Electronics LED Question

Discussion in 'Modding' started by GrimRaeper, 5 May 2003.

  1. GrimRaeper

    GrimRaeper What's a Dremel?

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    Hello Everyone!

    I'm new to the modding scene and have a question about LED's

    How do you work out what resistor you need for wiring LED's up in:-
    1. Series
    2. Parallel

    As I said I'm new to modding and electronics baffle me.

    Also can anyone recommend a good source for learning about electronics?

    Thanks in Advance
     
    GrimRaeper, 5 May 2003
    #1
  2. RTT

    RTT #parp

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    First and foremost, welcome to our forums :cooldude:

    To work out a resistor value for LEDs in series, you need to know:

    *the supply voltage (call this Vs)
    *the forwards voltage drop over each resistor (call this Vled)
    *the current each LED needs (call this I)


    Then we can use the equation Voltage = Resistance * Current (V=IR). Re-arranged, this gives Resistance = Voltage / Current.

    So for example, to work out the Resistance required for a power supply voltage of 12v, forwards voltage drop of 1.8v, and a current of 20mA:

    R = (Vs - (Vled * n)) / I [n being the number of LEDs]
    Therefore:
    R = (12 - (1.8 * 1)) / 0.02 = 510 Ohms.

    For 3 LEDs, the equation would be:
    R = (12 - (1.8 * 3)) / 0.02 = 330 Ohms.

    I am unsure for parallel, though I think it could be the same because the voltage drop over the LEDs should be the same as in a series circuit.

    Someone else can deal with that :p
     
    RTT, 5 May 2003
    #2
  3. bren2

    bren2 What's a Dremel?

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    okay with parrallel the voltage drop is the smae so in the case above ^^

    a 1.8Vled and 20mA
    okay one thing RTT forgot to mention is Power
    P=IV
    so
    P=(12-(1.8*1))*.02
    P=0.204W
    this means a 1/4W resistor will do

    okay now with parrellel if we were to do the case of the 3 LEDs but hook them in parrllel then the voltage drop would be 1.8
    but the current will be 60mA (20mA*3)

    so
    R=(12-(1.8*1))/.06 = 170ohms
    P=(12-(1.8*1)*.06 =0.612W
    so you would need a 170 ohm resistor which disapates 1W (closest vaule)

    understand?
    current increases in parrallel

    best thing is to tell us how many lEDs and some one will work it out and the best way to wire it

    but i recommend butting some in seris and some in parrellel

    note with parrllel you can use more then one resitor to be safe
     
    bren2, 5 May 2003
    #3
  4. GrimRaeper

    GrimRaeper What's a Dremel?

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    Thanks

    Thanks for the response!

    I havent actually decided on what I'm going to do, I just wanted to find out how to work out the value of the resistor that I would need to use in different case and whether it would be best to wire them up in parallel or series

    Thank Again
     
    GrimRaeper, 5 May 2003
    #4
  5. cpemma

    cpemma Ecky thump

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    The safest way with parallel strings is to work out the resistor for a single led and then use a resistor to each led. Then if one led fails, the others don't get too much current.

    There's linears led calculamatorer here that will ease the maths. :rock:
     
    cpemma, 5 May 2003
    #5

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