# Aluminum vs Copper vs Brass



## 350xfire (Oct 3, 2010)

Guys:
I am about to start building some SST 50/90 stuff and have noticed some using copper heat sinks. I have also noticed the big difference in price from copper to aluminum...

Is brass a good alternative to copper or not? Reason I ask is I have some laying around.

Is anyone making off-the-shelf copper heatsinks?


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## Connor (Oct 3, 2010)

The thermal conductivity of brass (~115 W/(m·K)) doesn't even hold up to pure Aluminum (237). 
Copper has 401 W/(m·K) and is the best choice for SST 50/90s.


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## 350xfire (Oct 3, 2010)

Connor said:


> The thermal conductivity of brass (~115 W/(m·K)) doesn't even hold up to pure Aluminum (237).
> Copper has 401 W/(m·K) and is the best choice for SST 50/90s.


 
That's what I needed thanks


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## PCC (Oct 3, 2010)

(Here we go again... :wave

There has been a lot of discussion about the relative merits of copper, brass, and aluminum as used for heatsinks. The conclusion that I came up with is that copper is best used when you are pushing the design of your light or the LED to the extremes. This is because C110 copper has roughly twice the heatsinking ability compared to aluminum. C110 copper (99.9% pure) is roughly half the cost of C101 copper (99.99% pure) but that 0.09% difference accounts for C101 copper being roughly 4% better as a thermal conductor. So, if you have a small heatsink and want more but cannot use more material due to size limitations then use C110 copper instead of aluminum. Likewise, if you are pushing an emitter really hard (or run multiple emitters hard) then copper would be a better choice. Don't forget that copper is much heavier than aluminum, so it will increase the weight of your light. In the 3D DD SSR-90 light that I built for BC the two inches of copper weighs about 1 lb (2.2kg). Brass is pretty close to copper in weigh by volume, I believe, so it, too, will add weight to your project. I'd rather use aluminum over brass any day due to the weight issue and, more importantly, the thermal performance is lacking compared to aluminum.


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## unterhausen (Oct 3, 2010)

if the copper is going inside an aluminum case, then the advantages steady-state are much diminished.


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## PMM (Oct 3, 2010)

Its a daft analogy IMV

Greater importance is the designs ability to radiate the heat away.

If you don't shift the heat be it ALu or Cu whatever slug you use will heatload to the point you will have a temp overload.

Copper is a better transferrer of heat
Aluminium is a better radiator of heat

Neither are any good unless you design to transfer that heat out to the air.


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## 350xfire (Oct 3, 2010)

PMM said:


> Its a daft analogy IMV
> 
> Greater importance is the designs ability to radiate the heat away.
> 
> ...


 
Ok this will be for a dive light application in maglite head and a single sst 50 or 90.
Thanks


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## Mick (Oct 3, 2010)

For very good heat transfer from the SST90 emitter you can solder the device to a copper heat spreader, then use Arctic Silver compound between the copper and the aluminum housing. I use an Indium solder that melts at 135 C and solder the wires with lead free that melts at 230 C. This way the leads will not fall off when attaching to the copper heat spreader. The Indium solder has a much better thermal conductivity than Bismuth low temp solder. (19 w/mK vs 73 w/mK). Arctic Silver epoxy has a conductivity of 7.5 w/mK so the Indium solder connection is ~10 times better at heat transfer.


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## wquiles (Oct 3, 2010)

Mick said:


> For very good heat transfer from the SST90 emitter you can solder the device to a copper heat spreader, then use Arctic Silver compound between the copper and the aluminum housing. I use an Indium solder that melts at 135 C and solder the wires with lead free that melts at 230 C. This way the leads will not fall off when attaching to the copper heat spreader. The Indium solder has a much better thermal conductivity than Bismuth low temp solder. (19 w/mK vs 73 w/mK). Arctic Silver epoxy has a conductivity of 7.5 w/mK so the Indium solder connection is ~10 times better at heat transfer.



Very interesting - thanks. Can you please let us know which specific Indium solder you use (part #, model, etc.) that has the low melting temp?

