Class A amps requires a lot off heatsinking. And there seems to be a constant stream of questions regarding this here in this forum.
There have been quite a lot of good info presented in this forum already. To collect all that and make a presentable info page could be a good idea, but I don’t feel quite up to something like that.
What I would like here is to share some of the things I have learned about it, and give some of you some ideas and food for thought. After all this is a DIY forum, and DIY’ers like to do as much as they can themselves.
There are three terms to consider. First is forced or convection cooling . Secondly the heat carrying medium, normally air or water (or other suitable fluids, like oil). Then there is passive or active cooling.
The main goal for heatsinking in amps is to enable the output devices to operate by in some way lead away the excess energy dissipated in the amplification. To most of you there is only one way of doing this, and that is to attach the power devices to conventional heatsinks that is capable of dissipating the heat generated at the temperatures required.
This is what’s known at passive convection cooling. The advantages of this method are many. First of all it is by far the easiest method to implement. All that is normally needed is to attach the heat-source mechanically to a suitable heatsink. Most amps use this method. It’s only when the heat dissipation is large that other methods is starting to become an alternative. And since the needs in the amps we are building here is in this category I thought I’d give you some ideas and facts on the other alternatives.
After “normal” heatsinks the most used method is forced cooling, and to most of you this is air, water or other fluids that is lead in good temperature contact with the heat-source. To get the needed heat transfer there normally still needs to be some kind of heatsinks. These heatsinks are normally made in other ways than normal heatsinks, and sometimes also in different materials.
About the heat-carrying media, this is normally air as this is the most convenient an accessible media. But a fluid is also possible to use as heat carrying media. Water is the easiest accessible, and at the same time one of the most efficient one (it is one of the fluids with the highest heat carrying capabilities).
It is possible to have both convection and forced fluid cooling. The most used one is forced. This is because it is much more efficient (as is forced air cooling compared to convection). It is often that since you have had to go to the step and use water-cooling in the first place it is most likely to be because you have such high cooling needs that active cooling is needed.
But for us amp builders passive water-cooling is a really attractive alternative. The way a normal heatsink is working is (partly, there is also radiation heat) by heating the surrounding air and make the air expand and rise, making new and cool air rush in and get heated in the same way. The exact same thing is possible in water-cooling. The thing about active cooling, be it air or water, is that it almost always makes noise! That is a very unwanted thing in a high-end amp (that is after all what we are trying to make here, right?). That is what makes passive water-cooling so attractive. It is possible to make it completely silent, and at the same time capable of handling large amounts of heat.
Now what can be done is to use water or oil to move the heat in a more efficient way out to large area heatsinks. By using oil or other media there is a possibility to take advantage of other attractive properties that is achievable, like higher expansion to heat, thus making it easier to make the medium flow.
There are several advantages of using fluids for cooling, and one of the most attractive one is the capability to take away large amounts of heat radiated in a small area. This is possible since it is possible to make the heat resistance lower. There are also lots of more advantages that can be made use of, but I’ll come back to that later.
The third way to cool things is the active way. There are several ways of achieving this, but the point is to take away the heat generated and moving it actively to other parts. The most common ways are known as phase-change and peltier. Common for these method is that they use energy to move more energy. So by using this method you are actually using energy on the cooling process itself in addition to the energy you want to get rid of. This is something to have in mind when using one these methods.
For amp cooling both of these methods can be used. In terms of ease the Peltier is by far the best. It is a device you putt between the device and the heatsink, and when applying power to it it takes energy from one side and transports it to the other side together with the energy used in the process to move the heat. One quite large downside is that you have to have even larger heatsinks, as they have to dissipate both the energy dissipated in the heat-source and the heat from the peltier used in moving the heat. This heat can often be a great part of the total as the efficiency of the peltier is quite low! So if your goal is to find a way to use smaller heatsinks peltier is NOT the way to go. If you goal on the other hand is to be able to dissipate large amounts of heat dissipated on small areas there can be an advantage in using peltiers. If you for example are trying to build amps using only a few output devices and want to run them at very large dissipation levels (like using only 4 power devices in a AlephX with 300 W dissipation, meaning 75 W idle on each device) peltiers could make this possible!
But the far most used active cooling is the phase-change. This is the way most refrigerators work, and is a perfect way to cool semiconductors. I don’t know of any amps that use this cooling method, but I have heard of people on the forum that have thought about it. And to be honest I think it is a perfect way of doing it. I’m even considering it myself. If interested in more knowledge go to www.phase-change.com .
Now lots of my knowledge on cooling comes from studying other amps and normal literature about the subject. But one great source of information and knowledge on the subject is from Over-Clockers. There have for a long time been a development in the computer industry to make more and more power-consuming CPU’s. And this has lead to an enormous development of cooling methods. The thing about computers is that at the present moment the CPU’s are dissipating so large amounts of heat that they are way past what we use in each output devices we are using in our power amps.
As an example I can mention that my trusty old AMD Athlon Thunderbird puts out something like 70W on 0.5 cm2 ! That is way more than any of us (except for maybe Nelsson Pass in this thread: http://www.diyaudio.com/forums/showthread.php?postid=263016#post263016 ) dissipate in each power device.
I think we have a lot to learn from these guys as they have no alternative as we have to parallel devices. You can’t just parallel two CPU’s in a computer to give a lower heat resistance 🙂 . And when they even increase these figures by cranking up the voltage to mage the CPU’s go faster, and at the same time try to get them as cold as possible to make them go even faster than that…..
Then there is passive phase change, or heat pipes as they are normally called. These work by making a closed loop of evaporating and condensing a selected media. This media is picked to have a boiling point in a suitable range for us, and is put in thermal contact with the heat-source and evaporated taking energy in that process. The steam from this process is lead along a tube and condensed at the other end of the pipe that is normally finned to be able to give of the heat given of by the condensing fluid. The fluid is then brought back to the heat-source by a wick, and evaporated again closing the circle.
