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Disadvantages of Bottom-Mounted PSU?

Last response: in Components
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August 19, 2012 10:15:59 PM

Back in 2008 Tom's did a review of mid-range cases and selected the Antec 300 as most bang for the buck.

That case has the power supply on the bottom, and as a newbie, I wondered if that configuration had any disadvantages.

For instance, does that require the PSU to be installed upside-down?

What does it do for cable management?
a b ) Power supply
August 19, 2012 10:21:55 PM

Its like your comp upside down, the PSU should be positioned so that the fan or vent is facing inside the case, not the wall.
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a c 111 ) Power supply
August 19, 2012 10:29:00 PM

The point of the PSU to be bottom mounted is so you can draw air from the bottom into the power supply and eject it out the back.

Not drawing air from the inside of the case and exhausting it out the back.


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a c 111 ) Power supply
August 19, 2012 10:34:26 PM

No, it actually is a disadvantage to put it on the top!


Putting it on the bottom is the best choice. Every current case has its psu on the bottom.
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August 19, 2012 10:34:29 PM

Thanks - I get the "hot air rises" part of putting it on the bottom, but it seems most are mounted on the top. So, are there any disadvantages involved with putting it on the bottom?
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a b ) Power supply
August 19, 2012 10:38:28 PM

Wouldn't thing so as cases that require you to mount the PSU on the bottom are designed like top mounted PSU cases just at the bottom if that makes sense.
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August 20, 2012 2:16:52 AM

Okay, thanks - in all the old reviews I read they were on the top and some folks found they had problems with them when they were on the bottom, but I didn't know what the problems were. If the new ones are all like that then it must no longer be a problem, and they psu are all likely designed for it.

I appreciate the help.
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a c 157 ) Power supply
August 20, 2012 2:27:35 AM

The bottom of the case is the natural place for a PSU. Especially a high powered PC. Fresh air in... warm air out. Never deals with case air. Top mount are a throw-back to the old IBM PC days when towers simply were desktops turned on end. Besides, why have a top-heavy PC?
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a c 158 ) Power supply
August 20, 2012 1:01:18 PM

IMO the primary disadvantage of bottom-mounting PSUs is cabling especially on full tower] cases. The PSU is typically further from the 24-pin mobo power connector and the 4/8-pin CPU power connector. If the PSU's cables aren't long enough then you may have to get extensions or do some ugly cable routing. Most quality PSU mfrs have adjusted cable lengths to account for bottom-mounting PSUs but there are still some short cables out there.
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August 20, 2012 4:32:36 PM

I had a problem once with an old PSU not having long enough cables to reach the motherboard in a bottom mounted case, but I prefer having the power supply on the bottom.
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a c 158 ) Power supply
August 20, 2012 5:56:50 PM

I had an OCZ ModXstream 500W in an Antec P183 and had to get cable extensions so I could route the cable behind the mobo tray.
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a c 165 ) Power supply
August 20, 2012 6:19:52 PM

Jack15911 said:
Back in 2008 Tom's did a review of mid-range cases and selected the Antec 300 as most bang for the buck. That case has the power supply on the bottom, and as a newbie, I wondered if that configuration had any disadvantages. For instance, does that require the PSU to be installed upside-down? What does it do for cable management?


having built plenty of PCs with the PSU in every possible position including missionary and doggy, the disadvantage in the bottom position (as stated first by rugger) is cable management. in many full cases, you will see both options for PSU install.
http://www.enermax.com/home.php?fn=eng/product_a1_1_1&l...

the major advantage on having the PSU on the bottom is stability if you place the PC on a desk (or another place that can become unstable) and the use of the case as a filter to help keep dust out of the PSU. It also allows you to install a case fan on the top of the case (the blowhole....which has now become blowholes on most modern cases). PC case brands love fan openings because PC brands also sell after market fans.

also, while heat does rise in a case with no airflow...it does not rise as much as people think when that heat is blowing across the case by a 1500RPM CPU fan into a rear 1200RPM exhaust fan.
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a c 157 ) Power supply
August 20, 2012 7:15:08 PM

One other point... I've found that many lower wattage (430W and less) PSUs seem to be intended for top mount because they usually come with shorter 24 pin and 4/8 pin motherboard power cables. And they generally have a fan at the rear as opposed to at the bottom. Most of your higher wattage PSUs will be designed to live happily at either location.
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August 20, 2012 9:40:31 PM

Quote:
Top mount are a throw-back to the old IBM PC days when towers simply were desktops turned on end.


I remember once literally doing that (thought it looked cool) :sol: 

EDIT - in my defence I was probably about 8 or 9 at the time
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a c 157 ) Power supply
August 21, 2012 12:47:30 AM

wr6133 said:
Quote:
Top mount are a throw-back to the old IBM PC days when towers simply were desktops turned on end.


I remember once literally doing that (thought it looked cool) :sol: 

EDIT - in my defence I was probably about 8 or 9 at the time

Don't feel bad. Anyone old enough to remember when desktops that had their CRT sitting on top were the norm, tried something similar. (And some of us weren't 8 or 9) ;) 
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August 21, 2012 1:35:25 AM

If a top mounted power supply computer is being transported and the PSU came loose it would fall and hit the CPU heatsink and/or the GPU.

