Planned Ducting Question

Hey Guys, Seeing as how it's now offically summer, I think it's time to do a cooling upgrade. What I'm planning to do is get an sk-7 and do a little duct mod. I plan to do it by putting a 120mm fan on my case and ducting that down to the heatsink. What I'm wondering is should I put a fan on the heatsink too? If I would it would probably be a 7v 80mm. I don't know if the 80mm would hinder more than help because it might block the airflow that the 120mm is pushing down...


Here's a pic of my plan. (my paint skills in action )

First it sounds like you are running without a CPU fan. Your idea is good but think of this. The distance between you 120mm fan and the CPU HS if you have a heatsink? I would rather opt for pottung a good HS and a good HS fan. Probly cost you less and render better results. Just a suggestion!!! Good luck.

I would do that, but then also put a nice high cfm fan on the heatsink.

Well the reason I'm going with a 120mm is for quiet cooling. I thought that ducting a fan down to the hs is actually better than actually having a fan sit right on the heatsink, because the dead spot in the middle was reduced. Is this right? But then by putting the 80mm on the heatsink wouldn't that put the deadspot right back on there? I don't think I would want a high cfm fan on the heatsink, if one was on there, as I'm going for quiet. And would it really have to be a high cfm since the 120mm will be pushing plenty of air? Thanks for the input!


EDIT: oh and BTW if I didn't put a fan directly on the HS I would plan to attach the duct directly to the HS somehow...

i just did a duct mod to my K6 with a 92mm fan (found at the recycling center).
my setup is similar to what you have planned. i put a rheostat to control
the fan speed. i used a Taco-Bell cup (large) as the duct. i opted to not
have a noisy HSF.

i ran prime-95 for 2 hours and opend the case and felt the HS. it wasn't
even warm.

so i would say you have a good plan, and i vote for no HSF.

let us know how it goes.

P.S. i found that around the edges of the hole i could feel air coming
back out. this is caused by the restriction of the HS. the air seems to
be escaping at the outer most part of the blades.

the next hole i cut for a fan i'm going to make it a little smaller to try
and prevent this from occurring.

I would put the fan on the heatsink. The further you get from a fan the less pressure there is.
With my duct I only have a 21dB panaflo on my heatsink. I have negative pressure in my case which helps pull more air in through the duct. There's pics in the link in my sig.

Personally I like having a good heatsink and fan on my CPU. However I would definatly ADD a duct. That way i can get a lower noise fan for my HS and have cool air duct as well. I wouldnt feel comfortable not having a fan on my HS. Espeicially when OCing.

"Most computers have three cooling fans, one inside the power supply, one on the case itself, and one on the CPU."

article here

sorry bout that little bit of spam, i just thought it was funny. We have 3 fans on the back of our computer alone...It's in the second paragraph also. anyway with ductmodding i saw this thing at cool pc that's similar to what you're talking about. Personally i say put a fan on the case and HS. it won't hurt to have a quiet fan(or even still a stronger one) and a nice powerful 120 blowing on the CPU.

Hmmmmmm, that Thermaltake duct seems like it could work well. Wonder if i can rig something to work with my SLK800.

Well from your guy's responses so far it looks like I might put a quiet 80mm on the HS. Whenever I decide to go ahead and do this I'll experiment with/without the extra fan on the hs and let you guys in on the results. Thanks for the comments!

hey mr SD, check out Randy's Monkey Mod from the front page.

pelikan has a good point about the negative pressure drawing air in.
thats prolly what my K6 duct mod needs.

Clutch_Head said:

hey mr SD, check out Randy's Monkey Mod from the front page.

pelikan has a good point about the negative pressure drawing air in.
thats prolly what my K6 duct mod needs.

Click to expand...

You dont want too much negative pressure or you will suck in all kinds of dust and dirt. I try to keep my system on the positive pressure side so as to minimize my system from becoming a vaccuum.

CGR said:

You dont want too much negative pressure or you will suck in all kinds of dust and dirt. I try to keep my system on the positive pressure side so as to minimize my system from becoming a vaccuum.

Click to expand...

It's all about optimal cooling to me. If my system doubles an an air purifier I don't care. With a passive duct you need major negative pressure. The duct made a 6C drop in temps. I can get another 4C drop by turning my front intake around so it exhausts.
Fortunately, I have an air compressor with a long hose so I just bring the nozzle inside and blast the dust out.
Of course a good filter would be an option too.

After its running for a couple weeks and you dont have layers of dust then you should be ok.. If after that time you have enough dust to push around with your finger and its covering everything, then you might think about filters

I've had this duct in place for about two months. It seems to take about a month for dust build up to start raising my temps. So when I see a 2C rise on the cpu I clean it out.

You get a lot of dust buildup on the HS under the fan?

That happened to me a lot until I added filters. In fact it was so bad one night my temp went up to 55c and started yelling at me. I shut it down took the fan off the HS and there was this thick layer of dust on top of the HS. it was so bad I just peeled it off intact.

Installed filters on all intakes and have not had that problem since. Never want that problem again either.

I've got a VERY similar design in my system. Best aircooling temp : noise I've been able to come up with so far. Takes a little time, but it is so worth it.

Hehe, it's so quiet, I can hear my PSU fans (faintly)! Even though I have to cool down an OV'd & OC'd Palomino. As for the second little fan on the HS, you could try it, but I think you're going to need a highspeed fan with the extra noise. I never tried it, but I would imagine a quiet one would just get in the way of the ariflow.

