# Peltier cooled high power LED



## gandbag (Dec 20, 2005)

I have recently aquired some small peltier junction chips, 1-5v, 4-6w. One of these thermoelectric devices would easily fit onto the metal PCB of a luxeon or similar LED, possibly two of them.

Problem: 
As you run a 1 watt LED at higher and higher wattage, more and more of the electrical input would be turned into heat rather than light tending to damage the LED. 

Calculation:
(Note, this calc is not based on real numbers, just a hypothetical situation.) Say your 1 watt LED is being driven at 5 watts, and has the low efficiency of 40%. This means you are getting 2 watts of light and 3 watts of heat (negating electrical resistance of the connections etc). 

Solutions:
1. Use a higher wattage LED. However, this isn't always possible.
2. Get a bigger heatsink. Also, not always possible.
3. Use Peltier cooling. This requires a substantial increase in electrical energy, a bigger heatsink and potentially a lot more circuitry. However, for "wow" lights or other unusual applications I can think of, this is potentially a good idea. 

Comments:

A patent was recently awarded for a peltier cooled lighting system, complete with temperature sensors etc (The PDF has diagrams). However, this is for stage lighting, not flashlights, which makes sense. 

I will play around with this idea today, but would love to hear feedback on this idea.


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## andrewwynn (Dec 20, 2005)

I bought a couple higher power peltier's.. (12W).. for doing exactly what you describe in a flashlight.. i want to have a 35-50W flashlight and though i know i'll need a fan to cool it.. i've considered using a combination of fan and peltier.. the model i have is only like 2" square and can freeze water on one side and boil on the other at 12W.. i would not need to run it that hard to be useful.

since LED are brighter when cooler.. i can handle if the hot side of the peltier is over 200F if it means my heatsink can be closer to 100F or less.. 

The trick is how to dump the extra heat! in my case i have it solved because i have a big internal airspace that is vented to the outside.. in most flashlights this would be a problematic thing. 

-awr


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## HarryN (Dec 20, 2005)

I have run the math on this several times, because it seems like a good idea. In the end, it usually does not work out for battery applications. Uou gain more light from running either more LEDs or more power into the LED, then you gain from running the LED and power into the cooler. There Peltiers use a substantial amount of power to move the heat.

It might make sense for a demonstration project where the ultimate goal was to get as much light as possible from a single LED vs max light per watt.


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## greg_in_canada (Dec 20, 2005)

Peltier modules are very inefficient. To remove 1 watt probably takes 2 watts of power to the Peltier module. So now your run time is 1/3 of what it originally was. And you need to cool the hot side of the Peltier or it will not be able to keep the cold side cold. So your heatsinking requirements just went up.

There is a company (coolchips.com) that is working on an improved cooler. Quote "Cool Chips use thermotunnel technology to deliver up to a projected 55% of the maximum (Carnot) theoretical efficiency for heat pumps. Conventional refrigerators operate at up to 45% efficiency and current thermoelectric systems (Peltier Effect) operate at 5-8% efficiency".

If they ever get it commercialized then cooling LEDs might be worthwhile.

Greg


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## cratz2 (Dec 20, 2005)

This thread has some comments re: use of Peltier devices in lights.

If you have everything you need, I think it is worth persuing, if only for the experience, but unless the application is pretty extreme (such as AWs 35-50W goal) I can't see them having a useful application in modest lights. I mean, if you want 1W output with more effeciency and less heat, it would be easier to just underdrive a 3W LED rather than to overdrive a 1W and have a Peltier. 

And the 5W LEDs don't seem to have a stunning record of reliability when driven at 5W.


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## greg_in_canada (Dec 20, 2005)

This article http://www.overclockers.com/tips45/ has some good stuff if you want to calculate the temperature difference and Peltier power.

Greg


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## gandbag (Dec 20, 2005)

Thanks for all the great responses so far! 

One very well done walkthrough of a peltier-cooled beer cooler/tea warmer is here. This guy goes to extraordinary length building and documenting his creation. He also supplies some basic calculations, although he assumes the peltier is 100% efficient, which is obviously not the case, as greg_in_canada pointed out.


My purposes are not to produce a better flashlight, just to experiment with a novel method for fun. 

More updates to come.


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## andrewwynn (Dec 20, 2005)

I came to similar conclusions but noted that with my megasonic i am able to get heat sink temps into the 140F range w/o much difficulty, and have a lot of battery overhead (running 12W light from 60WH battery).. it could be worth the effort.. a fan is far more efficient, but in the case of jamming 35W of emitters in the light.. a fan might not get enough heat out of the sink.. and i don't mind if the fan is blowing 200F air out if it means i can keep the heat sink 20-30F cooler. 

-awr


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## Mike Painter (Dec 20, 2005)

20% seems to be the maximum efficency of such a device and apparently there is a "sweet spot" temperature. Anything above or below this gives lower performance.


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## andrewwynn (Dec 20, 2005)

whoa on the 20% figure that does present a big problem for making this a useful venture.. that's not a bit deal if you are talking about a one-time event like cooling a cup of water... but if you want to draw 20-30W out of a heatsink means 100-150W of energy to do so.. and well.. i think the peltier i have is like 12W meaning i can expect 2-3W of heat transfer.. which well that will get quite warm / cold only if it doesn't have much heat transfer in/out of it. 

regardless, i will definitely test out the modules i have.. if for nothing else i can use them on the bench to keep my test LEDs cold, even if the other side is flaming hot. 

