DC Series Circuit Help

Discussion in 'The Projects Forum' started by deadfire55, Feb 6, 2011.

  1. deadfire55

    Thread Starter New Member

    Feb 14, 2010
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    I'm working on a project to hook up a bunch of LEDs in parallel to a DC source from an outlet. The transformer I have is rated at 12V and 850mA, this is my first attempt at using power from an outlet and I really don't want to burn out a bunch of my LEDs so I would appreciate it if someone would look over this circuit.

    My project is based off this diagram but not exactly like it. (Disregard the arduino).

    [​IMG]

    My first row has 6 blue LEDs (4V, 30mA)each with a 270 Ohm resistor.

    The second row has 3 red LEDs (2.5V, 30mA) each with a 330 Ohm resistor.

    The third two has 3 orange LEDs (2.5V, 30mA) each with 330 Ohm resistor

    The fourth has 6 white LEDs (4V, 30mA) each with a 370 Ohm resistor.

    Would this setup work alright or would my LED's instantly burn out?
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    It will work, however, you can use 270R resistors for the white LEDs to achieve more brightness since they have the same voltage drop and current rating as the blue LEDs.

    Is the 12V power source regulated?
     
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  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
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    Perhaps your 4th row should also be 270Ω per LED, rather than 370Ω.

    Otherwise, it's unlikely you would have any problems.

    Presumably your "transformer" has 12V DC output - not AC?
     
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  4. deadfire55

    Thread Starter New Member

    Feb 14, 2010
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    Thanks, what does regulated mean?

    Also, my power source is 850 mA, I didn't factor that into any calculations, should I have?
     
  5. mik3

    Senior Member

    Feb 4, 2008
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    Regulated means that the voltage is held constant at 12V whatever the output current is (being lower than 850mA in this case).

    You don't need to worry about the output current in your calculations. This power supply is a voltage source and not a current source. In a voltage source, the output voltage is constant and the current is determined by the load, i.e. the LEDs. The only thing you have to worry about the current is not exceeding the maximum output current of the power supply (850mA in this case).

    Do you have more information about the power supply as we can tell you if it is regulated?
     
  6. deadfire55

    Thread Starter New Member

    Feb 14, 2010
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    This is the one I have: http://www.amazon.com/ENG-AC-Adapter-48-12-850D-Transformer/dp/B0035XP432
     
  7. mik3

    Senior Member

    Feb 4, 2008
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  8. deadfire55

    Thread Starter New Member

    Feb 14, 2010
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    Haha, I didn't think it would help too much either. It doesn't have any thing written on it.

    I have about 10 other transformers, would it be safer to use a lower amp one first?

    Nevermind, I used info from this google page: http://answers.google.com/answers/threadview/id/753665.html

    and found a regulated one using a multimeter (the last response on that page).

    So I should be good to go now, right?
     
    Last edited: Feb 6, 2011
  9. mik3

    Senior Member

    Feb 4, 2008
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    If you have a multimeter, measure the voltage with nothing connected to the output of the power supply (no load). If the voltage is close to 12V then it is regulated otherwise it is unregulated (about 18V).
     
  10. deadfire55

    Thread Starter New Member

    Feb 14, 2010
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    Updated the post right above just before you posted :D
     
  11. mik3

    Senior Member

    Feb 4, 2008
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    It is good you know how to use google. :p

    What are the measurements results then?
     
  12. deadfire55

    Thread Starter New Member

    Feb 14, 2010
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    The transformer is rated at 12V and my multimeter switches back and forth between 11-12V.
     
  13. mik3

    Senior Member

    Feb 4, 2008
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    Do you get different results if you connect a load?

    Use an oscilloscope if you have.
     
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