Convoy S3 - highest continous current?

On any of the single cell small pocket lights. Threaded pill, integral shelf, fins or no fins, doesn't matter.

I only use cheap white MG Chemicals silicon-based paste in the big bulk 10oz tube... I keep going on like a broken record about how at these power levels the Miracle Homeopathic Nano-Quantum Astrology Paste doesn't perform any better, but nobody wants to hear it.

It’s impossible to have a sane conversation on this since neither side has empirical data. Or has that changed?

EDIT: Added my emphasis in the quote in case it wasn’t clear what I was referring to.

You can kill a LED on a non-direct-thermal aluminum MCPCB with a single cell even if said MCPCB is bolted to a 16-ton piece of copper.

I'm tired of trying to convince you guys that the blue sky is really blue, and not green. Sure, whatever, Tinkerbell is real. Happy?

Which do you think would make me happier, data or Never Never Land? The best data we have so far is from tests like this one by pflexpro, which does not directly address this topic.

Yes, good thread, unfortunately Fujik vs. solder is not the kind of thing I am advocating, not at all. Why do my arguments always get twisted around to "ha! he thinks we should all be using lights made of Fujik, asbestos, and styrofoam, lol!"

Look at that and then explain how you get more light with excellent thermal paste under the star vs. average thermal paste under the star. The farther you get from the source of the heat the larger the contact area, which makes each joint less and less critical.

The substrate is pretty good stuff, but it will always be compromised since it also has to still be an electrical insulator.

But still, if there's no heat sag, how is a copper pill or better paste going to make more light come out? If the Tinkerbell theories are correct, why does a light with an aluminum pill and crappy paste not show any significant dropoff over time? The initial output is going to be the same no matter what since none of the downstream parts are saturated yet, right? So where in all this is the extra light output supposed to come from?

are there any tests showing difference in emitter temps on copper star vs. Aluminum star? I’ve got some emitter l emitters on aluminum so it would be good to know what are the max currents/temps involved.

I had some trouble following what you are saying in post #25. I’ve previously read djozz’s post you linked to. I glanced over it again just now. I’m still not really clear about what you want me to be looking for over there. Do you have a specific thing you want me to observe at that link?

[I understand the exact nature of what you are trying to express *and I think that it is incorrect.* I think I made a clear qualification when I linked to pflexpro’s post. It had nothing to do with twisting around what you were saying.]

Not sure if applicable for flashlights, but here’s my experience with different thermal pastes:

When I was younger I was really into the self built gaming computer thing. When a high power processor, specially a video card was overclocked and pushed into high loads it produced an insane amount of heat, and can only lowered to decent temperature by the use of a water cooling system or a huge copper-base heatsink with massive fans.

When upgrading from a ceramic based compound to a high-silver one, I noticed up to 15° C drop at high loads. This drop might seem small but it gives plenty of room for overclocking.

BUT, we are talking about a processor which is much more sensitive to temp changes with an area much larger than any LED MCPCB, instant temperature raise on load, it could be idle @40° C and only seconds later at 90° C, this is really when the thermal compound plays an important role. A LED in the other hand is far less complex (greater heat tolarance) and doesn’t heat up as fast.

I have many times intentionally and unintentionally left a light on the highest setting and get an actual burn when touching it, and never killed one, or permanently reduced its output.

So in flashlights, I do think different types of thermal compounds makes a small difference, but in most, if not all cases these differences are so tiny that only exists in paper.

If this is really the case? Why do we all obsess and observe measurable differences when using AL vs CU mcpcb? (Same goes for water blocks and heatsink a for computers.)
Fast heat or slow heat aguement makes no sense to me, it needs to get out.
Even when your computer is idle at 40C, it would be more like 45C if you used cheap thermal paste or applied too much, or had a poorly lapped heatsink, or a small fan, bad enclosure ventilation, etc.

It’s all part of a system that works together and every part makes a difference all the way to the end.

The faster the heat transfer, the better it is for the emitter, driver, CPU, ram, north bridge, caps, whatever it is.

When talking about thermal paste in a flashlight, yes it’s further down the line after the mpcbs, but it doesn’t mean that it doesn’t make a difference.

To each their own thoughts about the subject really.

End rant.

The heat flux, or density - amount of heat load x contact area - is what's being completely ignored here. At low densities the quality of the paste becomes less critical. Down at the ~15 watt range, with a 16mm or 20mm dia contact patch, the paste's quality is irrelevant. If the cheap paste fills the voids, and doesn't dry out over time, it will not get any better than that with better paste. It just is not stressed enough for the on-paper advantage of the better paste to ever show up. Raise that to 200 watts, with a 1cm square CPU die, and the quality of the paste can be the difference between stable operation and failure.

