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From: Paul on 7 May 2010 05:59
me wrote:
> OK... I live in the dark ages... but what's with "modern" power
> supplies blowing INTO the case instead of out of it? Pushing hot air
> in can't possibly be good - why not blow it right out and let the draw
> cool the rest of the case?
>
> Are most of you opening up your PS and reversing these back-asswards
> fans?

If the power supply was low efficiency (68%), and the computer was
a high power unit (big gaming machine), you'd be crazy to leave it
that way. If you know the power dissipation of your rig, and you know
the rough figure for power supply efficiency, you can work out how
many watts of heat the power supply would be dumping into the computer.

If the computer is relatively low power (integrated graphics, dual core
65W processor), it might not be important enough to worry about.

In terms of airflow analysis, consider *all* the fans in your computer
case, and whether they work with each other, or against each other. Say,
for example, you had a rear 110CFM exhaust fan, and a PSU "blowing out".
The exhaust fan could pull so hard on airflow, as to actually reverse
the direction of airflow through the PSU. If the PSU has a temperature
controlled fan, it could always speed up the fan, but a cheap PSU might
be a constant speed setup.

If you have the large exhaust fan, and the PSU "blows in", then the
fans could be viewed as "working together". There would then be
a short loop, in the processor area, as the exhaust from the PSU, is
pulled immediately into the big exhaust fan. Some "bleed air" flows
from the front computer case vents, over the hard drives, and they
get cooled. It isn't a total disaster.

Like all cooling questions, you really have to observe what is going
on with the cooling. For example, on one case I had, I had multiple
fans, and due to fan imbalance, air was actually flowing backwards
through one of the fans in the front of the case. So in fact, that
fan wasn't doing anything of value, and I disconnected it and removed
it (since a bigger fan was doing all the cooling anyway). Look at
your processor temperature, video card temperature, and decide whether
something needs to be done.

Your number one priority, is ensuring the hard drives are getting
cooled. You don't really want them running at 50C. Next, look
at the processor. Is it running above the throttle temperature ?
If so, you're losing the performance you paid for. For the
video card, the concern would be the GPU running so hot as to be
unstable. I use GPUZ to check mine, and it says I hit about 45C
when gaming (a pretty crappy card). If you were hitting 90C or
100C, you might think about improving things.

As long as none of your temps are astronomical, you could leave it.

Also, some PSUs have a sticker over one of the screws, and
removing the sticker and the screw to open it up, voids the
warranty. If the company is known to have sucky warranty service,
you might not care.

HTH,
Paul
From: GMAN on 7 May 2010 13:27
In article <i847u51mln1i5ggn8f913t2e3rl8ltgcbh(a)4ax.com>, me <noemail(a)nothere.com> wrote:
>OK... I live in the dark ages... but what's with "modern" power
>supplies blowing INTO the case instead of out of it? Pushing hot air
>in can't possibly be good - why not blow it right out and let the draw
>cool the rest of the case?
>
>Are most of you opening up your PS and reversing these back-asswards
>fans?
I have never known a power supply that was purposely designed to blow air in.
Most likey the person in China or wherever the PS was built, accidently
mounted the fan bASSackwards!!!!
From: Paul on 7 May 2010 17:23
me wrote:
> On Fri, 07 May 2010 05:59:08 -0400, Paul <nospam(a)needed.com> wrote:
>
>> As long as none of your temps are astronomical, you could leave it.
>>
>> Also, some PSUs have a sticker over one of the screws, and
>> removing the sticker and the screw to open it up, voids the
>> warranty. If the company is known to have sucky warranty service,
>> you might not care.
>
> Paul:
>
> I snipped your detailed reply, but thanks for all the expert info.
>
> Here's my specific situation... maybe we can get a little closer to
> suggestions: Asus P4P800, P3.0G, 512x4, ATI 9800XT/256m w copper sink
> and fan, two 2.5" drives, one PCI (firewire) card. PS is a 500W
> Rocketfish with a 5" temp controlled inbound fan and tested efficiency
> was 85% up to 300w, which is roughly what this system likely pulls.
> Case is a mid tower Mitek modified by having a about three square
> inches of opening in front of the 80mm temp controlled front case fan.
> I set up the front fan to pull air out of the case since the PS is
> pushing air in. The only other possibility for ventilation is to open
> some slots on the rear.
>
> At idle, with the case closed, the MB and CPU temp is about 47-49C,
> open it runs about 41-42C. I haven't run any 3D tests and the ATI card
> is cool at idle, so I suspect there would be a noticeable, but not
> critical rise in case temp when cranking it. I noticed right away that
> there was a lot of hot air coming through the PS, and it blows
> directly on the CPU, which fights back with its own fan.
>
> Back to my original post. I do plan to do a bit of gaming. My thought
> is that these temps are high for idle. Also, it seems like it's
> backwards: the two devices generating the most heat are back to back
> at the TOP of the cage with just a small rear vent next to the PS. Hot
> air rises, and I am trying to pull all that hot air down with a fan
> smaller than the PS bringing it in and/or relying on natural
> convection or the PS fan's push to get the hot air out. I'm almost
> thinking that I should create a screened vent in the top of the case
> and let the heat rise out.
>
> But, the inbound air seems seriously wrong from an engineering
> perspective to me.