This is also an appealing way to do it in an amp because it’s efficiency and low thermal resistance. It is also noiseless if the heatsink in the dissipating end is made with large enough heat fins. It is probably not that easy to make a DIY-version of this, but it will probably be doable. This method has lots of appealing qualities, and is one I’m going to look deeper in to.
One method is kind of on the side, and is possible to combine with several of the above-mentioned methods. I for one have made serious thoughts about using it both in amp cooling and OC’ing. What I’m talking about is submersion. The whole idea is to submerge the power device itself in to the cooling liquid. The whole point is to take away one of the heat resistances.
Witch brings me to another thing to think about here. The heat resistance is built up of several resistances in series. The whole point is to make the total resistance as small as possible, but there are only some of the resistances that are possible to do something about.
In submersion one of these resistances that is normally always there is taken away. In applications with very high dissipation levels this is of outmost importance, and it is therefore a very effective tool in increasing dissipation capabilities. But it demands a lot more than normal cooling in mechanical design.
When it comes to calculating the different types of cooling devices mentioned here there are huge differences in how this is done. Especially when it comes to phase-change methods there is no longer talk about heat resistance, but energy moving capability. Remember that the heat is carried away by a medium, and the specific heat capacity together with the mass flow determines the energy movement. There are of course resistances, but there are what could be looked on as voltage or current sources in the heat path.
Due to measge length limitations to be continue
There have been quite a lot of good info presented in this forum already. To collect all that and make a presentable info page could be a good idea, but I don’t feel quite up to something like that.
What I would like here is to share some of the things I have learned about it, and give some of you some ideas and food for thought. After all this is a DIY forum, and DIY’ers like to do as much as they can themselves.
There are three terms to consider. First is forced or convection cooling . Secondly the heat carrying medium, normally air or water (or other suitable fluids, like oil). Then there is passive or active cooling.
The main goal for heatsinking in amps is to enable the output devices to operate by in some way lead away the excess energy dissipated in the amplification. To most of you there is only one way of doing this, and that is to attach the power devices to conventional heatsinks that is capable of dissipating the heat generated at the temperatures required.
This is what’s known at passive convection cooling. The advantages of this method are many. First of all it is by far the easiest method to implement. All that is normally needed is to attach the heat-source mechanically to a suitable heatsink. Most amps use this method. It’s only when the heat dissipation is large that other methods is starting to become an alternative. And since the needs in the amps we are building here is in this category I thought I’d give you some ideas and facts on the other alternatives.
After “normal” heatsinks the most used method is forced cooling, and to most of you this is air, water or other fluids that is lead in good temperature contact with the heat-source. To get the needed heat transfer there normally still needs to be some kind of heatsinks. These heatsinks are normally made in other ways than normal heatsinks, and sometimes also in different materials.
About the heat-carrying media, this is normally air as this is the most convenient an accessible media. But a fluid is also possible to use as heat carrying media. Water is the easiest accessible, and at the same time one of the most efficient one (it is one of the fluids with the highest heat carrying capabilities).
It is possible to have both convection and forced fluid cooling. The most used one is forced. This is because it is much more efficient (as is forced air cooling compared to convection). It is often that since you have had to go to the step and use water-cooling in the first place it is most likely to be because you have such high cooling needs that active cooling is needed.
But for us amp builders passive water-cooling is a really attractive alternative. The way a normal heatsink is working is (partly, there is also radiation heat) by heating the surrounding air and make the air expand and rise, making new and cool air rush in and get heated in the same way. The exact same thing is possible in water-cooling. The thing about active cooling, be it air or water, is that it almost always makes noise! That is a very unwanted thing in a high-end amp (that is after all what we are trying to make here, right?). That is what makes passive water-cooling so attractive. It is possible to make it completely silent, and at the same time capable of handling large amounts of heat.
Now what can be done is to use water or oil to move the heat in a more efficient way out to large area heatsinks. By using oil or other media there is a possibility to take advantage of other attractive properties that is achievable, like higher expansion to heat, thus making it easier to make the medium flow.
There are several advantages of using fluids for cooling, and one of the most attractive one is the capability to take away large amounts of heat radiated in a small area. This is possible since it is possible to make the heat resistance lower. There are also lots of more advantages that can be made use of, but I’ll come back to that later.
The third way to cool things is the active way. There are several ways of achieving this, but the point is to take away the heat generated and moving it actively to other parts. The most common ways are known as phase-change and peltier. Common for these method is that they use energy to move more energy. So by using this method you are actually using energy on the cooling process itself in addition to the energy you want to get rid of. This is something to have in mind when using one these methods.
For amp cooling both of these methods can be used. In terms of ease the Peltier is by far the best. It is a device you putt between the device and the heatsink, and when applying power to it it takes energy from one side and transports it to the other side together with the energy used in the process to move the heat. One quite large downside is that you have to have even larger heatsinks, as they have to dissipate both the energy dissipated in the heat-source and the heat from the peltier used in moving the heat. This heat can often be a great part of the total as the efficiency of the peltier is quite low! So if your goal is to find a way to use smaller heatsinks peltier is NOT the way to go. If you goal on the other hand is to be able to dissipate large amounts of heat dissipated on small areas there can be an advantage in using peltiers. If you for example are trying to build amps using only a few output devices and want to run them at very large dissipation levels (like using only 4 power devices in a AlephX with 300 W dissipation, meaning 75 W idle on each device) peltiers could make this possible!
But the far most used active cooling is the phase-change. This is the way most refrigerators work, and is a perfect way to cool semiconductors. I don’t know of any amps that use this cooling method, but I have heard of people on the forum that have thought about it. And to be honest I think it is a perfect way of doing it. I’m even considering it myself. If interested in more knowledge go to www.phase-change.com .
