I guess that if the SST-50 in that build is a top-bin one, then 500 OTF would be possible w/ 1.8A.
I can assure you that it is! That is, unless my supplier flat-out lied to me, which is highly unlikely.
At 3.5A on the SST-50 the scaling factor appears to be roughly 1.8 (=180%). From my experiences with SST-50 so far, most WJ bin tend to sit toward the low end of the range for brightness... so at 3.5A, I would expect to see 500 x 1.8 = 900 lumens at the emitter. That seems entirely plausible given what BC was observing.
At 1.8A, the scaling factor is probably closer to 1.10. Assuming bottom-of-bin as above, that suggests 550 lumens from the emitter.
It's also likely the meter itself introduced some added resistance in the circuit, which means the actual current draw in both cases was probably a bit higher than measured... not dramatically higher, but a little. So both lumen ratings above are probably a bit low. In the case of 3.5A, the heat probably did de-rate the output... again, not dramatically, but a little.
My guess is that the heat kills the OTF lumens with the IMR cell... The flux ratings are at 25 degrees celcius.
I suspect at 3.5A that heat does play a role, but only minor... and whatever role it plays exists from the very beginning. The big drop from 1s to 30s is a lot simpler to explain than that: the IMR cell cannot sustain that sort of current draw for more than a few seconds before the voltage under load sags enough to bring down the current, and hence the output. That's supported by the discharge curve of pretty much any lithium-chemistry cell: in the first instants of the run, the cell's voltage drops my roughly 10% before settling into a very flat discharge for most of the remaining runtime. That's exactly what we see here.
(Also, for reference, Ni-Zns run about
1.7V each at 1.5Amp discharge. At 1.8Amps, it'll probably be ~ 1.6V each, just a guess. Looks like you have a low Vf emitter)
Thanks for the link to the graph! That's handy. :thumbsup:
The graph seems to show 1.6V for most of the cell's runtime at 1.5A discharge. I'd respectfully suggest that 1.8A pulls things down closer to 1.5V, although you're right, in the first seconds of the run your voltage guesstimates are probably about right.
Yes, the emitter has a particularly low Vf. That's no accident! With this Room Sweeper Special Reserve, as with just about all the builds in the Milky Labs, I hand-selected the emitter for best match to the light and its intended circuit (in this case direct drive) and power source. I design lights in terms of the overall system rather than a collection of individual components. Wrote a
very long-winded post about the design methodology years ago when I introduced the Project-M family.
Most important to me in this case: hope BigChelis likes his Room Sweeper!
!!!
Now; she said I better leave it with her. She 1st confiscated my M30 w/VME twistie keychain and now she is begging for this roomsweeper. 