Will


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## Mick (Oct 3, 2010)

I need to clarify a couple issues on the Indium soldering. I got most of my technical info from: http://www.indium.com/ but I bought the solder from: http://www.micromark.com.
The reason being Indium Corp appeared hostile to small users; they wanted to sell me a sample kit for $350. I think they are used to doing business with the Govt where the price is no object.
The solder I got from Micro-Mark is called TIX and is made by Allied Mfg. Co. in Bozeman, MT. I do not know the alloy composition. I had trouble finding them on the web so I don't know the exact thermal conductivity but guessed from info on the Indiun Corp website.
According to an engineer I emailed at Indium Corp it is not recommended to solder directly to copper with Indium solder as a brittle alloy is formed.
Ref: http://www.indium.com/techlibrary/applicationnotes.php
See: http://www.indium.com/_dynamo/download.php?docid=14
Indium/Copper Intermetallics

I solved this problem with a nice Nickel plating kit from Caswell:
http://www.caswellplating.com/kits/plugnplate.htm
I bought the optional pen wand with the dome point and it work great. It takes about two minutes to plate just the area that the SST90 thermal pad will sit on. Then everything is OK to solder with the TIX Indium solder. I used the TIX flux also.

I will try to do a nice "Will" type tutorial on my method in the near future.


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## wquiles (Oct 3, 2010)

Mick said:


> I will try to do a nice "Will" type tutorial on my method in the near future.


Thanks - that would be awesome!

I recently did solder an SST-50 directly into a custom copper heatsink, and although it took a couple tries, I was able to solder the two power wires from the sides (while the emiter was in place!):












So that you are doing is of a lot of interest to me as that would have made my life easier for this custom project I am working on :thumbsup:

Will


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## Mick (Oct 3, 2010)

Here is a photo extracted from the Alibre CAD of a SST90 sitting on my copper heat spreader. The wires get soldered first then the LED gets placed in a jig with the copper disk on top. The wires are in the grooves, This unit is then flipped over and placed on a hot plate to re-flow the Indium solder. Pardon the salmon colored copper. LOL 






assembly:


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## 350xfire (Oct 3, 2010)

Cool 3D stuff!!!
So question becomes- if I use a copper heatsink, the heat will initially be dissipated quick until it hits the aluminum, right? Once that happens the aluminum's thermal characteristics will determine how fast total heat is dissipated... So, is it even worth using copper on an aluminum based head? Especially on a single LED light?

Thanks for all the discussion guys!


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## Mick (Oct 3, 2010)

The copper conducts the heat rapidly away from the small thermal pad on the led then spreads the heat out over a large surface area into the aluminum. This improves the thermal path to the outside of the aluminum body where it can be removed by radiation and convection. A better explanation would require math and an understanding of thermodynamics. If your really interested a good book is Heat Transfer Engineering by HilbertSchenck,Jr.


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## precisionworks (Oct 4, 2010)

The P7 Mag from Mac had the emitter bonded to a huge copper sink, and the SST-50 Catapult V2 uses a "2 oz brass PCB". Gene Malkoff has always used a thick brass shell (although I don't know how his thermal path from emitter to shell works).



> is it even worth using copper on an aluminum based head? Especially on a single LED light?


Way back when, meaning two or three years ago, there were few power LED's available. Most emitters were running in the 1 watt or 2 watt range. Then Cree brought out the X-Lamp and everything changed.

I can't remember the amp draw on the P7, but the SST-50 Catapult V2 measures 1700 mA @ 8 volts. That's *13.6 watts*, from an emitter driven at a moderate level of 3500 mA. I spoke recently to a modder that's running an SST-50 at 5000 mA drive 

My best guess is that a good thermal path is critical to long emitter life when the light level exceeds around 50 lumens OTF ( roughly 75 bulb lumens). Most everything today pumps out way more than that


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## UnderTheWeepingMoon (Oct 4, 2010)

precisionworks said:


> Way back when, meaning two or three years ago, there were few power LED's available. Most emitters were running in the 1 watt or 2 watt range. Then Cree brought out the X-Lamp and everything changed.



I think that heatsinking has been a concern for longer than the the introduction of the X-Lamp. The old Luxeons had prodigious cooling requirements. If anything, the X-Lamp reduced the need for heatsinking because of its improved efficiency, although it's true that we drive LEDs much harder these days than we used to, with better electronics available.

I think you're right in that we saw many improvements in heatsinking about the time that the X-Lamp came out and a movement away from the use of plastic in LED lights. Some old Luxeon lights still had pretty impressive heatsinks by today's standards, though, such as this one by Icarus.


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## precisionworks (Oct 4, 2010)

> 4xUWOJ LuxIII emitters sit on a custom copper heatsink with individual McR-20 reflectors


Yow 

I had no idea the Luxeons put out that much heat.


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## Mick (Oct 4, 2010)

This is a Lumen / Watt definition from the dept. of Physics, University of Georgia.