Data is worthless if it is not applied to each situation correctly. Context is everything. I am not saying that emitter junction temperature is irrelevant. I am saying that the parts downstream of the LED's thermal pad, once the MCPCB dielectric is eliminated, can be really really poor and still be good enough to keep the junction temp low and stable - because the contact area between those parts is so large.

On paper, different solder alloys have very different thermal conductivities. As do different solder layer thicknesses. Yet, there is zero change in light output between 'bad' 63/37 PbSn and 'good' SnAgCu solder, or between a thick layer and a thin layer. How can this be, if these things 'really do make a difference'? If that were so, and these details resulted in a meaningful difference in junction temperature, wouldn't the 'good' setup give more light output? Why doesn't that happen?

Just some info I found around the net…

Socket 1156 Intel I5 960 45nm Package size: 37.5mmX37.5mm
CPU die size: 296mm(2)
CPU to heatsink contact area: +/-30mmX30mm
CPU to heatsink contact area: +/-900mm(2)
CPU power stock: 95Watts

All this adds up to about 9.5mm(2) per Watt through the thermal paste if using the CPU cover to calculate Watts per area.
Or 3mm per Watt through the thermal paste if using CPU die size to calculate Watts per area.

Cree XM-L Package size: 3.75mmX3.75mm
Emitter to MCPCB contact area: 3.75mmX3.75mm
MCPCB to Pill contact area (16mm star): +/-200mm(2)
Emitter power stock: 10Watts

All this adds up to about 20mm(2) per Watt through the thermal paste

Pushing an XP-L to 6 Amps would get it to 10mm per Watt through the thermal paste.

To further discuss…
I am not accounting any heat losses through other means… but it does show that you may be totally right comfychair. But then I think about that huge fan blowing air right on the CPU heatsink cooling it down way faster than the body of a flashlight ever could.
I am not saying that cheap thermal paste is not up to the job, just saying that to my limited knowledge, it could possibly make a difference.

I think people are getting confused on the idea of the difference between pastes at this particular scale and thickness is not enough to see, and confusing it with the idea that “there is no difference at all” between pastes.

3.04 Amp.
If you find that too hot in your hand or just too bright for a small flood EDC light, then 1.48 Amp works as well.

Running the LED at 20 or 30 watts doesn't mean you have 20 or 30 watts of waste heat to deal with, LEDs aren't 1.5% efficient like Peltier coolers...

Using even Cree's overly pessimistic "75% rule" makes the picture of what the system has to deal with even easier. I think it's plainly obvious this is the explanation for why there's no difference in light output between a thin brass pill, an average aluminum pill, and a completely over-engineered copper pill. At these power levels this stuff just does not matter.

And... there's one joint in the system we can't modify, the joint between the die & substrate and the conductivity of the substrate itself. I know Cree uses material in the substrate that's as good as they know how to make it with current technology, but it still has to be an electrical insulator first, and then a good heat conductor second. Good electrical insulators are usually poor thermal conductors. And the area between the die & bottom of the substrate is the smallest of all in the thermal path, therefore it's the most critical to overall performance, and there's nothing we can do to get in there and improve it. If the bare die were mounted direct to copper, then the other stuff downstream might become the new bottleneck... but as it is now, it's just not. The bottleneck is right there under the die.

I'm so confused from reading this... I haven't seen or heard of any comparative tests on pills for junction temps or resulting lumens. This thread by pflexpro seems to be the best/closest thing around. It does seem to indicate that junction temp and resulting lumens output are dependent on materials in the thermal path, even after the pill. So, is that test not realistic or am I mis-understanding something?

Fujik is not thermal paste, no matter how carefully it's used! It's a completely different category of stuff. If that were an extremely detailed comparison between solder and an asbestos shim, would it be wise to use that data as a meaningful picture of how well solder performs?

Or maybe, a comparison between Fujik & asbestos. Would you use that test to decide you should use Fujik because it did so much better in the test?

comfy - who is this directed to? I linked the P60 wrap test thread.... Nothing to do with thermal paste whatsoever - it's more about materials - copper foil, alum foil, copper tap, alum tape, etc.

Sorry, we were discussing this one earlier, I assumed it was the same thread.

As for the wrap tests... in my opinion, too many variables I don't feel were taken into consideration.

Much the same as the silicon carbide potting issue. If epoxy + silicon carbide works better than no potting at all, that doesn't tell you anything about the role played by the silicon carbide, since there's no comparison to potting with epoxy alone.