Now lots of my knowledge on cooling comes from studying other amps and normal literature about the subject. But one great source of information and knowledge on the subject is from Over-Clockers. There have for a long time been a development in the computer industry to make more and more power-consuming CPU’s. And this has lead to an enormous development of cooling methods. The thing about computers is that at the present moment the CPU’s are dissipating so large amounts of heat that they are way past what we use in each output devices we are using in our power amps.
As an example I can mention that my trusty old AMD Athlon Thunderbird puts out something like 70W on 0.5 cm2 ! That is way more than any of us (except for maybe Nelsson Pass in this thread: http://www.diyaudio.com/forums/showthread.php?postid=263016#post263016 ) dissipate in each power device.
I think we have a lot to learn from these guys as they have no alternative as we have to parallel devices. You can’t just parallel two CPU’s in a computer to give a lower heat resistance 🙂 . And when they even increase these figures by cranking up the voltage to mage the CPU’s go faster, and at the same time try to get them as cold as possible to make them go even faster than that…..
Then there is passive phase change, or heat pipes as they are normally called. These work by making a closed loop of evaporating and condensing a selected media. This media is picked to have a boiling point in a suitable range for us, and is put in thermal contact with the heat-source and evaporated taking energy in that process. The steam from this process is lead along a tube and condensed at the other end of the pipe that is normally finned to be able to give of the heat given of by the condensing fluid. The fluid is then brought back to the heat-source by a wick, and evaporated again closing the circle.
This is also an appealing way to do it in an amp because it’s efficiency and low thermal resistance. It is also noiseless if the heatsink in the dissipating end is made with large enough heat fins. It is probably not that easy to make a DIY-version of this, but it will probably be doable. This method has lots of appealing qualities, and is one I’m going to look deeper in to.
One method is kind of on the side, and is possible to combine with several of the above-mentioned methods. I for one have made serious thoughts about using it both in amp cooling and OC’ing. What I’m talking about is submersion. The whole idea is to submerge the power device itself in to the cooling liquid. The whole point is to take away one of the heat resistances.
Witch brings me to another thing to think about here. The heat resistance is built up of several resistances in series. The whole point is to make the total resistance as small as possible, but there are only some of the resistances that are possible to do something about.
In submersion one of these resistances that is normally always there is taken away. In applications with very high dissipation levels this is of outmost importance, and it is therefore a very effective tool in increasing dissipation capabilities. But it demands a lot more than normal cooling in mechanical design.
When it comes to calculating the different types of cooling devices mentioned here there are huge differences in how this is done. Especially when it comes to phase-change methods there is no longer talk about heat resistance, but energy moving capability. Remember that the heat is carried away by a medium, and the specific heat capacity together with the mass flow determines the energy movement. There are of course resistances, but there are what could be looked on as voltage or current sources in the heat path.
Due to measge length limitations to be continue
I have plans to write up more detailed info on this and more on each of the above mentioned methods here if there is interest for it. And if others feel like contributing, or have specific questions this would be a great way to try to condense some knowledge that would be great to have when thinkering about Class-A amp building and cooling them by DIY-means. I for one think that there is lots of possible ways of doing this that deserves to be looked in to. And there are certainly lots of good sources out there to supply this knowledge. The problem is to find it…. And since this is such a great forum I think this should be a suitable place to find it.
Anders
Anders
Peltiers are most certainly NOT a viable method of cooling an amplifier. They work "acceptably" at cooling a computer's CPU or GPU because there are only one or two heat sources, and even then, massive (275+ Watts for a single CPU peltier) power supplies and actively-cooled radiators (for water-cooled pelts) are necessary. Now, take an amplifier with 75 watts of idle dissipation on each device. That means for a peltier to maintain the same temperature on both sides, you need a 75-watt peltier element (for each device). This would obvioulsly not be desirable since the peltier would dissipate 75 watts of heat itself, and thus would result in nothing more than a net doubling of the idle heat dissipation. In order to cool a device to ambient, you would need a minimum of a 200-watt peltier for each device, and a power supply capable of running all of them.
Then you must have heatsinks capable of dissipating 275+ watts per device, while keeping the "hot side" of the peltier no more than 70°C above ambient. Obviously, this won't be possible with any "conventional heatsinking," and you have only managed to increase your idle dissipation for those same four devices to 1100 watts and also requiring a minimum of 800 watts DC to run the peltiers, all to lower the temperature of your output fets to ambient, and provide no real benefit. The mosfets won't last longer, because the system would be far more prone to failure if you were using TEC's. 226-watt peliters are used by overclockers in water-cooled (with powerful fans and pumps) systems to keep their CPU below ambient temperature. This creates its own problems in terms of preventing condensation, and if the peltier fails (as they can easily do), it becomes a layer of thermal insulation between the CPU and the water block, which is not good.
I also don't like the idea of "completely passive" water-cooling. While it is technically possible by using convetion currents, it would not be able to transfer sufficient heat without active liquid circulation. Even then, an even larger passive radiator (no, not a speaker) would be required than an ordinary heatsink. And, while you aren't adding any noise, it also would provide worse thermal performance and much greater cost than a normal aluminum heatsink.
The only truly effective way to silently improve cooling without going to extreme measures like air conditioning your amp chassis would be to use copper heatsinks. Copper has approximately twice the thermal conductivity of Aluminum, and can dissipate far more heat without raising the temperature. It is also much more expensive and much harder to find in large heatsinks suitable for amplifiers. Silver is more thermally conductive than copper, but only slightly so, and will give only about half a degree C of a performance improvement. Water cooling does work, and if you can put your pump and radiator in another room with the tubing as short as possible, you can have good, silent results, but a huge fan-cooled radiator, about the size of that needed for a car engine, will still be necessary to dissipate about 800W of heat (a couple of class-A amps), and still don't expect much of an improvement in temperature.
