Cases and heatsinks are a problem for DIY builds.
I made quite a few amplifiers with thick machined front panels, heavy finned heatsinks and aluminium cases. Such parts need machining and tapping.
I devised a way of making cases, which eliminated these problems and made for easier case design, lower costs and quicker builds.
Cases
Made from sheet aluminium alloy of preferably 3mm so only single sheet of material needed.
Depending on the facilities you have available these can be made manually. I get the parts laser cut by a company which will also supply the material. Alloy 5251 lasers and anodises well. The case parts need holes to be countersunk where necessary and are then taken for surface finishing, (bead blasting and anodising in my case).
I then take the front panels to be screen printed with the graphics I provide. The assembly is with corner posts and angle brackets cut and drilled, and bolted together. I only drill and tap corner posts to attach base and top panels. The case is basically a box with a front panel on to cover the front of the box.
Heatsinks
I became aware of porous ceramic heatsinks and realised that these small, light self-adhesive items would solve problems. I bought a few and tested to see if they did what was claimed. A single 50mm square of 10mm thick could dissipate 5-10W stuck on sheet aluminium. To make heatsinks you only have to bolt the semiconductors directly to the 3mm plates and place the ceramic heatsinks as needed.
Edit; a link to these was omitted, http://www.amecuk.co.uk/ Element14 has them in many countries.
https://www.newark.com/c/cooling-thermal-management/heat-sinks?brand=amec-thermasol
They are not expensive, and with a range of sizes you can arrange heatsinks of different shapes. I was concerned that they might unstick but the opposite has been true, they are hard to remove.
They are not pretty and can be easily chipped so I contain them inside the case and organise slots above and below to act as a chimney to allow convection. This works well and they do not run hot. The porous ceramic devices are very effective.
I have found that this method is much easier to procure and build. The amplifiers built this way can be smaller and lighter. These techniques can be adapted to any case whether needing heatsinks or not.
I should say that these heatsinks are small and they don't weigh much but that each amplifier on either side of the case dissipates about 14.5W and the heatsinks are only warm. (Edit; Further explanation a few posts below)
I made quite a few amplifiers with thick machined front panels, heavy finned heatsinks and aluminium cases. Such parts need machining and tapping.
I devised a way of making cases, which eliminated these problems and made for easier case design, lower costs and quicker builds.
Cases
Made from sheet aluminium alloy of preferably 3mm so only single sheet of material needed.
Depending on the facilities you have available these can be made manually. I get the parts laser cut by a company which will also supply the material. Alloy 5251 lasers and anodises well. The case parts need holes to be countersunk where necessary and are then taken for surface finishing, (bead blasting and anodising in my case).
I then take the front panels to be screen printed with the graphics I provide. The assembly is with corner posts and angle brackets cut and drilled, and bolted together. I only drill and tap corner posts to attach base and top panels. The case is basically a box with a front panel on to cover the front of the box.
Heatsinks
I became aware of porous ceramic heatsinks and realised that these small, light self-adhesive items would solve problems. I bought a few and tested to see if they did what was claimed. A single 50mm square of 10mm thick could dissipate 5-10W stuck on sheet aluminium. To make heatsinks you only have to bolt the semiconductors directly to the 3mm plates and place the ceramic heatsinks as needed.
Edit; a link to these was omitted, http://www.amecuk.co.uk/ Element14 has them in many countries.
https://www.newark.com/c/cooling-thermal-management/heat-sinks?brand=amec-thermasol
They are not expensive, and with a range of sizes you can arrange heatsinks of different shapes. I was concerned that they might unstick but the opposite has been true, they are hard to remove.
They are not pretty and can be easily chipped so I contain them inside the case and organise slots above and below to act as a chimney to allow convection. This works well and they do not run hot. The porous ceramic devices are very effective.
I have found that this method is much easier to procure and build. The amplifiers built this way can be smaller and lighter. These techniques can be adapted to any case whether needing heatsinks or not.
I should say that these heatsinks are small and they don't weigh much but that each amplifier on either side of the case dissipates about 14.5W and the heatsinks are only warm. (Edit; Further explanation a few posts below)
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@gcl - just in case I'm getting something wrong here - are you saying that sticking eg 5 of these on a 3mm aluminium plate will suffice instead of the normal deep fined heatsinks - the ones that are 120mm wide and 300mm long? Your picture shows 5 blocks on the alu plate, and you mention 30w being dissipated safely enough - what temp rise would you expect for this?
