Questions about PSU fan orientation

May 26, 2012 at 01:04:48
Specs: Win 7
Two power supplies that I found on look
as though they are designed to be mounted in the case
with the fan on the inside, not the outside:

Sparkle Magna R-SPI900GCM
Zalman ZM600-HP

The locations of the screw holes, the orientation of the
labels, and the orientation of the power supply in some
of the photos strongly suggests that they are intended
to be mounted so that the 120 mm fan is on the bottom,
away from the outside. However, nobody mentioned
anything like that.

Do the fans on these two power supplies blow into the
PS or out of it? If either of them blows in, I want one.

Also, the reviews for the Zalman say it has a terrible
reliability issue: It knows when the warranty is up and
immediately dies. Is there any further info about that?

-- Jeff, in Minneapolis

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May 26, 2012 at 06:32:07
All PSUs mount the same:

Notice the pattern of the mounting screws. This prevents the PSU from being mounted incorrectly. However, there are different types of computer towers & the tower dictates how & where the PSU is mounted. The top mount design with the PSU located above the motherboard is preferred. With this design, the PSU cooling fan doubles as a case exhaust fan. As far as I know, all PSU fans "suck" air into the PSU & "blow" it out the rear of the case.

The bottom mount design has been catching on but it actually is a poorer design. It's supposed advantage is that the PSU sits beneath the motherboard with its cooling fan drawing in fresh outside air from under the case, rather than drawing in warm air from inside the case. The thinking is that the PSU will run cooler. But with the fan directly exposed to the outside, it tends to suck in dust, dirt, hair, crumbs, etc. & if not cleaned regularly, it will clog & overheat. And since the PSU fan is no longer acting as a case exhaust fan, another fan has to be installed, adding both cost & noise. Also, since warm air rises, the heat from the PSU rises up & the 1st thing in it's path is usually the video card. Another possible problem is cable length. On some PSUs, the cables may be too short to reach the 24-pin ATX & 4-pin ATX12V connectors on the motherboard.

Here's an article from Tom's Hardware about it:

The Problem of Bottom-Mounted Power

As for the two PSUs you mentioned, I wouldn't recommend either one of them. They are way overpriced plus they have multiple +12v rails. Look for a model with a single +12v rail with high amperage. Check the Corsair line.

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May 26, 2012 at 09:43:29
Someone changed the title of the thread, making it wrong.

The computer case does NOT have the PSU at the bottom.
It goes at the top. The question is whether the PSU mounts
with the fan on top of the PSU, on the outside, or with the fan
at the bottom of the PSU, with the fan on the inside. As I said,
the screw holes and label orientations suggest that these two
power supplies should be mounted with the fan on the inside.

However, it is possible that the screw holes in the computer
case would allow for mounting any PSU upside-down, whether
it is intended to go that way or not. There is a notch in the edge
of the PSU opening which appears to be designed to accept
the offset screw when the PSU is installed upside-down. It is
exactly like the notch which accepts the offset screw when it is

The thing is, my computer case does not have a top hole for a
top fan. If these two PSUs are intended to be mounted with the
fans on the inside, then they are exactly what I want: They blow
out the back.

However yet again, you said that as far as you know, all PSU
fans "suck" air into the PSU & "blow" it out the rear of the case.
I have been assuming that PSUs with the fan on top blow out
the top of the case. Is that wrong? They actually suck in the top
and blow out the back, so that they do NOT double as a case
exhaust fan?

-- Jeff, in Minneapolis

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May 26, 2012 at 12:26:29
The fan should be on the bottom (inside the case) so that it acts as a case cooling fan. That is by ATX design. If you flip the PSU upside down so that the fan is on the top, where it it going to draw air from? Here's a couple of pics showing the proper PSU/fan orientation:

Here's a couple of PSUs to consider:

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Related Solutions

May 26, 2012 at 15:22:27
You are looking at the PSUs the wrong way. ATX cases have 4 mounting screws to hold the PSU. The top left screw hole is inset toward the center so the PSU can only mount one way. The intake will either be on the inner end or the bottom.