*Luminous Flux *

The radiant power is the total radiated power in watts, also called radiant flux. This power must be factored by the sensitivity of the human eye to determine luminous flux in lumens. The standard definition is as follows:






As you can see a incandescent bulb is horribly inefficient at 2.5%.
A LED that produces 100 Lumen / Watt would be about 15% efficient. So 85% of the applied power is lost as heat. The incandescent bulb radiates much of this lost energy as infrared radiation. A LED does not emit infrared so the heat must be removed by the heat sink / light body.


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## archer6817j (Oct 4, 2010)

We are just talking about the ability to dissipate a given amount of heat over a given amount of time right? So, wouldn't an ice cold aluminum heatsink (maintained at that temperature) potentially dissipate more heat than a copper heat sink at room temperature?


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## 65535 (Oct 5, 2010)

Well yes, but only because of the high temperature gradient in the material.

You'll notice the units for thermal conductivity contains, temperature, distance, and energy.


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## MikeAusC (Oct 5, 2010)

archer6817j said:


> We are just talking about the ability to dissipate a given amount of heat over a given amount of time right? So, wouldn't an ice cold aluminum heatsink (maintained at that temperature) potentially dissipate more heat than a copper heat sink at room temperature?


 
What sort of light will have it's heatsink maintained at 0 Deg C ?


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## HarryN (Oct 5, 2010)

MikeAusC said:


> What sort of light will have it's heatsink maintained at 0 Deg C ?



A light in MN.


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## MikeAusC (Oct 5, 2010)

HarryN said:


> A light in MN.


 
But only after midday in July.


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## PMM (Oct 5, 2010)

Is it your intention to directly solder heatpad of SST90 to copper heatsink ?
or just thermal adhesive / paste 

If soldering.. I would go Copper as long as you clamp well & paste the copper to aluminium bond tight the heat spread to the out Alu shell will be more desirable.

However if you using std paste/thermal adhesive I would go fully ALU because your introducing 2 layers of thermal loss through the paste/adhesive so using ALU you limit that hopefully to 1.

Alot of older (Pre-heatpipe) computer heatsinks were mix metals Nickle plated copper base press forged into an Alu Base/fins to gain best of all senerios.

My experiences with CPU cooling shows that thermal paste and applied pressure >50lbs play greatly in optimising heat transfer... something like egraf graphite thermal pads may be better but your want 70-90lbs clamping still.

If you going to use a paste / thermal adhesive "Arctic Alumina" is a better choice over Artic Silver it works better with lower temperatures which you may have if using in a Dive Light.... If temps are still likly to be high esp if overdriving the LED you maybe better off with something like Innovation cooling IC Diamond 7 or 24 but again decent clamp pressure needed.

Thermal paste is not for plugging large gaps but more micro scratches / pits you design so 2 surfaces can be as closely joined as possible with the maximum pressure possible then the TIM((thermal paste) is as thin as possible thus allowing maximum transmission of heat.

So the mating of all joining surfaces need to be as good as possible else your just you introducing barriers to the thermal flow... less barriers the better but if you can't get away from it tight joins/good clamping pressure & good quality thermal paste.


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## MikeAusC (Oct 5, 2010)

PMM said:


> . . .
> However if you using std paste/thermal adhesive I would go fully ALU because your introducing 2 layers of thermal loss through the paste/adhesive so using ALU you limit that hopefully to 1.
> . . . .


 
I don't understand. 

No matter in which part you use it, Copper will ALWAYS deliver less temperature difference (so reduced temperature at LED) than Aluminium.


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## archer6817j (Oct 5, 2010)

I should have said "ice cold" instead of ice cold  I'm just taking theory. However, in a practical application (say a dive light) having a copper heat sink may not produce performance that is "significantly" better than an aluminum heat sink, given that it can conduct to the water.


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## Slartibartfast (Oct 5, 2010)

I went with C101 for the heatsink for my SSR-90 build. Thin layer of AS5 between the star and the copper and between the heatsink and the body of the [email protected] So far so good.


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## unterhausen (Oct 5, 2010)

MikeAusC said:


> Copper will ALWAYS deliver less temperature difference (so reduced temperature at LED) than Aluminium.


I botched my previous comment, but this is what I was trying to get at. Let's say your aluminum is in ice water and your copper is buried in insulation. The led attached to the aluminum is going to be cooler than the led attached to the copper. If the copper is not allowed to conduct the heat away to somewhere else, then it's not going to out-perform an aluminum heat sink that is conducting the heat away. Since each interface between materials introduces some inefficiency, it may be the case that a solid aluminum heat sink will be better than a copper heat sink attached to an aluminum heat sink.


