Some personal stuff - and prototypes building!

[EvilDragon]

Bro, plastic also conducts heat, albeit slower than metal: from there it'll dissipate into the air, desk, or hands. The CPU produces an amount of heat energy in a concentrated area, the heat spreader and heat sink take that energy and spread it around the case; lower concentration of heat means lower necessary transfer rate. Yes, the CPU is producing more heat than can be dissipated in its tiny window, but by spreading it around the amount of heat transfer required is much lower; assuming EvilDragon isn't lying then we can be assured that the amount of heat, spread over the whole surface, is lower than the heat transfer rate of the plastic, making it 100% sufficient, probably better than.

Well, I am pretty sure it will be impossible to keep it running for an extended period of time with full CPU strength.
That doesn't work for ANY system out there. Heck, I don't even know a smartphone that doesn't get REALLY warm in your hand if you play some complex games for extended periods of time.

So yes, unless we use a fan, it will NEVER be possible to max out the CPU. More recent ARM SoCs (anything newer than A9, excluding the low-power ones) have not been designed for that.
They have been designed to be able to PEAK at full CPU power for a few seconds, so that webpages render faster, etc.

It won't work, unless you have the space for a REALLY huge heatsink.

So yes, I can assure it's not enough if you plan to max out the CPU usage with 1.5GHz.
But it's enough to not heat up in your hands when doing normal stuff (or playing games), which is better than what most smartphones manage.

 

[fusion_power]

I hope the USB socket does not get so warm that it desoldering itself.

Well, I am pretty sure it will be impossible to keep it running for an extended period of time with full CPU strength.
That doesn't work for ANY system out there. Heck, I don't even know a smartphone that doesn't get REALLY warm in your hand if you play some complex games for extended periods of time.

So yes, unless we use a fan, it will NEVER be possible to max out the CPU. More recent ARM SoCs (anything newer than A9, excluding the low-power ones) have not been designed for that.
They have been designed to be able to PEAK at full CPU power for a few seconds, so that webpages render faster, etc.

It won't work, unless you have the space for a REALLY huge heatsink.

So yes, I can assure it's not enough if you plan to max out the CPU usage with 1.5GHz.
But it's enough to not heat up in your hands when doing normal stuff (or playing games), which is better than what most smartphones manage.

They never built any Smartphone that does not throttle under full load? No crazy cooling solution or anything innovative? I mean "Gaming-Smartphones" exist I've heared. I just ask because I see some market possibilities if you can speed up everything under load without faster chipsets, just by keeping the peak load longer than other devices. This would have valuable usages, dont forget: they built folable Smartphones just because they can! (even if nobody ever asked for this )

 

[levi]

I hope the USB socket does not get so warm that it desoldering itself.

The melting point of solder (including the lead free stuff used in a RoHS compliant Pyra) is north of 200°C. If you've got that sort of heat inside a polycarbonate case, I'd expect something else to go pop before the solder starts to melt. And in case that worries you, we already know that the CPU will throttle itself if it gets above a specified temperature which'll be well south of 100°C (my x86 machines tend to hover around 60 degrees before they start spinning up their fans and throttling back processors)

 

[Hellfleck]

ah well ... plug all holes and flood it : https://www.engineeredfluids.com/

 

[EvilDragon]

They never built any Smartphone that does not throttle under full load?

Of course they throttle. They all throttle when the CPU reaches critical temperature. But until that happens, they will heat themselves up - and they can get pretty warm in your hands.

 

[docbroke]

But when one need to extract performance from an older CPU chances of reaching critical temperature are much more compared to modern CPU that will be at ease doing the same thing. Ofcource one can argue that most modern smartphones are already under pressure due to modern OSes running on them, without doing anything useful.

 

[WizardStan]

Well, I am pretty sure it will be impossible to keep it running for an extended period of time with full CPU strength

Sorry, my misunderstanding. I thought you said ptitseb had been using it at max speed without it throttling, but now that I reread you only mention that it didn't immediately throttle, not that it doesn't eventually. I'd be interested to know how long it does take: is it minutes? Hours? What is the max clock speed it can run at that doesn't produce more heat than the case itself can absorb?
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They all throttle when the CPU reaches critical temperature

My Pixel 2 just shuts down. Of course, this was with a vent-mounted holder while I was driving with maps up in the middle of winter and the heater cranked as high as it would go, so that may be on me.

 

[Zwerg01]

Bro, plastic also conducts heat, albeit slower

Only 1600 times slower than metal why i would call "plastic" a thermal isolator. But the copper block isnt attached to the case properly. There are air gaps between. And air is even worse in conducting thermal energie. This copper block acts only as a thermal capacitor with a very small capacitance. Not worth the effort.

 

[Djoga'Ro]

@Zwerg01 I also don't see much of an effect here, but there is not none. The heated volume is much bigger, than if it was the SoC alone. So is the surface area, which can get rid of heat via radiation. It will receive more thermal radiation, too, but it's facing way more cool surface area of outermore parts (also outermost actually) and will not get them up to speed temperature-wise so quickly.

 

[fusion_power]

Of course they throttle. They all throttle when the CPU reaches critical temperature. But until that happens, they will heat themselves up - and they can get pretty warm in your hands

Ok, let me ask different: there is no modern Smartphone that has a thermal solution that is powerful enough to run the CPU for a long time under full load? Like a normal PC can for instance? Or asked the other way round: all modern Smartphone CPUs are basicly to powerful to be built in such small devices?

