values, which are much more precise than the 5% E24 values.

    Here is a decade table of standard resistance values:
    http://www.logwell.com/tech/components/resistor_values.html
    Bookmark/favorite that page.
    The green columns are E24 values, which are frequently available without specially ordering them.
    E48 and higher values are of course more precise, but are usually more expensive than the lower E-series, and most hobbyists don't keep stocks of them due to the expense and space required.
    Please read the introduction to the decade tables at the top; it explains how to use it.

    Note that the E6 table works for capacitors, too. Electrolytic capacitors are frequently not available in the finer E-series.
     
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