Top mounting, most older boards are not well laid out for a bottom mounting PSU.

Scubs wrote:

Top mounting, most older boards are not well laid out for a bottom mounting PSU.

As long as you have good airflow through the case, bottom mounted is the way to go.

It will keep the power supply cooler and make it last longer as it will not be sucking the heat from the rest of the system through the power supply.

Tbh, unless you're going for a very late Win98 system with power-hungry P4 / SoA CPU and AGP monster like the 9700Pro, it really won't make too much of a difference. If its the SE440BX system in your sig, the only consideration is that the ATX connector is relatively high on the board - but depending on the case you can run it under or in front of the motherboard. Cables for drives can definitely be run under the board, so I'd not worry about PSU location at all. Thermals are also hardly an issue with a Katmai and moderate AGP card. Just choose the case you like most.

If on the other hand it's the E8400 with 7950GT you're talking about, thermals become very relevant indeed - but that doesn't necessarily rule out bottom PSUs, it just means you need good clean airflow one way or another.

cyclone3d wrote:

Scubs wrote:

Top mounting, most older boards are not well laid out for a bottom mounting PSU.

As long as you have good airflow through the case, bottom mounted is the way to go.

It will keep the power supply cooler and make it last longer as it will not be sucking the heat from the rest of the system through the power supply.

I fail to see how air can't be pulled down the case and into the psu.

If you would use new-ish case with bottom mounted old PSU, you will almost certainly have to use couple of extensions for some cables. Cables in old PSU aren't long enough, and older motherboards sometimes use absolutely insane positions for some connectors. Case in point (no pun intended), with my build (where I route cable behind the motherboard for cleaner cable management), I had to use extensions for 20 pin ATX cable, 4 pin EPS cable and one Molex cable.

Scubs wrote:

cyclone3d wrote:

Scubs wrote:

Top mounting, most older boards are not well laid out for a bottom mounting PSU.

As long as you have good airflow through the case, bottom mounted is the way to go.

It will keep the power supply cooler and make it last longer as it will not be sucking the heat from the rest of the system through the power supply.

I fail to see how air can't be pulled down the case and into the psu.

Cases with bottom mounted CPUs have the power supply pulling in cold air from under the case. This makes it so the power supply is not pulling air to cool itself from inside the case which is generally going to be a lot warmer air than air from outside the case.

Hot air rises. It is best to have a case with an exhaust fan either on the top of the case or at the back of the case very near the top edge. Trying to make the heat travel downwards is counter-intuitive.

Even with a top mounted PSU, the air inside the case near the top of the case can be a good 10-15C hotter than the air outside the case if you have components that put off a decent amount of heat. And if you have really bad airflow through the case, you are looking at 20-25C hotter than ambient air temps. That hot air being pulled through the PSU is going to not only make the components wear faster, it is also going to make the PSU less efficient as the hotter the components in the power supply get, the less efficient they get.

Most cases with a bottom mounted PSU that I seen still pull the air from within the case. Some do pull air from outside the case, But top vs. bottom mount does not effect that. A top mounted PSU can suck air from outside the case too.
Most PSU have vents on the back, with outside air intake and a side mounted fan those vents will blow some hot air into the case.

I fail to see how it would make much if any difference. The only thing that would be of help is air being such in from out side the case, and that has nothing to do with where the psu is mounted.

Just stick to the old cases and the PSU that is on the top, bcuz you will have only problems if the PSU is on the bottom, also old case is more cheaper then newer one, and look more original..

The talk about "prolonging the life of the PSU" is probably just nonsense. There is most likely not a single study that showed any effect of top vs bottom mounting PSU on longevity. Whatever small effect it might have would probably by negligible compared to other factors (luck of the draw most likely having the biggest effect).

The way I see it:

* You can have specific boards and/or cases that favor one configuration or the other, and you should research that.
* Bottom-mounted PSU helps the stability of the case by shifting the center of weight down.
* Top-mounted PSU favors small, cheap cases with no exhaust fan of their own, as the PSU will serve as the exhaust.

And I think these are all the relevant considerations.

dr_st wrote:

The talk about "prolonging the life of the PSU" is probably just nonsense. There is most likely not a single study that showed a […]
Show full quote

The talk about "prolonging the life of the PSU" is probably just nonsense. There is most likely not a single study that showed any effect of top vs bottom mounting PSU on longevity. Whatever small effect it might have would probably by negligible compared to other factors (luck of the draw most likely having the biggest effect).

