Note: All of this may be unnecessary. It is conjecture and considerations to have on the table should ED deem them needed.
For my version the sheet exiting the unit would fold over and down and back leaving a couple of cm on either side for the palms - no burns AND at 15cm^2 of exposed aluminum surface would have the ability to dissipate heat at a rate similar to a sheet of reinforced plastics 1m square. This little 5cm wide, 3cm folded over the leading edge sheet of aluminum can transport and dissipate heat at roughly 2.8 times the rate of the entire Pandora's plastics. It may feel warm to the touch, but is out of the way. This is in addition to the plastics dissipation - so, the net is that it will have ~3.8 times the rate of the Pandora. I believe this option to be less expensive in both materials (stamped sheet aluminum) and application (exits the case where there is already a seam at SD card slots).
So where exactly would that 15cm2 surface be on the unit ? below the battery ?
You mention it may get warm, but won't it get more than just warm if it transports all the heat faster than the plastic case ? with a directly exposed hot surface (even if you say it's out of the way, you never know how people will hold the device when they stopped using it and want to put it back) you may incur the risk of injuries or at least incomfort. Any example out there of commercial, portable device that actually has this kind of design ?
1. Think of this as a letter C with one long end. The long end goes between the battery and the SoC. It connects to the SoC via a thermal transfer pad. It -replaces- the piece of plastic that would otherwise be between the SoC and the battery. It is 1/3 of a mm thick. As such it adds no, or nearly no thickness. So half of it's surface area and volume is inside the case. The OTHER half comes out under the SD card slots and folds down, then back under the front edge of the case. This exposed half is 15cm^2. It is only 5cm wide. The case is 14cm wide. This leaves 4.5 cm on either side of it. So it is -not- where the hands hold the unit.
2. It will get warm but very unlikely to get 'hot'. It will get -less- hot -because- it is a broad surface area of a highly thermal conductive material that will dissipate the heat -faster- than the case plastics otherwise could. The Pyra will output X watts of energy per hour as heat. The aluminum heat sink/exchanger that I'm describing can port heat out of the case roughly 500 times faster than the rest of the case plastics combined. Because it's getting the heat out faster, the heat never has a chance to build up enough to get 'hot'. It will, by definition, be colder than the case plastics would otherwise have to be in order to dissipate the same heat.
3. Example of a portable device that has a metal rim to dissipate heat? Easy. iPhone.
From the mini-table above, you'll notice that aluminum is approximately 800 times better at transporting heat than the case plastics can be. Put another way, 1cm^2 of exposed (out of case) aluminum surface can do a similar job of dissipating heat from the SoC as 800cm^2 of plastic surface area.
From what I can recall, there is a difference between a material being able to
conduct heat (800 times better) and
radiate heat (??? times better).
You are correct. However, in order to radiate the heat, it first has to pass through the material. Copper or aluminum will initially increase in temperature faster, but then level off at a -lower- temperature than plastic will as they are more capable to transport the heat to the surrounding atmosphere.
How about an analogy?
Two buckets. One has a small hole in the bottom. The 2nd has a hole 500 times the size in the bottom.
Every second one liter of water is added to each bucket. If the bucket fills, the water has to stop pouring.
The water is heat. The bucket with the small hole is case plastics. The bucket with the big hole is aluminum or copper. If the heat maxes out (fills the bucket) then the unit has to throttle (stop adding water).
Please re-examine the solutions that Askarus and I have put forward.
While I could see Askarus idea work (leaving aside the question wether it would be sufficient to get rid of enough thermal energy or beeing even very efficient), I'm not very "comfortable" with your idea (but I am certainly less of an "expert" in that regard then you are).
The first question that came to my mind (back then when you first proposed it, months ago) was (obviously): Why hasn't anyone else done this before ? It is either not cost effective or has some drawbacks that make it an unviable solution. Don't get me wrong, I have no interest in dismissing your idea, I am just wondering about potential problems that may occur if you are creating an almost direct connection between the user and the inner workings of an electrical device. Are there any obstacles bringing such a device to market, like a special certification beeing needed? And there are of course mechanical problems, like how you integrate it into the case, or what would happen if the case has to endure a shock that leads to a plastic deformation of the metal part, while the synthetic material easily absorbs the shock by elastic deformation. How to avoid corrosion due to the acidic fluid humans usually produce ?
Others have done this before. iPhone, every 'silent' computer on the market with an exposed fin, major amplifier companies mount large aluminum fin blocks on the sides of their component amplifiers to avoid fans. It is actually FAR more common in consumer electronics than you might think - just a bit odd in a handheld device.