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## PMM (Oct 6, 2010)

MikeAusC said:


> I don't understand.
> 
> No matter in which part you use it, Copper will ALWAYS deliver less temperature difference (so reduced temperature at LED) than Aluminium.



I mean pretty much what 'unterhausen' mentioned.

If your using a Copper slug and mounting to Alu then your using paste twice LED to copper slug & copper slug to Alu sink.

Because the metals are not one the paste is a thermal barrier to the flow of heat and if your not clamping above 50lbs with close mating surfaces you may as well just opt for the one metal Alu.

Copper is good at absorbing and conducting heat but not so good at radiating that heat away into another body.

End of the day you have to still move the heat out of the copper into the Alu if that is not efficient no point having the copper in place it will either equalise out with the Alu temp within reason remember heat only flows from a warmer to colder surface or if the joins between mating surface are naff you may see elevated die temperatures and a need to run at a lower current to avoid thermal stress on the LED.

In a dive light certainly the best design option is getting the water as close to the LED cooling plate as possible and flowing to extract the heat away as close to source as possible.


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## archer6817j (Oct 6, 2010)

In terms of bonding the copper to aluminum, has anyone tried shrink fitting a copper slug into an aluminum shell without thermal paste? So, a copper cylinder with say a .001 interference fit...heat the aluminum sink to expand it and put the copper slug on ice to shrink it...then mate the two together. Assuming the surface finish on both parts is very smooth, this might be the best way to get a lot of contact area instead of say gluing the bottom of the copper to an aluminum sink with thermal epoxy or screwing together with thermal paste.


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## Mick (Oct 6, 2010)

http://www.customthermoelectric.com/TIMs.html


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## tylernt (Oct 6, 2010)

archer6817j said:


> In terms of bonding the copper to aluminum, has anyone tried shrink fitting a copper slug into an aluminum shell without thermal paste? So, a copper cylinder with say a .001 interference fit...


Oh yes the friction force for interference fit is quite high. I imagine that'd make a lovely thermal connection with no paste etc. Case in point, I've seen more than one computer CPU cooler with a copper slug pressed into the middle of aluminum fins.


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## 350xfire (Oct 6, 2010)

That is what I usually do. Build the heatsink to fit a mag body pressed in. Then use my hydraulic shop press to press it in!


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## precisionworks (Oct 6, 2010)

> has anyone tried shrink fitting a copper slug into an aluminum shell without thermal paste?


Even a tight press fit (Class V) doesn't assure full contact between surfaces. The problem is that most surfaces are far from smooth, with a typical machined finish measuring about 120 Ra. A very fine machined finish will go about 60, rough grinding will yield 30, fine grinding at 15, super fine grinding 8, near mirror at 4, full mirror at 2.

Press together a pair of parts, both having a 2 Ra finish, and there is nearly 100% contact. Press together a pair of "average" machined parts having 120 Ra & 25%-45% of both surfaces might be in contact.






The photo above clearly shows this. The aluminum sleeve (that looks like it has fine grooves) was finished as nicely as possible on my lathe. Slow feed, enough DOC to engage the nose radius, fast rpm, lots of lube, etc. Looked like a 60 to me. Pressing it into the quill (that had just been bored) shows how rough the surface really is. I would guess the contact between those parts, which was a tight fit requiring a 5# sledge for assembly, might be 30% to 40%.


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## Mick (Oct 7, 2010)

The thermal compound will also prevent any galvanic corrosion between the dissimilar metals. Press fit if you like but also apply Arctic Silver 5.


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## tylernt (Oct 7, 2010)

Mick said:


> The thermal compound will also prevent any galvanic corrosion between the dissimilar metals.


I thought galvanic corrosion only happened in the presence of water or other electrolyte? There might be a little water vapor between the pressed parts, but not much...


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## MikeAusC (Oct 7, 2010)

PMM said:


> If your using a Copper slug and mounting to Alu then your using paste twice LED to copper slug & copper slug to Alu sink..


 
There is a very small area behind the LED where all the heat has to pass through - you might have a 5 degree drop with copper, but an 8 degree drop with aluminium.

Hopefully the interface from copper to the alumium slug will be large and this may only add 1 degree drop.


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## MikeAusC (Oct 7, 2010)

PMM said:


> . . . . Copper is good at absorbing and conducting heat but not so good at radiating that heat away into another body . . . . .


 
But it's easy to surface-treat or coat any metal to make it as good as the best.

There's thread here somewhere that documented tests on this.


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## CKOD (Oct 7, 2010)

PMM said:


> Copper is good at absorbing and conducting heat but not so good at radiating that heat away into another body.


