Hello folks,
I built this case for my Class D amp.
It is made up of extruded rectangular tubing, plus two plates I made for the end caps.
Beneath the smaller groups of holes are two amp modules and one SMPS module. There's a complementary set of holes on the bottom of the case too. The amp modules have heatsinks that clamp to the case (those two small black screws you see on the side.) I was hoping that this would create enough convection airflow to cool the case, but it is still too hot.
The amps and SMPS are only supposed to dissipate a few watts idle, but after about an hour or so, the case heats up to about 55+C, and one of the power supply capacitors (I have a temperature sensor temporarily attached to that, which is the brown wire coming out of the case) gets up to 62+C.
I figure one way would be to attach heat sinks to the side of the case, but I think they are only worth a few C/W. Another option is to get one of those quiet computer case fans, and have it blow air thru the case.
Are there any other good and compact (passive) cooling ideas?
I built this case for my Class D amp.
It is made up of extruded rectangular tubing, plus two plates I made for the end caps.
Beneath the smaller groups of holes are two amp modules and one SMPS module. There's a complementary set of holes on the bottom of the case too. The amp modules have heatsinks that clamp to the case (those two small black screws you see on the side.) I was hoping that this would create enough convection airflow to cool the case, but it is still too hot.
The amps and SMPS are only supposed to dissipate a few watts idle, but after about an hour or so, the case heats up to about 55+C, and one of the power supply capacitors (I have a temperature sensor temporarily attached to that, which is the brown wire coming out of the case) gets up to 62+C.
I figure one way would be to attach heat sinks to the side of the case, but I think they are only worth a few C/W. Another option is to get one of those quiet computer case fans, and have it blow air thru the case.
Are there any other good and compact (passive) cooling ideas?
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The color is absolutely not important, just anodise. Why? Because "black" is mostly only "black" in the visible range of wavelength, not in the thermally importand IR-range.
Can you describe the conductive heatflow path for the main dissipation parts?
If the lowest thermal resistance path is shortest to the side wall mounts on your case, with significantly less heat ending up being dissipated in to the enclosure, then it would be very appropriate to add some form of spreader and/or finned radiator to the side walls where the dissipation parts are closest to.
Conductive flow to the lowest temp region will be your simplest attack method.
If the lowest thermal resistance path is shortest to the side wall mounts on your case, with significantly less heat ending up being dissipated in to the enclosure, then it would be very appropriate to add some form of spreader and/or finned radiator to the side walls where the dissipation parts are closest to.
Conductive flow to the lowest temp region will be your simplest attack method.
The two amplifier modules have a built-in heatsink that is bolted to the side of my case.
The SMPS has little heat sinks on it, but otherwise it is just mounted on non-conductive stand-offs.
The temperature sensor was mounted on one of the electrolytic caps on the SMPS, so the only cooling that will have is from air. I suppose if I lowered the overall case temperature with heatsinks, then the ambient air temperature for the SMPS would be lower too.
Heatsinking a smps is problematic, as it can introduce parasitic interference conduction paths, and may breach isolation barriers.
If you could improve the heatsinking on the smps, then that would reduce the temperature rise of the related parts, which would certainly reduce the temperature of parts nearby, and generally reduce the temp of all smps parts.
If you could improve the heatsinking on the smps, then that would reduce the temperature rise of the related parts, which would certainly reduce the temperature of parts nearby, and generally reduce the temp of all smps parts.
Black anodised aluminium will radiate heat away more efficiently than silver. That is why heatsinks are normally mat black and kettles with brushed aluminium/stainless finish hold the heat for longer than dark shades.
Make two cups of tea. One in a white mug and one in a black mug. The black mug cools faster.
Keep an eye on the SMPS, the transformer gets hot as do the tuning capacitors. A small fan is probably the best aesthetic answer.
Make two cups of tea. One in a white mug and one in a black mug. The black mug cools faster.
Keep an eye on the SMPS, the transformer gets hot as do the tuning capacitors. A small fan is probably the best aesthetic answer.
That case cools by two methods, radiation and convection.
To improve convection, improve your airflow as best you can. Open up the bottom of the case as best you can, put it on taller feet, etc.
To improve radiation, anodize your aluminum - black/white don't make a big difference, the main thing is that you get the heavy layer of oxide on there. There's a huge difference in plain aluminum and anodized:
Emissivity Coefficients of some common Materials
Hell, a thin coat of paint will improve the emissivity.
To improve convection, improve your airflow as best you can. Open up the bottom of the case as best you can, put it on taller feet, etc.
To improve radiation, anodize your aluminum - black/white don't make a big difference, the main thing is that you get the heavy layer of oxide on there. There's a huge difference in plain aluminum and anodized:
Emissivity Coefficients of some common Materials
Hell, a thin coat of paint will improve the emissivity.
This is not true, doctor.
_black_ is the key here, not anodizing as such. Anodizing is just the most efficient way to 'paint' aluminium surface in black to make it radiating more efficiently. One may use other means to black it - a very thin layer of black paint, for instance. This also will help to give away more heat than just raw aluminium, but it will not be as efficient as anodizing, as the paint itself will act as a thermal insulation (anodized aluminium, in contrast, has a very good thermal conductivity).
Thanks for the suggestion of anodizing. Is there something special about the aluminum oxide that improves the emissivity, or is it just the fact that it adds some color? For example, how thick layer of anodize would I need? Would I get the same effect if I just dipped the whole case in black dye?
(edit: I saw new posts show up since I started writing this one)
I read across one web page that claimed hard anodize had an even higher emissivity than Type II.
Anyway, I used an online Stephan-boltzman radiation calculator and used:
Tambient = 25C
emissivity .8
area = 900cm^2
It gave 12W for a case temp of 50C and 7W for 40C and 18W for 60C.
So not counting convection (which I already know is not much since it wasn't able to get the case cool in the first place), it looks like relying on radiation will still lead to a case temp of maybe 45+C, and the inside air would be hotter.
For now, I got a 140mm quiet case fan and just plopped it on top. The case is pretty much ambient temperature now, and I am sure the air temp inside is also ambient. Too easy
(edit: I saw new posts show up since I started writing this one)
I read across one web page that claimed hard anodize had an even higher emissivity than Type II.
Anyway, I used an online Stephan-boltzman radiation calculator and used:
Tambient = 25C
emissivity .8
area = 900cm^2
It gave 12W for a case temp of 50C and 7W for 40C and 18W for 60C.
So not counting convection (which I already know is not much since it wasn't able to get the case cool in the first place), it looks like relying on radiation will still lead to a case temp of maybe 45+C, and the inside air would be hotter.
For now, I got a 140mm quiet case fan and just plopped it on top. The case is pretty much ambient temperature now, and I am sure the air temp inside is also ambient. Too easy
White color, same effect. But think what you want.
Even if wikipedia is not a valid science source, there's a valid statement regarging to surface effects and color.
Source: http://en.wikipedia.org/wiki/Thermal_radiation
The properties of radiation is then further described by Planck's law and Wien's displacement law.
Reflection of sunlight on clothing is a different story.
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