Top-mount vs. Bottom-mount PSU

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srothman

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So I got all my stuff from Rebeltech today, and I noticed that even though it was described as being a bottom-mounted PSU case, I notice it is actually a top-mounted PSU case.

So... do I make a huge fuss about it, or is the hype about bottom-mounted PSUs over-rated?

For those who have followed my other posts, I really couldn't care less so long as I am not worse off than I am supposed to be...
 
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srothman said:
...
and I noticed that even though it was described as being a bottom-mounted PSU case, I notice it is actually a bottom-mounted PSU case.
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Am I reading that correctly?

I'd say the bottom mounted PSU cases are better. I'm pretty sure we've had this discussion before not too long (a couple of months or perhaps a year even) ago.
 
With a top mounted PSU I would suggest that you try and get your system temperatures as low as possible (below 75'C if you can), because the PSU's don't really like running hot. They'll become noisy and inefficient.

If you're not going to run high end gaming components in that case, then you should be fine. Like I'm running an i7 860 + HD 5670 in a top-mounted PSU case without any issues. I do have an aftermarket CPU cooler, but that was just so that I can overclock my CPU.
 
Been running everything non-stop for a couple of hours now, installing software, watching movies, etc etc and my temps haven't gone over 45c as yet. I have a CM Hyper 212 that's working really well, and it is situated in such a way that it and the one 120mm case fan is working greally well to suck the hot air out.

Meh... if I run into issues I'll change the case, but so far so good
 
srothman said:
Antec VSK-1000. I checked now on the Antec site that it doesn't specify it to be a bottom-mounted PSU case. Rebel however specifies it as one. My own fault for not doing my homework I suppose.



LOL... I made an error in my first post, and I blamed the meds I am on for it....
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Hi,

I can across this post just now.

I am sorry to hear that our specs are wrong - I have emailed the disti and Antec for clarification.

If you would like to replace the case with something else - please email us on [email protected] and we can make an arrangement.

Thanks
 
Nah no worries. The case actually works really well. Running really cool and quiet, so life is good :-)
 
Honestly, neither is great.

Unless your PSU is drawing air in from the actual bottom of the case (eg. fan facing down and there is an opening).

Heat moves upward so by having a PSU at the bottom, the air is moving counter to convection which doesn't make much sense really.

IMHO top is better since the CPU doesn't generate that much heat and most of the other heat is already pulled out by the rear case fan.
 
Gnome said:
Honestly, neither is great.

Unless your PSU is drawing air in from the actual bottom of the case (eg. fan facing down and there is an opening).

Heat moves upward so by having a PSU at the bottom, the air is moving counter to convection which doesn't make much sense really.

IMHO top is better since the CPU doesn't generate that much heat and most of the other heat is already pulled out by the rear case fan.
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+- 90watts isn't that much heat :wtf:

It's usually the graphics card and processor that generator most of the heat...
 
scotty777 said:
+- 90watts isn't that much heat :wtf:

It's usually the graphics card and processor that generator most of the heat...
Click to expand...

Maximum TDP is 90w, that is Intel's rating for the maximum power the CPU consumes when every gate is switched. In reality it doesn't use nearly that much even under maximum load.

And the PSU will pull in more heat from the GPU if it is facing upward in the bottom of the case (which is pretty close to the GPU hotspot).

An average GPU is rated 180watt TDP (7850 which is incredible efficient is rated 150watt).

Which one would you rather have the PSU pull heat from?

As I said, the PSU facing downward at the bottom of the case is the best but after that I would take top of the case every time.

Just my 2c.
 
Gnome said:
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As I said, the PSU facing downward at the bottom of the case is the best but after that I would take top of the case every time.
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All the decent bottom-mounted PSU cases should come with rubber feet (or similar things that lift up the case) so that the PSU can suck cool air from the bottom. You'll be worse off (than with a top-mounted PSU) if the PSU is bottom-mounted and sucking air from the top (same space as the graphics card).

+1 to everything you said actually ;)

With a low-mid range system a top-mounted PSU won't hurt, since the heat generated by the CPU + GPU won't be that much.

However, with old high end components, the heat generated by the GPU(s) & CPU could be a considerable amount (500W+ of it).

Luckily the latest generation components from Intel, AMD & NVidia have considerably lower TDP values for the same/better performance than the previous generation components.
Like the i7 920 had a TDP of 130W, where as the Ivy Bridge i7 3770k has a TDP of only 77W!

Lastly, just take note that the TDP values are for stock voltage & frequency, so you can easily double the power consumption & heat by overclocking it (and also increasing the voltage) with 30%.

So you shouldn't have any issues with a top-mounted PSU when you run the latest generation components at stock frequencies & voltages ;)
 
If you've ever read one of the Intel or AMD system builders manuals, there's a fairly good section on thermal efficiency and design etc (They sometimes even use the widely used 'grains of rice' measurement for thermal interface material). I'm not sure where I spotted it, but it must have been around the 2002-3 version of the Intel guide, it has a page about CPU fan failures and it makes quite a lengthy mention that in most home/office chassis, the top mounted PSU, pulling air from above the CPU and exhausting it is more important for system stability than the CPU cooler itself.

It makes a lot more sense if you think of the case as a closed system, if there's a problem with any exhausting fans for example, then the hot air running over the CPU HSF is only going to be dissipated very slowly, as such you'll raise ambient temperatures on an accelerating curve. If the CPU cooling has failed (or is completely passive), it's easy enough for the exhausting action of the PSU to hold a thermal throttling/low C/P-state load.

So in the end, while the efficiency in a gaming machine might not be influenced in a very noticeable way, the safety offered in top mounted units certainly has seemingly a solid standing.
 
Yes. We've established that. The confusion came in when the website I bought it from said bottom-mounted.
 
If you have a push pull airflow you are unlikely to run into thermal problems....

Going against the tide (and on a knitpicking factor) is that one benefit of top mounted PSU's in full mid/full tower cases is that you are less likely to run into the "my cables are to short" problem and having to get extensions and what not.
Caveat, naturally dependent on the brand of PSU
 
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