How much power can you shove through a single XML2 before the bond wires vaporize? Since that's what the picture in the OP shows, let's stick to that. Single XML2. How many watts?
Around 35 or so.
If you had a CPU that had a TDP of 35 watts at its maximum overclocked speed, would the thermal paste make any difference? If you move the discussion to a TDP of 200W, then I'll agree, the paste will make a difference. Because there is more heat that has to be moved across the junction. At the levels involved in flashlight stuff it just does not matter.
Comparing like-for-like, copper star, flat surfaces with proper contact, proper clamping force, you will not see a single lumen more with the latest carbon nanotube/diamond hybrid miracle paste than with plain white silicone based paste. Prove me wrong.
I don’t know about 12 amps to an xml2. I’ve heard some have acheived close to 9, I think.
Who was it here that was driving an emitter under water to very high amps for extended periods of time? I don’t know what he got up to.
Trying to solder the wire to the LED after soldering the LED to the post proved most challenging. A better method would have been to high temp solder the wire to the LED first, then low temp solder the LED to the post. This is not a low cost design-for-assembly option.
I have a technique to make that wire connection very simple. That is why I use solid 22AWG wire. It is already attached to the driver and can be bent to hold itself in place. A quick touch with a small tipped iron and a little solder; poof, connected. I do this with all my pills.
The idea is that surface tension of the solder on the stub will center the emitter… that is why I use the term “float”. This will avoid the shorts. The real challenge is removing the heat form the pill in time. I’m thinking water around the heating post once the emitter settles.
Many kudos for getting this to work on an XP-G, Crux! I won’t attempt that
I’ve been wondering this too. The XM-L has 3 bond wires and the XM-L2 only has 2. I suspect the XM-L has a little margin over the XM-L2 for max current if thermals can be managed.
We already know the failure point for XML2s; XML may be able to run at higher current, but it will put out less light and that's what matters, not how much current you can run it at. If you want max current and don't care about how much light it makes replace the LED with a little square piece of copper, you can run really high current with that setup.
35 watts is nowhere near 12 amps... that would require a LED that did 12 amps at 2.9 volts. Not gonna happen. And 35 watts is probably a bit higher than the actual limit, and less power makes the thermal issues even less critical, not more. You cannot put enough power through a XML2 for the quality of the thermal pastes to be an issue (again, just a reminder that we're doing this properly, so no aluminum stars glued to hollow pills in a plastic light).
MTG2 doesn't have bond wires to blow like little annoying fuses, but the light output still drops off above a certain point regardless of temperature (same way a CPU will have an upper speed limit no matter how extreme the cooling is - some of them won't go any faster at -30 than they do at +30). MTG2's upper limit is still not that extreme, at least not compared to CPU levels of heat vs. contact area. Above 12-13 amps it makes less light the more you shove through it. 12A x 7.6v = 91W.
Plus, depending on which host it's in the outer surface of the light and its ability to shed heat into the outside world will be the limiting factor, once that limit is reached improving thermal performance of the innards is totally pointless.
I was thinking 36V at 3 amps… . and I fully appreciate the limited return of photons. But pushing those bounds is what we are all about, right?
Who said this had to be a handheld? My boundaries are expanding
Even with the early works of the Q5 and the pushing the limits of the XM-L shows there is significant margin in the Cree designs.
Of course, optics are the next horizon, but maximizing an emitter at the bleeding edge is still a worthwhile challenge.
BTW: I did some looking on Noctigon and thermal conductivity. Do the Noctigons now have a coined heat pad or some other way to make it flush with the + and - pads?
I am not happy about the numbers for tin/lead as a thermal barrier. The early reports of varying gaps is somewhat disturbing. If you go through the math, thermal conductivity is indeed a significant factor as you go through the stack.
Seriously, I am not ignorant of all the ramifications of pushing the limits. However, I am well trained in the scientific method. Why in the world would you try to stifle creativity? I appreciate you sharing what is known… but there is a lot to learn with every new opportunity.
I'm not trying to stifle anything, I'm just telling you that what looks 'bad' on paper is not significant in actual use. You are falling for a type of logical fallacy - attributing too much value to things on paper that do not have an effect in real life.
Along those same lines, the different types of solder have been tested in real-world scenarios, not the world of datasheets and whitepapers, and the thermal conductivity of the solder alloy is not significant. It doesn't make any measurable difference. Folks here have even tested a correctly-manufactured direct thermal MCPCB with all the pads level (for the thinnest possible solder layer) against the knock-off copper MCPCBs that have a dielectric layer under the thermal pad, but with the dielectric cut away and the resulting huge trough filled with a much much thicker sub-optimal solder layer, and found they put out exactly the same amount of light.
Other people have already done this work and it's been checked and verified by others - why are you dismissing actual data in favor of math taken from datasheets?
If it makes an improvement it's a judgement call as to if the amount of improvement is worth the extra cost/effort; but how much are you willing to spend for zero improvement? This is not a matter of 'good enough' vs. squeezing out the last 10% of performance... there is nothing left on the table to pick up. It's not a matter of that last bit of performance not being worth the cost.
If 94 octane gas is good for a high compression turbocharged car then it should also be good for a 90hp 1.5L economy car too, right? That's the kind of faulty analysis of the data I'm talking about.
Once you have a MCPCB with no dielectric layer, and flat surfaces on both the MCPCB & pill, and some type of paste in the middle, it will not be any better in any way if you go beyond that. The boost to whatever you're imagining just is not there to be had! Doesn't exist!
Miracle paste vs. cheap paste, brass pill vs. aluminum pill vs. copper pill, direct-thermal MCPCB vs. emitter mounted direct to a pillar, none of those things will give any measurable change in the light output. For whatever reason you don't believe me, but this is not just my opinion, it's what has been proven in real-world testing of actual parts. I really suggest you gather up some of these parts and do your own testing, since you're not getting this for whatever reason. Please do test it, in no way am I trying to stop you from discovering anything new. It's already been checked and found there's nothing there once you go beyond a certain level of prep work & parts used.
Yes, try water cooling out and come back with the results please. Why not put an XM-L2 onto an already existing water cooling setup for a CPU and see what it does? Anyone done that yet? At least it would tell you if there’s any huge benefit. I am kind of doubting it will be enough of a benefit to be worth it. There’s always an upper limit, no matter what, but finding it can be something very individual and necessary. Sometimes one has to just try it all, to realize what the limits are and that’s all part of modding.
The difference between modding and real life, is 6 amps.
I like the questions you're asking NightSpy. I probably am missing some critical info because I don't think we know the limits for sure yet. The fantastic work performed by djozz and Match is much better than anything I could do, but the testing I have seen has been with very small samples and has sometimes been limited by available resources and imagination of the possibilities of the time. For instance. Match tested directly on copper like you propose in the OP, but he only tested up to 6+ amps. There are folks now pushing xml2 on copper emitter bases to around 9 amps now.
I think it is good to have people with different perspectives and knowledge bases to ask these questions and possibly design new tests or approaches. I hope djozz drops by to share his thoughts. He is by far the most qualified person I know of in this area.
Why not put an XM-L2 onto an already existing water cooling setup for a CPU and see what it does? Anyone done that yet? At least it would tell you if there’s any huge benefit. I am kind of doubting it will be enough of a benefit to be worth it. There’s always an upper limit, no matter what, but finding it can be something very individual and necessary. Sometimes one has to just try it all, to realize what the limits are and that’s all part of modding.