Crash-testing a XM-L2 and a XP-G2 on copper Sinkpads

How many Amps does it take to vaporize Phosphor? :stuck_out_tongue:

My bet is, there’s some folks here that aim to find out! lol

Could a thin piece of brass sheet, or copper sheet, be curved into a “half pipe” then bonded in place over the connection points on either side of the gap using the liquid solder? Hmmmm…….

Ok, this really got me brainstorming….why couldn’t a thin strip of the very dome that’s been removed be sliced with an XActo knife to fit over the gap and cover the emitter side exposed plate so the liquid solder won’t short the 2 sides, then use the liquid solder in a solid sheet right over the top of the silicone strip joining the connecting plate to the die? The liquid has a tendency to pool, a needle point can be used to drag “traces” where they need to go. The material dries to a hard but not unbreakable solid, they call it a glue but it doesn’t have any real elasticity to it and will flake/break if stressed or pried on. I think it’s infused with graphite. It does stick fairly well, but not like an epoxy.

This could be used to re-enforce existing wires so they wouldn’t blow under higher amperage. Or so it seems to me.

Edit: For the record, the gap doesn’t need bridging as is evidenced on this XM-L, but the layout is different on the XM-L2 and I assume the XP-G2 as well. If the 2 sides cannot be connected, then this bridging method may work to provide an answer.

You know what? I was just thinking of the ' half pipe' and then I saw you writing it down :-) . It will be difficult still...

I guess there is a maximum current /die surface area, since the xm-l2 has a surface area that is about twice that of the xp-g2, I expect a maximum output at about 12 amps when the bond wires are reinforced so that they do not limit the current.

It’s a very thin liquid that sets up pretty fast. Easy to get it where it doesn’t belong, I’d guess. I have an XM-L2 I was thinking of de-doming, will see how it would work to re-enforce the bond wires on this bare sample.

I’m thinking that the dome top can be sliced off, then a secondary layer sliced to approximate the thickness of the die board and this layer used to cut the strip for the bridge. Then a light scoring of the remaining layer will facilitate the gasoline removal method for a clean de-dome in as short a time as possible.

Vinh Nguyens bare emitter heating then slicing method might be preferable here to soften the dome a bit for an easier cut.

Hey Ferb, I know what we’re going to do today…

(yes, I have a child that watches too much television)

Edit: Wonder if the thin copper sheet could be curve matched to the bond wires, then slid under them so as to allow a visual on the wires laying on top of their re-enforcement, then the liquid solder could fairly easily be placed atop the thin sheet of metal bonding the wires to it. Minimally invasive and least possible shadow thrown when the light is on.

I wonder if beefing up the bond wires would demonstrably lower Vf…something for Tom E to try for his monster C8 builds :wink:

very nice thread, ty djozz

Thank you very much djozz for posting all these. XM-L2s and XP-G2s are the LEDs that I’m currently very interested in and the information in this thread is just awesome. :slight_smile:

I just put an XP-G2 R5 2B on a 16mm Noctigon, with a huge aluminum heat sink and wired up to a Q-Lite 3.04A driver. With a single AW IMR18350 it will pull 2.99A. But stacking chips on the Q-Lite give it nada. No gains. Why is that? With 4 chips stacked and 4V reading on the AW , I got a Vf of 3.43V on the emitter. So why are the stacked chips doing nothing?

Maybe try a different battery. Voltage drop may be too much

I tried an 18650 Efest IMR, also an 18650 Samsung 20R. The chips didn’t allow extra amperage over the standard 3.04 board.

Therefore we can’t stack additional chips to the 3.04 Amp drivers? I’d better stay away from them then and use the old reliable 2.8 Amp Nanjgs.

Regular solder paste won't jump the gap between the anode and cathode planes on the substrate, even if applied across the gap it will separate when it melts. There's nothing in the gap it can stick to. The connection onto the die is the tricky part to deal with.

I did something similar lately: stacked 4 extra 7135's (380mA) onto a qlite (a very neat solder job I must say, the chips well heatsinked against the pill) and put it in a flashlight with a (dedomed) xp-g2, with a fresh cgr18650ch IMR battery. I expected about 4.5A, but I got only 3.6A tailcap reading (so without the switch resistance). So a bit more than the stock driver but not the full potential of the 12 chips. I did do all the possible resistance reductions, braided springs, thick wires etc. (I got 170klux throw out of the light, so I was happy anyway :-) )

Scroll up to post#55. You'll need a buck driver and 2 or more cells in series to go past what it will do in direct drive.

Ok, my driver wants to deliver 4.6A, to feed that to a XP-G2 it needs to deliver that at 3.8V (my own measurements). The driver itself eats 0.1V (or a little bit more?), so it needs at least 3.9V input. The cgr18650ch at 5A delivers that voltage only in the first minute (HKJ's measurements), so it does not stay in regulation very long . So yes, the desired 4.5A is a bit wishful thinking, but I could see that the first minute unless the switch eats away voltage as well (or in case of tailcap reading the DMM+leads). Pity, you are right comfy, I did not count on the higher voltage of the XP-G2, a XM-L2 needs 0.2V less for 4.5A current, so that should work a bit better.

I'm getting just over 4 amps on a Nanjg with 4 extra 350 7135's with a de-dedomed XP-G2 on copper. Also I've added 380 7135's stacked on QLite drivers - no problem. The Pana CH cell is good, but not as good as Samsung INR 20Q or 20R or SONY 30A rated cells. 4.5A may not be achievable though. Cells must be freshly charged - it ain't gonna last too long... I always pre-test my stacked drivers on a XML T6 mounted on a big heat sink to verify the amps it puts out -- much easier with XML's than XM-L2's because of the Vf issue.

Yeah using NCR-PD’s or Sammy 20R’s should help.

XP-G2 seems harder to push current through than XM-L2

Yes - and I swear de-doming an XP-G2 drives it up further - this has been noticed by RaceR86 too.

emitter magic!

It’s not an issue with stacking chips on a 3.04A driver, I have several that are doing just fine. It’s the requirements of the emitter itself that is causing the issue. It will take another type of driver running 2 cells to get the demands of the XP-G2 met with enough leeway to enjoy some run time.

Keep on keeping on!

Thanks Comfy, djozz, really appreciate the feedback.

You could build a test rig on an old heatsink with something otherwise useless, like a bunch of leftover XREs in parallel, that would be the right kind of load to let the driver run at max without frying anything. That would tell you if the driver is capable of doing what it should but not whether it will do that theoretical max on any one particular emitter.

For example two XMLs in parallel will run at ~5.7 amps direct drive off a cell that will only do about 4 amps direct drive into a single XML.