Wiring LEDs

Discussion in 'Computer Support' started by Ming the Murphyless, Nov 9, 2008.

  1. I need to wire four white LEDs to run off a 12v dc supply (regulated).
    The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    2 LEDs in series. Can I wire all four in series without using a
    resistor or are there good reasons for having it? The LEDS will be lit 24/7

    TIA

    Bob
     
    Ming the Murphyless, Nov 9, 2008
    #1
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  2. Ming the Murphyless

    Dan C Guest

    On Sun, 09 Nov 2008 18:03:57 +0000, Ming the Murphyless wrote:

    > I need to wire four white LEDs to run off a 12v dc supply (regulated).
    > The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    > 2 LEDs in series. Can I wire all four in series without using a
    > resistor or are there good reasons for having it? The LEDS will be lit
    > 24/7


    You didn't even bother reading the reply to your IDENTICAL post that you
    made an hour ago? The other guy answered your question already, you dumb
    ****.




    --
    "Ubuntu" -- an African word, meaning "Slackware is too hard for me".
    The Usenet Improvement Project: http://improve-usenet.org
     
    Dan C, Nov 9, 2008
    #2
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  3. Ming the Murphyless

    ian field Guest

    "Ming the Murphyless" <ming@*merciless*littleold.me.uk> wrote in message
    news:gCFRk.4756$...
    >I need to wire four white LEDs to run off a 12v dc supply (regulated).
    > The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    > 2 LEDs in series. Can I wire all four in series without using a
    > resistor or are there good reasons for having it? The LEDS will be lit
    > 24/7
    >
    > TIA
    >
    > Bob


    Ask on News:sci.electronics.basics
     
    ian field, Nov 9, 2008
    #3
  4. philo wrote:
    > "Dan C" <> wrote in message
    > news:p...
    >> On Sun, 09 Nov 2008 18:03:57 +0000, Ming the Murphyless wrote:
    >>
    >>> I need to wire four white LEDs to run off a 12v dc supply (regulated).
    >>> The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    >>> 2 LEDs in series. Can I wire all four in series without using a
    >>> resistor or are there good reasons for having it? The LEDS will be lit
    >>> 24/7

    >> You didn't even bother reading the reply to your IDENTICAL post that you
    >> made an hour ago? The other guy answered your question already, you dumb
    >> ****.
    >>
    >>
    >>

    >
    >
    >
    > Sheesh Dan
    >
    > maybe he tried the LED's with no resistor and was too blinded to read the
    > other post
    >
    > you never know
    >
    >

    I wouldn't normally bother to reply to the foul-mouthed such as Dan but
    my "original" post has no replies that I can see.
     
    Ming the Murphyless, Nov 9, 2008
    #4
  5. philo wrote:
    > "Ming the Murphyless" <ming@*merciless*littleold.me.uk> wrote in message
    > news:gCFRk.4756$...
    >> I need to wire four white LEDs to run off a 12v dc supply (regulated).
    >> The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    >> 2 LEDs in series. Can I wire all four in series without using a
    >> resistor or are there good reasons for having it? The LEDS will be lit

    > 24/7
    >> TIA
    >>
    >> Bob

    >
    > I know that in theory the voltage drop is supposed to be about 3.3 v across
    > a white LED...
    > but I'd start out with a series resistor anyway...
    > grab a 47 ohm (approx) resistor from your junk box and give it a try.
    >
    > If they lightup OK, then leave the resistor in as a safety factor
    >
    >

    Thanks philo, better safe than sorry I suppose.
     
    Ming the Murphyless, Nov 9, 2008
    #5
  6. Ming the Murphyless wrote:

    > I need to wire four white LEDs to run off a 12v dc supply (regulated).
    > The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    > 2 LEDs in series. Can I wire all four in series without using a
    > resistor or are there good reasons for having it? The LEDS will be lit
    > 24/7
    >

    With 4 leds in series and exactly 12V, you will not see a very bright
    light - evern without a resistor.
    But, when you turn on the car engine and the voltage rises to 14.2 v or so,
    you will first see a bright light, then a bad smell. In the end it will be
    dark again but you are a bit wiser :)
     
    wisdomkiller & pain, Nov 9, 2008
    #6
  7. wisdomkiller & pain wrote:
    > Ming the Murphyless wrote:
    >
    >> I need to wire four white LEDs to run off a 12v dc supply (regulated).
    >> The Vf is 3.2-3.6 The calculation gives a resistor value of 220 ohms for
    >> 2 LEDs in series. Can I wire all four in series without using a
    >> resistor or are there good reasons for having it? The LEDS will be lit
    >> 24/7
    >>

    > With 4 leds in series and exactly 12V, you will not see a very bright
    > light - evern without a resistor.
    > But, when you turn on the car engine and the voltage rises to 14.2 v or so,
    > you will first see a bright light, then a bad smell. In the end it will be
    > dark again but you are a bit wiser :)
    >

    ??? What car engine would that be then ???

    Seriously, what I'm trying to do is to illuminate a small box, roughly a
    cubic foot or so, from a regulated 12v mains adapter. I have a bunch of
    5mm white LEDs for the job so I need to find the most efficient way of
    doing it. The box has been lit this way for a few years using 4 white
    LEDs which were designed to run on 12v each. The light from them has
    faded considerably so they need replacing. I thought that rather than
    buy four more (expensive) 12v LEDs I could do it using LEDs I already have.
     
    Ming the Murphyless, Nov 10, 2008
    #7
  8. Ming the Murphyless wrote:

    > wisdomkiller & pain wrote:

    .....
    > ??? What car engine would that be then ???
    >

    Well, every generator while charging the 12V car accumulator, raises voltage
    up to about 14.4V or up to 2.4V per cell while the motor is running fast
    enough.

    > Seriously, what I'm trying to do is to illuminate a small box, roughly a
    > cubic foot or so, from a regulated 12v mains adapter. I have a bunch of
    > 5mm white LEDs for the job so I need to find the most efficient way of
    > doing it. The box has been lit this way for a few years using 4 white
    > LEDs which were designed to run on 12v each. The light from them has
    > faded considerably so they need replacing. I thought that rather than
    > buy four more (expensive) 12v LEDs I could do it using LEDs I already
    > have.


    LEDs are more like zener diodes - you have to limit the current that flows
    through them. "12V"-Leds do have a current limiter built in, therefore they
    are not as cheap. You may get away with 2 or even 3 leds in series, with a
    proper resistor OR one of the diodes internally regulated and therefore
    limiting the current for the others as well. But that diode will need 5V at
    least.
     
    wisdomkiller & pain, Nov 11, 2008
    #8
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