-awr


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## IsaacHayes (Dec 25, 2005)

What if you were to take a high performing luxeon, say a Ubin luxIII or W bin LuxV, and have a VERY large reflector, and mount it to a peltier. Crank up the power as much as you can without melting the bond wires (is it 2amps, or 2.5?). You could have a "lantern" design with a handle and free air to the peltier or with small fan too. Yes, runtime would suffer a lot, but you'd have perhaps the worlds farthest throwing LED setup.

Actually, maybe a tighter spot could be achieved via NewBie's asphyrical lens setup. It would be all custom so why not?

It may not be practical to have peltier LED flashlight, but a Peltier LED spotlight? Hmmmm!! Throw in a SLA with a buck circuit for the LED and you're set!!


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## andrewwynn (Dec 25, 2005)

that's brilliant actually. I think it is primarily heat that causes problems with too much current.. with 12w devoted to cooling i could probably keep the junction temp close to room temperature even at 1.5 to 2A on the emitter.. and the host i'm thinking i'd put it in is a 28V 3AH battery solution.. thanks for that idea very cool.. well maybe if i can get another of my megasonic lanterns that has a much bigger reflector so that might be a better host.


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## mattheww50 (Dec 25, 2005)

Peltier devices are horribly inefficient energy transporters. In addition, you have grossly overestimated the efficiency of the LED. For purposes of estimating heat produced by Luxeon, start by assuming the efficiency is ZERO. 1 watt is 500+ lumens (varies according to wavelenght), so even at 50 lumens per watt, a Luxeon would be 10% efficient.

How bad are Peltier devices? Most mechanical refrigerators have a coefficient of performance in the range of 2-3. a COP implies that the use of 1 joule will transport 3 joules of heat.

An Air condition with an SEER of 10 has a COP of 3. My experience with Peltier devices is that by the time you provide forced air cooling for the hot end, you are lucky if you can get a COP of .3 . In other words it will take 3 joules to move 1 joule of heat with a Peltier device. 

So if you drive a Luxeon(s) with 5 watts, it will for all practical purposes you will dissipate 5 watts.
A Peltier device then consume another 15 watts getting rid of the 5 watts, so you need 20 watts to drive the Luxeon at 5 watts. 

The only real electronic requirement on a Peltier device is protection. If the cooling on the hot end fails, and you don't cut off the power, most will fry in a lot less than 1 minute.

Peltier devices are attractive if you are severely constrained on space, but have lots of power available. Otherwise, you are much better off to consider using a heat pipe to move the heat. Even a small heat pipe (6mm/.25 inch) can move 100 watts. a Heat pipe is basically a tube filled capillaries that contain a working fluid such as Ammonia, some form of Freon, or even water.
At one end, as it heats, the liquid absorbs the latent heat, and vaporizes. The Vapor then diffuses to the cold end, where it gives up the latent heat, and liquifies. The Liquid then returns to the hot end either via gravity or Capillary action.

It works because latent heat is very high.
For example 100 calories will convert 1 gram of water a 32F to 1 gram of water at 212F. But it takes about 270 calories to convert 1 gram of water at 212F to 1 gram of steam at 212F!

A heat pipe allows you to efficiently transmit heat from a place that you don't want it to a place where you can get rid of it.

As an example I have two portable electric refrigerators. One is an Igloo Peltier device. I have measure it with about 55 watts in, pumping about 50btu/hour. It doesn't have a thermostat because it is simply incapable of freezing anything.

It is just about impossible to get colder than about 35F below ambient. 

It cost about $50, and weighs about 8 pounds. It works far better as heater than cooler. As a heater, for every 3 joules (watt seconds) that you drive it with, you get 4 joules of heat.

The other unit is an Engle/Norcold mechanical refrigeraor with a novel linear compressor design. It draws about 45 watts.
It is half the size of the Igloo unit, but weighs almost 30 pounds and cost close to $500. It has a thermostat, because it can easily achieve temperatures of -20C/0F with an ambient temperature of nearly 100F in about 20 minutes, and it can easily make ice. They are common used in remote areas because they are exceptionally tough, and can reliably keep temperatures well below freezing even with ambient temperatures well above 100F.

Peltier cooling for a portable device is frightningly inefficient...


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## andrewwynn (Dec 25, 2005)

Heat pipes.. very interesting thought.. i remember seeing something not too long ago about using one of those.. that is a faaaar more efficient idea.. i just happen to have..

1) extremely over-abundant power plant
2) host to put it in. 
3) small 12W peltier. 

It's obviously a experiment of principle not practical.. but with the V.28 battery pack.. it's an 86W pack and if i run an over-driven K2 emitter say at 2A... maybe i can keep it cool enough that the Tj is at only 10-20C over ambient even if it costs me 12+W in cooling, that would be a worthy experiment to me. 

The heat pipe idea is extremely interesting though.. i saw a thread not too long ago showing them.. have any information about where some are available to actually purchase that would be small enough to incorproate into a light.. and what requirements are actually involved to keep the circular cooling cycle to go w/o a pump. 

-awr


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## NewBie (Dec 26, 2005)

Old Story...

Funded by the Defense Advanced Research Projects Agency, RTI engineers concocted a heat pump using two atomically precise superlattices of bismuth telluride, one layered with antimony telluride, and one with bismuth telluride selenide. The result: a device that conducts electricity and insulates against heat transfer better than anything ever seen. Way better - it's 2.5 times more efficient and 23,000 times faster than the stuff it replaces.

