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Wondering how to wire led series

  1. Sep 12, 2009 #1
    Hi there, I have a series of LEDs that I need to get running. i plan to use this series in my car as a cutom LED guage cluster (you know, speedometer, fuel, engine heat). Anyhow, I've got 17 white LEDs

    Voltage Supply = Unkown
    17 LEDs
    3.1 Voltage
    20 - 30 mA

    I was wondering if anyone may know the amount off voltage needed to power something like this and also the best way to wire them (i was thinking series).

    Using a resistor calculator Ive been told that I need 100 oHm resitistors. (this was with a 12V example) which doesnt make sense as the 12V's couldnt posibly illuminate this seires.

    Thanks in advance

  2. jcsd
  3. Sep 12, 2009 #2
    Hi Darryl-
    You have to design this string to work on about 14 volts, the maximum voltage when the engine and alternator are on. My guess is that you want 4 LEDs and 100 ohm resistor in a string. There will be 12 volt drop across 4 LEDs in series, and 2 volts across the 100-ohm resistor. You could also do 3 LEDs and a 240 ohm resistor in series.
    Bob S
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