So what actually controls the fan???

Okay so what does actually control the fan speed? Is it CPU temp? Is it a collection of the hot sync temp? I am just curious cause I have started using smc fan control so that when I video chat or watch a movie or something, I can run the computer cooler (I believe it will help the longevity of it, could be wrong on that but it is piece of mind for me) anyway. I had it running about 3200rpm (uMB here) and watching the temps occasionally and was noting the times it would kick up didn't neccessarly correspond to any particular temp...

I guess my question is what does the fan in a uMB neccessarly cool and what does the computer watch to control the fan? Also, what temps (in degree F) should I strive to keep my computer around?

 

From what I've seen the fans will spin up depending on the cpu usage. If a program has a memory leak, and starts to eat up all the cpu cycles and memory, my fans will kick in as the cpu is working at 100% and then the temperatures rise.

But it also is kinda a chicken and an egg situation. The more the cpu works, the hotter it becomes, so whether or not the fans spin up specifically because of the cpu or the heat, I wouldnt know.

But from what I've seen, its mainly the cpu usage. If I have a program that all of a sudden is using 70% of my cpu, my fans will kick in and start to cool the laptop, even before it gets hot. This can be annoying sometimes, as I may only be using that program for 30 seconds, but yea.

And whatever the requirements are for the fans to spin up, I'm sure they take into account the ambient temperature, and adjust accordingly.

 

On my 1st gen Alum MB, the fanspeed appears to be linked with cpu temp and not cycles as encoding with Handbrake doesn't break 60% checking with iStat - fans seem to start ramping up through 2500 and 3000 once the temp passes around 70-80C.

Since we're seeing different patterns my guess is that the BIOS coding was changed between the SR/Merom and current Penryn systems. Happens a lot with engineers when they tinker with things.....

 

I'm smarter than my computer, so I choose what the fan speed should be. Basically, I run the necessary RPMs to keep the CPU temp below 50C when possible.

 

Honest I never noticed my fan change on my MBP 13. I was encoding something a few days ago, and the fan was putting along at 2000rpm at 86C. Needless to say, I installed SMCfancontrol, and I just control the fan speed myself when I need to.

 

anyway, i don't know if anyone said yet...

but its the smc that controls the fans. there is a "system management controller". it ultimately decides the fan speed and uses a variety of information to determine that speed.

a) there is a minimum fan speed set in the smc, which smcfancontrol can change. this is 2000 rpm by default (basically dead silent).

b) temperature information from a variety of sensors in your machine:
- case
- hard drive
- cpu
- gpu and gpu heatsink
- wifi card
- others?

c) power availability

- the fans require energy, if you are on the battery, the smc will decide to have a higher threshold for heat before it increases the fan speed in order to conserve energy.

 

The big one is CPU, but there's a variety of factors!

Ex: Start streaming video, watch your CPU usage + temperature go up, and then the fan speeds .

 

In my experience CPU usage is the biggest factor. When I play starcraft or something, which for some reason takes up a 100% of processes, the fan starts to run really high, and the instant I exit it turns off. Other factors are general laptop design, if you had an old HP or Compaq it runs for no reason 24/7. Then there is heat, like when you have your notebook on the bed and there isn't enough ventilation

 

50 is kinda cool...

when I'm maxing out my computer even with the fans at 6200 rpm, it can sit around 86º ... sure under 50º is easy even at 1000rpm and my machine idle, but still... if your always shooting for under 50º your going to kill your fans way faster than your putting wear on your components.

 

thats true. i think your components have a greater tolerance for heat than your fans do for prolonged high speed rotation.

 

I rarely ever use my CPUs beyond 50%, so anything in the 3000-4000RPM range is generally sufficient to keep the temp below 50C. Of course, when I do something intensive, like watch 720p or edit in Photoshop, then I can't expect the temps to be anywhere near 50C. Replacing the fan is easy and cheap.

 

Wow, 50 C is awfully cool! My Mac usually hovers around 60 C. If it goes higher, I up the fan speed to cool it, but I'm fine with 60 .

 

Yeah, the T series chips are pretty much impossible to keep under 50C. I was content with under 60 when I had those. However, the P chips are pretty cool. The two other P8400 PC laptops that I have had were both in the 40C range when doing basic tasks. My uMB is around 45C at 3400rpm or so (18C room temp) doing usual web surfing (little or no flash).