Something wrong with my Convoy C8+ runtime?

I have been performing runtime tests on my lights and noticed something curious. I purchased a sand color S2+ and C8+ a few weeks ago. Both are U6-3A XP-L HI with 7135*8 chips, I did the tests with the same 3500 mah Sanyo NCR18650GA cell. Runtimes were done with a fan blowing on the lights.

What I noticed was a lower runtime at ~100% brightness for the C8+ than the S2. What I’m wondering is why? As near as I can tell with the app I have around the same brightness between both lights - ~750 “lumens” at 100%. So I had assumed the runtime would be the same. Is this just normal variation? Or maybe the increased heat shedding ability of the C8? But wouldn’t I be able to measure an increase in corresponding brightness? I don’t think this is a real issue and I’m happy with the lights, mainly just curious and trying to increase my understanding.

Detail runtime for the first 35 minutes - the C8+ drops from 100->98 in the first 5 minutes, the S2+ goes from 100->96. Overall the C8+ starts declining output at 17 minutes, the S2+ at 31 minutes.


Here’s the total runtime graphs:



(I know the lights aren’t regulated, that was more a note for myself)

The regulation stops when the voltage at the driver input drops below the Vf of the LED at ~3A. The difference you see could be caused by slightly different LED Vfs (even though they are the same model there could be variation), different circuit resistances (different springs or bypassed), or slightly different 7135 chips which could have different resistances or even be slightly different currents. The temperature of the cell (affecting the internal resistance) could even make a difference.

Thanks for the response. I’ve been a flashlight hobbyist for a while but am just now really learning more of the technical side, lots of threads on this forum to help but a lot to learn still.