Given that they are about 5e each for the biggest I can see in Farnell that means a class A cooling for around 50e (if you have the alu plate, or an existing case).
Interesting. Has anyone else tried these out? They could be very handy where maybe you undersized a heatsink a bit, or maybe want to push bias a bit higher on an older build.
Given that they are about 5e each for the biggest I can see in Farnell that means a class A cooling for around 50e (if you have the alu plate, or an existing case).
Interesting. Has anyone else tried these out? They could be very handy where maybe you undersized a heatsink a bit, or maybe want to push bias a bit higher on an older build.
Ultimately all of the heat has to convected from the sink, so this part of the physics doesn't change. Aluminium ceramics might be better thermal conductors, however aluminium is already pretty good. I think a major benefit from using ceramic heatsinks is that they are an insulated (non-conductive) material so the insulating washer and/or thermal spreaders can be left out. These parts often degrade the case temperate of the device being cooled substantially, by as much as several degrees per watt, so being able to bolt straight onto the heatsink is a huge gain.
Not sure what those heat sinks do but their specs are appalling.
Besides the florid salesman language used in their page, let´s go to hard numbers:
1) those shown in AMEC page show 10.1 °C/W , nothing to write home about, barely comparable to similar finned aluminum finned heatsinks.
2) their datasheet claims Conductivity:
Aluminum conductivity is:
Not even comparable.
AFAIK ceramics have a place as a "mica" replacement, we are talking paper thin.
As a direct to air heatsink, on their own? .....
Not sure why they bother to add "fins".
Besides the florid salesman language used in their page, let´s go to hard numbers:
1) those shown in AMEC page show 10.1 °C/W , nothing to write home about, barely comparable to similar finned aluminum finned heatsinks.
2) their datasheet claims Conductivity:
Aluminum conductivity is:
Not even comparable.
AFAIK ceramics have a place as a "mica" replacement, we are talking paper thin.
As a direct to air heatsink, on their own? .....
Not sure why they bother to add "fins".
Firstly I need to correct an accidental mistake that could cause consternation, because I overstated the dissipation. I will give details of this particular build of ES headphone amplifier. The power supplies deliver approx 16W to each amplifier and the PS pass transistors dissipate 10W into the base of the case. Total 42W.
I conservatively rate the FCH505010T at 5W so that it only runs warm. In this build there are seven stuck on each aluminium amp mounting plate so each side could dissipate 35W (certainly at the temperatures commercial amps run at).
Here is a pic of it in use now after two and half hours. The room temp is 19.5C. The sides of the case are 31C and the top 33C, the ceramics are 33-35C. This is pretty much the same as the finned aluminium ones I made 6 years ago. If you did push twice the power without increasing the plates or number of heatsinks you'd see more like 55C on the ceramics.
If you would like to try it, you could do an experiment as I did by screwing a power transistor to a few inches of aluminium and sticking the same ceramic item on. Connect a suitable dc supply and bias to dissipate around 5 W increase up to 10W.
I conservatively rate the FCH505010T at 5W so that it only runs warm. In this build there are seven stuck on each aluminium amp mounting plate so each side could dissipate 35W (certainly at the temperatures commercial amps run at).
Here is a pic of it in use now after two and half hours. The room temp is 19.5C. The sides of the case are 31C and the top 33C, the ceramics are 33-35C. This is pretty much the same as the finned aluminium ones I made 6 years ago. If you did push twice the power without increasing the plates or number of heatsinks you'd see more like 55C on the ceramics.
If you would like to try it, you could do an experiment as I did by screwing a power transistor to a few inches of aluminium and sticking the same ceramic item on. Connect a suitable dc supply and bias to dissipate around 5 W increase up to 10W.
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For anyone interested here is some fairly recent info from Amec Thermasol.
https://mec-uk.co.uk/new-admin/uploads/pdf/Ceramic Heat sink presentation.pdf
https://mec-uk.co.uk/new-admin/uploads/pdf/Ceramic Heat sink presentation.pdf
I should mention that the amplifier shown is not the only one built this way. I came up with this method of building them four years ago, and two very similar to the one shown have been in use without any problems since 2017.