 
A very small portion of the heat dissipated for our purposes is removed via radiation. Most heat would be removed by conduction and convection, and the difference between aluminum and copper should be minimal also in regards to cooling from radiation. 

There are a lot of theories and stuff about aluminum and copper mixed, and why they use it in commercial coolers.

Aluminum is lighter, cheaper, and stronger in some alloys/forms hence why it gets used. In some situations, the differerence could be only academic. (Where thermal conductivity of the metal isnt an issue, and surface of the heatsink is the determining factor of the steady state temperature) 

When pure thermal performance isnt the sole design factor, and cost, weight, strength, ease of manufacturing, durability, start coming into play, thats where aluminum takes the lead. You see copper slugs set into aluminum heatsinks because at the source of the heat, where there is a high temperature gradiant, and high "thermal density" (unsure of the actual term... Watts per mm^2) the advantage of the copper is significant. Once the highly conductive copper spreads it out, and you just need bulk surface area to get rid of the head, aluminum is the most cost effective option. 

Now, lets see some of the CPF manufacturers start friction welding some copper heatsinks into an aluminum body for the best thermal transfer across the parts


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## PMM (Oct 7, 2010)

MikeAusC said:


> There is a very small area behind the LED where all the heat has to pass through - you might have a 5 degree drop with copper, but an 8 degree drop with aluminium.
> 
> Hopefully the interface from copper to the alumium slug will be large and this may only add 1 degree drop.



Would you be surprised if I said you could experience 3deg+ alone at surface joins with differing brands of paste even at clamp pressures as high as 70psi which I can tell you that you won't be having with an SST90 led  on the bare emitter because the bare emitter will snap been there done that  so you could experience 6-10 deg additions per surface join area.

Have to admit never tested a sink without paste... good link above to the tims but I am going to be nit picky  in reality 2 surfaces will only touch at the 3 highest peaks so contact point is actually alot less there is a great IBM document on surface contact that is a really good read.

I have a testdie simulator at home for computer heatsinks capable of 0.001 deg resolution though I admit 0.01 is more than enough and have done some work recently comparing thermal pastes as test data for supplier of thermal paste... bit of an eye opener.

The delta-t of a computer die can be as high as 15-20 deg over ambient with low clamp pressures and cheap generic paste compared to a top brand paste clamped at say 70psi giving 8deg difference at a 45watt heatload.

Compound failure in notebooks (drying out/pumpout) of TIM has seen delta-t differences as great as 30deg when a quality TIM is reapplied.

That's food for thought.. a Power LED really is not that different from a CPU.


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## MikeAusC (Oct 7, 2010)

PMM said:


> Copper is good at absorbing and conducting heat but not so good at radiating that heat away into another body.
> .


 
Standard Emissivity tables suggest that in real-world situations, there is little difference between Copper and Aluminium.

HIGHLY POLISHED - Al 3 times better
Aluminum, highly polished and degreased 0.027
Copper, highly mirror polished, 0.008

POLISHED - no difference
Aluminum, semi-polished 0.05
Copper, polished 0.05

OXIDISED - little difference
Aluminum, anodized 0.776
Copper, oxidized 0.65


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## 350xfire (Oct 8, 2010)

MikeAusC said:


> Standard Emissivity tables suggest that in real-world situations, there is little difference between Copper and Aluminium.
> 
> HIGHLY POLISHED - Al 3 times better
> Aluminum, highly polished and degreased 0.027
> ...


 
Interesting!


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## precisionworks (Oct 8, 2010)

The problem with highly polished aluminum is that oxidation starts immediately when the polishing operation is finished 

I would guess that a highly polished aluminum slug, plated with electroless nickel, and polished again might be an excellent thermal conductor. 

Taking that one step further, electroless nickel immersion gold plating (ENIG) might be even better. A thin nickel layer is applied to the part, about 3-6 μm, followed by an even thinner gold plating of .05 μm. Sounds like a good project for WQuiles


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## turbodog (Oct 8, 2010)

precisionworks said:


> The problem with highly polished aluminum is that oxidation starts immediately when the polishing operation is finished
> 
> I would guess that a highly polished aluminum slug, plated with electroless nickel, and polished again might be an excellent *thermal conductor*.
> 
> Taking that one step further, electroless nickel immersion gold plating (ENIG) might be even better. A thin nickel layer is applied to the part, about 3-6 μm, followed by an even thinner gold plating of .05 μm. Sounds like a good project for WQuiles




Conduction does not equal emission. See below.


***

Standard *Emissivity *tables suggest that in real-world situations, there is little difference between Copper and Aluminium.

