Getting heat out of a box
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From: markp on 5 Aug 2010 20:17 "whit3rd" <whit3rd(a)gmail.com> wrote in message news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com... On Aug 5, 7:56 am, "markp" <map.nos...(a)f2s.com> wrote: >> ... I've got a design that dissipates about 30W and need to >> encase it in a sealed box (not hermetically, but to all intents and >> purposes >> there can be no airflow through the box). >> >> Current thoughts are an aluminium extruded box with large heatsinks > If the box has >30 square inches of external free-air surface, a > circulating > fan inside the box would do it. Or, does it have to be small? Do you mean and area of the sidewalls of the box externally > 30 square inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), with an internal fan, will get rid of 30W? What's the max temp rise above ambient internally do you think, and would I need to put heatsink fins inside the box as well as outside? The box is going to need to be big for the components, probably 12" x 4" x 3" external dimensions or so. That's a good 120 square inches available if you ignore the base and the two end plates. Those other free-air surfaces can also have quite large surface area heatsinks on them too. Having said that, I would really like it to be rugged and not have any moving parts in it at all. What do you think the chances I could keep all internal temps below, say, 20 degrees above ambient if I were to bolt the high powered stuff directly to the box walls inside? The 30W is spread out a bit component wise, but 20W of that comes from the PSU. Mark.
From: tm on 5 Aug 2010 22:03 "markp" <map.nospam(a)f2s.com> wrote in message news:8c12joFhf3U1(a)mid.individual.net... > > "whit3rd" <whit3rd(a)gmail.com> wrote in message > news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com... > On Aug 5, 7:56 am, "markp" <map.nos...(a)f2s.com> wrote: > >>> ... I've got a design that dissipates about 30W and need to >>> encase it in a sealed box (not hermetically, but to all intents and >>> purposes >>> there can be no airflow through the box). >>> >>> Current thoughts are an aluminium extruded box with large heatsinks > >> If the box has >30 square inches of external free-air surface, a >> circulating >> fan inside the box would do it. Or, does it have to be small? > > Do you mean and area of the sidewalls of the box externally > 30 square > inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), > with an internal fan, will get rid of 30W? What's the max temp rise above > ambient internally do you think, and would I need to put heatsink fins > inside the box as well as outside? > > The box is going to need to be big for the components, probably 12" x 4" x > 3" external dimensions or so. That's a good 120 square inches available > if you ignore the base and the two end plates. Those other free-air > surfaces can also have quite large surface area heatsinks on them too. > > Having said that, I would really like it to be rugged and not have any > moving parts in it at all. What do you think the chances I could keep all > internal temps below, say, 20 degrees above ambient if I were to bolt the > high powered stuff directly to the box walls inside? The 30W is spread out > a bit component wise, but 20W of that comes from the PSU. > > Mark. > So if we understand you, you have a 10 watt load and a power supply that is loosing 20 watts in the conversion to DC? That doesn't sound too "green" to me. :) tm --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Nunya on 5 Aug 2010 23:35 On Aug 5, 7:56 am, "markp" <map.nos...(a)f2s.com> wrote: > Hi All, > > I'm looking for a company that could help solve some thermal management > issues. Basically I've got a design that dissipates about 30W and need to > encase it in a sealed box (not hermetically, but to all intents and purposes > there can be no airflow through the box). > > Current thoughts are an aluminium extruded box with large heatsinks on the > outside, and a method of thermally bonding or piping any higher powered > components directly to to the box inside. I also need an AC-DC supply which > I think needs to be a baseplate cooled type and bond that directly to the > side of the box that has the heatsink. I'm unsure of size of box needed or > even whether this is a viable solution. > > I know it's a bit vague, but anyone know a company who could help > (preferably one with a vested interest in solving it, like an aluminium > extrusion box manufacturer)? > > Thanks! > Mark. I would go with conductive cooling. That means not only attaching a source device to the wall of the case, but you need an internal integrated block of Al that connects a sizable mass and conduction path between all the heat sources, and then couple that heat block to the case too. That way, all temps are held homogenously together you can use conductive pads to clamp it all up together. I would also conformally coat everything and make sure that thermal mating faces are bare afterward. This is what aircraft avionics do because the air at 70.000ft is so thin that it does not perform much cooling work. At least not efficiently so. I had to retrofit an external HD enclosure with a system recently. It was about 3/4" bigger than a laptop drive on all sides. Hardware encrypted, so it was actually a computer in the box. Probably the most advanced small form factor computer around currently. Absolutely secure, so even a lucky water fountain that ends up with one tossed behind it after being missing for several days would not even cause so much as a flinch.