More info on peltier developments:
http://www.nanoforum.org/dateien/temp/ER April 2004 total.pdf?20042005174151


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## Mike Painter (Dec 26, 2005)

NewBie said:


> Old Story...
> 
> Funded by the Defense Advanced Research Projects Agency, RTI engineers concocted a heat pump using two atomically precise superlattices of bismuth telluride, one layered with antimony telluride, and one with bismuth telluride selenide. The result: a device that conducts electricity and insulates against heat transfer better than anything ever seen. Way better - it's 2.5 times more efficient and 23,000 times faster than the stuff it replaces.



They don't say what it replaces but only claim 25% efficency - which is very good for such devices.
Here's a  link  that is not a pdf.


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## Mike Painter (Dec 26, 2005)

andrewwynn said:


> Heat pipes.. very interesting thought.. i remember seeing something not too long ago about using one of those.. that is a faaaar more efficient idea.. i just happen to have..


Heat pipes are interesting and fairly old. Most rely on gravity to circulate a liquid that runs in a sealed pipe and might not work well with flashlights. They also add a good bit of mass and volume.

I suspect the immediate future will see better designs that use everything as a heat sink. A good metal reflector would work and designs that dunp more heat into the body so that our hands can offer a better exit for the heat.
The near future can solve the problem with more efficent LED's...

Well, solve it so the general public can have really good lights at reasonable costs.

Unless 100% effeciency is achieved we will always be building things that need to get rid of heat.


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## pbarrette (Dec 26, 2005)

Hi Awr,

If you go with the peltier idea, there is something else you should keep in mind. When you turn off the LED, there is still heat which needs to be removed. So you will have to have some way to keep the peltier and fan running for a little while after you turn off the LED.

In the same vein, you should start the cooler before turning on the LED to ensure that it cools the LED in time. Since I'm assuming that the peltier and fan are doing all of the actual cooling, and there will be little to no passive heatsinking, it's a good idea to get the cooling system running first. Otherwise, the LED could be generating significant amounts of heat before the peltier and fan combo can remove it. In startup condition, the amount of lag time is probably on the order of less than a second, but it's better to be safe than sorry.

Look at the CPU cooling world for some tips here. They always fire up their active coolers before the CPU and always have a cool down period after the CPU is switched off.

pb


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## Rossitron (Dec 26, 2005)

This thread made me remember this old thread:
http://candlepowerforums.com/vb/showthread.php?t=33596

-Ross


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## IsaacHayes (Dec 26, 2005)

Andrew: glad you like it. Now it's up to you to build the worlds farthest throwing grossly overdriven portable luxeon spotlight!! :nana:

Rossitron: ah, cool you found that thread. I was thinking of it when I saw this thread.


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## mattheww50 (Dec 26, 2005)

Mike Painter said:


> Heat pipes are interesting and fairly old. Most rely on gravity to circulate a liquid that runs in a sealed pipe and might not work well with flashlights. They also add a good bit of mass and volume.
> 
> I suspect the immediate future will see better designs that use everything as a heat sink. A good metal reflector would work and designs that dunp more heat into the body so that our hands can offer a better exit for the heat.
> The near future can solve the problem with more efficent LED's...
> ...



While most will happily use gravity, just about all contains wicks,or similar devices so that they will function just fine without the aid of gravity due to capillary action. While it is desirable to have the hot end above the cold end, it is not a necessary condition. The vapor will always move across the pressure gradient created by boiling at one end and condensation at the other, and capillary action will operate even against the pressure gradient. There are already some CPU coolers that operate via heat pipes. Another inteesting technology is a variation on the heap pipe, which is a heat sink with a working fluid chamber. that operates essentially as a heat pipe.


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## NewBie (Dec 31, 2005)

Mike Painter said:


> Heat pipes are interesting and fairly old. Most rely on gravity to circulate a liquid that runs in a sealed pipe and might not work well with flashlights. They also add a good bit of mass and volume.




Modern heatpipes utilize a very efficient capilary structure to return the condensed liquid, which even work great, upside down. You will find these heatpipes in most modern laptops, with conductivities up to 2000 times that of copper, and the heat transport is also much more rapid. Being *very* thin walled devices, they add very little mass, and are suprisingly light. Volume will depend on the size you choose, but they do make them down to 2mm in diameter, but those don't work as efficiently.


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## NewBie (Jan 26, 2006)

Well, someone finally combined the heatpipes and LEDs, which I have been talking about for a few years here on cpf now.

Not only do they get superior cooling, they get higher than normal lm/W numbers at the same time, all the while, while overdriving them.


"In the NeoBulb structure, heat is effectively removed from the vicinity of the LED junction using a micro-heatpipe, and then dissipated using a series of circular fins surrounding the heatpipe. Heat removal is enhanced by using a longer heatpipe or larger-diameter fins. The chips are packaged and mounted onto the proprietary heat-pipe....the thermal conductivity of the finned heatpipe (made of copper ) is 100 times higher than copper itself, which is sometimes used as a heat-sink slug in high-power LED packages. "

http://ledsmagazine.com/articles/features/2/6/3/1


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## jtr1962 (Jan 28, 2006)

greg_in_canada said:


> There is a company (coolchips.com) that is working on an improved cooler. Quote "Cool Chips use thermotunnel technology to deliver up to a projected 55% of the maximum (Carnot) theoretical efficiency for heat pumps. Conventional refrigerators operate at up to 45% efficiency and current thermoelectric systems (Peltier Effect) operate at 5-8% efficiency".
> 
> If they ever get it commercialized then cooling LEDs might be worthwhile.


