Here is a nice test on that same XML2 U2 1A emitter by Texas_Ace
How far you can go with increasing amps will depend greately on the ability of the host to shed heat or become too hot to hold too fast.
Really 3A is a good target to retain brightness. You may seen and read some of the D4 tests and reviews in TK’s thread. Some tests, I think was CRX, showed how a small 18350 had more output for the time the battery depleted. The LED will dim pretty quickly as it almost immediately heats up. May not be visible as you eyes are still in shock from the initial turn on.
Heat is the enemy and it need to transfer away fast. DTP or direct thermal path copper MCPCB are Key.
I always take apart a light to see the quality of the work. It is amazing the dumb stuff you will find. Contact to the MCPCB to the SOLID shelf in a light may be bad. You want full contact. I have seen the center of a machined shelf have a Peak in it that was poor machining finish. This raises the MCPCB off the shelf you loose contact and heat transfer suffers. I am pretty anal and check the contact pattern using a black marker. I color one surface usually the MCPCB, lay it in the head or pill. Twist it while applying pressure and you will see where the black marker is removed. Ideally all the marker is gone but that NEVER happens. I also hand LAP the two parts together to get the best possible contact.
Here you see the marker on the back of the MCPCB and where it rubbed off, also the 800 Grit lapping compound on the copper spacer.
After some lapping… getting better.
And the final result of both surfaces. When I solder the MCPCB into a pill or spacer I also immediately apply pressure to it as it cools. Removes as much solder or flux from between.
I love copper lights like the S41 and have soldered the copper MCPCB directly into the copper head of the light.
Here is a pic of an S41 head with solderpaste in it sitting directly in an electric burner, waiting for the Melt…
And here is a copper Tpad Quad soldered direbtly into the head. Hard to see but the is some solder oozing out the sides.
In an S2+ you can solder the copper MCPCB into the brass pill.
Sorry I didn’t really answer the questions directly.
But you have some things to consider.
Again I am Anal about a light I make or want to make a stock one better. Most guys will just scrape off the Point in the machining and apply a thermal paste they prefer to use.
I kinda posted this from your post in the “what did you mod today” thread… didn’t wanns go there in that thread. But helps you understand “Why?’ from the comments.
But still that light is Better than it started. Here in USA we have Copper one cent that were made before (I think) 1982. They are solid copper and I have sanded a few Flat and used them as spacers. I have also sripped the traces off a bare copper MCPCB, sanded it flat and clean to use as a spacer.