As riider has stated neither of those PSUs are good choices. The sparkle is rated at 900w but all 4 +12V rails are only 20A. That is not enough for high end graphics cards. In addition the total wattage according to the specs 1210w. (V x A = w). Also only 1 year warranty.

The other PSU is only 600w. I find it odd you chose a 900w & a 600w PSU. The Zalman is even worse on the 4 +12V rails@ only 16A each.

If you live in the USA then check out the links below. is an excellent online vendor.

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May 26, 2012 at 16:48:37
Sparkle Magna R-SPI900GCM and Zalman ZM600-HP
both have the single fan on the bottom of the PS case because the fan is too big to fit at the back of the PS case !!
In that situation, a PS with a single fan has merely ventilation holes on the back side of the PS case instead of a fan.

A PS fan (or fans) always blow(s) air OUT of the back side of the PS case / computer case, one way or another.
The side of the fan where you can see the entire fan blade with no non moving part in the way is always the side air is sucked INTO.

The PS case is only 86mm high on the OUTSIDE of the case. When the fan in a PS is 80mm or smaller , it will fit at the back of the PS case, but if it's any bigger than that, it must be mounted on the bottom of the PS case.

I DO NOT recommend that you buy a Sparkle PS.

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May 27, 2012 at 21:00:39
Thanks. I'm still confused, but at least now I know I'm confused.

My computer case has no opening in the top. I know that many
gaming cases do. The large majority of photos of the PSUs on
Newegg show the PSU fan on top. I skipped past those and only
looked at PSUs which did not have a fan on top. The two I listed
were unusual in that they appeared to have the fan on the bottom.
I thought they were different from the others.

Now the impression I'm getting from you is that the fan goes on
the inside, not the outside, in all PSUs that have large fans.
If that is correct, then apparently I have a much, much wider
choice of PSUs than I thought. Before I saw those two PSUs
I assumed that I could only fit a PSU with an 80 mm fan.

Do I understand correctly now?
What is the opening on the top of those gaming cases for?
Why are PSUs almost always shown upside-down?

-- Jeff, in Minneapolis

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May 27, 2012 at 22:47:00
The fan in the power supply faces down when the power supply is mounted at the top of the computer case. Air travels in the front of the computer case and is sucked into the power supply. It is then blown out the back of both the power supply and the computer case. The pictures you see on Newwegg show the power supply upside down so that you can see the fan opening in the picture (it looks more impressive). The gaming cases you see have another fan mounted in the top or allow for the user to install one himself without modifying the case. I am almost sure you can go up to a 120mm fan in your power supply depending on your computer case.

I also highly recomend one of the Corsair brand power supplies. They have a good warrenty and good overall track record. I have installed many of them for customers and have only had to return one. When I get a system with a bad power supply it is what I recomend and I back it up by offering to replace it for free for a year on top of their warrenty.


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May 27, 2012 at 23:15:37
"My computer case has no opening in the top. I know that many
gaming cases do."

It used to be all standard desktop tower computer cases had the PS mounted at the top of case at the back.

Lately you can get "Gamer" or "Enthusiast" cases that have the PS mounted on the BOTTOM of the case at the back.

You can buy either type of case these days.

"What is the opening on the top of those gaming cases for?"

Whether the PS is mounted at the BOTTOM or the TOP of the case at the back, if there are any openings in the TOP of the case for fans, they're ALWAYS for CASE fans.

"The large majority of photos of the PSUs on Newegg show the PSU fan on top"
"Why are PSUs almost always shown upside-down?"

If the PS has a fan larger than 80mm,

- the pictures often show the PS upside down to show you what the fan looks like.

- the > 80mm fan is always on the BOTTOM of the PS case when the PS is mounted in the computer case.

The threaded screw holes at the back of the PS case and the holes for them at the back of the computer case are arranged such that that's the only way the PS will mount in the case, and also the opening in the computer case where the PS mounts usually has the metal cut out such that the fan grille or ventilation holes will only not be obstructed if the PS case is the right way up, whether the PS is at the TOP or the BOTTOM of the COMPUTER case.

"Now the impression I'm getting from you is that the fan goes on
the inside, not the outside, in all PSUs that have large fans."

