I modded a couple X60's for BLFers, but not sure what I did - probably swapped out the switch - that's what I usually do when I see a significant drop from it. My own stuff though always gets lowest priority - I never seem to get back to my own to improve it.
I don’t think a tail switch would matter though, current is the same everywhere in a circuit, if he measures 20A at the switch then he would measure 20A at the LED too.
It is the voltage that changes between components in series.
Thanks for doing the measurements, Tom.
The issue is that the circuit is altered when the current is measured. The tailcap and switch are removed and replaced with the current meter/shunt.
You’re right, that’s why I use a clamp meter, not sure what those guys used to measure.
clamp meter - UT210E
I think all the serious testers here use clamp meters (UT210E mostly) and wire. Anyone still running the circuit through a multimeter should know that they will never get accurate results (above a few amps at least).
The issue I’ve been talking about here is that the bypass used with the clamp meter can have less resistance than the tailcap/switch, so the current measurement can be inflated relative to what will actually flow with the tail cap in place. This is the opposite effect of what we see when people use ammeters with high resistance leads.
Yes and this is accepted.
Just like people using homemade “lumen tubes” as opposed to calibrated light spheres. You can only get so much accuracy because we are hobbiests, not scientists with a lab full of expensive testing gear.
So when it comes to factoring in the resistance of the rear spring and switch, I say as long as the spring has a bypass wire on it, a wire and clamp meter should not inflate the output by very much if at all. Maybe a tiny bit. This is the best we can do as hobbiests.
If you want to take it to the next level you’ll need to buy an assortment of common switches and springs and test equipment to put various loads through them and measure the output at various levels of spring compression and chart the resistance levels as more current is applied. You may also have to account for switch wear due the contacts creating arcs every time they touch and over time adding more resistance.
I think that is a bit overkill.
The context here is just that I was trying to identify any factors that might contribute to discrepancies between the output/current trends observed by djozz and those observed by the couple users who have measured the XHP70.2 in flashlights.
In this case it looks like the L6 switch is low resistance and so it is probably not the source of a big difference.
I don’t think that is a concern here, the point is that those guys did their measurements and found an increase in output from 15 to 20 amps while DJozz did not.
So whether the current is the same with a switch or not is not really relevant to the fact that there was an increase from 15 to 20A.
UNLESS they measured current and measured intensity at different times, which honestly wouldn’t make much sense.
Then you’re right, if they measured the intensity with the flashlight in normal condition and then used a bypass for measuring current then there could definitely be a difference in performance due to current.
Yes, this is what happened, as I noted when I first talked about this issue on the previous page.
AH i see now.
A method I like to use to determine actual current in setups that I can’t get a good measurement otherwise is a two step approach and does require a power supply and a bit of time, but results are as real as you can get when currents are as high as they are with the 70.2 and triples, quads, etc.
1.) Ideally while installed in the light/host, generate a Vf vs I curve. Do this by soldering on long temporary leads to the LED connected to a PS. For most accuracy record values at multiple times, for example: turn-on, 3sec, 10sec, 30sec, and 120sec. This will result in 5 different tables/graphs.
2.) Reconnect driver and then just record your voltages. You now have a look-up table to determine your current. Remember that LED temp will play into these numbers so make sure you match it to the right table.
Does anybody have a generic Vf to I curve for the 70.2?
Besides the one in the CREE specs? No, not that I'm aware of. Sorry, no time for setting something like that up, besides not knowing WTH I'm doing to accomplish that.... 
This is why I bought a led lenser flashlight for EDC.
I can choose between spot and throw and not have to deal with inconveniences of both at the same time.
This probably isn’t for you though, it’s far from cheap.
If you want more suggestions, instead of discussing it in this thread just make another topic 
@Jason:
*expensive does not neccessarily equal accurate, as I have found many times, and also the opposite I have often found: cheap and simple can be very accurate. Sometimes you can not get around an expensive component though 
*with these high currents, a (even well bypassed) tailcap can lead to significantly lower current than a thick copper loop, although I would be surprised if that is the 5 amp difference we are looking for to explain our differences.
I agree.
Maybe we should measure emitter temperature when we measure amp load and lumen output?
Maybe your emitter is getting much hotter as someone mentioned. Adding a temperature curve to the results might explain the drop in output your getting.
I forgot, did you reflow your 70.2 onto the mcpcb yourself? If not, maybe it wasn’t done well and there is too much solder paste in there with the emitter floating on top? Was this already discussed?
I reflowed it myself, and re-did it for the second set of measurements, I believe I did it well, there was enough solder and not a huge excess, and earlier tests did not find a measurable effect of thicker/thinner layers of solder between led and PCB.
Measuring MCPCB temperature would be a very nice addition to my test set-up, but it would add to the work-load of doing emitter tests. In practice that will lead to less emitter tests because I’m limited in hobby time and also the extra work will raise my treshold for doing tests, which is already higher than when I started doing them 
Djozz, you are measuring the current at the led? Right?
The others at the tailcap before a driver?
Maybe that can explain something.
With these high currents weird things can happen.