Indirect measurement of efficiency or LED current is not the way to go. Is it 80% or is it 85% is all ?????. Who knows.
It's possible that your DMM sense resistor could be causing the regulator to fall out of regulation. A lot of DMM use a fairly high value like 1 ohm for the high current range.
It's possible that without the DMM in the tailcap it could be delivering 1A to the LED as expected. Since it is hard to derive from a tailcap measurement I would suspect the setup to be part of the measurement error.
It's always best to measure the current to the LED. Since you say you have two that measure the same I would suspect that both are doing exactly what they should be doing. I'd have a hard time imagining that two SOB1000 are both identically wrong.
My recommendation is to always use a bench setup and test the converter with the LED on the bench where the current to the LED is easier to measure or get to. After bench testing you can button it up and know for certain what it is doing.
I have a drawer full of different LEDs mounted to a heatsinks for this specific purpose. It allows me to hook them up to a converter on the bench and then measure with extreme accuracy what the current to the LED is.
Wayne
Thank you again for your help.
If the SOB fell out of regulation at the start, wouldn't it run DD, and thus I would expect even higher tailcap current draw? I tested with 4xDuracell123A, and 2x(AW16340, IMR16340, and AW17670).
For clarification, I wasn't trying to back estimate SOB efficiency. I was just trying to get a seat of the pants estimate on what might be going on with the LED and SOB.
The specs for my meter claim 0.1V drop on the 10A DC scale. I suppose that could make a difference for the 2xLi-ion case, especially combined with other system resistances like the springs, the SureFire body contacts, etc. But the 4x123A case should be at at lest 10V input.
Note that in my tailcap current measurements, I remove the SF tailcap and complete the circuit using the DMM, touching one probe to the bottom battery contact and the other probe to the unanodized contact of the SF flashlight body at the tailcap threads. Thus, the tailcap is not in the circuit during my DMM measurements.
The DMM accuracy specs for DC current are fairly poor at +/-(2% + 10 digits), which can add another few hundredths of an amp error.
I believe that my estimates of battery voltage in are reasonable (~10V for the 4x123A and ~7.6V for the 2xLi-ion). At the measured tailcap currents, I get about 6W power from the batteries, ignoring any SOB efficiency issues. Unless the Vf of the MC-E ie exceptionally low, for 1000ma out of the SOB and 500ma to each MC-E die, I estimate Vf to be around 3.3V giving a total voltage drop of 6.6V from the LED. That gives 6.6W of power to the LED. Hard to do that if you deliver only 6W to the SOB unless efficiency is greater than 100%.
I specifically tested 4x123A to try to avoid "running in the margins" in terms of voltage headroom to run in regulation. I would think that 10V nominal for the input voltage should be more than enough. But I measured only 0.6A at the tailcap.
I suppose we can do a crude sensitivity analysis. Assume that Vbatt is closer to 10.4V-11V, not the 10V I've assumed for 4x123A. Then for 0.6A at the tailcap, power to the SOB could be 6.24W-6.6W. Suppose we factor in DMM measurement error (I'm going to ignore the 0.1V DMM voltage drop for the 4x123A case). That could add about +/-0.02A for the measurement error. That gives about 6.45W-6.8W power (assuming the error is +0.02A, not -0.02A).
Now if the MC-E Vf is very low at 500ma per die, say 3.1V instead of the 3.3V I assumed, then I need to deliver 6.2W, not 6.6W to the emitter. Then the tailcap draw has to be at least 0.62A, and now we are in the regime of the DMMs accuracy specs. If the SOB is running at 90% efficiency, then I need 6.89W from the batteries, which is still close to the 6.8W figure in the previous paragraph.
Also, my initial comparative lux measurements for the MC-E tower (before I did any DMM current measurements) vs some of my other lights, plus my visual perception of the light output from this MC-E tower in a SureFire TurboHead, had made me believe I was getting full light output. The tower really lights up a room.
I did measure the current to an emitter that I thermal epoxied to a heat sink -- a Cree P4 taken from an old Chinese drop-in for a SureFire 6P (intent was to use this Cree to test for function, not to test for accurate drive current -- I may have to set up another LED for that). I got something like 0.54A, which I thought was so far off that I dismissed it as setup error due to my skinny hookup wires (maybe 6"-8" long for each) used to connect the 2x16340 to the SOB 1000. The hookup wires have alligator clips on their ends, and I use small magnets to stick those clips to the battery + and -. The 16340s are also connected via a small magnet.
I also have about 2"-3" of 26 gauge stranded wire soldered to the Cree, each terminating in a spring-loaded test clip. Unfortunately, no specs on the test clips. They are the type that use a little curved metal tip to hook a wire or component. The spring action then pulls the metal tip back into the test clip to hold the wire or component in place.
I measured the current to the emitter by placing the DMM in series between the LED+ lead of the SOB and the LED+ lead of my test Cree.
So I guess after all of this long-winded discussion on my part, I am tending to believe that all is well and that small differences in the various values used in my calculations could add up to give an erroneous conclusion. I guess what still gives me some slight pause is my Cree P4 bench measurement.
Do you think I am off-base anywhere in the above discussion?
I may try one more build using an SOB 1200 and see what I measure.
