Thermal Compound - Results Posted

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NeutralFan
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Enderman wrote:
If he is measuring the body temperature of the flashlight then the temperature should be greater because more energy is being transferred to the body. The better the thermal path, the higher the body temperature should be and the lower the MCPCB temperature should be.

I agree with this and that was my rationale for the experiment. Assuming a better heat transfer from the LED MCPCB to the shelf using the dot method versus the spread method, I would expect the temperature to increase faster near where the shelf is located.

The driver was in direct drive turbo mode and the same battery was fully charged before each set of measurements.

I’d rather use my flashlight around the house than turn on the lights.

Jerommel
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Enderman wrote:
Jerommel wrote:
I don’t know how big the difference in efficiency between a properly cooled LED and a badly cooled LED can be.

Well unless you push an LED pretty far, it seems like the difference isn’t very significant:
http://budgetlightforum.com/node/53514
In those tests the thermal path seems to turn out well because the LED board is clamped down on the cooling body.
‘Bad cooling’ is not tested there.
But you can see the differences better in tests between DTP and non DTP boards.

2Q19

Enderman
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Jerommel wrote:

Well unless you push an LED pretty far, it seems like the difference isn’t very significant:
http://budgetlightforum.com/node/53514
In those tests the thermal path seems to turn out well because the LED board is clamped down on the cooling body.
‘Bad cooling’ is not tested there.
But you can see the differences better in tests between DTP and non DTP boards.[/quote]
Yeah but it’s still bad cooling, you do that to a computer and it will instantly overheat.
It’s just that LEDs don’t make a lot of heat unless you push them hard.
Lightbringer
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Enderman wrote:
Jerommel wrote:
I don’t know how big the difference in efficiency between a properly cooled LED and a badly cooled LED can be.
Well unless you push an LED pretty far, it seems like the difference isn’t very significant: http://budgetlightforum.com/node/53514

I was going to point to the powder-coated S2+ thread, but… Big Smile

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NeutralFan
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I was a little surprised by the results. It makes sense that the middle dot method is preferred for applying thermal compound. After all, the spread method can lead to air gaps which is not good. I only measured the temperatures up to 4 minutes since I was genuinely concerned that the LED would get too hot if I went longer. I did not want to damage the LED due to not applying the thermal compound correctly.

Was the time I spent to change out the thermal compound worth it? In hindsight I would say no. But since I didn’t know, applying the thermal compound the correct way gave me piece of mind. That in itself is worth the hour or more I spent on this.

Perhaps with a more powerful flashlight the results would have been different, and probably even more critical on a computer CPU, but it appears that the 2 methods I used to apply thermal compound was equally effective.

Here are the results again from the surface spread method:

  • Start – room/flashlight temperature at 67 degrees Fahrenheit
  • 1 minute – 84F
  • 2 minutes – 95F
  • 3 minutes – 104F
  • 4 minutes – 113F

Here are the results after I used the middle dot method, look familiar?

  • Start – room/flashlight temperature at 67 degrees Fahrenheit
  • 1 minute – 84F
  • 2 minutes – 95F
  • 3 minutes – 104F
  • 4 minutes – 113F

Thanks to all that gave their predictions and knowledge about thermal compounds. I took a thermal dynamics class back in college, but that was many years ago and I don’t recall any mention of thermal compounds. Certainly many of you have a lot of knowledge about this and I continue to learn from BLF.

I’d rather use my flashlight around the house than turn on the lights.

chinooker
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some of the best negative results I’ve seen lately
acutely portended by most
so as long as the surfaces are flat, then it’s superfluous to add compound?

clemence
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The only reliable way to measure a miniscule thermal difference vs LED junction temp is to monitor LED voltage by at least 3 decimal digits. This is one of the simplest method used by advanced LED driver to regulate temp or to maintain true constant brightness/power.

Enderman
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chinooker wrote:
some of the best negative results I’ve seen lately
acutely portended by most
so as long as the surfaces are flat, then it’s superfluous to add compound?

With low power stuff like most LEDs yeah.
If you’re like me with an XHP70 at 12A making 100W of heat, then no you certainly need thermal paste to keep the LED from melting.
There’s no harm in adding thermal paste though just to be sure.
Rufusbduck
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At the very least it will indicate how well the two surfaces are mated or whether there’s a lip on a wire hole, a screw hole, or the center is high. It’s all to easy to declare something proven yay or nay, it’s another to go deep enough to understand what’s really going on and be able to explain it. It may be the case that the host temp is almost identical but a variation in thermal transfer could mean a still small but more readily detectable difference in mcpcb temp simply because the energy not transferred is left focused in the much smaller mcpcb rather than spread throughout the host. It’s the same effect we see in the difference between DTP and non DTP save that it’s much more crucial at the heat pad solder point because the heat is even more focused there in the die. DTP copper is much more forgiving but it doesn’t mean you can take the next transfer completely for granted. At some point a poor thermal transfer will show up as diminished output, it may take higher current but that’s why we use DTP in the first place and why some go to the extreme of soldering mcpcb’s to heat sinks.