Then you must have heatsinks capable of dissipating 275+ watts per device, while keeping the "hot side" of the peltier no more than 70°C above ambient. Obviously, this won't be possible with any "conventional heatsinking," and you have only managed to increase your idle dissipation for those same four devices to 1100 watts and also requiring a minimum of 800 watts DC to run the peltiers, all to lower the temperature of your output fets to ambient, and provide no real benefit. The mosfets won't last longer, because the system would be far more prone to failure if you were using TEC's. 226-watt peliters are used by overclockers in water-cooled (with powerful fans and pumps) systems to keep their CPU below ambient temperature. This creates its own problems in terms of preventing condensation, and if the peltier fails (as they can easily do), it becomes a layer of thermal insulation between the CPU and the water block, which is not good.
I also don't like the idea of "completely passive" water-cooling. While it is technically possible by using convetion currents, it would not be able to transfer sufficient heat without active liquid circulation. Even then, an even larger passive radiator (no, not a speaker) would be required than an ordinary heatsink. And, while you aren't adding any noise, it also would provide worse thermal performance and much greater cost than a normal aluminum heatsink.
The only truly effective way to silently improve cooling without going to extreme measures like air conditioning your amp chassis would be to use copper heatsinks. Copper has approximately twice the thermal conductivity of Aluminum, and can dissipate far more heat without raising the temperature. It is also much more expensive and much harder to find in large heatsinks suitable for amplifiers. Silver is more thermally conductive than copper, but only slightly so, and will give only about half a degree C of a performance improvement. Water cooling does work, and if you can put your pump and radiator in another room with the tubing as short as possible, you can have good, silent results, but a huge fan-cooled radiator, about the size of that needed for a car engine, will still be necessary to dissipate about 800W of heat (a couple of class-A amps), and still don't expect much of an improvement in temperature.
tpenguin said:
The problem is not likely to be conductivity, and Aluminium has a higher emissivity - thus it is in fact wrong to say that Copper can dissipate more heat than Aluminium - it might but it would require major design changes. The advantages of Copper is that you can make finer, denser products but that means forced air cooling. Also, the weight of Copper is so high that you will likely not want to build a Copper heatsink. I am surprised that heatsink manufacturers don't make black anodized Aluminium over Copper heatsinks for their finest forced air CPU coolers.
Submersion is very cool (no pun intended).
The cheapest way to go is tap water cooled with exhaust being dumped. I had some friends with an amp like that - turned ugly when some fool shut the water off 🙂
Petter
Well, speaking as an overclocker who has tried various different cooling methods, including water, copper heatsinks provide significantly better performance than aluminum, whether using forced-air cooling or semi-passive (fans on case only). Copper-Aluminum hybrid heatsinks are also used quite successfully, but all-copper is still by far the best. Submersion in water (especially tap water) is a bad idea. Tap water contains lots of dissolved minerals, which will deposit on whatever it touches in addition to being highly electrially conductive, and distilled/deionized water is extremely corrosive and will destroy any metal it touches very quickly. Submersion cooling should be done with a completely inert liquid, which water most certainly is not. Pure water would work well for a while, though.
Petter said:
Here is Zalman's passive water-cooling radiator. This is intended to be used for a CPU, and maybe a video card, totalling less than 150watts. It is obviously quite large, and two would be needed to cool one chanel of an AlephX, along with a good pump. It still would be worse than direct heatsink mounting because of the extra thermal bariers between the waterblocks and the water and the water and the radiator.
Attachments
Petter said:
It's not just dissolved "solids" -- if you aren't changing the water and using "agents" you get "biologicals" in the water!
30 years ago I used to follow a couple of companies in the water-treatment industry -- Betz, Nalco, Dearborn, Petrolite -- there are aspects of cooling water treatment which are fairly easy to deal with, but there's a reason that engineers from the aforementioned companies are on site at the Exxon or Dow Chemical refineries.
I would used distilled water or ethylene glycol.
The 'best' quiet PC cooling system that I have seen so far is also from zalman, and as you can see from the pic below, they are basicaly follwing the same idea that you will find on a lot of the high power amps produced here. The only other way which I have seen to give good, quiet cooling, was to burry a large metal tank in the ground (quite deep down where it is always cold), fill it with water and use this with a pump to cool waterblocks (Have a look here).
You can also read a bit more about the zalman case here.
You can also read a bit more about the zalman case here.
An externally hosted image should be here but it was not working when we last tested it.
Althought the Zalman flower coolers are really no good for amplifier cooling they do work well in the PC environment. I have one (the ALCU varient) and needless to say the power supply produces more noise then the CPU cooler. Which is not a lot of noise, you have to be actively listening for the PC to be aware of it which is great!. You should hear the other two PC's in the house BUZZZZZZ HUMMM WHURRR!, nitemare I tell you. Oh and copper is better then AL for a cooler on a CPU. We recently got a Thermal take volcano 7+ for one of the PC's, on its low fan speed setting it is about 10 degrees cooler then an aluminium sink.
Forced air cooling
Hello all,
Just thought I add my 2 cents.
I am collecting parts to build 4 channels of Aleph 5 and since I already have the heatsinks and they are a bit on the skimpy side, I will be using forced air cooling.
In my last job I worked at a firm that designs video projectors, and since I am a mechanical engineer, a lot of the design is influenced by thermal aspects. This is because a beamer (or LCD projector) with a 200watt bulb puts out a lot of heat. Getting rid of this heat is no picknick because the housing is getting smaller and smaller, so you can't just put a big fan in there. Furthermore, even if you can use a bigger fan, you can't just have the fan run at it's intended (or max) voltage because it then would produce to much noise. So all of the fans are controlled from software (temperature) and are as big as possible because a large fan running at a lower voltage produces less noise than a small fan running at a higher voltage (and both fans producing the same flow).
In a LCD projector two types of forced air cooling are used:
"Spot" cooling using radial fans
"General" cooling using axial fans
For instance LCD's and polarisers are cooled using a high velocity airstream but low cfm, to cool a specific spot.
