2009 Big-W LED Voltage Measurements

Discussion in 'Lights - Store Bought and Home Made' started by AussiePhil, Jun 29, 2010.

  1. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    Taken from my post at DIYC
    Hi all,
    been using the cool white, blue and green so far this year.
    Due to questions about voltage and resistor I thought i would do some actual measurements of current versus voltage.
    Quite interesting.
    Equipment
    2 DMM one measureing Voltage the other current
    1 Bench top Power Supply adjustable to 31v

    ALL READINGS ARE DC Voltages
    and are for Big W LED Connectables extension sets of 120LED's.
    All readings taken with string sets, the icicle sets have the same Led's per segment and should be the same.

    Here's what i found
    Red
    120 Leds - 15 Led per Segment, 4 segments per negative.
    Expected current per half string at 20mA nominal for leds was 80mA
    Visibly on - 24v @0.1mA
    27v - 10mA = 2.5mA/segment
    28v - 29mA = 7.2mA/segment
    29v - 56mA = 14mA/Seg
    29.64 - 80mA = 20mA/Seg
    30v - 100mA = 25mA/Seg

    All Other colours are 120 Leds - 10 Led per Segment, 6 Segments per Negative
    Expected current for nominal 20mA led current was 120mA for 6 segments

    Warm White
    Visibly on - 24v @ 0.1ma
    27v - 12ma = 2mA/Seg
    28v - 28mA = 4.7mA/Seg
    29.32v - 60mA = 10mA/Seg
    31v - 120mA = 20mA/Seg

    Blue
    Visible on - 24v @ 0.1mA
    27v - 11ma == 1.84mA/Seg
    28v - 23.8mA = 3.96mA/Seg
    29.92v - 60mA = 10mA/Seg
    31v - 87mA = 14.5mA/Seg
    Note: PSU would not go above 31v

    Green
    Visibly on - 22.5v @ 0.1mA
    24v - 1.4mA = .23mA/Seg
    27v - 17.9mA = 2.98mA/Seg
    28v - 30mA = 5mA/Seg
    29.56v - 60mA = 10mA/Seg
    31v - 107mA = 17.8mA/Seg
    Note: PSU would not go above 31v

    Cool White
    None available to test - update in the future

    Summary
    All the tested colours are significantly underdriven at 28v DC.
    Red has reached it's nominal forward current at 29.6v DC
    All the others require 31v DC plus to achieve 20mA nominal current.

    I don't have a starter kit at home to measure the voltage supplied normally, there is one at work though.

    The Swithed Mode Power supplies driving my show this year are set to 28v DC and the blue's Greens and cool whites all look great at this voltage and I can now see they are significantly underdriven.

    Conclusion
    For DC use NO resistor is required for any colour when the voltage is keep under 29.5V

    Hope this is of help.

    Cheers
    Aussiephil
     

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