Architectural Model, 700+ led array, designing help!

Discussion in 'The Projects Forum' started by Bernardo, Nov 20, 2014.

  1. Bernardo

    Thread Starter New Member

    Nov 20, 2014
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    Quick background: I am a model maker for architecture firm currently making a tower model with individual LEDs in each floor plate. I need between 16-25 leds per floor and the tower is 35 floors so that's between 560 -870 smd LEDs that I need to map out in the most efficient and logical way and I need help! (because I know very little about circuits and wiring... hence why I'm a model maker and not electrical engineer)

    I am using this led: http://www.kingbrightusa.com/product.asp?catalog_name=LED&product_id=AA2214VR4D1S-N1

    OR possibly this unit: http://everlightamericas.com/white/33/eahp3030wa3.html


    I have attached a diagram with the four possible wiring configurations that I can think of. Currently I am making samples with model A since it was the most intuative for me when I started. I need the floor plates to be be removable so wiring between plates must be simple. Currently I have positive and negative contact strips running up the length of the elevator core and each plate connects via touch (not soldered) as they slide on and off... Then inside each plate I have my two wires snake around the perimeter with the LEDs all soldered in parallel. But I'm doing more research and finding out this may not be the best method.

    SO this is what I need: which wiring plan is the best for what I need to accomplish and what power supply / resistors do I need based on the specs for the led I am using which is 3.3 Vf draw and 20mA current. I looked into the led array calculator but it only offers two solutions in 2 and 3 led configs and I need between 16-25.

    I can provide more info if needed, but this should be enough to start I hope.

    Any help is hugely appreciated!
    Thanks!
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    "C" is the best solution.. each floor will require 2 series strings of 8 to 13 leds per string (16 or 26 per floor).
    A resistor is needed for each string. That resistor will need to be determined after you know the number of LEDs in each string.
    I would suggest a 48VDC supply large enough to support all the strings or splitting it up into multiple smaller circuits with a 48V power supply for each sub circuit.

    and that sucker could put off some heat (and light obviously). But I suspect with that many LEDs this is a LARGE model..
     
  3. Bernardo

    Thread Starter New Member

    Nov 20, 2014
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    Thanks for the quick reply! I uploaded two images of the floor plate sample I'm currently working with. (One open, one closed). It's a 3d printed structure with a laser cut floor and ceiling plate glued on... The open image has the floor plate removed for viewing. The model actually isn't that large... it's 1:250 metric so just under 3 feet tall. You can see my hand in the images to give a sense of how big each plate is.

    The LED I was using before (used in the image sample) was this: http://www.kingbrightusa.com/product.asp?catalog_name=LED&product_id=APT2012QWF/F

    I am discontinuing use of this unit because it's a cool white and I need a more neutral 3500-4000k look... This unit also only had a luminous intensity of 500 vs the 1250 of the new unit I plan to use (still shipping to me)... So I may need fewer leds per floor but with 16 of the previous one, it was not bright enough and also created hot spots on the floor... which I think the only way to correct at this scale is to increase the volume of lights so the hot spot is continous and not seperate.



    OK so I will likely use C then... easy enough. Can I ask why I need two strings of 8+13 or whatnot instead of one string per floor? Also if I do two strings, do I need two seperate contact strips on the core? One for all the 8s and one for the 13? Or can they hook up to a single contact strip?

    Thanks again!
     
  4. mcgyvr

    AAC Fanatic!

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    Split into 2 strings per floor to keep power supply voltages low/safe (below SELV values)
    In "C" its just 2 of those horizontal rows per floor.
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Two strings are in parallel so no extra contacts required.
     
  6. Bernardo

    Thread Starter New Member

    Nov 20, 2014
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    Hmm ok interesting. I also asked a few friends with more knowledge of this and all recommended A or B solely based on the fact that in C if one led goes out, the whole floor goes out and in D if one is out, the whole array is down.

    Is there any serious benefit for running the lights in series by floor but parallel over the whole circuit (version C)?

    Is there a downside to A or B that makes it less desirable?

    As far as I understand; for say 25 per floor at 35 floors run in model A, that's a total of 875 units. 20mA per light translates to 57.75 watts and 17.5 total amps so if I use I use a 3v power supply with 80 watts and 17.5 amps, I have an ideal situation, right?
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    A and B are essentially the same.. each of A/B/C/D has pros/cons..
    A and B require a resistor for each LED but can also use a lower voltage power supply (5V supply.. 3V is too low as the Vf of the LEDs is higher) and can use a lower wattage resistor.

    and yes the downside of C is that if one goes out so does that individual string.. but you only need 1 resistor per string (but may be larger wattage versus A/B)
    How long do you expect these lights to be on? or how long do you need it to last I guess..
    If you drive them at 10mA (and even 20mA really) you should easily get 50,000 hours.. kingbright makes good LEDs..

    D is not at all good as the power supply voltage would be very high to overcome the sum of the VFs
    example.. if 100 in series then you need a 3.3x100 = 330VDC (or higher) power supply which is unsafe for a hobbyist.
     
  8. Bernardo

    Thread Starter New Member

    Nov 20, 2014
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    This model will run twelve hours a day, likely six days a week.

    Between A and C - as I understand, correct me if I am wrong.

    A is most fail safe (if one dies, only that one dies) but will require a seperate resistor for each led (700 leds, 700 resistors). *But don't I only need a resistor if the current is more than 20mA to each led? If I use a power supply with a total amps equal to the sum of amps required for all leds to run optimally, why do I need resistors? Are they simply used for surge protection, if you will?

    B is less fail safe (potential for part of an entire floor to die) but will only require one resistor per string (70 resistors most likely).

    If the only drawback to A is additional soldering work, then I will go with A. Cost/time is a non-issue to optimal setup. I can't risk the potential for an entire floor to go out... I really can't even let one single one die. But we will see. For now I am planning on hand soldering but am considering making myself a little reflow setup...
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Open to review, but I believe that there is a greater chance of failure in connecting floors to power with low V & high current than with high V & low current.
    For low current, self adhesive backed Cu tape could be used for series parallel arrangement, just a 1 mm cut at each LED location.
    I have a line operated LED night light that has been on 24-7 for over 7 years & is a little dimmer now. 'Had one LED failure in making under counter lighting; LED was moved too many times & was over heated causing lens to fall off- but the light " kept on ticking". 2W LEDs were soldered to .03 X .5 " Cu strips.
    My vote is still C.
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    leds ALWAYS need some form of current limiting..
    You must use resistors. Thats the only way you can ensure they get 20mA

    constant current drivers/power supplies are another method to limit current to LEDs but are out of the scope of this project as the number of LEDs is too large.
     
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