The rest of the inside apparatus is cooled using a higher cfm and low velocity airstream.
In my Aleph 5's I will use the same technique, the fets will receive "spot" cooling with radial fans and airguides. While the fins on the heatsink will be cooled using axial fans
Regards,
Jarno.
Hello all,
Just thought I add my 2 cents.
I am collecting parts to build 4 channels of Aleph 5 and since I already have the heatsinks and they are a bit on the skimpy side, I will be using forced air cooling.
In my last job I worked at a firm that designs video projectors, and since I am a mechanical engineer, a lot of the design is influenced by thermal aspects. This is because a beamer (or LCD projector) with a 200watt bulb puts out a lot of heat. Getting rid of this heat is no picknick because the housing is getting smaller and smaller, so you can't just put a big fan in there. Furthermore, even if you can use a bigger fan, you can't just have the fan run at it's intended (or max) voltage because it then would produce to much noise. So all of the fans are controlled from software (temperature) and are as big as possible because a large fan running at a lower voltage produces less noise than a small fan running at a higher voltage (and both fans producing the same flow).
In a LCD projector two types of forced air cooling are used:
"Spot" cooling using radial fans
"General" cooling using axial fans
For instance LCD's and polarisers are cooled using a high velocity airstream but low cfm, to cool a specific spot.
The rest of the inside apparatus is cooled using a higher cfm and low velocity airstream.
In my Aleph 5's I will use the same technique, the fets will receive "spot" cooling with radial fans and airguides. While the fins on the heatsink will be cooled using axial fans
Regards,
Jarno.
Part 2, spreading the heat.
Ok, just as I expected.
The reason for starting this thread is to try to get some beliefs out of the way, and lead as many of you to a different way to see things. The heatinks is a system consisting of several parts. When you all design or modify amp circuits you all obediently follow simple rules like Ohms law (I hear there’s severe punishments for those trying to break that law… 🙂 ). And the different part of the system is physically consisting of different parts, like transistors, resistors and condensators.
But many of you seem to think there’s something magical or something that comes in to play in heatinking. I just want to remind you all that heat flow in an amp should be handled with the same degree of care as the operating point with correct voltages and currents. The problem is that the different values of the parts are much more uncontrollable and unpredictable.
Heat flow is about the same as current flow, and temperature is the heat’s voltage. A more correct approach to heatsinking is therefore to go over the heat path with the same care as the currents through the amp.
The last Excel sheet for calculating AlephX is a really good starting point. On the bottom of it there are complete calculations for the heat path. And you will see that it is separating the different parts of the heatsink system. Now what I would like is to take it even more apart. Getting rid of heat is done in several steps, and all of them have to be taken care of.
What I’m trying to get at here is that where OC’ers is really starting to realize that there are ways of increasing the cooling capacities. As I mentioned they have already passed the barrier of what is possible to dispense of heat with normal passive heatsinks no matter what material they are made of. They have even reached a level of heat produced per area that normal forced cooling is starting to give up, or at least other even more efficient methods are wanted.
These needs have made them start exploring ways of cooling only used by extremely expensive machinery only a few years ago. And the thing to do then is take a closer look at what the different parts the heatsink job is.
You guys have already started the discussion on witch of the materials copper or aluminium is better for heatsinks. The thing is that there is no such thing as best. It’s like comparing oranges and bananas. One is good for one thing and the other for another. Copper IS a better heat conductor. That is a fact, and depending on use this is more or less the most important criteria for a good heatsink. But this is only part of the truth. The other important factor is the materials ability to transfer this heat over to the surroundings or the cooling media, be it water or air (whatever used). There are two ways of transferring heat, and one is direct radiation, and the second is contact transfer. These require different mechanical properties of the heatsink material. Radiation is best done from a black surface, and by anodising aluminium it is possible to get a very emissive surface. One other thing that helps aluminium to have such a high emission is the way the black coating surface is possible to be made. On most metals (including copper??) there have to be put on some kind of paint or other layer of material on the surface of the material. This layer should have as good thermal conductivity as possible, and also be in as good contact with the material as possible. That is not that easily achieved. When anodizing aluminium this layer is made up of aluminium oxide that binds in the colour in the surface in a very thin layer. This layer is made up from aluminium from the material itself, and is therefore in perfect contact with the material. And AlOx is even a very good heat conductor.
All of this gives aluminium the possibility to have a rather high heat emissive capability. This is also why some of you claim that aluminium is a better heatsink material. Now this is not necessarily true, even if it CAN be in some cases. It all depends on the way heat is transported away from the heatsink. In a normal passive heatsink a lot of the heat is disposed of as radiation. The heating of air and direct conduction to the cooling media is a smaller part of it. For this use black anodised aluminium is less expensive, lighter in weight and more efficient than copper.
But when we start moving in to less radiation and more directly contact transfer copper with its higher conductivity is better suited.
To make an example to illustrate this lets think of a plate made of our chosen heatsink material. If it is heated in spot the heat will spread out to all the parts of the plate. The heat given of by the plate is determined on both it’s ability to radiate the heat, heat the surrounding air and it’s ability to spread the heat to all parts of the plate. This is not an easy equation, and it all depends on LOTS of things. I’m not going to get in to any of them here, just consider the following: If radiation is the main dissipating effect the dissipating capabilities of the material is important. But as the size of the plate increases to give larger surface to radiate from the distance from the heat source the temperature resistance to the farthest part of the plate are going higher. And at one point it is high enough to make the plate incapable of working as heatsink since the heat are unable to reach that part of the plate. Now to help that it is possible to increase the conductivity of the plate by either use a thicker plate, or use a better conducting material. Now if we say we use the later method and go from aluminium to copper we have one problem, and that is the chosen form of dissipation is radiation. Copper have not so good dissipating capabilities, but at one point we are going to have a benefit after all, and that is due to the fact that the heat is capable of reaching a larger part of the plate to give of heat. And a higher surface temperature has higher radiation. And since the outer parts of the plate now has a higher temperature since the plate is capable of transporting the heat out there we have a better heatsink after all.