And if they make large multiwatt modules with some tens to hundreds of watts heat pumping capacity these have potential in lots of other applications. In particular, the closer a thermoelectric module can get to Carnot efficiency the lower the minimum temperatures. Present bismuth telluride modules can manage to keep a cold plate at around -40°C if you use water cooling on the hot side. In winter when tap water is colder I've even managed to get down to -50°C. 45% Carnot efficiency might enable temperatures well under -100°C from a single stage module, perhaps even under -150°C. It all depends if the module's Carnot efficiency remains the same over temperature (bismuth telluride actually gets worse at lower temperature). A module with 100% Carnot efficiency over temperature could theoretically approach absolute zero. I'd be happy with a single stage module which could get into the liquid nitrogen temperature range.


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## metalhed (Jan 28, 2006)

I am (obviously) not an engineer, nor do I have the great amount of knowledge you guys have regarding heat exchange problems in modern flashlights. But I have one of those 'someday-maybe?' questions, and I think it relates to this thread.

I've read of the Stirling Engine and how they turn heat into kinetic energy, so I've wondered:

Could these ever be miniaturized to draw heat from a heatsink (presumably covered with LEDs), and then turn that heat into additional electrical energy to recover some of the LED's wasted energy? 

It wouldn't need an electrical draw of any kind, right? Is there any way to generate electrical power from such a miniaturized, low-power device?



Just wondering. Any thoughts?


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## Mike Painter (Jan 28, 2006)

metalhed said:


> Could these ever be miniaturized to draw heat from a heatsink (presumably covered with LEDs), and then turn that heat into additional electrical energy to recover some of the LED's wasted energy?
> 
> It wouldn't need an electrical draw of any kind, right? Is there any way to generate electrical power from such a miniaturized, low-power device?
> 
> Just wondering. Any thoughts?



The first rule in physics is that you can *never* break even.
Heinlein said it best TANSTAAFL. (There Ain't No Such Thing As A Free Lunch.)

Some of the energy could be recovered and reused but it would be a very, very small percentage and a net gain in heat. 
I'd guess that if you could recover 10% of what went in you would be doing well.


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## andrewwynn (Jan 28, 2006)

there are always losses with conversion.. you coud try to use a heat engine to generate electricty from the heat generated from the electrical device, but it very very quickly becomes no a viable enterprise. You could for example end up bumping the efficiency up from 90% to 92% in such an endeavor.. but at what price.. a lot.. it boils down to it's not worth the effort. Now.. in a car using regnerative breaking is a different story.. the efficiencies are much higher in harvesting the energy that would normally be lost as heat.. That said.. depending on where you live.. the heat dumped from lighting helps warm the house so it's not lost, however of course in summer that's flipped into costing more to cool. 

-awr


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## metalhed (Jan 28, 2006)

I didn't expect that such a device could harvest much electrical energy from the heat captured, and didn't mean to imply that such a device could power a light (of any kind).

But I thought that as an additional by-product of a primary function of cooling the heatsink (and LEDs), it would be kind an interesting way to scrub that heat.

Since the whole purpose of the Stirling, the way I understand it, is to convert heat into kinetic energy; I thought it might have uses in heatsink applications.


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## Mike Painter (Jan 29, 2006)

metalhed said:


> But I thought that as an additional by-product of a primary function of cooling the heatsink (and LEDs), it would be kind an interesting way to scrub that heat.



The problem is that the conversion of the heat to electricity would also generate heat and you would have a net gain in heat.
The Peltier device is probably the best way to do this and they are not very efficient even when run at the very narrow ideal temperature they want to see.


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## NewBie (Sep 28, 2006)

Still, using a heatpipe for cooling LEDs is a great idea, imho.


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## evan9162 (Sep 28, 2006)

Peltiers need a high temperature differential between the hot and cold side in order to supply power. In most cases, you need a 50C difference to supply some appreciable amount of power.

This means that your hot side (LED in this case) should be 50C hotter than your cold side (heat sink).
So if you stick a peltier in between your LED and cooling apparatus, you've just made your LED hotter in order to supply it with some power. This is a terrible tradeoff.

I don't know about you, but i'll skip whatever power I can extract from that and run my LEDs cooler.

You can't use the same peltier to both cool something by putting power in, and extract power from it due to the temperature difference at the same time. It doesn't work that way. You can either cool something or power something, but not both. You can stick a peltier inbetween everything to generate power, but when you do that, you're just trying to generate free energy, and that doesn't work at all.


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## chesterqw (Sep 28, 2006)

now we need a spiky heat sink and a thing to spray liquid nitrogen on it in short burst.


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## Illum (Sep 28, 2006)

Peltiers arent really very efficient unless you stack a few to achieve a greater temperature difference...

peltiers draw quite a bit of current too..


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## tonyd (Sep 28, 2006)

Heat transfer info. How intersting. Recently seen several chips with a diamond substrate for the ultimate in thermal conductivity. I for one have seen modern heat pipes work very well, and in conjunction with eutectic mixtures. I have thought of copper sinking some emitters to NaK diastats. For the relatively short duration a flashlight runs this should remove substantial heat load.