...

***


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## turbodog (Oct 8, 2010)

PMM said:


> Its a daft analogy IMV
> 
> *Greater importance *is the designs ability to *radiate the heat away*.
> 
> ...





I don't know the percentages, but I'd be willing to make a major bet that conduction to air/water/your hand/etc dwarfs radiant emission of energy from an led based, metal bodied light.


If *RADIATING *the heat away is so important, why are you mixing that up with *CONDUCTING *the heat into the air?

 


That's what I love about these heat transfer threads. There's so much great info mixed with so much wrong info.


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## Epsilon (Oct 10, 2010)

I've expirimented with and built a lot of different types of cooling on computer systems. From simple aircooling with relatively small heatsinks and jet-like noisy fans to water cooling, peltier cooling, dry-ice cooling (-80C /86F) and even phase-change type cooling (like refridgerators) at -55C / -60F.

*Radiation* of heat is as


MikeAusC said:


> Standard Emissivity tables suggest that in real-world situations, there is little difference between Copper and Aluminium.
> 
> HIGHLY POLISHED - Al 3 times better
> Aluminum, highly polished and degreased 0.027
> ...


stated, not really different from copper to aluminium. And is just not enough to keep the light cool, unless you can spread the heat to a large enough surface area (pumping heat with liquids or liquids/gas like in heatpipes).

In terms of *Conduction,* the facts are easy (~220 for alu ~370 for copper), copper wins by a mile. Silver (~400) and special Silver/Copper alloys (up to ~500) are even better, but more expensive. And after the metals you arive at very exotic (some engineered) carbon based materials (like diamond). But, cheaper solutions like heatpipes as used in CPU coolers nowadays are 50 times more "conductive" as copper.

The formula of heat transfer by *convection* is a Q = k * A * dT

k is a factor which depends on the coolant, surface type etc. A is the area and dT is the time.

k is more or less set. The materials used are fixed, the coolant is fixed and the finishes are fixed (design of the light on the exterior). The surface area is one of the factors that you can change, by for example, making fins of the normaly smooth maglite head. Or, conduction the heat to a larger area (like the handle).


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## MikeAusC (Oct 10, 2010)

Epsilon said:


> . . . . But, cheaper solutions like heatpipes as used in CPU coolers nowadays are 50 times more "conductive" as copper. . . .


 
I can't agree more ! I'm just assembling my SST-90 searchlight and for the first time ever, I'm using a Heat-pipe heatsink. It's a two-tube CPU cooler rated up to 60 watts.

The LED mounts on a copper block 30x30x5 and I'm amazed how cool the LED stays even with no fan running.

I've mounted the Thermistor from an LCD Thermometer on the LED, so I'll be able to see how hot it's getting.

I'll post photos next week.


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## Epsilon (Oct 11, 2010)

Very interesting project!

I will be trying to make my own heatpipes soon (1/4" tubing filled with water + vapor). Which when flattened, can fit in a Mag-D when there are 26650cell in there too.


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## MikeAusC (Oct 11, 2010)

If you want the tubes to work as well as commercial pipes, you need to treat the inside of the pipes to encourage capillary action to return the liquid - 

- grooving on inner wall
- sintered liner
- braid

The Heatsink I used is a "Zerotherm Atom 30H" - it was on special under $30 from iibuy.com.au because no-one uses low powered CPUs anymore (<120watt !!!).

I no longer have to specify that it's $Aus - because for the first time in 25 years, it's about the same $US and $Cdn !!!


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## turbodog (Oct 11, 2010)

Epsilon said:


> Very interesting project!
> 
> I will be trying to make my own heatpipes soon (1/4" tubing filled with water + vapor). Which when flattened, can fit in a Mag-D when there are 26650cell in there too.



You need a liquid which boils around or below your target temp. Drawing a vacuum on the tubing helps also.


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## wquiles (Oct 12, 2010)

The one area I feel is important that has not been addressed yet is: what happens to the heat/energy that has been moved away from the "hot" LED by the heatsink? Answer: it keeps raising the temperature of the body/light until an equilibrium is found, or until you can't hold to it any longer and have to turn it off, or until the LED self-cooks itself and dies from too high a temperature. Even for a large size light (say 3D Mag size), the longer you run the high power LED, the higher the temps will get, since we lack the active cooling of fans that help CPU heatsinks achieve lower temps. 

Anyone what has held any small/medium LED light with more than 10-15 watts knows this - the body of the light gets warmer and warmer, until it gets uncomfortable to hold. Those 3x P7's or 3x MC-E, or the SST-90's being driven hard (close to 8-9 amps) are the worst offenders - most builder/owners admit that after 5-10 minutes they can no longer hold on to the light - it is too darn hot, regardless of the heatsink used!.

