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PSU Mount Orientation

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Darr247

New Member
Joined
Sep 12, 2012
The top-mounted 380W power supply in my sister's HP Pavilion died, so I bought a Cooler Master 500 (RS-500-PCAR-A3) on sale ($35) at newegg to replace it. I see I could have gotten it for a net $30 if I wanted to wait 10-12 weeks for the $10 rebate that started today.

The stock supply had a 70mm (or 80mm, depending how you measure... blade tip to tip is 70mm) fan drawing air through it and exhausting out the back.

The Cooler Master has a 110mm (the box says 120mm, but I measure 110mm edge to edge on the blade, and the opening the blade sits in is only 112mm, so I don't know how they can call it 120mm) blowing IN to the power supply, which still exhausts out the back.

So, I went through a few threads here seeking a definitive answer to this question, but they all dealt with bottom-mounted supplies.

The mounting plate on the back of the case has extra screw holes placed so it can be mounted fan up or fan down.

Should I mount the fan towards the motherboard or towards the top of the case?

There is no vent on top of the case, and I'm not going to take the dremel to it to make any (it's not MINE). There is about 15mm (19/32'') of clearance between the power supply and the top of the case. It's open on the 'front' edge and the side with the removable cover... except for a 10mm gap near the back corner, it sits tight against the backplane on the other 'side' and tight against the back, of course.

So, 15mm x (140mm+150mm+10mm) gives 45 cm² (about 6.975 square inches) of opening if I mount the fan facing the top.

I figure that should allow a flow up to 40 cubic feet per minute (@5.8CFM per square inch of opening, though I see Panaflo fans are rated at 7.9CFM per square inch; it's NOT a Panaflo fan), but I don't find any specs for what the minimum CFM should be through the power supply.

e.g. Manual
Spec Sheet

The maximum the 112mm opening should flow is ~88 CFM using that same formula. i.e. 3.14159 (2.2'' x 2.2'') 5.8 CFM/in² = 88.2 CFM

However, with the IEC socket and the on/off switch, plus the grill blockage, the openings on the back are smaller, and that opening should max out about 65CFM.
 
Without pictures, your explanation is a bit confusing. I wouldn't put the fan towards the top of the case with 15mm clearance. I don't understand why you couldn't put it facing down.

The fan in the power supply is likely controlled by the unit itself. Meaning, when the power supply gets warmer, it spins the fan up faster. In my many years building my own systems, I've never worried about air flow through the power supply.
 
That PSU will run "cool" with the light load it will be facing in a older HP Pavillion. I would mount it "normal" (parts inside the PSU facing upwards as they normally would) but I am doubtful that it matters.

The way I understand your comparison between the fans is as such: Original unit had fan mounted at the back of the PSU and pulled air on and pushed it right out. New unit pushes air into the unit and the air escapes out the back. If this is the case, there shouldn't be any change in how much air can enter the case.

Barring a super powerful fan, there should be sufficient airflow already. You might increase the negative air pressure in the case a bit but without knowing the exact CFM, this is essentially a fruitless discussion. The new unit might have less RPM then the old one and therefore push less air.

I would just run it and if the fan whines or makes noise do to lack of air then remove a bay cover on the front or one of the PCI expansion slot covers instead.
 
If i was you i would put it in fan down towards the board....
You could just be sucking in more heat.
Or less air flow.

And im sure its a 120mm fan for a resin... maybe depends on vrand? i have no idea lol is it 120mm across?
 
It is normally 120mm between the (diagonal) mounting holes. The fan itself can be larger or smaller.
 
I'd mount it fan towards motherboard. No reason to restrict it's airflow by aiming it at a wall :D
 
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