Ladies and gentlemen your services are required!!

Discussion in 'General Electronics Chat' started by Gorton, Jun 20, 2013.

  1. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    I have spent numerous hours recently researching ways to wire LED's so far for a home project I am working on which involves wiring:
    33 red
    38 blue
    471 white LED's.

    Unfortunately there I no scope for reducing the number of LED's so that is has to stay the same. I kinda knew I would end up hAving to seek your professional help on the matter eventually as nothing would elucidate an answer so to avoid asking silly or obvious questions I have worked out that:
    The red circuit will require:
    1454mW
    120mA

    Blue:
    3208mW
    260mA

    White:
    38,622mW
    3140mA

    With total requirements from the source being:
    3.52A
    43.28W


    Please see the incredibly crude diagram of how I'm planning on putting the strings together.

    The reason why After my research i have decided to wire it like this is because I've been told with very long strings in parallel, it will incur a voltage drop from one end to the other.

    Now for the questions:
    The driver that I have been looking at is a 45W driver with a 4A output - With the shorter red and blue strings (all circuits to be connected in series and paralell) being attached straight to the power supply will the high power output cause an issue with it? I read somewhere that the power rating of a driver merely what it can HANDLE as opposed to what the actual output and I guess according to ohms law the power is generated in the circuit not given out.

    Secondly with having all the strings connected in a 'spider circuit' formation, does this mean that each string will get the full 4A of current thus will need resistors to bring it back down to size or is it true that the individual circuits will conduct only what they need?

    Thirdly which is more of an extension of the first, because the power rating of the driver is 1.72W over what the circuit requires, will this require some additional resistors before unleashing it to the mercy of the LED's?

    Fourthly - is 157 LED's per string connected in 52 separate sub branches of series far too many so the LED's at the start will be brighter than those at the end?

    Please forgive me if my nomenclature isn't up to par - electronics is not. Something I have ever studied before and I have made a concerted effort to try and not waste your time!
    Kindest regards
    Gorton
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    Ideally all the leds should have their own series resistor, and then connect all leds in parallel like this, its just a matter of working out their voltage drop from the supply, to get the resistors balanced.

    What is the supply voltage from your psu?
     
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    4,770
    970
    Numerous hours but all you give is that worthless "diagram".
    No details on this "45W" driver? part number/manufacturer?
    Specs on LED's? Forward voltage drop/current rating?

    Do not do anything until you have a "proven" schematic/wiring diagram.

    What are you doing that requires soooo many LED's and can't use less/higher power LED's for?

    Any plans for heat management?
     
  4. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I think the easiest solution is to buy strips of LED's that work on 12V.
    You can buy the strips in any color you want. They have the LED's already in series and have the current limiting resistors already installed. You can cut the strips for the number of LED's you want or ned
     
    Last edited: Jun 20, 2013
  5. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    Mcgyvr as I quite clearly stated this really isn't my field ... I'm bound by the same restrictions every human being is on the face of this earth I.e I have my strengths and weaknesses. This is a weakness - physically I'm very strong and I am guessing would probably humiliate you in that field like you are trying to humiliate my weakness here so I'd like to ask you to either leave this thread, or come up with some suitable input instead of engaging in some ridiculous slanging match which will no doubt result in us trying to use ever more complex words to try and insult each other
     
    rougie and arun the curious like this.
  6. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    Thanks Dave - yeah the output is 12V. Wen you say ideally can you not just put 1 resistor in each series of 3?
     
  7. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    I wish I could but unfortunately because of the shape of what I'm making all the LED's need to be individual. What I am making is a 54"^2 LED sign of a picture with some writing so ... It unfortunately can't be a solution
     
  8. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,986
    745
    yes you could put 3 in series, you just need to know the voltage drop per led.
     
  9. Shagas

    Active Member

    May 13, 2013
    802
    74
    DO link power supply details/datasheet and Led details and anything else you can think of because without that you will not get a decent answer.
    I think that the way you want to do it isn't very efficient . Provide info mentioned above

    Also , what board and how big are you planning to put the led's on . Also , Through-hole or smd?
     
  10. Papabravo

    Expert

    Feb 24, 2006
    10,142
    1,790
    In an open forum you don't get to dictate the terms of engagement. You have to take the good with the bad. Have a thicker skin and don't get preachy. Other people may want to learn from the exchange, so even if a members comment is of no use to you, just let it go. It may help someone else understand what is going on and it urges you to improve the methods and quality of your requirements and specifications.