It's also easy to fit bottom mounted PSUs and in general it's easier to setup the cable management and loose cables can just site on the bottom instead of hanging down (or tied to the top of the case somewhere).

the only disadvantage is that there tends to be allot of dust under the PC and dust build up can be a problem and filters need to be cleaned on a regular basis to prevent blockages.
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a c 165 ) Power supply
August 21, 2012 2:11:08 AM

mikes1992 said:
If a top mounted power supply computer is being transported and the PSU came loose it would fall and hit the CPU heatsink and/or the GPU.

.


i've never seen that happen, and i recall most cases with a slot that held the PSU up in case it wasn't screwed in.
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a b ) Power supply
August 21, 2012 2:45:58 AM

Its best on the bottom, the air doesn't even have to enter the case from the PSU in the newer cases.

One disadvantage would be, that not all the PSU cables are long enough to reach the mobo. But its mostly with older PSU's.

Looks better that way and u can have the top fans blowing the air out of there.
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a b ) Power supply
August 21, 2012 3:18:19 AM

nikorr said:
Looks better that way and u can have the top fans blowing the air out of there.

Many top-mount cases have the 120mm CPU-area rear exhaust as well instead of relying solely on the PSU for that.

Another technical reason for bottom-mount is that it lowers the center of gravity, which makes it somewhat more difficult to accidentally tip cases over. The only heavy items left near the top of the case are the CPU HSF and DVD/BD drive.
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a b ) Power supply
August 21, 2012 3:25:13 AM

BTW, are they still selling the cases with PSU on top for the mainstream desktop users?
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a b ) Power supply
August 21, 2012 3:26:51 AM

InvalidError said:
Many top-mount cases have the 120mm CPU-area rear exhaust as well instead of relying solely on the PSU for that.

I think u misunderstand to what I wrote. I meant the air that comes into the PSU, never actually enters the case. And if it is on the top, it blocks the space where another fan could be.

Not to mention if one wants radiator on the top : ) Well, one wold not to choose that case now...

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a b ) Power supply
August 21, 2012 3:38:02 AM

nikorr said:
BTW, are they still selling the cases with PSU on top for the mainstream desktop users?

On NewEgg's "Computer Cases" section, select "More Options", "PSU Mounting Position" and then "Top" from the drop-down.

I see 149 results.

I bet at least one of those is intended for mainstream with prices starting at $20, lol.
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a b ) Power supply
August 21, 2012 4:14:10 AM

Is any of them a good one?
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a c 165 ) Power supply
August 21, 2012 4:18:27 AM

nikorr said:
BTW, are they still selling the cases with PSU on top for the mainstream desktop users?


antec's sonata series comes with the PSU on top for as long as i can remember. newegg sells a combo with the HCG 620w PSU

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a b ) Power supply
August 21, 2012 4:38:37 AM

Would u look at that. All the cases I looked lately, just by judging what I should get,

so I can replace my Antec p180, and I didn't stumble on top mounted : )


Cool. That is actually OK case ...
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a c 144 ) Power supply
August 22, 2012 3:19:36 PM

amuffin said:
The point of the PSU to be bottom mounted is so you can draw air from the bottom into the power supply and eject it out the back.

Not drawing air from the inside of the case and exhausting it out the back.

That is a largely theoretical consideration.

The original Antec 900 case did not have holes cut into the bottom of the case. And unlike the extra 3 or 4 holes in the motherboard tray, I chose not to cut them. So the PSU fan faces up toward the middle of the case. Even drawing "warm" from inside the case, the PSU exhaust air is maybe 3 or 4 C above ambient air temp. And it also helps cool the lower drive bay. The highest hard drive temp I have ever seen was 29 C. and they typically run 26 - 27 C.

clutchc said:
Don't feel bad. Anyone old enough to remember when desktops that had their CRT sitting on top were the norm, tried something similar. (And some of us weren't 8 or 9) ;) 

Me, neither. :) 
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a b ) Power supply
August 23, 2012 6:26:06 AM

jsc said:
The highest hard drive temp I have ever seen was 29 C. and they typically run 26 - 27 C.

I would take any temperature readings from embedded sensors on devices that aren't FDA-grade or better calibrated thermometers with multiple grains of salt. One of my HDDs always reports 2-3C below ambient while another always reports 2-3C above and they are both behind the same 120mm front fan with about 3/4" in-between.
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August 23, 2012 7:12:16 AM

The only problem I have with bottom mounted PSUs is the cabling has not changed to match the requirements.
For example, the SATA power cables are all still made to have the cable go from top to bottom, powering 2-3 drives as it goes along. If you have the cable going from bottom up (as is the case mostly), the connectors are all reversed, and the cables need to be twisted.
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a b ) Power supply
August 23, 2012 7:35:01 AM

proton007 said:
If you have the cable going from bottom up (as is the case mostly), the connectors are all reversed, and the cables need to be twisted.

If the first connector is far enough on the cable to reach the 'top' drive, you can go straight down from there.
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August 30, 2012 9:18:02 PM

Best answer selected by Jack15911.
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