There is nothing 'magical' about connecting the 'user' to the 'inner workings of an electrical device'. Besides, unless you've got the weirdest grip ever and hold the Pyra by the center 1/3 of the front edge of the device, you're not even going to touch the heat sink/radiator - which won't be hot to the touch because it's dissipating heat FASTER than the plastics could.
Integration to the case goes through widening the existing slot on the front edge under the SD card slots by 1/3 of 1mm.
The C channel of the aluminum heat sink/radiator clips to the leading edge.
A thermal pad gets stuck to the internal end where it interfaces to the back of the SoC.
Case assembly continues as normal from there.
Impacts: Since it wraps around the plastic on the leading edge, it isn't going to deform unless the impact is great enough to also damage the case plastics behind it. In order TO impact it, the Pyra would have to be dropped on a rail since the exposed radiator portion only covers the center 1/3 of the lower front edge of the device. If anything, the metal will reinforce the plastic there near the SD slots.
Corrosion: The piece of aluminum would obviously be anodized to match the case color.
Grench, how easy is it to assemble the Pyra with your solution?
Mine won't have an impact in complexity at all.
The machine will take the bridge and place it where it onto the solder pads.
Then you simply have to put the whole board into the case.
(Global Components working) time is money as well as complexity.
For me the whole folding and putting it between something process sounds too complex.
Maybe you could simplify it a little.
Would make it make a lot more usable.
Assembly: Two step process.
1. Snap the radiator/heat sink onto the bottom case plastic.
2. Apply the thermal pad to the heat sink
Continue case assembly as normal.
Manufacturing the 30ga aluminum sheet is pretty simple.
1. die cut the shape from a sheet of 30ga aluminum.
2. fold one edge into a C channel.
3. anodize.
It would weigh nearly nothing - about the same as a bone dry empty soda can.
Any metal stamping company can handle making this in quantity on the cheap. It is beyond simple.
Manufacturing the copper block option:
1. start with a custom molded lump of pure copper, which must be molded in a vacuum to prevent oxidization during the molding process. It is an expensive and very custom chunk of copper that will require significant development and lead time.
2. The main board is VERY crowded to the point where they had to rotate a chip to a wonky angle to make it all fit. The copper block would have to mount right over the top of the charging port on the keyboard side using VERY fat pads to allow conductivity.
3. Next the main board will need to be re-designed to add giant fat copper traces from the spot facing the SoC back to the copper block in order to pipe the heat to the block.
The weight added would be significant. That bar of copper is going to weigh something as will the giant thick copper traces.
There is no way to really prevent the copper from corroding short of painting it with a clear coat.
I don't know what I'm talking about -- I failed a course in Thermodynamics about 15 years ago, and that's about it
But I think the Pandora has no heat problem, and the Pyra should not consume too much more power than the Pandora or else its battery life will be crap. If it gets too hot, there should be a mechanism that slows down the processors, to a Pandora level of performance or even lower if needed.
In bursts (e.g. when booting or when starting an application), you want to use the full processing power, but not constantly. It's fine if it can't sustain its max performance for hours and hours.
It's a handheld. Weight and battery life are more important than sustained high performance. I don't want to make it significantly heavier just to get a heatsink/radiator that can sustain top performance for weeks, even though one battery charge will only last an hour at that level of performance.
We will already have a heavier battery and probably a heavier screen. I really want the Pyra to be not too heavy -- it's not just the volume, but also the weight that determines its pocketability (and ergonomy!).
Is it worth the weight of a bone dry empty soda can to allow sustained high performance?
This is a bad thing to assume. For example, Exophase did good job parallelizing DraStic and it makes good use of multiple cores. With slow SDL scaling and slow Xorg updates it can already max out both cores.
Maxing out both GPP cores can happen easily enough. But maxing out both GPP cores
and the GPU
and the DSP
and whatever else is in the SoC, simultaneously, that I think is pretty unlikely.
That may be true, but I'm thinking probably not really relevant to the discussion at hand... Maxing out just the CPU core on the Pandora for any extended length of time it tends to get very hot. And as Notaz pointed out maxing out both cores for extended periods is much less unlikely than one might think.
I'm the type of person to leave a program running for hours on end and come back to it when I have time.
When I was playing a turn based RPG in DOSBox it seems it was running the CPU at full burn the whole time... even when the program itself was apparently idle. The first time I came back to it after leaving it be for a while I found that the Pandora was hot - and uncomfortably warm to the touch when I next picked it up.