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## milkyspit (Sep 29, 2006)

Where does one find smallish but efficient heat pipes for potential use in portable lighting? Hopefully inexpensive enough to get some to experiment with!
:thinking:

Also, is there any potential toxicity... for instance, is the fluid inside the heat pipe at all toxic?


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## Sawtooth (Sep 29, 2006)

NewBie, where do you buy heatpipes. I have searched online and there are companies that offer custom solutions (e.g. for laptop design). But where can you buy simple stock
heatpipes? You showed some pix of some heatpipes in some older threads, but where does one buy them from? I think a real obstacle in using these things is that they dont seem to be readily available for people to play with...


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## NewBie (Oct 1, 2006)

The heatpipes I have are made by Furukawa AVC Electronics (Suzhou), and are 80 times better at transferring heat than copper, and 160 times better than aluminum. The company also produces micro heatpipes with a diameter of 2mm.

One of the interesting things about heatpipes, is that they are thin walled, and are extemely light, much lighter than the equivalent diameter of aluminum.

They can be found here, click on the heatpipe pictures at the bottom:
http://www.avc.com.tw/products/NB-Thermal.htm#

You need to locate the distributor in your area to get them.

However, here is the office in North America to contact:

AVC North America
[email protected]
TEL : +1-310-783-0885
FAX : +1-310-212-3284 

One of the contacts there, if it is still good:

[email protected]

Heather Smith 
Regional Sales Manager
AVC America, Inc. 
528 Amapola Avenue 
Torrance, Ca. 90501 
www.avcamerica.com
PH: 310-783-5472 
CL: 310-999-8534 
FX: 310-783-0875


A list of distributors in your area:
http://www.avcamerica.com/Dist/index.htm


Sales reps in your area (many of the reps are not even aware they can obtain heatpipes as they are used to only selling AVC heatsinks, but if they inquire, they can easily obtain them):

Mfg. Rep./Contact Name 
Address 
Phone / Fax 
Territory 

Clark Sales, LLC 
27600 Farmington Road, Suite 209
Farmington Hills, MI 48334 
248-553-0610 
IN, KY,OH, MI 
(Jack Adams, **** Harvey, Heather Devlin) 
248-553-7330 F 

Exis Manufacturers Rep. 
631 Riveroaks Parkway
San Jose, CA 95134 
408-944-4600 
N. Ca 
(Ralph Voner Har, Nancy Carnathan-Cribbs) 
408-321-3200 F 

Martan Inc. 
1100 Woodfield Road, Suite 145
Schaumburg, IL 60173 
847-330-3200 
IL,WI, IA,NE, KS, MO 
(Bob Tanka, Colette Schaefer, Roman Budek) 
847-330-0024 F 
(Todd Schwerm, Melanie Abel) 
6936 Mount Pleasant Dr., 
West Bend, WI 53090 
262-241-4955 
262-241-8365 F 
(Scott Misbauch) 
2846 Dardenne Links Dr.
O'Fallon, MO 63366 
636-294-2310 
636-294-2312 F 

Mission Technology 
16466 Bernardo Center Dr. Ste 188
San Diego, Ca 92128 
858-674-6191 
S. Ca 
(Ed Wahlroos, Anne Axelson, Anthony Mitchell) 
858-674-6196 F 
(Mike Fitch, Shye Nakabayashi) 
24422 Avenida De La Carlota
Ste. 265, Laguna Hills, Ca 92653 
949-951-3696 
949-951-3874 F 
(Mike Miskinnis) 
505 Firecrest Court
Newbury Park, Ca 91320 
805-381-1801 
805-371-9524 F 

Pipe Thompson 
2155 Dunwin Dr. Unit #7
Mississauga, ON L5L 4M1 
905-607-1850 
Canada 
(James Pipe, Dave Cochran, Lorenzo Crupi) 
905-607-1858 F 
(Sherman Sum) 
22020 Cliff Ave
Maple Ridge, BC T2A 6L3 
604-467-4251 
604-467-4351 F 
2033 Thorne Avenue
Ottawa, ON K1H 5X4 
613-723-6494 
613-723-0969 F 

(J.D. Pipe, Marc LaFontaine, Mark Howell) 
25 King's Landing Private
Ottawa, ON K1S 5P8 
613-723-6494 
613-723-6494 F 

(Michel Leroux, John Rosse) 
32 Labrador
Kirkland, QC H9J 3W8 
514-697-6853 
514-697-6863 F 
4880 Couture
St. Leonard, QC H1R 1C4 
514-323-9045 
514-323-8957 F 

RunningBrook Inc. 
P.O. Box 161
New Market, Alabama 35761 
256-379-4840 
AL,TN,GA, MS 
(Pat Brooks, Harry Brooks) 
256-379-4845 F 

S.J. Associates 
500 North Broadway, Ste 159
Jericho, NY 11573 
516-942-3232 
CT,DE, NH,NY, NJ, MA,MD, ME,PA,RI, VA,VT, 
(Mark Wachtel) 
516-216-4943 F 
(Tom Faherty) 
33 Boston Post RD. W., Suite 310
Marlboro, MA 01752 
508-485-2700 
508-485-2702 F 
(Shane Erickson 
15 Coventry Lane
Naugatuck, CT 06770 
203-723-4707 
203-723-1629 F 
(Dan Rysz) 
131-D Gaither Drive.
Mt. Laurel, NJ 08054 
856-866-1234 
856-866-8627 F 
(Jeffrey Land) 
803 West Broad Street, Suite 750
Fall Church, VA 22046 
703-533-2233 
703-533-2236 F 