Convection should not be a big contributor to the airflow picture.
It would be a consideration if there were zero fans, but once
powered fans are present, they're the dominant item. There is
no need to go punching holes from a convection perspective.
You bought fans, and they should be doing the work.

When temperatures rise, once the side is put on the unit, that means
there isn't sufficient airflow through the case. If you take the side off
the case, you get immediate mixing with room air. What should happen,
when the side is put back on, is the temperature should drop. A good
thru-case airflow, removes the "cloud" of hot air, around the
CPU heatsink or around the video card cooler.

I worked some power numbers, and I get 221 watts load inside the computer.
The 85% efficient power supply, dissipates 39W. If the power supply
blows its hot air *inside* the case, then the total power inside the
computer is now 260W.

There is a general formula for case cooling. For a well cooled case
(minimal temperature rise with respect to the room air), we set the
last term there to 7C or 10F degrees. In other words, if the room was
25C, the inside of the case would be 32C.

CFM = 3.16 * Watts / Delta_T_degrees_F
= 3.16 * 260W/10F = 82CFM

For a single fan, that would be a pretty loud and substantial fan. I
have a 120mm square by 37mm thick fan, that I think is around 110CFM.
You couldn't sit next to that, if it was running full speed.

Based on your description, it sounds like there might be less than
82CFM at work on your case.

For cooling, you want

1) Defined airflow. A typical flow is front to back. Intake at front
allows the hard drives (in front) to stay cool. Items further back
can take more heat than the hard drives do.

2) Sufficient vent cross section, for the volume you're trying to move.
On my Sonata, I got a bit of "vacuum cleaner effect", where the fan
audible note rises, when the side is closed. That tells me the front
vent area wasn't large enough. Once I removed some plastic trim, I
got to use more of what the fan had to offer.

3) Don't overdo it. Embellishment to the basic cooling concept, can actually
work against you. For example, if you had six fans, some blowing in, some
out, might be doing less good, than one well placed fan. You can
create unintentional dead spots, if you sprinkle fans all over the place.
It is pretty hard to work out in advance, what is actually going to happen,
if you use six fans.

What this can boil down to, is some computer cases you can buy, are just a
mistake. They have tiny fans on the back (like a 60mm), no vent space
on the front, and so on. To fix the worst of the sins, might take
too much metal work, or simply not be possible. Buying the right case to
start with, will make this easier.

To give an example, at the current time, I'm still using a case I got more
than ten years ago. Because it is ten years old, by definition, it can't be
a good one. They didn't use large fans back then. Airflow was choked.

To fix mine, there wasn't any space on the rear of the computer, to add
a fan. On my Sonata, there is room for a 120mm on the back. On this (antique)
case, the only fan on the back is the PSU. If I cut a hole in the back,
the raised area on the back only leaves a flat space for a 60mm. It sounds
like a disaster.

I added a metal assembly, in front of three of the drive bays. I placed
a 120mm fan there, plus a frame to hold it in place. That blows cool air,
right over top of any installed hard drives. (Currently there are two
3.5" drives installed.) The optical drive occupies the fourth bay, at the top,
just above the cooling assembly. (You have to be careful when loading a DVD,
to not stick your fingers into the fan :-) ) The cool air, blows by the bottom
of the optical drive housing.

By leaving PCI slot covers open at the back, that is my exhaust vent space.