It doesn't matter where the fan is in the PS case as long as the fan BLOWS air out the back of the PS case one way or another - ALL standard sized PSs DO.

Some PSs have more than one fan - an 80 mm fan (or smaller fan) at the back of the PS case, and another fan on the bottom of the PS case - I've even seen a few that have three fans.

For a standard width computer case, which varies somewhat (it must be at least wide enough so that the width of the PS case is horizontal) , the PS case is a standard size.
Standard (PS/2) power supply size - 86mm high, 150mm wide, 140mm deep, or 3 3/8" h x 5 7/8" w x 5 1/2" d , or very close to that, though the depth can be more or less for some PSs.

"I assumed that I could only fit a PSU with an 80 mm fan."

You can install ANY PS/2 sized PS case in ANY "generic" standard width computer case.

There were some brand name system computer cases in the past that had oddball sized or shaped larger PSs / PS cases in standard width computer cases n the past, but that has been rare since the early 2000's.

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May 28, 2012 at 08:02:31
The standard for PSUs is to draw air from inside the case and discharge air out the rear.

Any case with a hole in the top is designed to have a CASE fan installed in that position. I don't recommend getting a case like that. If you have one then block the hole and disconnect the fan.

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May 28, 2012 at 11:08:05
You don't need a computer case that has a place to install a case fan on the top of the case unless the system has an extreme heat problem.

- the bios settings are overclocking the cpu and/or the memory
- the heat sink / fan combo on the CPU is inadequate for whatever situation.
- you have a graphics card installed in a slot that produces a lot of heat. It's fan may be inadequate
- you have more than one graphics card installed in mboard slots.

Installing more fans in the case than it takes to get the interior of the case to a reasonable temp only pulls in more dust, lint, etc. and that will accumulate faster and need to be cleaned off more often, especially if the case is on or near the floor of a wall to wall carpeted room. .

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May 29, 2012 at 06:11:50
Thanks to whoever fixed the thread title.

Thanks for all the answers!

I'll start from the beginning looking for a new PSU. From your
comments, apparently almost all of the PSUs I skipped over
could go into my case. I wondered why there was no separate
selection criterion on Newegg for small rear vs large top fan!

Another question on the same subject:

My current PSU does not get hot. It doesn't even get detectibly
warm. Less than body temperature! So cool that I'd guess it
doesn't really need a fan. But that's the thing. I happened to
notice that the fan isn't running. Several times after powering
the computer on, I saw the fan stop turning a minute later. Now
it apparently never starts. But then the motherboard gets too
hot, so I had to increase the speed of the case exhaust fan from
the low setting to medium.

Is it possible that the PSU fan is designed to stop when the
internal temperature of the PSU is low? The literature doesn't
mention any such thing, and it seems unlikely.

Antec Earthwatts EA-500 (Not the "D" model.)

-- Jeff, in Minneapolis

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May 29, 2012 at 08:27:35
Better PS models have larger, more efficient heat sinks inside of them, and weigh more than lesser quality PS models partially because of that.
The fan may have a temp sensitive control that spins the fan slower when the temp inside the PS case is lower. I haven't heard of such a temp sensitive control that allows the single fan to STOP spinning if the temp is low enough - that's possible, but NOT likely.
However, in any case, the fan SHOULD spin when the temp inside the PS gets hot enough to trigger that.

Sometimes you have to look on the PS manufacturer's web site in order to find out if the fan on the particular model is temp controlled. That may be indicated by something within the specific model number on the label of actual PS you have.

Some PSs have more than one fan - in that case, the fan on the bottom of the PS is nearly always temp controlled. The lower fan MAY stop stop spinning when the temp is low enough, but I've never come across that.
Both fans may be temp controlled.

Your Antec Earthwatts EA-500 has a 500 watt (output) capacity. If your system doesn't need anywhere near 500 watts of total power, the PS components will stay relatively cooler.

Antec has two lines of PSs for the same or similar wattage capacities.
The lower line which includes Earthwatts models have a shorter warranty than the higher line which includes the TruePower (True Power ?) models. It used to be Antec made only the latter.

