Power supply fan flow

[albumleaf]

So i've got this thermaltake sviking case. It packs two 120mm fans, one in the front and another in the back. I also have a superflower 520w three fan psu (one exhaust, one next to psu, one facing front of case) inside of it. Now i've gotten somewhat annoyed with the noise that the full size 80mm fan in the psu makes, so I have a panaflo on the way. The question is this: do i want to have the psu blowing air in or out of the case? I'm thinking about switching all the fans inside the psu to suck in, as the way it is now the psu just takes hot air right off my cpu and pushes it out. It seems like if i had air blowing into the case right above the cpu to get pushed out by the rear 120mm fan it would work quite well, in addition to the fact that my psu would be cooler.

opinions?

 

[wisdomtooth]

Sounds to me like you are an AOL user who wants your computer to fry like a mozzarella stick. :laugh:

If you have the PSU blowing into your case, you are blowing hot air already heated by the PSU at your CPU. Worse, that 120mm case fan blowing out air re-heated by the CPU will simply be sucked in again by the PSU and the hot air just gets recirculated into your computer..

3 fans in 1 PSU is pretty pointless... The amount of air being expelled by the PSU is limited by the size of the vent to the exterior (80mm diameter) and the single fan pushing air out of the PSU case. So your 3-fan PSU does not vent any better than a PSU with just one single 80mm fan.

I would just ditch that contraption and get yourself a PSU with ONE single 120mm-fan. Those vent MUCH better, move MORE air, and would be MUCH quieter than three eggbeater fans.

Get yourself a Seasonic S12-500.

HTH.

 

[Navid]

Not a good idea to mess with the PSU!
Do you have a link to this PSU with 3 fans?
If you have to modify the PSU, have it suck air from the case and exhaust air out of the case.

 

[imported_llama]

exhaust, take a leaf out of the book of the ocz and tagan, one fan oposite the other, one inlet from where the cables come out, the other venting out the back of the box. This is the best and quietest way to do it afaik.

EDIT (Just to clarify) Intake on the Inside of the case

 

[imported_fatal]

A fan blowing in through the power supply would be like attaching a heater to your case :thumbsdown:

 

[wisdomtooth]

Originally posted by: llama
exhaust, take a leaf out of the book of the ocz and tagan, one fan oposite the other, one inlet from where the cables come out, the other venting out the back of the box. This is the best and quietest way to do it afaik.

EDIT (Just to clarify) Intake on the Inside of the case

Actually, those two-80mm-fan PSUs don't vent any better than a single-80mm-fan PSU, and since it has TWICE the fans, it will have TWICE the noise.

One 120mm fan can move more air than a 80mm fan. One slow-spinning 120mm fan can move the same amount of air as a fast-spinning 80mm fan, and be more quiet.

That's why if quietness is important to you, get a 120mm-fan PSU. That's one of the reasons why SilentPC Review recommends the Seasonic Super Tornado/S12 series as THE PSU to get if you want quiet.

 

[Zepper]

Fans in PSUs should generally move air from inside the case to the outside (exhaust). I would condsider any PSU with three fans (if they are really needed for cooling) to be poorly designed... Often all those fans are in there in hopes that at least some noob consumers will get sucked in by the bullet points..

.bh.

 

[Slaimus]

You do not want opposed back exhaust and PSU fan directions. If you do, one would just be sucking in hot air exhausted by the other, and then recirculating it again.

 

[albumleaf]

well, here's the deal. I don't care much about my cpu temp. I'm much more concerned with keeping my psu at a decent temp. At this point i may just turn off the 80mm fan next to the psu and leave the exhaust 80 and the one other on the inside running. I figured that giving my psu fresh air would keep it cooler than letting it eat hot cpu air. I'll run some tests later this week when i get my new fan and i'll tell you how it goes.

 

[imported_fatal]

Why the big concern with PSU temp? Well, good luck heating up your case :disgust:

 

[imported_rod]

Two fans do move more air than one, but not twice as much.

Three fans seem like alot for one PSU. Generally, a PSU can withstand much higher temps than a CPU, without any adverse effects. Most of the components inside a PSU can withstand temps upto about 80C, although with reduced effiency. As long as it is below about 60C-70C, there shouldn't be any problems.

But thats just my opinion.

RoD

 

[wisdomtooth]

Originally posted by: rod
Two fans do move more air than one, but not twice as much.

In order for two fans to move more air out of the PSU than a single fan, the two fans must BOTH be exposed externally, directly moving air across a barrier (i.e. both mounted on the back of the PSU).