Since my PSU blows outward, both the front and back fans work together to
encourage a front to back airflow. Video card heat, leaves the case via
the open PCI slot covers next to the slot occupied by the video card.
The processor heat is being pulled out of the case, by the PSU fan.

Anyway, I have a few ideas on how to fix minor problems, but if a computer
case is just a disaster to start with, there isn't much point beating
the hell out of it. Buy another case, one where you can see a cooling
rationale that makes sense, and use that as your basis for a build.
I recycled that old case, because I'm a cheap skate. I have several Antec's
here I could have used, but chose to make a project from that thing.

If this is your Rocketfish here, I can visualize the 140mm fan
blowing against the exposed heatsinks, and then the hot air
leaving by the "cheese grater" at the back. I was worried, that
if the airflow was reversed, there might be dead spots in there.
Note, that if you reverse the fan, there is a possibility the
blade will bang against the housing, so make sure you think through
how the fan is going to fit in there. You might have to build a spacer
of some sort, to provide enough clearance for the fan, if you reverse it.
If you do choose to disassemble the unit, check that the fan blade is
not jammed and stalled, before screwing it back together. If the blade
moves freely, then you're probably OK.

http://www.hardwaresecrets.com/printpage/748

If you have further questions, please provide a URL where there is a
picture of your computer case. I'm curious what it looks like.

One other comment. There is a picture of the label on the Rocketfish,
on that review web page. It shows 3.3V at 24A and 5V @ 15A. You got
lucky, because Asus motherboards of that era (like my P4C800-E),
used a lot of 3.3V. Mine measured 3.3V @ 14.4 amps load. My +5V
loading from the motherboard is very low, less than 1 ampere.
(That doesn't include power used by hard drives, video card or the like.)
If you used an Athlon board from that era, like an A7N8X, they
drew 15A+ from the 5V rail. Your Rocketfish wouldn't have
been a good choice, if you had one of those old S462 motherboards
in there. Your Rocketfish is designed for modern systems having heavy
12V and light other rail loads. It can be kinda difficult finding
a good all round supply, that covers all eras of computing well.
For example, my current supply is 3.3V @ 30A, 5V @ 30A, 12V @ 22A
(but not all at the same time of course), and that allows it to run
old or new motherboards. I've noticed a decline in the low voltage
rails in recent years, such that at least a few of the new supplies,
are no good for old systems. You can't buy my supply any more,
so mine better not blow up :-) I doubt I'll be able to find one
like that again.

Paul
From: peter on 7 May 2010 19:15
I have been building systems for about 20 years and I have yet to come
across
a reputable PSU that blows into the Case........
never heard of a 500W Rocketfish

peter

--
If you find a posting or message from me offensive,inappropriate
or disruptive,please ignore it.
If you dont know how to ignore a posting complain
to me and I will be only too happy to demonstrate :-)


"me" <noemail(a)nothere.com> wrote in message
news:48u8u51pdat2ttoaf3m7gkavltguhcrtej(a)4ax.com...
> On Fri, 07 May 2010 17:27:19 GMT, Winniethepooh(a)100acrewoods.org
> (GMAN) wrote:
>
>>In article <i847u51mln1i5ggn8f913t2e3rl8ltgcbh(a)4ax.com>, me
>><noemail(a)nothere.com> wrote:
>>>OK... I live in the dark ages... but what's with "modern" power
>>>supplies blowing INTO the case instead of out of it? Pushing hot air
>>>in can't possibly be good - why not blow it right out and let the draw
>>>cool the rest of the case?
>>>
>>>Are most of you opening up your PS and reversing these back-asswards
>>>fans?
>>I have never known a power supply that was purposely designed to blow air
>>in.
>>Most likey the person in China or wherever the PS was built, accidently
>>mounted the fan bASSackwards!!!!
>
> I dunno... I did some web searching to enhance my knowledge before
> posting and it seemed somewhat common.
>
>
From: DevilsPGD on 7 May 2010 19:24
In message <s91Fn.205$wV.141(a)newsfe11.iad> "peter" <peter(a)nowhere.net>
was claimed to have wrote:

>I have been building systems for about 20 years and I have yet to come
>across a reputable PSU that blows into the Case........

Amen. I'm a fan of positive pressure designs, but even so, I'd still
want my PSU exhausting in any system I've ever built, if only to avoid
dust build-up within the PSU.
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