And in the case where conduction is the main dissipating factor copper with its higher conduction is a better material almost no matter what. And that is why it is considered the material of choice in CPU and other computer cooling. This is because they almost always use forced cooling, and this is a form where conduction is the main dissipation form. This is also why the surface area to volume is so immensely higher in CPU coolers than in normal heatsinks. If you take a look at a radiator you find that this also have about the same surface to volume ratio. This is because this is found to be the best and most material efficient ratio.
Ok, now let’s say we increase the dissipated heat further. Now we don’t have the possibility to change to a better conducting material (ok there is silver, but I don’t think any of you will go that way, and there is not so much to gain either). So the only way is to use thicker plates to help distribute the heat to a further distance from the heat source. But as we do this the physical size is starting to grow FAST! And to double the dissipation the materials needed is doubled many times! And at one point there is even not possible to get more heat out of the device by normal heatsinks no matter how much larger you make it.
This is where we have to start looking at the different part of the heatsink’s job and se what can be done about the different parts.
As I mentioned, us amp builders just go to the step of paralleling output devices to allow for the increased heat load. And since computers can’t do the same they have to be more inventive in their ways of cooling CPU’s and so on. If you take a look at the latest CPU coolers you’ll see that they are starting to use heatpipes to help spread the heat to the outer parts of the heat fins of the heatsinks.
Heatpipes are using other physical phenomena (phase change, I’ll come back to that) to move the heat, and is therefore able to be used in parallel to normal hetasinks. Or it can be used to make normal heatsinks more efficient by helping spread the heat more evenly thus using the large surface area of the heatsink in a more efficient way. This is done in commercial amplifiers, and one I remember seeing this in is the STAX class-A amps from the 90’s. I have also seen it in much cheaper amps. And this could be taken as a hint that it is actually doable at a not so high cost. And as DIY’ers we should look for solutions that are probably demanding more work with less/cheaper materials over methods requiring little work but more/expensive materials. And in this regard heatpipes is very much in the first category.
The thing I’m addressing here is the heatsink’s ability to spread the heat internally in such a manner that it is possible to be as efficient as possible on an as large part of the surface.
I remember reading in this forum that P4 CPU’s actually REQUIRES a heat spreading copper plate to spread the heat enough for aluminium heatsinks to work properly! Although if a copper heatsink was used this plate is actually a disadvantage since it makes another material-to-material transition. This is a very good example to illustrate my point here. As the heat densities are starting to increase the heat conductivity in the materials used are starting to play a larger role. Therefore the preference for copper in CPU cooling area due to the very high power densities there. But to make my point, here the necessity to distribute the heat to make use of larger parts of the heatsink is perfectly illustrated.
Running in to length limitations again..... argh.... to be continued
Anders
Ok, just as I expected.
The reason for starting this thread is to try to get some beliefs out of the way, and lead as many of you to a different way to see things. The heatinks is a system consisting of several parts. When you all design or modify amp circuits you all obediently follow simple rules like Ohms law (I hear there’s severe punishments for those trying to break that law… 🙂 ). And the different part of the system is physically consisting of different parts, like transistors, resistors and condensators.
But many of you seem to think there’s something magical or something that comes in to play in heatinking. I just want to remind you all that heat flow in an amp should be handled with the same degree of care as the operating point with correct voltages and currents. The problem is that the different values of the parts are much more uncontrollable and unpredictable.
Heat flow is about the same as current flow, and temperature is the heat’s voltage. A more correct approach to heatsinking is therefore to go over the heat path with the same care as the currents through the amp.
The last Excel sheet for calculating AlephX is a really good starting point. On the bottom of it there are complete calculations for the heat path. And you will see that it is separating the different parts of the heatsink system. Now what I would like is to take it even more apart. Getting rid of heat is done in several steps, and all of them have to be taken care of.
What I’m trying to get at here is that where OC’ers is really starting to realize that there are ways of increasing the cooling capacities. As I mentioned they have already passed the barrier of what is possible to dispense of heat with normal passive heatsinks no matter what material they are made of. They have even reached a level of heat produced per area that normal forced cooling is starting to give up, or at least other even more efficient methods are wanted.
These needs have made them start exploring ways of cooling only used by extremely expensive machinery only a few years ago. And the thing to do then is take a closer look at what the different parts the heatsink job is.
You guys have already started the discussion on witch of the materials copper or aluminium is better for heatsinks. The thing is that there is no such thing as best. It’s like comparing oranges and bananas. One is good for one thing and the other for another. Copper IS a better heat conductor. That is a fact, and depending on use this is more or less the most important criteria for a good heatsink. But this is only part of the truth. The other important factor is the materials ability to transfer this heat over to the surroundings or the cooling media, be it water or air (whatever used). There are two ways of transferring heat, and one is direct radiation, and the second is contact transfer. These require different mechanical properties of the heatsink material. Radiation is best done from a black surface, and by anodising aluminium it is possible to get a very emissive surface. One other thing that helps aluminium to have such a high emission is the way the black coating surface is possible to be made. On most metals (including copper??) there have to be put on some kind of paint or other layer of material on the surface of the material. This layer should have as good thermal conductivity as possible, and also be in as good contact with the material as possible. That is not that easily achieved. When anodizing aluminium this layer is made up of aluminium oxide that binds in the colour in the surface in a very thin layer. This layer is made up from aluminium from the material itself, and is therefore in perfect contact with the material. And AlOx is even a very good heat conductor.