However, this is NOT the arrangement in the two- or three-fan PSUs-- Only ONE fan is externalizing air across a compartment barrier (from inside the PSU to the outside), limited by the size of the opening (80mm). That one external fan is the bottleneck.

That's why PSUs with one external exhaust fan and an internal intake fan will NOT vent any better than PSUs with just one external exhaust fan.

If you want a better-venting PSU, the answer is a unit with ONE bigger fan with as little restriction to airflow as possible out the back (large-area honeycomb grill).

It also behooves you to get a cool-running PSU. Ever wonder why is it that fanless PSUs like the Antec Phantom experiences higher-than-usual failure rates? (Rhetorical question.)

 

[imported_llama]

Originally posted by: wisdomtooth

Originally posted by: llama
exhaust, take a leaf out of the book of the ocz and tagan, one fan oposite the other, one inlet from where the cables come out, the other venting out the back of the box. This is the best and quietest way to do it afaik.

EDIT (Just to clarify) Intake on the Inside of the case

Actually, those two-80mm-fan PSUs don't vent any better than a single-80mm-fan PSU, and since it has TWICE the fans, it will have TWICE the noise.

One 120mm fan can move more air than a 80mm fan. One slow-spinning 120mm fan can move the same amount of air as a fast-spinning 80mm fan, and be more quiet.

That's why if quietness is important to you, get a 120mm-fan PSU. That's one of the reasons why SilentPC Review recommends the Seasonic Super Tornado/S12 series as THE PSU to get if you want quiet.

i agree that a 12cm fan one will be quieter but i cant notice any difference, i would have a fan pulling hot air out, rather than blowing air in, and because of restrictions on the ATX spec means that a 8cm fan is the largest that can be used (the way i want to do it). Just personal preference. If one of the fans in this OCZ fails the other should do an ok job at keeping the PSU alive, with just one its 2x as risky imo

 

[wisdomtooth]

Originally posted by: llama
i agree that a 12cm fan one will be quieter but i cant notice any difference, i would have a fan pulling hot air out, rather than blowing air in, and because of restrictions on the ATX spec means that a 8cm fan is the largest that can be used (the way i want to do it). Just personal preference. If one of the fans in this OCZ fails the other should do an ok job at keeping the PSU alive, with just one its 2x as risky imo

Just so there is no misunderstanding, the 120mm-fan PSUs do not suck air into the computer case. Just like 80mm-fan PSUs, the 120mm-fan PSUs expel air out the back. Except a good-quality 120mm-fan PSU can do it far more quietly per CFM.

As far as reliability of single-fan PSUs vs. dual-fan PSUs go, I don't think that's much of an issue. Look at Dell, which sells Business PCs by the thousands, and they got ONE PSU fan venting the whole system. If a single fan is reliable enough for business use (i.e the fan not failing through the lifetime of the machine), it's more than reliable enough for non-mission-critical home-use.

 

[imported_llama]

i know that the single fans underneath vent from inside the case although i didnt make that clear. your right about the dell thing but i would like to know what would happen to my OCZ if it had only 1 fan and it decided to die when say, my dad was on farcry, im sure it wouldnt last long without a fan

 

[Zepper]

That's why you use your hardware monitor software to sound the alarm when things go outside the normal range you set. If your PSU doesn't provide a fan speed sensor lead, install a three wire fan in it and connect it to the mobo or a fan controller panel.

.bh.

 

[imported_rod]

Originally posted by: wisdomtooth

Originally posted by: rod
Two fans do move more air than one, but not twice as much.

In order for two fans to move more air out of the PSU than a single fan, the two fans must BOTH be exposed externally, directly moving air across a barrier (i.e. both mounted on the back of the PSU).

However, this is NOT the arrangement in the two- or three-fan PSUs-- Only ONE fan is externalizing air across a compartment barrier (from inside the PSU to the outside), limited by the size of the opening (80mm). That one external fan is the bottleneck.

That's why PSUs with one external exhaust fan and an internal intake fan will NOT vent any better than PSUs with just one external exhaust fan.

If you want a better-venting PSU, the answer is a unit with ONE bigger fan with as little restriction to airflow as possible out the back (large-area honeycomb grill).

It also behooves you to get a cool-running PSU. Ever wonder why is it that fanless PSUs like the Antec Phantom experiences higher-than-usual failure rates? (Rhetorical question.)