When I accidentally left Widelands running overnight it not only failed to charge via the USB connection to my other machine, it was warm to the touch. (I woke just in time to see it shut down due to low battery)
- Neelix
I'm glad I'm not the only one who has made a Pandora get hot to the touch. I consider the Pandora's thermal conductivity envelope to be marginally adequate. If the device is in your hands using your blood as a liquid cooling system, it doesn't get nearly as hot as it does left running full tilt on the counter/desk/nightstand.
Is it possible to run the CPU board behind the screen and distribute heat through the glass like tablets do? Connect to the main board through a ribbon cable rather than being connected directly. The screen will offer 2 large surfaces to dissipate heat into, one being glass that is more conductive than plastic. And neither of which you will be holding directly in your hands. Also add a copper plate to distribute the heat more evenly to prevent damage to the LCD.
This is a nice idea, but this would delay PYRA another Two MonthsTM, I think, and would make the PYRA lid thicker and hence the whole device. Depending on the hinge design, we may have problem with this ribbon cable like we do on the Pandora. But yeah, I like this idea. Well, I like all ideas that prevent the SoC from being throttled down because of overheating. I am a gamer like Askarus, and I would like PYRA to run as fast a it could
Added development time aside, this is the time to think of and do such things, not later after it becomes a problem or when an upgrade is slotted to ship. The real engineering concern I think would be how to connect the mainboard to the daughter boards through the hinge with the high data rates etc. And not run into a problem the pandora had with corrupted or broken communication going through the hinge. That is a legitimate concern with that solution. These creative designers reinventing the wheel should be focused on that problem, rather than radiators etc.
If internal temperatures become a problem, engineering any physical solution that would allow for maximum heat dispersion is going add thickness and/or weight regardless. Thing is, SoC's seem to only get hotter as they become more powerful, the thermal footprint over time is on a upward trend in mobile. Even if boarder line acceptable temp limits today, tomorrow will likely not be and will need a redesign of some sort. So if ED wants something that is truely a single design future proof device for drop in replacements, I think he should go this route.
Size wise, If stacked, or side by side (CPU pcb + LCD pcb combined are smaller surface area wise than the main board
http://boards.openpandora.org/uploads/post-1-0-22204500-1403032996_thumb.jpeg) it's a good hand off to the alternatives.
The possible solutions I've heard are to add externally exposed radiators of different designs, cpu throttling, and passive air venting. But all of those solutions will still leave something hot in your hands. (external radiators might even cause injury and plastic is more of a insulator than a conductor) Mobile phones and tablets have been pushing heat slowly through the screen for years and I have personally yet to have one failed display because of it, and if you add a conductive heat shield to disperse the heat more evenly across the entire screen, it is less likely to damage to it, again, there's tablets and phones with way faster+hotter processors out there that are doing the exact same thing without problem.
EDIT: additionally, I'd rather have a hot screen than a hot battery, both of which generate additional heat when used.
Lets put a stop to this myth right now.
"The possible solutions I've heard are to add externally exposed radiators of different designs, cpu throttling, and passive air venting. But all of those solutions will still leave something hot in your hands. (external radiators might even cause injury and plastic is more of a insulator than a conductor) "
Reality simply does not work that way. By having a heat sink and radiator with MORE thermal conductivity, the overall unit AND the conductor/radiator both stay COOLER by shedding heat faster. That is the whole point. Transporting and shedding heat and 'getting hot' are different things.
I have a Samsung Galaxy Note II. It is supposed to shed heat through the screen. Playing Settlers of Catan (worlds most inefficient game for power usage) on it for 2 hours makes the back so hot it's painful AND it can't stay charged on a 2.1A charger. It's clear to me that this dissipating heat through the screen thing isn't all that it's cracked up to be.
Glass has a thermal conductivity of 0.9W/mK which is twice that of reinforced plastic at 0.5W/mK. Which is still 1/200th of the thermal conductivity of aluminum (205W/mK) and 1/400th of the thermal conductivity of copper (390W/mK).
http://en.wikipedia.org/wiki/List_of_thermal_conductivities
The idea with the thin sheet of aluminum is to transport the heat from both the SoC and the battery OUT of the case at a rate 400+ times faster than the case itself is capable of. Effectively tripling the heat shedding capability of the Pyra.
Again, it may all be unnecessary as ED still needs to run some tests. My objective has been to provide him a practical option to consider should it be needed.