 

[Coupo]

Ok, let me ask different: there is no modern Smartphone that has a thermal solution that is powerful enough to run the CPU for a long time under full load? Like a normal PC can for instance? Or asked the other way round: all modern Smartphone CPUs are basicly to powerful to be built in such small devices?

Yes. Exactly

 

[docbroke]

I agree to second part, smartphone CPUs are too powerful to be built in such small devices.

 

[fusion_power]

Well, how big should be a cooling soluion to handle a recent high end Snapdragon SoC for instance? Would it fit in a 10" Tablet at least?

 

[docbroke]

The issue is not of fitting cooling solution in a smartphone or tablet but industry focus on making devices slimmer with larger touchscreen which leads to sacrifice of ports, keyboards, cooling solutions, audio jack etc.,

 

[Djoga'Ro]

@fusion_power You'd only need to fit a heat exchanger and two hoses/pipes.

 

[EvilDragon]

Ok, let me ask different: there is no modern Smartphone that has a thermal solution that is powerful enough to run the CPU for a long time under full load? Like a normal PC can for instance? Or asked the other way round: all modern Smartphone CPUs are basicly to powerful to be built in such small devices?

Exactly, because what most people do on smartphones and tablets is browsing websites. It's important that these load up fast, hence the high-power CPU.
Once they're loaded, the power is not needed anymore.

Thanks to the overpowered SoC, the smartphone feels a lot faster and snappier when navigating or loading / rendering websites.

 

[levi]

Like a normal PC can for instance?

Normal PCs can't even, at least with the stock cooler. I updated the cooler on my six year old 65W Pentium server with a modern day 110W cooler and now it mostly doesn't throttle, but it does still momentarily drop the clock to half, according to my script that checks temps and clocks once per second.

 

[asimov-solensan]

If the tape contacts both the USB shield and the heatsink nothing prevents adding an exterior "USB" radiator.

Just a dummy copper plug (that doesn't short out the USB 5V) with fins.
Could even make a larger version that powers a tiny fan from the USB port but I doubt it'd be necessary.

Want to do a build or play heavier games? Plop that radiator into the USB port.
Need to store the Pyra away or just surfing the web, remove the external radiator.

It'd be similar to water-cooled laptop docks.

...but something much smaller than the Asus GX800.

Seems a great idea for a dock. You got the usb ports from the otg port and the full usb connected to a big heatsink exoposed to open air.

It may improve performance when used as a desktop.

 

[EvilDragon]

Well, how big should be a cooling soluion to handle a recent high end Snapdragon SoC for instance? Would it fit in a 10" Tablet at least?

Hm, hard to tell, as this depends on multiple things.

Basically, an SoC throttles if it overheats. So the general idea is to get the heat away from the SoC as fast and good as possible.
That's the first step. Metal has a good thermal conductivity, which is why copper heatpipes are used to move the heat away into a heatsink.

Let's imagine we have a totally closed environment here (so no heat exchange with the outside world):
Thanks to the heatpipe and heatsink, the heat moves away from the CPU into the copper block, slowly heating it up.

As soon as the copper has the same heat as the CPU is producing, it won't cool anymore - and the CPU will start to throttle to reduce the heat.

Now let's open that up to an open enviroment, where there's a cooler area around the heatsink.

The heatsink heats up and will start to emit the heat to the outside world, therefore, it will cool down a bit.
Thanks to that additional cooling, the heatsink won't heat up as fast as it would before, so the CPU will take even longer before it starts to throttle.
There's one more factor though: The bigger the surface of the heatsink is, the better it can emit the heat to the outside world.
If you use fins on the heatsink, you increase the surface (compared to having a flat one), therefore it will emit more heat.
(on the other side, the heatsink has less material so it will heat up a bit faster as well )

To be able to FULLY cool the SoC, the emitted heat has to be AT LEAST as much heat than the SoC produces.
(and of course the heatpipe needs to be capable enough to move the needed amount of heat from the SoC to the heatsink).

Once you reach that sweet spot, you can basically run the CPU with full load for as long as you like.

BUT there's another thing to take into account:
The heatsink emits heat - which means it will warm up the surrounding air as well. This will slow down the cooling overtime as well, unless the warm air is being replaced with cool air once again.
And that's what a fan does: A fan sucks cold air in, blows it through the fins and blows the hot air out. That's how you keep the air inside the fins of a heatsink always cool.
Again: The more surface the copper has, the better the fan does its job.

As quick summary:

1. The SoC produces heat. Depending on how much heat it produces, the surface of the SoC is enough to keep it cool (like with the Pandora).
2. If the surface is not enough, you need to increase the surface and add something that cools it down. For example: a heatsink. If you make it big enough and give it enough surface, you're done.
3. If the heatsink can't be put directly onto the SoC (because of space issues), you need to have a heat pipe to move the heat away from the SoC into the heatsink. The heatpipe needs to be big enough to be able to move away ALL the heat the CPU produces.
4. If you can't make the heatsink big enough to keep the CPU cool, you can add a fan to blow away the heat. The more surface (fins) the heatsink has, the better that works.
5. If ALL of that isn't enough to keep the CPU cooled, then it will only help to EXTEND the time until it throttles. Depending on the heat and the efficiency, it can extend the time by only a few seconds up to hours.

There are quite a few factors playing to the whole heat section

 

[Djoga'Ro]

To be able to FULLY cool the SoC, the emitted heat has to be AT LEAST as much heat than the SoC produces.
(and of course the heatpipe needs to be capable enough to move the needed amount of heat from the SoC to the heatsink).

That's easily achieved/designed. The crux is to design the cooling solution, so that that stable point occurs at a desirable temperature - say somewhere below the SoC's temp.-cap.