PS models that have shorter warranties tend to usually have a fan or fans that has or have bearings for the motor that are less durable.They're two cheap sleeve bearings that have oil impregnated into the pores of the bearing (e.g. oilite brand), or one sleeve bearing, one ball bearing, rather than two ball bearings or better (e.g. ceramic bearings). (If the label on the fan, or the specs for the fan, say ball bearing without an s, it probably has one sleeve bearing, one ball bearing.) Some fans have a sleeve bearing or bearings that has some superior method of keeping them lubricated (e.g. many Japanese brands) , but they don't last as long as fans with two ball bearings or better

If you find out your PS fan isn't spinning under any situation and it's supposed to spin at least a lower rpm at all times, if the PS's board has not been damaged by overheating yet, if you replace the fan with one of the same size and the same or similar or higher cfm rating - if you find no cfm rating one that draws about the same amount of ma or more usually has a similar or better cfm rating - the PS will work fine and the fan will spin as it's supposed too.
I recommend you replace the fan with a three wire case fan of the same size, that has two ball bearings or better bearings rather than a two wire PS fan, and run the fan's 3 pinhole connector to a spare 3 or 4 pin fan header on the mboard, if that header's available Some case fans can be connected to either a 3 pin fan header or a spare larger molex power connector. Some have a variable speed control or switch in their wiring. Some case fans have a superior blade design that moves more air and/or makes less noise when the blade spins faster.

If you connect the 3 wire case fan to a 3 or 4 pin fan header on the mboard, you can monitor the PS fan's current rpm in the bios, or use hardware monitoring software in Windows to monitor that rpm which uses the info the bios provides. Most retail mboard models come with such software on the CD or DVD that came with the mboard, or it can usually be downloaded from the mboard manufacturer's web site, from the list of software available for the specific model, or from elsewhere on the web site. If there is hardware monitoring software available from the manufacturer it's often been tweaked to make it as accurate as possible.
Sometimes you can set bios settings so you get a warning of some sort if the rpm is too low or zero. You almost always can set a software hardware monitoring program in Windows to do that in it's own settings.
In either case,
- if the fan is variable speed, or isn't but spins slower than the default setting, you may need to change the lowest rpm value from it's default value to suit the fan;s situation

Third party software such as SpeedFan makes assumptions and may need to be tweaked in it's own settings to have it read about the same as the readings you see in mboard's bios version, and sometimes it detects readings for inputs nothing is connected to (the reading is always the same, and/or is impossible).

I've replaced the PS fan with a two ball bearing case fan at least 4 times when a particular PS was working fine otherwise, other than the fan not spinning properly, and in all but one of those cases, the PS did not fail after that.

For the one case where PS failed after replacing the fan, it was a PS in a friend's computer I was working on, it had a conventional tower computer case with the PS mounted at the top of the case, and I accidentally noticed the case got HOT above where the PS is when the computer had been on a while. There was very little air coming out of the computer case at the back where the PS is mounted. When I opened up the computer case, the single fan on the bottom of the PS was wiggling back and forth instead of spinning. The friend had not noticed the problem, so who knows how long it had been doing that. I replaced the fan with a 3 wire case fan of the same size (Antec brand) that had two ball bearings and came with wiring connectors / adapters that could be connected to either a 3 pin fan header on the mboard or a spare larger molex connector from the PS, and it had a switch inline for selecting one of three speeds - I chose the fastest speed as I recall. The PS failed a couple of months later, the fan is still fine.
It was a Cooler Master model that turned out to have a 1 year warranty and probably a fan with two cheap sleeve bearings. The fan failed less than two years after the new PS had been installed - there is no one in the friend's household who used that computer all day except possibly on the weekends.
I replaced the PS with an Antec model with a 5 year warranty, and there have been no PS problems with that computer since then.

Tubesandwires, in Alberta, Canada.

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May 29, 2012 at 16:21:17
This is a good one in your wattage range:
Single 12V Rail
80%+ Bronze certified efficient
Active PFC
High praise on consumer generated comments

You have to be a little bit crazy to keep you from going insane.

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