something don't add up - notebook thermal design

hi

just received lenovo y470 today and was doing some web browsing and stumbled onto this pic. it's basically a pic of fan with the sticker that says "45W", which i assume to be the capacity of heat dissipation of the fan.

y470 i got came with 2630QM CPU (MAX TDP:45W) and NVIDIA 550M (TDP: ~40W to the best of my knowledge as i couldn't find the exact number)

so by simple math, the total MAX TDP seems to be at least 80W for my notebook, yet the fan that came with it has only 45W capacity.

I know it's unlikely to push the notebook to the MAX TDP but then I might just push it to the max if I'm playing some demanding games. In any case, fan that can handle half the possible TDP of the system seems too inadequate.

is it the standard practice of designing notebooks these days? or am i missing something?




btw, here's the link of the pic i mentioned. it's the 4th pic from the top.

[??] Lenovo ideapad y470 ???? - ?? ????(3)

 

The 550M is 32-35W TDP. Also, TDP isn't the power consumption, it's the amount of power the heatsink should be designed to dissipate.

 

that's precisely my point. y470, as the case of most 14- and 15-inch notebooks, has one fan that does the cooling for both CPU and GPU. the combined max TDP is at least 80W, while the fan capacity (of the amount of heat it can dissipate) is only 45W...

again, to me that seems inadequate.

 

I don't think that 45W figure relates heat, but fan power consumption i would guess. The fan by itself has no means of getting rid of the heat, it is the fan + heatsink together that serve that purpose.

EDIT: To add another precision, a specific fan at a given speed + heatsink will have a heat dissipation capacity measured in W/K (let's assume it stays the same with temperature).

 

That 45W sticker could mean literally anything. It could be a part number, something related to quality control, whatever.

 

I have the same sticker on the heatpipe and it says 25W. It lets you know that the heatpipe is designed to accomodate a 25W CPU. GPU is almost always soldered onto the motherboard so they already got that accounted for into the heatpipe design. I installed a 28W CPU once and the fan was mostly on med/high never on low or off. So it's best your CPU TDP meets the max rating on the heatpipe. So that sticker applies for your CPU only.

 

The 45w CPU refers to the CPU and integrated GPU inside the CPU running at full tilt. If it's just the CPU running, it'll only have a TDP of 35w.

 

no way on earth that fan is consuming 45Watts. Just look at the wires that power the fan - at 5V as most fans are, it would mean the fan will take some 9 Amperes to operate, and this will melt the tiny wires in 3 sec.

the 45W could be the heat dissipation that the heat sink + fan is able to handle at normal speed. If more heat is involved then the fan could spin faster (just like in my case, lol)

 

45W is just a guideline. For it to make sense, you really have to understand volumetric heat capacities.

Basically, if you have a power output X, if you want to dissipate that heat you need to heat up something else (in this case air). Power output X will heat up a certain volume of air by a certain amount above its previous temperature. If you double the power then you double the temperature rise. As a consequence, if you have less air to use, you have to heat it up more to dissipate the same amount of power.

If you have a power output of one watt, then in order for the temperature of the air to rise by 1*C, you need at 1.2L of air flowing through the system every second. Given that a power output of 1W is vastly inaccurate for a laptop and that it's closer to 60W or so at full load, you can see that in order for the resulting air temperature to only be 1*C higher is vastly impractical (you would need 72L of air flowing through the heat sink ever second for that to work, somehow I can't see that happening). Because of the limitations of the amount of air you can get through the system, the exhaust air temperature has to rise for it to be able to carry the same amount of energy.

Most laptop fans can give somewhere around 2.7L per second of air (6CFM), in order to dissipate 60W of power with that airflow, the air flowing through the heat sink has to rise in temperature by 26*C. If you want to dissipate more power through the same system then the exhaust temperature has to rise even further.

This is a gross oversimplification as it's assuming 100% efficiency and other things, but I hope it gives you an idea as to how cooling systems work and how various components affect its performance.

 

It's referring to the CPU placed inside the computer.

 

+1............ It's only for the processor.

 

Basically it may be a bit of a bad idea to slap a 2960XM in there.

 

This:

To clarify it means almost nothing about the actual capability of the cooling system. Its simply an indicator of the type of fan they use probably 1 of 2 models.

 

Your thinking about this waaaaay to much.

 

It's not unusual for a laptop with the same chassis to come with more than one type of heat-pipe depending on CPU TDP.

Usually manufacturers try to cut down on costs as much possible and using a smaller heatpipe/fan assy and can do that for the lower TDP CPU's.

The 45W is likely just a label for the assy where it was convenient to place the sticker on the fan to identify the assy as supporting CPU's to a TDP of 45W. That is, the manufacturer deems it sufficient for a CPU with a TDP of 45W, how it performs in real world may not be up to the same expectations as the user.