All of this gives aluminium the possibility to have a rather high heat emissive capability. This is also why some of you claim that aluminium is a better heatsink material. Now this is not necessarily true, even if it CAN be in some cases. It all depends on the way heat is transported away from the heatsink. In a normal passive heatsink a lot of the heat is disposed of as radiation. The heating of air and direct conduction to the cooling media is a smaller part of it. For this use black anodised aluminium is less expensive, lighter in weight and more efficient than copper.
But when we start moving in to less radiation and more directly contact transfer copper with its higher conductivity is better suited.
To make an example to illustrate this lets think of a plate made of our chosen heatsink material. If it is heated in spot the heat will spread out to all the parts of the plate. The heat given of by the plate is determined on both it’s ability to radiate the heat, heat the surrounding air and it’s ability to spread the heat to all parts of the plate. This is not an easy equation, and it all depends on LOTS of things. I’m not going to get in to any of them here, just consider the following: If radiation is the main dissipating effect the dissipating capabilities of the material is important. But as the size of the plate increases to give larger surface to radiate from the distance from the heat source the temperature resistance to the farthest part of the plate are going higher. And at one point it is high enough to make the plate incapable of working as heatsink since the heat are unable to reach that part of the plate. Now to help that it is possible to increase the conductivity of the plate by either use a thicker plate, or use a better conducting material. Now if we say we use the later method and go from aluminium to copper we have one problem, and that is the chosen form of dissipation is radiation. Copper have not so good dissipating capabilities, but at one point we are going to have a benefit after all, and that is due to the fact that the heat is capable of reaching a larger part of the plate to give of heat. And a higher surface temperature has higher radiation. And since the outer parts of the plate now has a higher temperature since the plate is capable of transporting the heat out there we have a better heatsink after all.
And in the case where conduction is the main dissipating factor copper with its higher conduction is a better material almost no matter what. And that is why it is considered the material of choice in CPU and other computer cooling. This is because they almost always use forced cooling, and this is a form where conduction is the main dissipation form. This is also why the surface area to volume is so immensely higher in CPU coolers than in normal heatsinks. If you take a look at a radiator you find that this also have about the same surface to volume ratio. This is because this is found to be the best and most material efficient ratio.
Ok, now let’s say we increase the dissipated heat further. Now we don’t have the possibility to change to a better conducting material (ok there is silver, but I don’t think any of you will go that way, and there is not so much to gain either). So the only way is to use thicker plates to help distribute the heat to a further distance from the heat source. But as we do this the physical size is starting to grow FAST! And to double the dissipation the materials needed is doubled many times! And at one point there is even not possible to get more heat out of the device by normal heatsinks no matter how much larger you make it.
This is where we have to start looking at the different part of the heatsink’s job and se what can be done about the different parts.
As I mentioned, us amp builders just go to the step of paralleling output devices to allow for the increased heat load. And since computers can’t do the same they have to be more inventive in their ways of cooling CPU’s and so on. If you take a look at the latest CPU coolers you’ll see that they are starting to use heatpipes to help spread the heat to the outer parts of the heat fins of the heatsinks.
Heatpipes are using other physical phenomena (phase change, I’ll come back to that) to move the heat, and is therefore able to be used in parallel to normal hetasinks. Or it can be used to make normal heatsinks more efficient by helping spread the heat more evenly thus using the large surface area of the heatsink in a more efficient way. This is done in commercial amplifiers, and one I remember seeing this in is the STAX class-A amps from the 90’s. I have also seen it in much cheaper amps. And this could be taken as a hint that it is actually doable at a not so high cost. And as DIY’ers we should look for solutions that are probably demanding more work with less/cheaper materials over methods requiring little work but more/expensive materials. And in this regard heatpipes is very much in the first category.
The thing I’m addressing here is the heatsink’s ability to spread the heat internally in such a manner that it is possible to be as efficient as possible on an as large part of the surface.
I remember reading in this forum that P4 CPU’s actually REQUIRES a heat spreading copper plate to spread the heat enough for aluminium heatsinks to work properly! Although if a copper heatsink was used this plate is actually a disadvantage since it makes another material-to-material transition. This is a very good example to illustrate my point here. As the heat densities are starting to increase the heat conductivity in the materials used are starting to play a larger role. Therefore the preference for copper in CPU cooling area due to the very high power densities there. But to make my point, here the necessity to distribute the heat to make use of larger parts of the heatsink is perfectly illustrated.
Running in to length limitations again..... argh.... to be continued
Anders
I’m not saying this have to be done in each system, but it is better to look at the different tasks separately to se if it is possible to do something about it.
One thing possible to do to improve the heat spreading capabilities of a cooling system is to physically move away the heat absorbed by some kind of media. This method is what I referred to as forced cooling in my last post.
I’m interested in getting feedback on this, and hopefully others can contribute too. But I hope you can try to keep is as consistent to the topic as possible. And if you have different views please elaborate. Have the courtesy do not just stating things as facts without really having thought about it. The point here was to give the newcomers (and all you others too🙂 ) a chance to learn a trick or two, hopefully without having to thread through lots of gibberish.
Anders
One thing possible to do to improve the heat spreading capabilities of a cooling system is to physically move away the heat absorbed by some kind of media. This method is what I referred to as forced cooling in my last post.
I’m interested in getting feedback on this, and hopefully others can contribute too. But I hope you can try to keep is as consistent to the topic as possible. And if you have different views please elaborate. Have the courtesy do not just stating things as facts without really having thought about it. The point here was to give the newcomers (and all you others too🙂 ) a chance to learn a trick or two, hopefully without having to thread through lots of gibberish.
Anders
I can only second your theory by practical experience on the copper heat spreaders. Its fairly cheap, easy and reliable...and it lowers the component temperature significantly. Sometimes more than 20%.
I have made a few experiments with copper heatspreaders due to the fact that i have copper bus bars available in pretty much any (usefull for this) size.
