Great tests
So not a great deal of difference so long as the star is nice n tight.
Dont suppose you want to repeat the test with the star soldered do you 
Not being a real modder, but every (MC)PCB that comes out of the bag takes a turn on the lapping-stone. A tiny bit of thermal paste and then some wiggling until the paste emerges on the side. The screws are used for positioning the led.
Interesting test.
Did you heat cycle the AS5 or give time to allow it to cure per the instructions?
Nice job! Interesting to see how much AS5 actually helps.
The light I have in which I noticed the paste the most is my modded Sunwayman C10R . The light started as a 1xCR123 light with electronic side switch. I modded it to triple XPL HI and upped the battery to a much larger and longer 18500. I replaced the stock driver with an e-switch FET driver from Mountain Electronics.
To make room for the longer battery, I placed the driver above the LED shelf, then sat the triple copper Noctigon above the driver. I used a strip of copper bent into a c-ring to keep the star elevated at the right height.
Naturally in that configuration, heat is an issue. This is a triple with FET driver and at max power with an IMR 18500 it pulls serious amps. The only heatsinking is where the sides of the star touch the head and where the edge of the bottom rests on the copper c-ring. There is no heatsinking at all below the center of the star. Like a hollow-pill but worse, because there isn’t even a built in ledge for the star to rest on.
I found that without any thermal paste, the wires to the star in the modded light would desolder themselves in about a minute when turned on turbo even with 30 second rampdown to 50% power. To fix this I liberally spread AS5 between the C-ring and head, and where the star contacts the C-ring and edges of the head. Problem solved! The head gets hotter much faster and the wires to the star no longer desolder themselves no matter how long I run the light.
Good subject and test, thanks…
Well, to me, the reason to use thermal paste is many.
It will more or less help negate all but the worst non flat shelves and star boards.
If one sands the star and shelf flat, and uses a coarser grit sand paper/crocus cloth on glass, or better yet, a coarse flat stone, this makes for more surface area from the coarse sanded pits and crevices, for better heat transfer(only with thermal paste). The pits and crevices, thermal paste will fill in all those crevices/scratches and transfer heat well with more surface area to dissipate/absorb heat…
So don’t worry about getting a perfectly smooth glass like surface, not needed. Flat, yes, get it as flat as possible.
JFYI,
I’ve seen tests in other thermal applications, of perfectly machined flat smooth surfaces compared to coarse perfectly machined flat surfaces, both with thermal paste, and the coarse(scratched) surface wins out…
On the lights with 2 screws on opposite sides, imo be careful of over tightening the star board and warping it out of flat…
All thermal paste is not created equal, some works much better than others in my experience (in other heat transfer applications), but any paste is always better then none. The correct application of these thick expensive pastes is critical for best heat transfer. Not always true, but usually you get what you pay for with thermal pastes. The very cheap stuff not as good.
ARCTIC MX-4 is my favorite, not electrically conductive like arctic silver and its cheaper then AS5.
jmo
Nice test, so with a single die led you can’t go wrong under 4 amps, hence the carelesness when mounting leds of most manufacturers
Correct me if I am wrong, but “IF” I am reading the T_A graphs & sac02’s summary table correctly, there is very little difference between “thermal paste clamped hard” and “thermal paste left loose”.
And both of these were at the top in results.
Am I reading and interpreting this correctly?
.
Great testing as always T/A! I hate thermal paste for the same reasons! I take the time to flatten and lap surfaces together whether it takes days,hours or minutes and use just a see thru ultra light swipe across the star surface of paste, then after centering and tweaking, heat cycling, lock the screws down or if I have enough clamping force between bezel, reflector and star, its good enough! Enough clamping force means I can smack the light against a thinly padded board and not loose focus! 
I’ve mounted many CPU:s during the years and learned a thing or two:
- Never reuse thermal paste
- Clean surfaces carefully before applying
- Apply thin and even
- Avoid bubbles at all costs (a small blob in the center that expands when the mounting force is applied often minimizes the risk of bubbles)
- Make sure that the force of the cooler’s mounting springs is high enough
- Thermal paste is absolutely essential
To be fair CPUs have something like 125w TDP, XPL2 is like 10 watts lol.
True, but the principle is the same, just even more critical.
Only 8 degrees difference between the very best-rated thermal compound, and lipstick toothpaste or diaper ointment. I don’t think the brand of thermal compound used matters that much.
Thank you.
Facts are highly appreciated.
Great work.
I’d like to see an added comparison, with the MCPCB soldered to the pill.
Solder has always seemed like the best thermal transfer material, to me.
Do note that this table itself does not say anything about boundary conditions, i.e. surface properties like roughness and presence of radius of curvature. It is interesting to see the difference between an arbitrary compound and not having any thermal compound (second from bottom); roughly 35 vs 62, which is quite a difference.
Think about how entertaining your flashlight will be when you tell your friends it was assembled with used diaper ointment! :sunglasses:
Exactly…. this would be the ointment of choice as far as I am concerned……
Aww…… :weary:
You did the test first!
Great job BTW :+1:
So Tex, our gut feeling was telling the truth. Not much different results from not usng any paste.
I still prefer the least amount of my trusted moly-graphite bearing grease and a fine lapped MCPCB (and base/heatsink whenever possible).
- Clemence
Correct!
But not many people realize the big picture. They get bullied by the upper rank brands. Good for marketing 
When you enter the realm of crazy high TDP and cooling solutions sucking the heat away like beeeeeeeeeeeeeeeeep, thermal paste differences are way more noticable.
But for our flashlight uses, it’s a moot point.
IMO, that chart is misleading at best, for us.
Its for cpu/heatsinks… not exactly the same parameters for flashlights.
A properly cooled and assembled cpu might have what ? a .0001” (or less) of TP film between it and its heat sink. Where as most of our off the shelf flashlights are no where near that thin a tp film, of course depending on who put the light together and if it was ‘worked’. Many of us never even check star boards/shelfs/pills for flatness in our modded lights… TP has a bigger job then.
I have commonly gotten copper/alum stars that have a potato chip warp giving many thousands of an inch gaps in the thermal path. Without correcting those gaps(flatness) in these stars/shelfs, I have reservations that .003”(or more) of lipstick filling those voids will transfer heat the same as AS5.
For us, in the flashlite hobby, star boards and their shelf, are not always made perfectly flat like cpu and cpu heat sinks, that are machined flat and smooth. And many times flashlights don’t have similar clamping force as cpu heatsinks. Commonly cpu’s have very very thin film of thermal paste in contact areas. And thin thin or no voids filled with anything (toothpaste.?) is a lot less critical then a gap 100 times or more that size, that must be filled with tp in many lights…
The less expensive TP do work, but tend to be thin and runny vs the better TP that are thick and have better heat transfer properties. The better TP being thicker are harder to apply correctly, but in our tests in the process cooling industry the better TP’s do work better.
That being said, if a star and shelf are perfectly flat and smooth (like a cpu&its heat sink) even with no TP but clamped tight, there will be good heat transfer with a solid path that TP might only help minusculely in those situations in our flashlight application.
Hence the 8° difference in your above TP CPU/heatsink chart. So the job of TP is to fill voids and still create good heat transfer thru the voids. If the voids are small or non-existent then tp has very little to do. If the voids are more substantial like in many of our lights, tp has a bigger job to do that a good quality thick tp probably will do better than diaper ointment…
jmo