Hope it helps,
N8

I see a duct like this as being beneficial because its getting cooler air to the fan on the HS. The question though is whether you lose any cooling effect from not having a fan on the heatsink.

I quess you can test it with and without a fan on the HS to see if there is any difference. I dont know if there would be a difference or not.

Thanks for the link CGR. Definitely something to look at for my duct. N8x2, yeah I'm thinking a quiet fan on the hs might get in the way too, but I'll try it both ways just to see what happens. Do you have any pics of your setup you could link to so I could take a look? Thanks!

whoooooosh

Man, I musta ate my wheaties this morning. Either that, or my roommate put crack in my coffee again ! After writing this little novel, I re-read your question... Just skip to the part between the >>'s. I'll leave the rest in case anybody is having trouble sleeping.

IN THE BEGINNING...

I just went for CRAZY cooling, just for kicks, ignoring all noise considerations. The pic below is the result.


EDIT: pic is older case design due to lack of digicam. I can post a pic of new setup through eyes of grainy PC cam, if you like.

Case = cheapest I could find, suitable for making mistakes with dremel
120mm fans = 5!!!!
Airflow = I dunno, close to windtunnel, I guess
Noise = could hear it upstairs
Weight = aircraft carrier anchor
Temps = REALLY COOL
Appeal to normal person = nil

INITIAL SETUP

Fans: Sunon KD1212PMB3-6A, 84CFM @35dBA
>> I don't recommend these fans, they've started to go on me
>> Regular 120mm @ 12V = way too loud and more air than you are going to need
>> Vantec Stealths should work much better, or any other slower turning, better quality fan
Fan filter: fine pore spiral shaped jobs found much cheaper at electronics stores than in the Startech bags at PC stores
Intake: 2x 120mm side and 1x 120mm front
Exhaust: 2x 120mm top and PSU
Equaliser: 80mm hole with 80mm fan filter in the back and hole under case front bezel, where bottom is chopped off. These are so that unequal fan 'pressure' can 'equalise', so to speak. IE, unequal fan 'pressures' aren't fighting each other as much.
Control: 2x PCMods 4 channel 6 Watt fanbus's (with shiny lights )
HS: Alpha PAL8045
Ducts: cerealboxes and tape
CPU: XP 1600+ Palomino @ 1.75V, 170MHz x 10.0, 50°C
Vid: Asus V7700 GF2 GTS @233MHz core and 411MHz Mem
RAM: Spektek 2x 128MB PC2700 @ 1:1 w/ FSB

EVOLUTION (all temps are full load temps for that component, and are approximate)

I noticed right away that the two top fans were doing close to nothing for the temps of any of my components (except, perhaps the top optical drive) so those were removed.
>> With the side and front on high (NOISY) the top fans could be off or full on, no difference in temps. With the side and front fans on low (quiet...), my component temps rised by about 2°C when the top went from full on to off.

DIALING IT IN (lowest speed means lowest possible after high voltage kick to get the fan spinning)

The lower side fan lowers the temp of my vidcard around 12°C from off to on it's lowest speed, and another 4°C from lowest speed to full on, so it just stays on lowest. More powerfull video cards would probably appreciate the extra cooling, but mine doesn't care.

Very similar story with my HDD and the front fan (temps with mobo temp probe), so it stays on lowest possible speed, too.

The CPU: I could crank up the upper side fan and core voltage and get around 1.8GHz out of it, but that's just noisy and mean to the little chip, so it runs as above with the fan at about 7V.

The front and lower front are so quiet, I can hear the PSU and HDD over them (reasonably quiet Enermax 300W dual fan and VERY quiet Fujitsu drive). The upper side fan is the loudest, and I can just hear the PSU and HDD with it on.

>>>>>>>>>>>>>>>>>>>>>>>>>>

THE DUCT

I experimented with a bunch of different shapes, and I will contiue to do so until I find a more meaningful way to spend my free time. Make sure it is sealed around the fan (easy) and the HS (not so easy, lots of recutting) and slopes gracefully from round fan output to square/rectangle HS input (FRICKIN HARD ) for optimum airflow.

The duct in the picture above is my old 4 sided square pyramid shaped duct. It preformed almost as well as my new 12 sided and more airflow friendly duct. As I said, I like to play with ducks.

Also, I had a duct off the lower side fan and then toward the stock vid core cooler, vid mem, and NB, and that helped each about 2-4°C, I think. Haven't built a new one for the new board, though.

>>>>>>>>>>>>>>>>>>>>>>>>>>

'CASE PRESSURE'

Yes, I know I have 3x 120mm fans blowing into my case and only the PSU exhaust, but they are all on very low speed and there is also 2x 120mm holes (with fan filters) and the 80mm hole and the area around the front bezel (discussed above) for air to escape on it's own, from the force of air being blown in, and IT DOES! If I put in the 2x 120mm back into the top (with enough 'airflow clearance' around the opticals) and run them about the same speed as the CPU fan, my temps only go down a few degrees, but my case is making about 50% (guesstimate) more noise. So I don't bother using them. If I want more cooling, I adjust the speed of my intakes, and this works MUCH better.

I can't beleive you read the whole thing! Where's that box of cookies?

N8