    Two principles of LED construction.
    1. You cannot put an LED across a power source
    2. Resistors are required to limit the current
    With those two principles in mind, I'd like to make a helpful suggestion. You need a way to identify each LED on both a drawing and on the physical realization of your design. If you cannot establish an immediate visual correspondence, then wiring and debugging your design will be IMPOSSIBLE. Worse if you do things wrong at the power levels you are considering, there is a high probability of damage or injury. If your admitted weaknesses endanger yourself or others then I would advise you to think twice about doing this on your own.
     
  11. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Welcome to AAC.


    Some things to keep in mind:
    • This is public forum focused on beginner electronics, one if not the best in my opinion. People are here because they want to learn or help or both, but it is strictly voluntary.
    • Please note mcgyvr has over 1500 posts and knows his stuff. What he said was not intended to humilate or insult you in any way; it was intended to make you think about things you may not be aware of.
    • We each have our own style or way of saying things. Some will jive better with you than others, but none are intended to make you feel inferior.
    • The moderators here are awesome and don't tolerate abusive people, so you're in a good environment here.
    • If we use termilogy you don't understand, just ask us to elaborate. We're not trying to make you feel dumb, we're just using the lingo we're used to.
    That said, let me see if we can approach your project in another way.



    Is the following correct?
    • You are either limited to or choosing to use a power supply rated at 12VDC at 4A, roughly 45W?
    • All the LEDs are going to be mounted to a board that is 54" x 54"?
    Now some questions:
    1. Have you already selected or decided which LEDs you're going to use? If yes, please post links to these.
    2. Will the LEDs be thru-hole such as 3mm or 5mm or SMD? There's also high power LEDs, but I don't think you'd be able to get that many on such a small area.
    3. Is this display going to be viewed indoors or outdoors? If outdoors, will it be viewed in sunlight, at night, or both?
    4. What is the closest distance someone will be viewing the display?
    5. What is the farthest distance someone will be viewing the display?
    6. Can you post a rough drawing or picture of the overall image you're trying to create with the LEDs? You don't need to draw hundreds of dots, just a line or shape will do.
    7. Are you simply wanting to have the LEDs on or do you want to be able to make some or all blink and/or fade?
    8. I'm curious how you got the current and wattage requirements for the LEDs. If I'm following correctly, it appears you've planned to connect three LEDs in series and parallel these sets. If so, then the red LEDs are getting 10mA each and the blue and white LEDs are getting 20mA each. Is this correct?
    9. What material is the board going to be made from? 1/8" plastic, 1/4" plywood, etc.?
    10. Will there be a cover over the display, e.g., glass, plastic, etc.?
     
    dthx and KJ6EAD like this.
  12. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    I accept your point on it and personally adopt a kaizen attitude of continual improvement within myself but I can't see that a dig of that nature helps anyone. However you are quite right about the whole 'not doing it on your own' bit :)
    I'd like you to stay tuned and I will get you a proper and accurate schematic done within the next day ... Can anyone recommend a decent website for drawing them in a manner you can all understand?
     
  13. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    Take a look at the free schematic software available from Express PCB.com. You can also look up Bill Marsden's blog here on AAC - he gives an excellent tutorial on making schematics with Microsoft Paint. If it is easier to draw by hand and scan in or take a picture, that works too. However you do it, save it as a .png and post as an attachment.
     
    Last edited: Jun 20, 2013
  14. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
    763
    Draw it by hand as neat as possible, scan it and post it here.
     
  15. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,795
    Getting a better schematic together along with some specs on the LEDs will help a lot. Other points to consider clarifying:

    1) Explain where your power/current numbers came from. It's not at all obvious and strangers that are asked for help are far more likely to help if you don't make them guess or reverse engineer your thoughts using a crystal ball.

    To try to answer some of your questions:

    If you use a 12V voltage source with a 4A rating, then it can supply UP TO 4A while holding the voltage at 12V (which would be 48W, not 45W, but that's in the ballpark). Each circuit that is connected across the supply will draw whatever current it will draw at 12V. As long as the sum of all such currents does not exceed 4A, then each circuit is independent and won't even know the other circuits are there (i.e., connecting/disconnecting one should have no significant impact on the others).

    I'm not picturing what you have in mind. 52x3=156, so what is up with the 157th LED?

