Limit of air cooling?

[CaptainNemo]

I've been experimenting with various combos of fans, voltages, and noise(!); the quietest combo (stock HSF + 2x80mm exhaust @ 7 volts) produces a 24ºC difference between core and mobo/case temps, whereas the noisefest from hell combo knocks this difference down to 14ºC (under load).

Anyway, the stock HSF is going because of all the noise it produces; it probably isn't that efficient either.

However, I can either replace with something not that special (but with a Sanyo Pico Ace 60mm fan on it), or I can splash out on something like an SLK-800. The thing, is there a hard limit on air cooling? What is the lowest difference between core temps and case temps that can be achieved?

 

[lhgpoobaa]

Its hard to say if there is a hard limit, but certainly with aircooling there is a law of dimishing returns.

Progressivly bigger and more massive heatsinks give you a smaller and smaller reduction in temps, as does increasing the fan speed.

The best ive seen is around a 10C delta between cpu and case temp... thats ASSUMING the reported temps are at all accurate.

Regarding your system... does it ever crash at full load on hot days? If not i think you are worrying about nothing.

A decent heatsink with a nice quiet lowspeed fan is a good allround solution. sk800 + panaflo is a good combo for instance.

<b>My Computer is so powerful Sauron Desires it and mortal men Covet it, <i>My Precioussssssss</i></b>

 

[CaptainNemo]

I had hoped that a lower temp (say 40ºC under full load) would allow for a higher overclock, but my Pal XP2100+ isn't stable beyond 1846Mhz (142Mhz FSB).

A max of 50ºC under load is nothing to worry about (it is still stable), so I just want to get the thing quiet now (with a decent sink + quiet fan, as you suggested). My plan was to build a quiet cool box that I could use for future systems; I'll just have to keep experimenting.

It's an interesting science though; having all of the fans on stresses my PSU (300w), so they probably generate as much heat as they shift!

 

[lhgpoobaa]

You know your overclock could be limited to other things you know.

FSB overclocking also pushes up ram speeds, as well as all PCI and AGP devices. Just one of them missbehaving can cauze crashes.
And it can happen at fsb's of 142.

Also, i suggest a better PSu for overclocking.

I imagine that 300W unit is really struggling, as you said it puts out alot of heat, and that could also hamper your OC, as well as reduce the lifetime of the PSU.
Fans actually dont draw much power... even the fastest fans dont draw much more than .2A or 10W. Insignificant compared to what an overclocked CPU can draw.


<b>My Computer is so powerful Sauron Desires it and mortal men Covet it, <i>My Precioussssssss</i></b>

 

[4Ryan6]

I've discovered something you probably will not believe, I was so fed up with the loudness of the different fans I had run, to try and get my temps down, the last fan I tried was a Delta 50cfm, it sounded like a small jet sitting on the runway waiting for takeoff clearance, the 2100+ is a hot running sucker, a lot hotter than my previous 1900+, I started taking a good look at the cooling fans I had bought. The problem with the standard cooling solution is the fan drive motor itself, the drive motor sits directly over the die producing a dead air space. Check it out for yourself with a standard house type fan, theres a dead air space directly in front of the fan drive motor, no matter how big the fan is, now when you move away from the fan you feel the air, the same thing happens with the smaller fans that almost every heatsink comes with, that dead air space is where you need the most concentration of air over the CPU DIE, but in a short distance the fan motor blocks it, and you don't get it because of the dead air space. Heres what I did, and it works great, and probably will work with just about any heatsink, I took 2 PCI slot case cooling fans, modified them to a back to back configuration, made a support bracket and mounted them blowing straight down on the heatsink itself with the regular heatsink cooling fan removed using just the bare heatsink, these fans produce 42cfm each making it a total of 84cfm, they are squirrel cage type fans and focus the air straight onto the die area itself, and they're 10 times quieter than the racket we've been listening to, believe it or not its actually nice to hear my hardrive doing its thing, couldn't hear that for the previous cooling fans. One fan will work but I used two for more cooling and if I lost one of them I'd still have the other. I'm using the Swiftech MCXC370 because it secures to the socket using the three fingers, instead of just one, If you do this, I recommend a thick base heatsink for safety purposes, but any will do even the stock AMD. I had to disable the CPU fan RPM senser, in the CMOS setup, so the M/B wouldn't automatically shutdown, but my temps are livable, and its quiet, its quiet, its so nice, its quiet. If this interests you and you want more information of what I did post what you need to know.




Details, Details, Its all in the Details, If you need help, Don't leave out the Details.

 

[LtBlue14]

wow that's amazing
so you have them taped back to back, with the flat part that's normally pointing out of the case pointing down on the heatsink? 84cfm too, wow

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[4Ryan6]

Thats the idea but they're not taped together, the support bar to hold them up goes in between the two fan cases, I drilled holes through, and ran screws through the support bar, and through the backsides of the fan cases, you see the fan cases will come apart, and snap back together making modifications pretty easy.

Details, Details, Its all in the Details, If you need help, Don't leave out the Details.

 

[4Ryan6]

Highest temps were 54c playing Soldier of fortune, with no overclocking, this is definitely not an overclocking cooling solution, but for non-overclocking its a quiet solution.




Details, Details, Its all in the Details, If you need help, Don't leave out the Details.

 

[LtBlue14]

good to know since i like to overclock haha

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[lhgpoobaa]

interesting idea, and good results but not completely original... the silverado was like that... i wish i could get two for my MCX-462... the dead spot problem has often been in my mind.

a solution with standard fans is a spacer and a aerodynamic cone over the fan hub.

<b>My Computer is so powerful Sauron Desires it and mortal men Covet it, <i>My Precioussssssss</i></b>

 

[4Ryan6]

Yes the squirrel cage fan idea is probably the way to go for an engineer design team to look into, bacuase they can produce an extreme amount of air vs low noise, but they would need to cover the entire heatsink area, not just focusing in the center, and the drive motor would need to be outside the cage, instead of in like the PCI cooler is, because the drive motor starts to produce heat itself after its run for awhile.



Details, Details, Its all in the Details, If you need help, Don't leave out the Details.

 

[lhgpoobaa]

dont think heat will be a prob... as the heat from normal fans also goes over the heatsink.

height may be a problem though.

<b>My Computer is so powerful Sauron Desires it and mortal men Covet it, <i>My Precioussssssss</i></b>