My point is that although it does help to have a good, efficient heatsink design to remove heat from the LED area, unless you have a way to remove heat from the body of the light at the same rate it is being generated, you are still going to have to deal with a body that gets hotter and hotter with time. 

The fact that we can use a supper duper, highly efficient" heat-pipe system to move heat away from the hot LED into the body of the light, only helps in spreading that energy into the mass of the light - it does not help eliminate the energy fast enough.

The time before this high power LED (again 15+ watts) becomes too hot to handle is directly proportional to the mass of the light in question and the amount of light exposed (surface area) to air (lest efficient since we don't have fans) or your hand (most efficient until it becomes too hot to hold). That is why an 18650 "EDC-size" SST-50 driven hard will get hotter much quicker than a 3D Mag driving the same SST-50 equally hard - the larger light with larger mass will absorb the heat/energy and will get hotter slower, but its temperature will still increase until the equilibrium point is reached.

Don't get me wrong, I love this thread, I love the efforts to improve heatsink design, but I still see it as a short term fix to buy you a few more minutes of usage time. In my personal experience during the last 5-6 years, that limit for a comfortable equilibrium that allows me to hold the light for more than 10 minutes continuously without being too uncomfortable is somewhere around 12-15 watts in a 2C size light. I can't see the physics of a 30 watt LED being held by hand in a 2D or 3D size light for more than a few minutes, regardless of heatsink design/material, since the air around the light and the blood in my hand can't remove that amount of heat fast enough. 

Will


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## MikeAusC (Oct 12, 2010)

wquiles said:


> . . .
> My point is that although it does help to have a good, efficient heatsink design to remove heat from the LED area, unless you have a way to remove heat from the body of the light at the same rate it is being generated, you are still going to have to deal with a body that gets hotter and hotter with time.
> 
> The fact that we can use a supper duper, highly efficient" heat-pipe system to move heat away from the hot LED into the body of the light, only helps in spreading that energy into the mass of the light - it does not help eliminate the energy fast enough. . . .


 
I agree - that's why I abandoned the traditional handheld torch format for my SST-90 Searchlight / Floodlight. I need to run it for an hour as a Searchlight or a Movie light. Low weight is also important for something you'll be holding for a long time.

The Zerotherm Atom 30 has a 30x30x5 mm copper block for mounting the LED. Two Heatpipes then transfer the 30 watts of heat to lots of thin aluminium fins which transfer the heat to the air without much temperature drop and without needing a massive block of metal to transfer the heat to the fins. The fins take up 100x85x20mm. It weighs 150g.

The copper block is also coupled to the Aluminium housing that helps pass the heat to the air - 120x90x50

The fans draws 1.5 watts, but that's trivial in a 40 watt light.

I haven't measured temperatures yet, but so far I'm really impressed with how cool the copper block stays - even without the fan.


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## Epsilon (Oct 12, 2010)

What wquiles is saying as absolutely right. An equilibrium has to be reached before the light stops getting hotter. If that's before or after the point that you cannot hold it anymore, is the thing we are trying to figure out. For small EDC lights, it's obvious that a SST90 will not work at full power for an extensive amount of time.

But that's mostly not the purpose of those lights of course. 

Spreading the heat to a larger surface area (entire length of a mag 2/3D) will encrease running time on full power. The mass of the light will buffer the heat, but the surface area will aid in cooling. Propably not enough though, so active cooling might be needed.



turbodog said:


> You need a liquid which boils around or below your target temp. Drawing a vacuum on the tubing helps also.


 
The things is, that it's pretty hard to do this. But I do have the tools (from my refridgeration type cooling mods) so will look into it. Will post the results when done .


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## PMM (Oct 14, 2010)

turbodog said:


> I don't know the percentages, but I'd be willing to make a major bet that conduction to air/water/your hand/etc dwarfs radiant emission of energy from an led based, metal bodied light.
> 
> 
> If *RADIATING *the heat away is so important, why are you mixing that up with *CONDUCTING *the heat into the air?
> ...



Just getting my word terminology wrong as it would seem you are 

<cough>Convection</cough>

Look I don't get that deep and meaningful I know the pit falls of having multiple segments and the losses caused.

End of day you need the heat to move out effectively and design is so important when mixing metals you have to be really good at bonding those surfaces to get your conduction and equally enough surface sinking to get rid of that heat through Convection.