The fan sucking air into the PSU from inside the case helps the one expelling the air out the back of the PSU. That's because it increases the relative air pressure inside the PSU, which allows the rear fan to move out more air per revolution. It also allows the fan to spin at higher maximum RPMs, due to the decreased load on the fan.


And you're right when you said "the two fans must BOTH be exposed [externally], directly moving air across a barrier.". But expelling air out the back is only one barrier. The other is the barrier between the inside of the case and the inside of the PSU.

If a second fan truly did nothing, why do so many reputable companys use the two fan design?

 

[imported_llama]

too true, and yes monitor the fan speed, if it fails whilst you arnt there (overnight folding for example) it wont make much difference, as you wont hear it anyway!

 

[Monkeyyy]

If you're really interested in keeping the psu cooler then you have two options:
1. keep PSU outside of case
2. use an air duct mod to give the psu intake fan fresh air from outside, (as opposed to hot air from inside of case)

never reverse the direction of the psu fans for the reasons that everyone else is saying.

I think I saw a ducted PSU somewhere, I just can't remmember where.

 

[wisdomtooth]

Originally posted by: rod
The fan sucking air into the PSU from inside the case helps the one expelling the air out the back of the PSU. That's because it increases the relative air pressure inside the PSU, which allows the rear fan to move out more air per revolution. It also allows the fan to spin at higher maximum RPMs, due to the decreased load on the fan.

And you're right when you said "the two fans must BOTH be exposed [externally], directly moving air across a barrier.". But expelling air out the back is only one barrier. The other is the barrier between the inside of the case and the inside of the PSU.

If a second fan truly did nothing, why do so many reputable companys use the two fan design?

These dinky 80mm fans do NOT generate enough static pressure (usually around 0.1"/2.5mm H2O) to make much of a difference in air pressure. Test it yourself-- Unplug the fan in the back of the PSU but leave the one inside running. If there is sufficient air pressure inside the PSU, it should spin the unpowered fan as pressurized air escapes through the opening. BUT IT DOES NOT.

Take a deep breath, hold an unpowered fan in your hand, and blow at it. You will see that it takes A LOT of air pressure to move a fan.

Also, spinning at a higher maximum RPM increases NOISE. That's why it's better to use larger, slower-spinning fans, and have a large-surface-area grill somewhere to essentially eliminate a barrier-- Like the grills on the back face of a 120mm-fan PSU.

The only good a second 80mm fan might do for a PSU would be to move some air past the heatsinks in the PSU, but you can do the same with a single 120mm fan. The vast majority of reputable companies by the way are also putting out 120mm-fan PSUs, including Antec (Neopower, TruePOwer II, etc.), Fortron (Blue Storm), Seasonic (Super Tornado, S12), Tagan, OCZ, etc.

Bottom line: 120mm-fan PSUs move more air, cool better, have greater internal volume for bigger heatsinks, and are more quiet.

 

[imported_rod]

Originally posted by: wisdomtooth
These dinky 80mm fans do NOT generate enough static pressure (usually around 0.1"/2.5mm H2O) to make much of a difference in air pressure. Test it yourself-- Unplug the fan in the back of the PSU but leave the one inside running. If there is sufficient air pressure inside the PSU, it should spin the unpowered fan as pressurized air escapes through the opening. BUT IT DOES NOT.

Take a deep breath, hold an unpowered fan in your hand, and blow at it. You will see that it takes A LOT of air pressure to move a fan.

Also, spinning at a higher maximum RPM increases NOISE. That's why it's better to use larger, slower-spinning fans, and have a large-surface-area grill somewhere to essentially eliminate a barrier-- Like the grills on the back face of a 120mm-fan PSU.

The only good a second 80mm fan might do for a PSU would be to move some air past the heatsinks in the PSU, but you can do the same with a single 120mm fan. The vast majority of reputable companies by the way are also putting out 120mm-fan PSUs, including Antec (Neopower, TruePOwer II, etc.), Fortron (Blue Storm), Seasonic (Super Tornado, S12), Tagan, OCZ, etc.

Bottom line: 120mm-fan PSUs move more air, cool better, have greater internal volume for bigger heatsinks, and are more quiet.

I agree that a single 120mm fan is better than 2x 80mm fans, but 2x80mm fans are beter than a single 80mm.

RoD

 

[wisdomtooth]

Interesting thing at PC Power & Cooling...

They don't think 2 80mm fans are better than 1 80mm fan either..

Then again, I'd just as soon avoid any 80mm-fan PSU and go with a 120mm-fan one.