2009 Big-W LED Voltage Measurements

AussiePhil

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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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