How to connect 50 Leds

Discussion in 'The Projects Forum' started by stinkykiller, Jul 24, 2010.

  1. stinkykiller

    Thread Starter New Member

    Jul 24, 2010
    10
    0
    Hi guys !

    I plan to convert my Fish Tank's lamp into LED's (previously florescent).
    I remove everything inside, I have 100 Led's (Bright White)
    That I bought on ebay, I just want to connect 50.
    Also bought a 3v 1000mA Power Supply (Like a cell phone charger)
    My fish tank has 2 lamps actually but I want 25x2= 50 LED's.

    I know Nothing of electronics this is my first attempt
    to make something "electronic"

    Please explain me like a boy of.... 10 years

    Thanks In Advance !!
     
  2. soda

    Active Member

    Dec 7, 2008
    174
    13
    You can use this link http://led.linear1.org/led.wiz
    All you have to do is to fill in your supply voltage,the amount of led's you gonna use and the current which is normally 20mA per led and if it's series or parallel . The wizard will then tell you what you need to do and show you a diagram how to connect the led's
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
  4. stinkykiller

    Thread Starter New Member

    Jul 24, 2010
    10
    0
    Thanks to both of you !!
    Soda the calculator you mention
    Helps me a lot !!!
    It don't ask me for the current of the source !
    It gives me the current I need. Right ?
    What if I got a power supply... let's says...
    5V, 700mA. It can't be calculate ?

    As I can see,
    I can't use the Power Supply that I bought.
    Need to find another :eek:(
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    What is the power supply? What are the LEDs? I'm not a fan of those calculators myself, I might be able to help.

    You need at least enough voltage to match the LED voltage specs. Once you've done that they are current driven.

    You are using white LEDs 5V is a good number, but 9V is better. At 5V you will need 2.5A, with 9V need 1.3A, with 13.7V you need just under an amp.
     
    Last edited: Jul 25, 2010
  6. soda

    Active Member

    Dec 7, 2008
    174
    13
    If your power supply voltage is too low, the wizard will tell you that and from my own experience, 5v for 50 led's would be too low.Use about 12v for your supply. The thing is this, if you use the led's in series which would the best way for 50led's then you have to add the forward voltage of each led you gonna use in one string.Let's say you choose red led's, then the forward voltage of each led will be 1.85v divide by your supply voltage. the answer you get is the amount of led's per string. You then place each string in parallel with the next one until you make up 50 led's. With 5v you will only be able to use 2led's per string.
    It's not so mush about the voltage but more about the current to set the brightness of a led. Just follow the instructions the wizard gave you and if there's something more you wanted to know then click on the FAQ link on the page. You can find all the different forward voltages of each led on that page. Have a look at the pic i added for you.
     
  7. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    The 3V, 1000mA supply is not a problem.

    It only supplies the current it needs. If you draw 10mA, then it will be fine. If you draw 700mA, it will still be fine. But if you draw 1100mA, you risk it overheating or going out of spec (for example the voltage may drop.)

    You can power most white and blue LEDs from 3V without too many issues.

    I recommend you just connect your 50 blue LEDs in parallel to the voltage source. Each will get 15mA-20mA, your total current will be no more than 1000mA. There are few other ways to do this, as you cannot create extra energy from that supply: it will give 3W max, it doesn't matter how you connect the LEDs.
     
  8. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
    24
    I hope you aren't growing plants in your aquarium. LEDs won't provide the right type of light for optimum plant growth. They require a certain range of wavelengths for proper growth.

    PS. My other hobby is tropical fish.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    No.
    Most white LEDs are 3.2V to 3.8V. They will be dim or not lighted with only 3V. Each LED will be at a different brightness which is why LEDs should not be connected in parallel unless they are tested and sorted to all have exactly the same forward voltage.
    The current in each "3.5V" LED will be only 3mA.