Technology Solutions 
462 NE Bluefish Pt
Port St. Lucie, FL 34983 
772-834-8553 
FL 
(Bill Jette) 
772-873-8060 F 
(Mike Rada) 
4550 47th Street W. Apt # 917
Bradenton, FL 34210 
941-761-2337 
941-761-2478 F 
(Janet Murphy, Paul Murphy) 
610 Hampshire Lane
Holmes Beach, FL 34217 
813-690-1838 
941-778-2395 F 
(Charlie Bostick) 
7340 NW 75th Street
Tamarac, FL 33321 
954-205-9717 
954-720-6111 F 

Western Technical Sales, Inc 
13400 Northup Way, Suite #20
Bellevue, WA 98005 
425-641-3900 
WA, OR 
(Bob Brunjes, Ralph Loesch, Sue Hopper,
Stephanie Labo) 
425-641-5829 F 
(Jim Wyland) 
122 N. Raymond, Suite #5
Spokane, WA 99206 
509-922-7600 
509-922-7603 F 
(Pete Thunem, Stanley Crisp, Scott Martin,
Cindy Meyer) 
3720 SW 141st Ave Ste # 200
Beaverton, OR 97005 
503-644-8860 
503-644-8200 F


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## jburgett (Oct 3, 2006)

NewBie said:


> Still, using a heatpipe for cooling LEDs is a great idea, imho.



Absolutely! I've been suggesting that to Wayne at Elektrolumens, since he likes to build over-the-top blazing lights. There is an application that cries out for heatpipes. It would improve the heat transfer from the luxeon to the body structure more than any other "practical" method I can think of. And lower the overall weight too. Definately a win-win scenario.

We can all learn from the current wave of CPU heatsink technology. Our flashlight applications are mere gentle warming compared to an overclocked CPU!


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## Sawtooth (Oct 3, 2006)

jburgett said:


> Our flashlight applications are mere gentle warming compared to an overclocked CPU!



Just my $0.02...
You could make a flashlight really cook if you wanted to -- but the LEDs wouldn't last long -- thats the whole problem. I think the passive cooling required in (most) portable lights is actually quite a challenge compared to CPU cooling (at least non-portable CPUs -- where you can use all the mass, volume, power and air (and/or liquid) flow you need.) 

Seven closely-packed Lux-V's would not be a gentle warming even compared to a CPU.
Especially when you consider that they arent very heat-loving to start with.


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## gandbag (Oct 10, 2006)

wow!

I'm very happy that this thread was rediscovered and given some serious thought to!

I am very interested in the heat pipe idea, but from the pictures it seems like it might be a challenge to attach the heat pipe to the led with a lot of contact area. I'm sure there are many ways to overcome this problem...

If there is enough interest, perhaps we should form a new thread on novel/experimental/theoretical cooling systems and their potential and theoretical limits, in terms of physics. 

Maybe a liquid nitrogen cooled LED is a little impractical, but PC overclockers use it all the time for record setting purposes. In the same spirit of exploration and experimentation, I propose we look forward to the physical limitations and benefits of active and passive cooling.

So far we have learned peltier cooling is largely impractical, but have gained key insights into thermodynamics. 

Responses?


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## Sawtooth (Oct 10, 2006)

Newbie, Thanks for the references. These should help alot! :thumbsup:



gandbag said:


> I am very interested in the heat pipe idea, but from the pictures it seems like it might be a challenge to attach the heat pipe to the led with a lot of contact area. I'm sure there are many ways to overcome this problem...



I agree. The heat pipes newbie showed seem a bit messy at the ends. What would be really nice is if they were nice and flat at the ends so they could be thermal-epoxied into the back of a heat-sink with no gaps or spaces. Since the critical issue with LEDs seems to be getting the heat away from the junctions, one could build a 2-stage heatsink. The 1st stage would be something like a PQS (but flat to allow more LEDs and thicker to allow good heat transfer to the pipes). Heatpipes would then connect the 1st stage to a more remote 2nd stage. Since I am interested in bike lights with external batteries, I can move the heat to the back-end of the light without fear of overheating batteries...


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## Loomy (Oct 11, 2006)

gandbag said:


> Responses?



LEDs are getting brighter and cooler as time goes on. There will probably never be a need or demand for heat pipes in a flashlight


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## jtr1962 (Oct 11, 2006)

Loomy said:


> LEDs are getting brighter and cooler as time goes on. There will probably never be a need or demand for heat pipes in a flashlight.


Yep. In a few years we'll probably be at 200+ lm/W with only 1/3 of the power going in coming out as waste heat. Given that a monster 2000 lumen flashlight would consume 10 watts power while producing about 3 watts waste heat. This is quite manageable even without heat pipes. A more reasonable light (say 300 lumens) would produce a mere half a watt of heat. Even a plastic flashlight could deal with that.


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## Sawtooth (Oct 11, 2006)

Loomy said:


> LEDs are getting brighter and cooler as time goes on. There will probably never be a need or demand for heat pipes in a flashlight


:huh2:
(1) There is a need now -- that is why they are being discussed and that is why we are interested in them...
(2) In terms of fixed LED lighting they are already being used (see references in newbie's posts and in the LED magazine). 
(3) LEDs are also getting more heat-tolerant but not necessarily cooler. 
(4) Heat pipes are so much more efficient and potentially lighter than current solutions -- so why not consider their use?