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Scott

tekwyzrd
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My prediction was based on my experience with thermal compound used mounting heatsinks to cpus. I’ve tried both spreading a thin layer using a plastic card (credit card, id, driver’s license, etc) and the ‘grain of rice’ method and found that there was little difference in the effectiveness even with heavily overclocked multi-core processors. This goes back to the days of good old 400MHz celerons oc’d over 1GHz on a dual processor board to more recent and more modestly oc’d core processors like a core 2 duo rated for 2.4GHz at 3.6Ghz. Using the same compound and heatsink the cpu temp was within a few tenths of a degree under heavy load (running a boinc app on all cores).

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Fasttech – recommended for buyers who like to wait long periods with ever changing arrival dates for items that were ‘in stock’ when ordered.

Rufusbduck
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It’s likely that in the case of cpu heat sink and thermal pad assembly the manufacturers are a bit more diligent about surface prep than the run of the mill light manufacturer. I daresay that a similarly poor standard of prep would result in more than a few tenths difference, especially if no thermal compound were used or so much that a bad fit was not apparent(both of which are common enough with lights). Granted, the majority of flashlights don’t push the limits nearly as far but it’s just common sense to increase the scrutiny as you increase the power.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

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Not entirely surprising, keep in mind, we only see up to a 5-10c difference between best and worst with computer heatsink pasting, and that’s pushing up to 600 watts of heat through a 2×2 inch square.

It’s never a bad idea to do it the best possible way, especially when it’s cheaper and faster though.

snakebite
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since the hot spot is the center of the mcpcb the dot in the center is best.
you want just enough to spread well but not make a mess or waste compound.putting the dot dead center ensures there is enough in the critical spot.
if you do that any differences are so far “down in the noise” that its not worth worrying about.
making sure the surfaces are flat goes further than obsessing on compound anyway.

The Miller
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And now a third test
This time,
Check with a new razor blade if the surfaces are flat, if not, no test dab thermal grease as you like you’re done Smile
If flat use a very little paste on both surfaces but spread it and then swipe with something flat (like that new razor blade slightly tilted away from cutting edge (so pull backwards so to say)) and get rid of all paste except the little bit that is filling the gaps it is supposed to fill (this is mentioned before in this topic)

This should be the best methods for it is only there where needed, I dislike the dab-push methods a lot for less is more and the obky way to be sure allnis covered is if it bulges out the sides, so one always have to use too much.
On CPUs using a credit card or something and spread so fine that the markings on the CPU can be seen then cooler pressed down with some wiggle before tightening is the best way to go and very easy, half a grain of rice sized for those large CPUs and a led star is much smaller.

NeutralFan
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It’s pretty bad when I’m spreading cream cheese on a bagel at work this morning and started thinking that it looks like thermal compound filling in all the holes and crevices! Too much cream cheese is not bad in this situation.

I’d rather use my flashlight around the house than turn on the lights.

NeutralFan
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chinooker wrote:
some of the best negative results I’ve seen lately acutely portended by most so as long as the surfaces are flat, then it’s superfluous to add compound?

Please see my Thermal Compound – Another Experiment post for another experiment I performed comparing no thermal compound versus using thermal compound. I think applying thermal compound is beneficial for any flashlight and is critical for higher powered flashlights.

I’d rather use my flashlight around the house than turn on the lights.

NeutralFan
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The Miller wrote:
And now a third test
This time,
Check with a new razor blade if the surfaces are flat, if not, no test dab thermal grease as you like you’re done Smile
If flat use a very little paste on both surfaces but spread it and then swipe with something flat (like that new razor blade slightly tilted away from cutting edge (so pull backwards so to say)) and get rid of all paste except the little bit that is filling the gaps it is supposed to fill (this is mentioned before in this topic)

This should be the best methods for it is only there where needed, I dislike the dab-push methods a lot for less is more and the obky way to be sure allnis covered is if it bulges out the sides, so one always have to use too much.
On CPUs using a credit card or something and spread so fine that the markings on the CPU can be seen then cooler pressed down with some wiggle before tightening is the best way to go and very easy, half a grain of rice sized for those large CPUs and a led star is much smaller.

I think I’m done with my testing. It seems to me that there would only be an issue in a flashlight if no thermal compound was used or if too much remained between the surfaces.

I’d rather use my flashlight around the house than turn on the lights.

Umpi2000
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Reviving a topic but will Thermal compound like Cooler Master MasterGel Pro CPU Thermal Compound work? I’m trying to find the right stuff in SA but it’s not that easy check their specs please for me http://www.coolermaster.com/cooling/thermal-compound/mastergel-pro/

Texas_Ace
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Honestly for flashlight usage the thermal paste you use really doesn’t matter that much. As I showed in some tested I did with proper clamping force even no thermal paste at all preformed within a few lumens.

The thermal paste just makes it a lot easier to get the best results.

I generally just use whatever I have laying around, the white silicone based paste works fine for most things.

I have switched from that to AC5 when testing LED’s before and saw virtually no difference in the results.

Even on computer CPU’s thermal pastes generally only change the temps by a few degrees.

Umpi2000
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Texas_Ace wrote:
Honestly for flashlight usage the thermal paste you use really doesn’t matter that much. As I showed in some tested I did with proper clamping force even no thermal paste at all preformed within a few lumens.

The thermal paste just makes it a lot easier to get the best results.

I generally just use whatever I have laying around, the white silicone based paste works fine for most things.

I have switched from that to AC5 when testing LED’s before and saw virtually no difference in the results.

Even on computer CPU’s thermal pastes generally only change the temps by a few degrees.

Thanks TA appreciate the info Smile

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