Overview:
Before committing to a power supply/wiring setup we wanted to get an idea of how much current each LED strand draws. When we first setup the Hell Lighting frosh year I ran similar testing, but didn't compensate for voltage drop, and the data was lost in any case.
Note: LED technology is changing pretty quickly, and these results are pretty much only relevant to the 2014 APA104 variant we used for Hell lighting.
Procedure:
To test current, one 5m LED strip was unrolled and connected to 5.00v every 2.5m by hooking micro-grabbers directly onto the exposed contacts. Note that due to resistive losses in the strip's ground rail, connections should be made to both 5v and ground. A UNIT UT580 was placed in the ground return path and used to measure overall current draw. The strand was controlled from a separately powered Arduino Mega ADK (any 5v Arduino can be used, though notably the DUE and 3.3v micro cannot be).
Once the setup was complete, we had the Arduino serially increase the power on our colors of interest by 5% with a 5 second delay between steps to allow us to write down the current draw. Since we want a little bit of pattern overhead even at max brightness I used a scale from 0% to 102% where a PWM value of 250 was 100%.
Results:
White Red Blue Green
100% 4.68a 2.71a 2.54a 2.58a
50% 3.27a 1.42a 1.37a 1.37a
25% 1.75a 0.64a 0.69a 0.68a
Each 5m strip of LEDs seems to draw about 4.7 amps when running white at full brightness. Throw in a little margin, and that becomes an amp per meter, which is going to be our working value going forward. It is interesting to note that the current drawn by the strip when running white isn't just the sum of the strip when running each of the component LEDs. Current use for each individual LED seems to increase linearly with set output, while white follows a more or less logarithmic growth pattern. It is possible that this is reflected in the brightness, though more testing would be required to determine that. At the simplest approximation it seems like the current used by a strip can be approximated as follows:
White Current = 1.7ln(%) - 3.31 R^2 = .961
Blue Current = 0.025(%) + 0.99 R^2 = .998
Green Current = 0.025(%) + 0.08 R^2 = .998
Red Current = 0.027(%) + 0.05 R^2 = .998
Links:
For the full current data in 5% increments click here.
For the Fast LED home page click here.