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## andrewwynn (Oct 11, 2006)

There are neat solutions using heat-pipe in consumer LED lighting already.. makes for a nice passive solution. 

As mentioned above.. only some moderate active cooling is needed for high-power luxeon lighting.. solid alum heat sinking to a hand works as good as needed up to 15-20W.. over 20W finning the head is probably all that is required.. so i'm not sure exactly where the benefit is.. here's the thing and was my point originally with piping in on this thread.. 

Luxeons loose OUTPUT when they are warm.. so spend some bat. power on active cooling.. keep the heat sink slug 20-40C cooler than normal and you'll get appreciably more output.. that said... 

you'll get FAR MORE output with passive cooling and an add'l emitter and running them ALL at a lower output level. 

for example.. driving a 5x K2 emitters to 1000mA you can expect about 530L at the cost of about 21W.. dial that down to 700mA/emitter and add an emitter.. now you can expect 492L but the cost is 16.8W.. you get 93% of the output for 80% of the power.. extend that even further down.. running a Lux3 luxeons at 500mA.. you get 35L/W.. so put NINE of them into the mix.. it will cost you 15.3w and you get 531L... 

So.. 9xLux3 at 500L is 15.3W and outputs identical amt of light at 5x K2 at 1000mA but that costs 21W or 37% more power to generate the exact amt of light. (just in much less space.. 5 emitters vs 9). 

Anyhow.. it quickly becomes an balance of how to you want to generate more light.. the max output of a single lux is just about 140L no matter how you dice it up.. and it could be possible to make a more compact solution with heat pipes or peltiers but the K2s don't need so much heat sinking to stay bright.. so.. a model of necessity needs to be drawn up.. what is the need or purpose? 

I have a couple peltiers waiting for a neat solution.. i tried to run a luxeon from a heated peltier but manoman that is so inefficient it's spooky.. by heating the peltier with a blow torch i was able to pump out a whole watt!

I do plan on mounting some K2s to a peltier and running 5-10W through it to keep it cool.. it would drop the electrical efficiency of the module by maybe 30%.. but would likely boost the lumen efficiency by maybe 15-20%.. so it's a worthy test on the size host i'm planning.. the heat sink can convection cool and would pump out some seriously warm air but wouldn't require a fan. 

I've done a fan-cooled luxeon light.. putting 3x Lux3 into a small head drill lantern.. w/o the fan i got the heat sink up to 210F pretty quick.. i put in a small smally fan+ heatsink (about 2 1/4" square heatsink and with the fan maybe 1/2" thick).. glued the lux stars directly to it.. it works amazingly well. 

I even hooked up the fan in parallel to the luxeons with a series resistor and the fan spins slower when i have the light dialed down.. it's a wonderful solution.

-awr


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## Sawtooth (Oct 11, 2006)

jtr1962 said:


> Yep. In a few years we'll probably be at 200+ lm/W with only 1/3 of the power going in coming out as waste heat. Given that a monster 2000 lumen flashlight would consume 10 watts power while producing about 3 watts waste heat. This is quite manageable even without heat pipes. A more reasonable light (say 300 lumens) would produce a mere half a watt of heat. Even a plastic flashlight could deal with that.



2000 lumens on 10W, from LEDs, in a few years!? I hope you are right -- but Im not going to hold my breath. Unless there are some major breakthroughs happening right now, I don't think this is very likely at all... I suspect that what you are describing is very far off if it is even acheivable at all. 

And, even if such LEDs were available today, there would still be a desire to push them as far as the thermal issues would allow. In other words, heat management is always likely going to be an issue. Why settle for a 2000 lm flashlight when you could do alot better with a good heat management plan?


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## Sawtooth (Oct 12, 2006)

Excellent points andrew! 

I am interested in bike lights, so liquid-cooling (i.e. blood) via contact with a hand is out. But your point about using the otherwise wasted energy on active cooling makes alot of sense. The fan is a nice idea. 

Currently, we can't make a tri-lux V (15+W) that can maintain output for long (except maybe ones with active cooling employed). I suspect that heatpipes could solve this problem in the passive cooling realm: (1) cheaply, (2) easily(?), and (3) without too much extra mass.


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## jtr1962 (Oct 12, 2006)

Sawtooth said:


> 2000 lumens on 10W, from LEDs, in a few years!? I hope you are right -- but Im not going to hold my breath. Unless there are some major breakthroughs happening right now, I don't think this is very likely at all... I suspect that what you are describing is very far off if it is even acheivable at all.
> 
> And, even if such LEDs were available today, there would still be a desire to push them as far as the thermal issues would allow. In other words, heat management is always likely going to be an issue. Why settle for a 2000 lm flashlight when you could do alot better with a good heat management plan?


Cree already achieved 131 lm/W. It'll probably take a year or 18 months for that to trickle down into production. 200 lm/W isn't that much of a stretch.

As for pushing these hypothetical LEDs why even bother? The reason people do it today is because even overdriven today's LEDs aren't at the lumen level of some incandescents. Once you have LEDs capable of 500, 1000, 2000 lumens I suspect there will be less interest in overdriving.

A more practical reason is the power source. To sustain even 10 watts for any reasonable amount of time requires a huge weight in batteries. Unless there is a factor of 5 or 10 increase in battery capacity the runtime of a 10 watt light would be measured in minutes. While such a light may have great wow factor it is hardly useful in the real world. On the other hand, consider a 300 lumen light using 200 lm/W LEDs. This would use 1.5 watts of power. It could run for about 2 hours off one of today's NiMH cells while providing a very useful amount of light, or last an entire 8 hour shift with four cells.