    Here is an article from Maxim: http://www.maxim-ic.com/app-notes/index.mvp/id/3256
     
  10. tom66

    Senior Member

    May 9, 2009
    2,613
    214
    Maybe my 3V lithium coin cells are 3.5 volts because I power my blue and white LEDs with reasonable brightness (they certainly could go brighter) from a single coin cell.
     
  11. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Datasheets from Energizer and Duracell are temporarily unavailable.
    I think a new lithium cell is 3.2V.
    When a 3.5V LED has "only" 3.2V then it has reasonable brightness.

    But some "3.5V" LEDs are actually only 3.2V and they will be very bright and maybe burn out if the coin cell can provide enough current.

    EDIT:
    Maxim has this graph showing a lithium coin cell with a little more than 3.4V when new:
     
    Last edited: Jul 25, 2010
  12. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    If he is using white LEDs it is a major problem, unless he builds circuitry to boost it. Much easier to get a right power supply to begin with.
     
  13. stinkykiller

    Thread Starter New Member

    Jul 24, 2010
    10
    0
    windoze killa It's Tropical Fish (Africans Cichlids)

    Led's info:
    Diameter: 5mm,
    Color: White,
    Forward Voltage: 3.2-3.4V,
    Current: 20mA,
    Luminous Intensity: 16000MCD,
    View Angle: 25 degrees

    I bought a bulk of them 100 pcs., I hope no need of sorting it.

    To those who approved my Power Supply (3V, 1000mA)
    Do I need to use resistors ? Which of them ?
    Any array indeed ?

    Bill_Marsden Which you recommend me ?
    the more cheap the more Happy you make me !!
    Hahaha

    Found this under $4.00
    5V 1000mA
    5V 500mA
    12V 1000mA
    Could any of them help ?
     
    Last edited: Jul 25, 2010
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The 12V 1000mA power supply can power 16 strings of 3 LEDs in series with a 100 ohm 0.25W resistor. Each string will have a current of 21mA and the total current is 336mA.
     
  15. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    What Audioguru said. If you need a schematic I can draw it easy enough.
     
  16. soda

    Active Member

    Dec 7, 2008
    174
    13
    The forward voltage of a white led is 3.7v and the current is 20mA. If you goes higher on the current it will shorten the life of your led's. 12v @ 1Amp power supply will be a good choice if you use the led's in a series configuration.Thought, always leave a few voltage left to enable the led's to light up correctly
    Type this in the fields on the page i showed you. The wizard will then give you a layout of the diagram. When you see the diagram, scroll down until you see the spec's around this diagram. It will tell you what resistors you need and also the wattage of each resistor. It will also show you the amps and watt's the complete diagram is going to use. I build a running display with 215 led' and it's going on very well. I got all my details from the wizard
    What more is there to say. Just do it and get it over and done.
     
  17. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Average voltage of white is 3.3V Vf, as stated by the OP in post #13. Three per chain as Audioguru describes is 9.9V. This leaves 2.1V headroom. If you use 100Ω resistors you will get 21ma. The difference is our assumptions of voltages. Audioguru used the specs stated by the OP. I'd go with the 3.4V myself, but that still works out to 18ma, which is plenty for the OPs requirements.

    I truly do not like wizards, they lack any common sense, and often give nonsensical answers. You are much better off going with experience tech and engineers any day.
     
  18. stinkykiller

    Thread Starter New Member

    Jul 24, 2010
    10
    0
    Ok !
    Let's says I use the diagram attached, (copied from: led.linear1.org)
    There's no problem that "the array draws current of 340 mA from the source"
    And I have 1000mA on the power supply ?
     
  19. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The power supply is fine. Why not drop the resistors down to 100Ω ¼W as suggested? You have got ¼ less current with 120Ω. You could even make it 51, and make that last link standardized. It will affect the brightness a little (just a little though). You could even use 91Ω for that little extra, and it would still be within spec.
     
  20. stinkykiller

    Thread Starter New Member

    Jul 24, 2010
    10
    0
    Something like this ?
    (New Diagram)

    91 Ω ¼W

    You guys are the Masters,
    I'm just learning !!
     
    Last edited: Jul 26, 2010
Loading...