As I mentioned in the LED Ring construction post, I wanted to make sure 4 AA batteries would power my 25 RGB LEDs through a good 3+ hours of trick-or-treating. The Adafruit doc provides a good battery life estimate, but I figured I might as well measure it.
Fortunately, I had a myDAQ handy, and hooked it up to measure battery current and voltage as follows:
Note: the power consumed by the 1N4001 diode is not measured with this setup.
I then wrote a quick LabVIEW VI to measure & log the battery voltage and current every second. This way I could see the voltage and current drop as the batteries discharged.
With some fresh AA’s, I powered up the LEDs and ran the ‘RainbowCycle’ pattern from the Adafruit WS2801 library, shown below (all 25 LEDs are on driving different colors, this should be a good worst-case current draw mode).
The myDAQ logged data to a CSV file for about 8 hours, you can see the resulting current, voltage and power vs time below (click for a larger version):
The graph shows about 5 hours of LED power before the current drops off, plenty for my application. In total the LEDs consumed about 1900 mAh during the test, which is in line with the original estimate.
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