That's the point I am making losses can be high when your surfaces are not under high clamping pressures with also a good thermal transfer medium (Thermal paste) it kind of makes mute the use of a copper heat spreader with 2 thermal layers the heat has to navigate through.

I see so many diy peeps accepting a copper slug put inside a tube as being a heatsink and running the risk of burning the LED out or even overheating batteries to the point of venting/explosion... I think that is how the Maglight got its nickname to a world war 2 stick bomb when modded.

In my book ALu for air cooling & copper if water cooling.

Anyhow good luck to the OP the fun is in the making.


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## turbodog (Oct 22, 2010)

PMM said:


> Just getting my word terminology wrong as it would seem you are
> 
> <cough>Convection</cough>
> 
> ....



I try not to split hairs, but this has been a semi-detailed talk about heat transfer. 

My original post "CONDUCTING the heat *into *the air?"

Yes, the original transfer TO the air is still conduction. The transfer through the air is convection.


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## 350xfire (Oct 22, 2010)

So what about when used in a dive light? Safe to assume that water will take in some of the heat and then make it possible to run the light "forever"?


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## wquiles (Oct 22, 2010)

350xfire said:


> So what about when used in a dive light? Safe to assume that water will take in some of the heat and then make it possible to run the light "forever"?



Being under water if not a guarantee - you "must" have a good thermal path from the LED to the outside surface of the light (in other words, an LED on an Al/Copper heatsink inside a plastic body is generally speaking "not" a good solution). Assuming a good thermal path, then yes, since the light is surrounded by water (with practically an infinite thermal capacity), you would have a great solution as you can't heat the water fast enough - the water will be taking away heat faster than your high power LED can dish it out  . The equilibrium point would be based more on the temperature of the water than on any other factor within the light.

Will


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## ascubadiver (Apr 4, 2011)

There seems to be some confusion in this thread. Indeed copper is a better thermal conductor than aluminum which in turn is much better than brass, but that is often largely irrelevant in practice, except maybe right adjacent to the LED, and depends significantly on the heat sink geometry employed (cross sectional area good, long heat path length from LED bad). In cases where the separation between heat source and sink is unfortunately large one may consider a forced fluid convection alternative for thermal transport enhancement (like the radiator in your car), or a rather specialized version known as a heat pipe in which a fluid is contained in a tube and operated right around the liquid/gas phase change boundary (e.g. it boils at the operating temperature). 

Another practical consideration is that both copper and brass are easy to soft solder, whereas soldering to aluminum which forms a robust native oxide layer is only possible with a specialized fluxed solder (such as Alusol from Multicore solders, but it is a respiratory health hazard and relatively hard to obtain). 

In nearly all heat sink designs the limitations are at the interfaces rather than the choice of bulk material (assuming it is a somewhat good conductor like most metals and the heat sink geometry is rationally designed, i.e. short and fat, not long and thin in the direction of heat flow). At reasonable temperatures (<100C) radiation thermal transport is negligible so we'll rule that one out. Most interfaces within an LED assembly are solid to solid and so conduction limited. Therfore it is the interface material, thickness and cross-section that matters. For this reason most interface and bonding materials (thermal grease, thermal adhesive, silicone pads etc.) are capable of being applied or squeezed into thin layers, and are highly loaded with a high thermal conductivity powder. This may be either metallic such as aluminum, copper or silver, or ceramic such as boron nitride or aluminum nitride, even berylia is used in some technical applications though it is highly toxic if the powder is inhaled. Often the choice of filler is determined by whether electrical conductivity is also desired as in the case of silver loaded epoxies. 

The other interface problem to consider is usually where the heatsink terminates in a fluid, in which case convection normally dominates beyond conduction into the immediate boundary layer. For "dry" applications this usually means air is the transport medium, either by forced convection as in projectors, hair dryers etc. with a fan, or by natural convection like the heatsink on the back of your stereo receiver. In either case well designed fins help by increasing the effective area swept by the fluid. Ideally the fins should be thick enough at the base to transport heat to the distal regions which can be thinner, but machined heatsinks usually have constant thickness fins for simplicity. In the natural convection case the fins are preferably vertically oriented to assist with the chimney effect (hot air is less dense and rises). As a scuba diver designing for in water use, the heatsinking to the fluid (water in this case) is much more efficient than to air. The density and thermal capacity of water is much greater, so although the viscosity is high compared to air, a reltively small contact area to the metal heat sink (e.g. anodized aluminum) is all that is necessary. However such designs may need a thermal cut out or at least current limitation in the circuitry in case of extended operation out of water as they will no longer be effectively cooled.


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