    As long as you use sufficiently large wire to connect the brnaches to the string, the voltage drop along the string can be as small as you want. How long, physically, will the longest string be?
     
  16. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,172
    397
    # 20 wire should be adequate. If all LEDs are in parallel, then 11 amps needed, 2 in series= 5.4A & 3, white & blue, 4 for red, in series = 3.56A. I can think of no case where series parallel connections cannot be used, with exception of bi-color LEDs.
    One mounting method I used for 147 3mm LEDs on 10" X 7 " panel was a sheet of tin plate steel, .02", backed by 1/16 " of cork sheet drilled for a tight fit. Another project, 4 ft. X 5 ft. used corrugated cardboard with ea. hole location dampened & compressed with blunt end, 150 W, hot soldering iron.
     
  17. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    right sorry guys for taking such a long time to reply I've been mega busy and knew it was going to take a couple of hours to work out how to use the programme and create the darned thing!! hopefully you will be able to decipher the necessary information even if bits are the wrong way round. I shall requote the information I was asking about and hopefully you guys will be so kind to guide me through this :)

    just a quick aside:
    is there any point in a 1ohm resistor or is this the value they have to give a resistor of no resistance so equations dont equate to zero??
    also for those asking what I'm planning on for heat management, the LED's will be sat amongst tiles, next to a window so hopefully with the weather here in blighty being cold and wet with no individual perrenialism, combined with the low SHC of the tiles, it should work :D
     
  18. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    I have spent numerous hours recently researching ways to wire LED's so far for a home project I am working on which involves wiring:
    33 red
    38 blue
    471 white LED's.

    Unfortunately there I no scope for reducing the number of LED's so that is has to stay the same. I kinda knew I would end up hAving to seek your professional help on the matter eventually as nothing would elucidate an answer so to avoid asking silly or obvious questions I have worked out that:
    The red circuit will require:
    1454mW
    120mA

    Blue:
    3208mW
    260mA

    White:
    38,622mW
    3140mA

    With total requirements from the source being:
    3.52A
    43.28W


    Please see the incredibly crude diagram of how I'm planning on putting the strings together.

    The reason why After my research i have decided to wire it like this is because I've been told with very long strings in parallel, it will incur a voltage drop from one end to the other.

    Now for the questions:
    The driver that I have been looking at is a 45W driver with a 4A output - With the shorter red and blue strings (all circuits to be connected in series and paralell) being attached straight to the power supply will the high power output cause an issue with it? I read somewhere that the power rating of a driver merely what it can HANDLE as opposed to what the actual output and I guess according to ohms law the power is generated in the circuit not given out.

    Secondly with having all the strings connected in a 'spider circuit' formation, does this mean that each string will get the full 4A of current thus will need resistors to bring it back down to size or is it true that the individual circuits will conduct only what they need?

    Thirdly which is more of an extension of the first, because the power rating of the driver is 1.72W over what the circuit requires, will this require some additional resistors before unleashing it to the mercy of the LED's?

    Fourthly - is 157 LED's per string connected in 52 separate sub branches of series far too many so the LED's at the start will be brighter than those at the end?
     
  19. Gorton

    Thread Starter Member

    Jun 20, 2013
    51
    3
    Oh yeah - and it's worthy to note I have bought NOTHING except a few of the LED's so any advice on the type of wire resistors, power supply would be hugely appreciated
     
  20. WBahn

    Moderator

    Mar 31, 2012
    17,743
    4,795
    Read the thread -- all of these issues have been addressed except the new one you've introduced.

    Let's look at the string with the 1Ω resistor.

    You haven't specified what your voltage source is (unless I missed it somewhere) other than that it is 45W at 4A, which would make it 11.25V. But let's call it Vs. Let's call the the LED diode drop Vd and the resistor value R.

    What is the current, I, in the string with 6 LEDs?

    I = (Vs - 6Vd)/R

    Now, plug in the following values:

    A) Vs = 12V, Vd=2V, R=1Ω
    B) Vs = 12.5V, Vd=1.8V, R=1Ω
    C) Vs = 12V, Vd=1.8V, R=1Ω
    D) Vs = 12V, Vd=2.2V, R=1Ω
    E) Vs = 12V, Vd=2V, R=1.1Ω
    F) Vs = 12.5V, Vd=1.8V, R=0.9Ω
    G) Vs = 12V, Vd=1.8V, R=1.1Ω
    H) Vs = 12V, Vd=2.2V, R=0.9Ω
     
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