I looked all over the site, but I can not find a runtime graph for the Maglite 3D LED, the one
that has 131 lumens and 79 hours of runtime. If anyone has that info, could you please post it here?
My interest is stock and modified D-cell MagLites. I am compiling a spreadsheet of performance data for various stock and custom D MagLite builds operating on alkaline, NiMH, and Lithium cells. With all due respects to the Mag Instrument Company, I question their published 79-hour runtime of the 131-lumen model of the 3D LED.
Here's why: The runtime for this light is way outside the pattern of data I have collected for the other lights. So I investigated a little further. This is a limited investigation, as I have neither the time nor the equipment to generate runtime curves.
Here is what I did, and what I found:
I measured the tailcap current of the 3D LED 131-lumen light I have, with new alkaline D cells installed, using a Fluke 75 multimeter. Tailcap current was 0.60 amperes initially, stabilizing at 0.55 amperes after about a minute. 0.55 amperes for 79 hours works out to 43 ampere-hours. Consulting performance charts published by Duracell company for their Coppertop - the cells I used for this test - I find that ampere-hour capacity for this cell peaks at about 14 ampere-hours
at a .25 ampere rate. At 0.55 amperes, the capacity is about 12 ampere-hours. I am using the discharge-to-1.0-volts curve. Discharging to a lower voltage, e.g., 0.8 volts, will stretch this a little, but not to 43 ampere-hours. Also, I suspect that as the cell voltages drop, the LED driver will pull more current to compensate, which would decrease the runtime somewhat.
Using the Duracell curves, I estimate 12 AH effective cell capacity, and about 19 hours runtime at .55 amperes, for this light.
Perhaps there was a transcription error when the tests were run, and 19 was read as 79??? Just a thought.
The 3D LED MagLite is a good light. It would be worth the time of someone who is so equipped, to verify, modify, or refute my findings.
Regards.