My results have been that to cancel out the extra barrier you get from the contact from the copper heat spreader to the heatsink, you have to exceed 4 times the footprint of the component, where the heatspreader/-heatsink it connected.
You additional get the benefit of avoiding the insulator between the mosfet and the heatsink, since you can put the insulator between the heatspreader and the heatsink, where you have much bigger area to tranfer the heat...thus lower resistance in the entire chain, since you are allowed to use any silver compound you please (arctic silver for instance, there sure are other just as good compounds) between the mosfet and the heatspreader.
I actually once offered heatspreaders for sale here on this forum, back when i found out how much of a benefit they represent...but somehow nobody liked the idea back then.
Magura🙂
I have made a few experiments with copper heatspreaders due to the fact that i have copper bus bars available in pretty much any (usefull for this) size.
My results have been that to cancel out the extra barrier you get from the contact from the copper heat spreader to the heatsink, you have to exceed 4 times the footprint of the component, where the heatspreader/-heatsink it connected.
You additional get the benefit of avoiding the insulator between the mosfet and the heatsink, since you can put the insulator between the heatspreader and the heatsink, where you have much bigger area to tranfer the heat...thus lower resistance in the entire chain, since you are allowed to use any silver compound you please (arctic silver for instance, there sure are other just as good compounds) between the mosfet and the heatspreader.
I actually once offered heatspreaders for sale here on this forum, back when i found out how much of a benefit they represent...but somehow nobody liked the idea back then.
Magura🙂
Another option is condensation cooling. That can be done at DIY level.
If anyones interested i can explain.
Magura🙂
If anyones interested i can explain.
Magura🙂
Computer CPU cooling and audio amplifiers cooling are very different because the requirements aren't the same.
In a computer, the CPU can have to dissipate nearly 200W, on a tiny surface, and even worse: the CPU has little space around it to put a heatsink
-> the classical solution is to put an as-big-as-you-can heatsink, and a big fan blowing on it
alternative methods, like watercooling, phase change, heat pipes, (peltier is somewhat different)... don't cool "more", I mean: they aren't more efficient, or not significantly more. they advantage is to move the heat out of the small computer box, and put it at another place where you have more room to put a big heatsing
With amplifiers, especially DIY ones, you can design the case as big as necessary, to fit big heatsinks.
I don't see the need for alternative cooling methods for amps. Unless you prefer small amps with water tubes runing to a big heatsink, or if you don't pay the water
In a computer, the CPU can have to dissipate nearly 200W, on a tiny surface, and even worse: the CPU has little space around it to put a heatsink
-> the classical solution is to put an as-big-as-you-can heatsink, and a big fan blowing on it
alternative methods, like watercooling, phase change, heat pipes, (peltier is somewhat different)... don't cool "more", I mean: they aren't more efficient, or not significantly more. they advantage is to move the heat out of the small computer box, and put it at another place where you have more room to put a big heatsing
With amplifiers, especially DIY ones, you can design the case as big as necessary, to fit big heatsinks.
I don't see the need for alternative cooling methods for amps. Unless you prefer small amps with water tubes runing to a big heatsink, or if you don't pay the water
Bricolo said:
You could be surprised if you were to build a X-SOZ or the like.
I guess most people dont like to cross the 50KG mark (100pounds), and that happens real easy if you dont do something besides the regular heatsink stuff. The component temperature will per definition get rather high.
Another fact to keep in mind is that most people dont have the possibility to build something that big. Just start out by asking how many here could process 25mm (1") aluminium plate?
Did i mention the cost ?
Thats when the heatspreaders, the heatpipes and all the other little tricks gets into the picture.
Magura🙂
You got point, I didn't consider the cost of big heatsinks.
watercooling stuff has become very affordable during the last years
watercooling stuff has become very affordable during the last years
No need to go as far as watercooling...it is still a troublesome approach.
Actually even something as simple as a copper heat spreader can help the size of the whole thing a bit down.
With a correctly dimensioned heatspreader you can increase the transfer = lower component temp...higher heatsink temp, and higher dissipation for the respective size heatsink.
Magura🙂
Actually even something as simple as a copper heat spreader can help the size of the whole thing a bit down.
With a correctly dimensioned heatspreader you can increase the transfer = lower component temp...higher heatsink temp, and higher dissipation for the respective size heatsink.
Magura🙂
Well a piece of machined copper busbar is all there is to it.
Biggest limitation is that most people cant get a small piece of busbar (hence my offer to make a bunch for sale), but besides that, its the ticket. In most cases its possible to mount a heatspreader in an existing design, so its basicly a win-win situation.
If a need to transfer the heat over longer distances should be there, copper busbar does the trick as well. With copper 300 mm (approx. 1 foot) is no big deal. For mass production heatpipes are more attractive due to their low mass production price, but to go spend some 80 usd on a heatpipe as an end user would have to is not a lot of bang for the buck. That can be made in copper for the same price, and with a far better result.
Ive been working a lot with copper both due to my craft (toolmaker in diecasting) and for DIY, in both cases used for heat transfer reasons. I am 100% sure there is nothing that can compare to copper when it comes to heat transfer, for common mans money.
Magura 🙂
Biggest limitation is that most people cant get a small piece of busbar (hence my offer to make a bunch for sale), but besides that, its the ticket. In most cases its possible to mount a heatspreader in an existing design, so its basicly a win-win situation.
If a need to transfer the heat over longer distances should be there, copper busbar does the trick as well. With copper 300 mm (approx. 1 foot) is no big deal. For mass production heatpipes are more attractive due to their low mass production price, but to go spend some 80 usd on a heatpipe as an end user would have to is not a lot of bang for the buck. That can be made in copper for the same price, and with a far better result.
Ive been working a lot with copper both due to my craft (toolmaker in diecasting) and for DIY, in both cases used for heat transfer reasons. I am 100% sure there is nothing that can compare to copper when it comes to heat transfer, for common mans money.
Magura 🙂
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