From: Nunya on 5 Aug 2010 23:36 On Aug 5, 7:03 pm, "tm" <the_obamun...(a)whitehouse.gov> wrote: > "markp" <map.nos...(a)f2s.com> wrote in message > > news:8c12joFhf3U1(a)mid.individual.net... > > > > > > > "whit3rd" <whit...(a)gmail.com> wrote in message > >news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com.... > > On Aug 5, 7:56 am, "markp" <map.nos...(a)f2s.com> wrote: > > >>> ... I've got a design that dissipates about 30W and need to > >>> encase it in a sealed box (not hermetically, but to all intents and > >>> purposes > >>> there can be no airflow through the box). > > >>> Current thoughts are an aluminium extruded box with large heatsinks > > >> If the box has >30 square inches of external free-air surface, a > >> circulating > >> fan inside the box would do it. Or, does it have to be small? > > > Do you mean and area of the sidewalls of the box externally > 30 square > > inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), > > with an internal fan, will get rid of 30W? What's the max temp rise above > > ambient internally do you think, and would I need to put heatsink fins > > inside the box as well as outside? > > > The box is going to need to be big for the components, probably 12" x 4" x > > 3" external dimensions or so. That's a good 120 square inches available > > if you ignore the base and the two end plates. Those other free-air > > surfaces can also have quite large surface area heatsinks on them too. > > > Having said that, I would really like it to be rugged and not have any > > moving parts in it at all. What do you think the chances I could keep all > > internal temps below, say, 20 degrees above ambient if I were to bolt the > > high powered stuff directly to the box walls inside? The 30W is spread out > > a bit component wise, but 20W of that comes from the PSU. > > > Mark. > > So if we understand you, you have a 10 watt load and a power supply that is > loosing 20 watts in the conversion to DC? > > That doesn't sound too "green" to me. :) > > tm > > --- news://freenews.netfront.net/ - complaints: n...(a)netfront.net --- Better to supply it via dongle and keep the device all device.
From: markp on 6 Aug 2010 08:07
"tm" <the_obamunist(a)whitehouse.gov> wrote in message news:i3fqft$1376$1(a)adenine.netfront.net... > > "markp" <map.nospam(a)f2s.com> wrote in message > news:8c12joFhf3U1(a)mid.individual.net... >> >> "whit3rd" <whit3rd(a)gmail.com> wrote in message >> news:db6a66cd-1a00-45f7-a7c3-8a6b80e2d110(a)d17g2000yqb.googlegroups.com... >> On Aug 5, 7:56 am, "markp" <map.nos...(a)f2s.com> wrote: >> >>>> ... I've got a design that dissipates about 30W and need to >>>> encase it in a sealed box (not hermetically, but to all intents and >>>> purposes >>>> there can be no airflow through the box). >>>> >>>> Current thoughts are an aluminium extruded box with large heatsinks >> >>> If the box has >30 square inches of external free-air surface, a >>> circulating >>> fan inside the box would do it. Or, does it have to be small? >> >> Do you mean and area of the sidewalls of the box externally > 30 square >> inches (that's equavalent to 5.48" x 5.48" for ease of visualisation), >> with an internal fan, will get rid of 30W? What's the max temp rise above >> ambient internally do you think, and would I need to put heatsink fins >> inside the box as well as outside? >> >> The box is going to need to be big for the components, probably 12" x 4" >> x 3" external dimensions or so. That's a good 120 square inches >> available if you ignore the base and the two end plates. Those other >> free-air surfaces can also have quite large surface area heatsinks on >> them too. >> >> Having said that, I would really like it to be rugged and not have any >> moving parts in it at all. What do you think the chances I could keep all >> internal temps below, say, 20 degrees above ambient if I were to bolt the >> high powered stuff directly to the box walls inside? The 30W is spread >> out a bit component wise, but 20W of that comes from the PSU. >> >> Mark. >> > > So if we understand you, you have a 10 watt load and a power supply that > is > loosing 20 watts in the conversion to DC? > > That doesn't sound too "green" to me. :) > > tm No, this design is actually a custom power supply. The total heat dissipation inside my box is 30W, there's an AC-DC converter in there which is dissipating 20W of this, and is powering another circuit internally which is dissipating the remaining 10W. This additional circuit provides an output from the box and delivers power to another box. The overall efficiency of my box is about 70% (series combination multiple of the efficiencies of the AC-DC supply and my additional circuit), so basically it is consuming 100W and delivering 70W to another box. Mark. |