So 2.6A / 3 = 0.87A, sounds reasonable. But, The battery is still being drained by 2.6 amps, right? So 2.6 amp draw on a 2000mAh cell isn't going to last very long, right? Can I guesstimate 2000mAh (battery capacity) / 2600mAh (current draw) at 0.77hrs ~ 45minutes? I thought others were getting over 1hr 15mins. Perhaps on models not being driven as hard?
And the "divide that by around 3" - is that because the boost circuit is boosting by about a factor of 3?
-Garry
That is partly correct. I do not measure tailcap current, especially not on single 1.5V cell lights, that would give a huge error.
Instead I prefer to do this kind of graphs:
The problem with just measuring tailcap current is that you do not know what voltage the light gets, this depends on the battery and on the meter and probes and even 0.1 ohm is very significant at 1 to 1.5 volt and 2 ampere.
The red curve clearly indicates that amperage (measured at some point in the circuit) is neither a linear curve (a straight line with constant slope) nor constant. If it was constant, we could multiply it with a factor and then guesstimate either the brightness or the runtime.
In all of HKJ's red graphs we see that a regulated light doesnt have a constant current at any time, since with time the voltage decreases and amperage has to go up to maintain constant power ( P = U * I ) which is related to brightness (e.g. proportional relationship, P ~ brightness ).
My new DMM has a data cable for PC connection (serial/USB-port) and comes with PC software. I could collect continuous data of amperage over time and get the red graph. But that's about it.
Game over kreisler!! 
could you link the meter you got?
no, to you, thanks
although HKJ has probably commented on his equipment before and I'd like a link to that, too 
edit:did it come w/ serial to usb?
you're not hijacking Garry's thread are you lol?
the shipment is in transit, so i have no practical clue. but here 2 helpful links:
tear down thread ( many people there interested in this multimetro digital económico ;=)
I do not believe I have posted my typical flashlight measuring setup or what equipment I usual uses.
For light meters I uses 3 different:
The Extech HD450 can directly be connected to a computer, the Tecpel 530 can be connected to a DMM and the AEMC CA813 has the best precision.
These 3 meters are the ones I usual use, each has some capabilities, the others do not.
When doing voltage sweeps or heat test I uses this monster power supply to power the lights (Sorry about the bad picture, but the power supply is busy with a battery test).
Most of the equipment can be computer controlled and I have written my own software to handle all the equipment simultaneous, where I have scripts for different tests.
most impressive (and thanks for all!!!)
you invest and work and publish, and i s*cker read, enjoy and profit.
life is unfair 
bookmarked! i'm drooling
I have a decent (i think) multimeter w/ temp, several cheap ones, a great hobby charger, a poor light meter and an old used 12V controlled? power supply lol
but I'm headed in your direction. I think the power supply would ideally be next, since that is a huge gap, but I'm scared to ask what one like yours cost, and it will take me awhile to learn enough to where I'll be comfortable deciding how much to spend anyway 
I doubt Gary minds...but the topic, of your equipment and procedures, really deserves its own thread. If you haven't posted it before, you're either to modest, or two busy having fun w/ all that stuff!!! But, it would be very valuable to those of us that would like to advance our level of testing and development...
How dare you take my thread off topic!!! Just kidding, although this kind of information can be lost because people don't know it's contained in an off-topic thread. I often wonder if I am missing something important / interesting when I pass over a thread due to the topic not interesting me.
-Garry
I paid around $2000 for that power supply, but then prices are extra high in Denmark. That power supply is dangerous, especially on manual, just touch the voltage button and you have fried a light.
I do also have a smaller version of it, that I uses at one of my battery test stations (you can see it here).
If I had wanted a power supply without computer control it would have been considerable cheaper (I do have some of these also).
I hope to write something about that sometime, but I always wants to do more than I have time for. But, at least, I have written about how I do charger tests and battery tests.
I think there is some confusion in this thread regarding battery draw. When you measure the amps at the tailcap with a reliable multi-meter, what you are seeing is REALLY what the battery is discharging at that moment.
True, some of that voltage doesn't get all the way to the emitter, but it is definitely coming out of the battery, and I think you can estimate run-times pretty accurately based on what you see, as long as you take into consideration that output will drop (as seen on the graph above) specific rate as the battery capacity gets lower.
At the very least, it gives you an idea what kind of stress your driver is putting on the battery. I think we all saw that with Foy's first reviews of the 980L, and all the resulting driver failures that ensued. His tailcap reading were the primary reason why I didn't buy that light.
HKJ - I really like the clamp/leads idea. I have 5 of those hanging overhead at my vice and that has never occured to me, despite fiddling with lots of inferior methods I think I'll do the same thing but maybe fasten one end to the wall.
It looks like your smaller version runs $600! That's a lot of money, but much more obtainable than $2k lol
thanks for the info - I should put a picture of that thing in my wallet as a reminder of what I could do if I stopped spending impulsively lol
Measuring tail cap current is extremely useful. I can't believe you haven't found it useful before?!
It gives you a very good indication of expected runtime. Without the fuss of sitting there with a light meter logger or sitting there watching with a stop watch!
Just saw this. I measured it once, and it wasn't nearly as high as your figures. I will check it again and post back, also compared to my other SK-68s. The "campingsurvivals" SK-68 has been shelved as a backup. I dislike it compared to my others, mostly due to the tailcap and overall build quality.
i will measure tail cap currents as soon as i receive my ordered multimeter (DMM, uni-t). then we can see how reliable those measurements are in comparison to real runtime tests :)
as we know, tail cap current is dependent on voltage (i.e. time). on a fresh battery the current will be low. when the voltage begins to drop, the current begins to rise.
if you use your measurements along w/ the info for your battery type from this link
you'll probably get a good estimate of runtime
the graphs show how terrible alkalines are at 'high' current
I just measured tailcap current on the three SK-68s that I currently have available.
Tomtop-
14500: 1.9A
AA alk: 1.05A
Silver Sk-68 branded:
14500: 1.9A
AA alk: 1.05A
Campingsurvival:
14500: 1.7A
AA alk: 2.4A
So yes, the Camping survival light certainly had a driver that behaves differently than my other SK-68s. It doesn't seem any brighter on AA than the others. I also ran all three on my desk with AA for over an hour and there was no discernible difference in light ouput at an hour so I stopped that test. I don't know enough about flashlight drivers to know what this means or why the tailcap current would be so different on this light with AA battery compared to other SK-68s.