Another thing I'm thinking is that as we go into the higher efficiency realm there may be little or no gain in output from overdriving. Let me explain. Today's LEDs put out about 85% heat, 15% light. If they're overdriven the die temperature increases somewhat but it's already relatively high to begin with. As a result you still get some extra light but even so by the time a LuxIII reaches 1.2 or 1.3 amps there's little more to be found. Now consider an LED where you get 30% heat, 70% light. At maximum rated current the die will still be fairly cool. However, as with all LEDs if you overdrive the efficiency drops. You might end up with 50% light, 50% heat. The die temperature will be much higher than before. This die temperature increase will counteract any increase you get from the increased current, and you'll have little if any extra light. In a sense higher efficiency LEDs will already be overdriven compared to the ones we have today. A package capable of taking ~3 watts of heat might be used for a 3.5 watt LED using today's technology, or a 10 watt LED if they reach 200 lm/W. The difference in output is even more dramatic-100 lumen per package today, or 2000 lumen per package with the LED I mentioned.


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## jtr1962 (Oct 12, 2006)

I should also add that active cooling _may_ make some sense _if_ two conditions are met:

1) The LED output is very sensitive to temperature swings. The red-orange and amber Luxeons are good examples of this. In my experiments I increased the output of an amber Luxeon by a factor of nearly 3 _without overdriving_ by taking the heat sink to -44°C.

2) More efficient coolers are developed. Since such coolers would have a myriad of other uses besides cooling LEDs. I'm sure within a decade or two they will exist. If we can get to 50% Carnot efficiency then cooling an amber or red-orange LED will provide a net efficiency increase.

There is still the practical problem of dealing with condensation/frost on the LED if you go below dewpoint. This may make active cooling of limited value in humid environments.


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## NewBie (Oct 12, 2006)

Sawtooth said:


> Newbie, Thanks for the references. These should help alot! :thumbsup:




No sweat, any time!

Here is a solution that is more along the lines of what you were dreaming about- it looks more like thick copper tape:

A new heat spreader technology from Celsia Technologies uses ultra-thin
chambers of fluid divided by a vaporization zone that are 1.4mm thick, and
boast a thermal conductivity of over 5,000 w/m-K, compared to 386 w/m K for copper or 205 w/m-K for aluminum, two common heat spreader materials. As an example of the price-performance of the Microspreader, George Meyers VP of sales, claims a personal computer design that currently relies on a $4 fan assembly could replace it with a Microspreader with a similar cost that is
lighter, smaller and more reliable.

http://www.edn.com/blog/1470000147/post/230004823.html?nid=2432&rid=1016492294


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## Walterk (Apr 5, 2010)

Once Newbie,

Any idea where to get plain heatpipes, without curves and attached sinks? Didnt find any yet. (Besides the link you gave in one of above postings.) 

Heatpipes really would be perfect for my projectlight.

I can house a heatsink to capture the heat, but it has little air to cool to the outside air. I have (close to endless ) room for fins once I can transport the heat a couple of inches. 
And it is passive so near failproof.
I think heatpipes are the answer. 

I am a bit hesitant to spend loads of bucks on PCU-heatsink that need more adapting (cutting away fins ) then plain pipes.
Bending pipes is to tricky to from what ive read on PC overclocking forums.


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## jugornot (Apr 5, 2010)

Perhaps use mineral oil to fill the flashlight. Electrically non-conductive and it spreads the heat to the entire surface of the light. Heat pipes are efficient but require air circulation to work. Using liquid cooling spreads the heat load and increases cooling efficiency. The water cooling rig I use for my computer uses non-conductive fluid, in case of an emergency.


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## saabluster (Apr 6, 2010)

Walterk said:


> Once Newbie,
> 
> Any idea where to get plain heatpipes, without curves and attached sinks? Didnt find any yet. (Besides the link you gave in one of above postings.)
> 
> ...


Newbie no longer roams these halls unfortunately.


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## Walterk (Apr 6, 2010)

@Saabluster : Thx, Will probably try a laptop heatsink then.
@ jugornot : Each problem has its own solution, borrowd here, borrowed there


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## circa (Apr 6, 2010)

Although not a peltier or heat pipe, www.ledcoolers.com . Solid sinks are ok, but thinking of CPU stuff, why can't ours be finned too?

One product on there is nearly the right size for a D mag.


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## Walterk (May 4, 2010)

I am going to use an old lap-top assembly.
It has three heatpipes and copper fins, was force ventilated by two fans.
The Intel Pentium 4 was still attached, I believe this P4 is rated at 65 Watt, so for non-forced cooling ventilated to outside air I guess it should cope well with 30 Watt like the SST90 Led. 

Used Dremel grinder to work off the obsolete material, and bend the 90 degr angle back to a straight line by hand. Glad I didnt break anything after all the work in grinding clean, but the copper is really soft.

In doubt if I will use aluminium or copper to lead the heat to from the led to the heatpipes. 
Copper is difficult to drill deep but can store more heat, but alu guides it quicker to the heatpipes and after all thats why it is there...


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## Fallingwater (May 4, 2010)

Why run a peltier and fan in a flashlight? If you're going for active cooling just put the LED on a finned heatsink and be done with it.


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## Futuman (Jan 13, 2016)

Hi, could this be any use of this invention?

http://www.overclock.net/t/1587620/peltier-cube


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