6x 20mm XML-ledboard comparison

Interesting.... Copper has such a small effect on output and thermal sag over aluminum? Hhmm.... Our custom made copper pills have more volume of metal than the stock pills, so the measured differences may be more related to total mass/volume as opposed to the source material, I suppose.

Then I'm a bit stumped. Where is that thermal performance advantage of copper going to? It's there I suppose, but such a small factor only at higher amps/temps.

That sounds great. Either djozz or relic38 would be great. Djozz didn't mention it in his post at the top of this thread, but he also stress tested a direct bond copper mcpcb for the Cree MT-G2. I think it'd be great if you could send samples to both testers if they're up for it, especially of that multi XML board since that may offer something that no one else does.

The graphic is a bit disingenuous, but it's minor compared to the results of independent testing. If the results are good, I'll be posting the test results in this forum and at least one other, not that misleading graphic.

I would think a thermal imaging of the emitters on the stars, with and without dielectric aluminum vs copper would be a good comparison

Heck I would like to see some of the homebrew budget mods on test as well (the ones where they drill out the aluminum under the star and install a copper slug from a wire)

It's a head scratcher, especially that dielectric that performed surprisingly well. As far as the metal of the pill and flashlight, I think it comes down to emissivity. I bet the best combination is something like this.

Use copper to quickly absorb lots of heat and conduct it to a layer of aluminum with lots of surface area. Maybe the current set up is good enough not to suffer significant sag, but this concept should increase comfort. Where lights typically only get warm around the pill, a longer copper sleeve would spread the heat more evenly throughout the body, which should decrease the heat felt at any particular area since there's more surface area of aluminum to dissipate the heat. Increasing contact area is already something lots of you guys do with P60's...and I'd do it too if I had any of those.

Don’t underestimate the heat SINKING properties of aluminium compared to copper.
You can put much more heat in a given mass of alu than in the same mass of copper, before it actually gets hotter / warmer.

I have tried to explain that one before, but there is the widespread misconception that more mass means more heatsinking. If you compare copper and aluminium by volume (that is what you do in practice when you swap aluminium parts for copper parts) the copper part does win for storing heat, but only by a factor 1.4 compared to aluminium (while it is 3.3 times as heavy).

I didn’t know copper is better per volume as a sink !?
Thanks.

1.4 correlates well enough with this data.

I don’t think we should emphasize mass too much, volume is the factor is most cases, unless you’re flying it to space or something. So copper still have the edge hands down in most applications.

Copper pills are highly overrated. Unless you believe in them. There seems to be many believers though. The measured differences are usually between zero to minor depending on the current in a typical XM-L2 hotrod build.. In a fully hotrodded MT-G2, there is more gain, due to having up towards 3-5 times as much heat going through the MCPCB and into the pill, but even then. Not really noticeable by eye..

If id had not been for the copper hype here on BLF, the difference between the best copper and aluminium MCPCB would`t be as shocking to some..

'Copper is better than ___!!!' has turned into some kind of cargo cult.'But I build all my lights with copper everything, and they are all really bright, therefore if you want it to be bright you have to use copper!'

The numbers just don't back up what you find in those thermal conductivity charts. They're irrelevant.

We've kind of blasted brass as being the worst thing possible, now sinkpad uses a 135W/m.K rated aluminum for those boards, most likely 5052 which is the most common specified alloy in alu MCPCBs, now we have the "poor" common brass at 125W/m.K....

Is there a chart anywhere that shows how many lumens per W/mK? No? Why not?

"My dog thinks that if he barks at a telephone he can make it stop ringing. Since the phone does eventually stop ringing, that proves he's right."

Outside flashlight world, brass is considered a high thermal conductivity material actually. Also I remeber 7075-T6 aluminum which is a really strong alloy also being kind of blasted for being only 135W/m.K rather than 160W/m.K like 6061-T6.

“My dog thinks that if he barks at a telephone he can make it stop ringing. Since the phone does eventually stop ringing, that proves he’s right.”
lol!

So never mind the artificial diamond then, the kind that conducts heat several time better than copper, yet does not conduct electricity.
I forget how it’s called…
It’s not even that expensive though.

No, if you're talking about what's right below the tiny little thermal pad of the LED, that's different. Much smaller area, so the material (or presence/lack of dielectric layer) does make a difference. But the contact area between MCPCB and pill, and between pill and light, is so much larger by a factor of whatever, that the thermal performance of the materials really makes very little if any difference.

It’s called CVD
You can even buy small discs via AliExpress.
No dielectric layer needed as it’s an electrical isolator.

The cutter MCPCB being discussed earlier uses a DLC layer to bond the copper traces on top (which will readily accept solder) to the aluminum substrate (which will not readily accept solder). If the base material can be soldered to directly, there is no need for a dielectric or any other kind of layer inbetween.

Is this a quote from somewhere?

Yes, but I can't remember from where. It's one of those things I stuck in my 'stuff I might find useful someday' text file and I didn't include the source.