The way I see it:

* You can have specific boards and/or cases that favor one configuration or the other, and you should research that.
* Bottom-mounted PSU helps the stability of the case by shifting the center of weight down.
* Top-mounted PSU favors small, cheap cases with no exhaust fan of their own, as the PSU will serve as the exhaust.

And I think these are all the relevant considerations.

Go look at the life expectancy of electrolytic capacitors and what higher temperatures do to their life expectancy.
There is no need to test specific power supplies to determine that the higher the temperature inside the PSU, the shorter the life of the PSU.
http://www.rubycon.co.jp/en/products/alumi/pdf/Life.pdf
http://jianghai-america.com/uploads/technolog … imation_AAL.pdf
https://en.wikipedia.org/wiki/Electrolytic_capacitor

We all should know the hotter a part runs the shorter the life span. But that has nothing to do with top vs. bottom mounted PSU's

cyclone3d wrote:

http://jianghai-america.com/uploads/technolog … imation_AAL.pdf

Am I reading this right, that they estimate that the lifetime expectancy of a electrolytic capacitor running at an ambient temperature of 55C is 13 years?

Scubs wrote:

We all should know the hotter a part runs the shorter the life span. But that has nothing to do with top vs. bottom mounted PSU's

The claim that a bottom-mounted PSU will run cooler is reasonably sound, as it does not suck hot air from around the CPU and the GPU.

Or should I say - depending on orientation. If the bottom-mounted PSU is flipped upside down with the intake vent facing the case, then I agree it makes little difference; I had the impression that most cases with bottom-mounted PSUs do not use this orientation, but orient the PSU so that the intake is at the bottom.

A bottom-mounted PSU may be slightly cooler than a top-mounted one, but that means other case components, such as the voltage regulators on the motherboard, get warmer and if they're low quality they'll need recapping sooner.

If you don't want to have to recap *something* you need to buy devices with good components, which is far more significant than where in the case they are installed.

Scubs wrote:

We all should know the hotter a part runs the shorter the life span. But that has nothing to do with top vs. bottom mounted PSU's

Yes it does. On bottom mounted PSUs, the PSU draws cool air through the PSU from the outside of the case.

On top mounted PSUs, the PSU draws in warm/hot air though the PSU from inside the case.

It has EVERYTHING to do with top vs. bottom mounted.

dionb wrote:

A bottom-mounted PSU may be slightly cooler than a top-mounted one, but that means other case components, such as the voltage regulators on the motherboard, get warmer and if they're low quality they'll need recapping sooner.

If you don't want to have to recap *something* you need to buy devices with good components, which is far more significant than where in the case they are installed.

Anywhere from 10-25C cooler PSU temps is not "slightly" cooler. For every 7C cooler, you about double the life expectancy of the capacitors inside a PSU.

You only have component heat issues if you have poor circulation through the case. Pretty much all cases with bottom mounted PSUs have good/great airflow through the case because of extra intake/exhaust fans.

With top mounted PSUs, you still get a nice pocket of hot air near the top of the case. With exhaust fans either in the top of the case or at the back edge right near the top, you don't get that pocket of hot air.. especially when you have exhaust fan(s) on the top of the case.

I've been building computers for about 27 years; have taken temperature reading with probes to compare temps and have just a bit of experience with modifying cases in order to make everything run cooler.

cyclone3d wrote:

Anywhere from 10-25C cooler PSU temps is not "slightly" cooler.

Where are the numbers 10-25C coming from? Were they actually measured in top vs bottom-mounted CPUs in "all other things equal" situation?

cyclone3d wrote:

For every 7C cooler, you about double the life expectancy of the capacitors inside a PSU.

I think it said 10C in one of the articles you linked to.

cyclone3d wrote:

You only have component heat issues if you have poor circulation through the case. Pretty much all cases with bottom mounted PSUs have good/great airflow through the case because of extra intake/exhaust fans.

The same is true for many top-mounted PSU cases as well. And for cases with bad circulation a top-mounted PSU will help extract the hot air out. So PSU may run hotter, but other components may run cooler. What's more important?

cyclone3d wrote:

I've been building computers for about 27 years; have taken temperature reading with probes to compare temps and have just a bit of experience with modifying cases in order to make everything run cooler.

Do share those numbers if you have them handy. It is very useful information in a topic where most approaches are based on feelings and not actual measurements.

I have seen a few myth-busters in the past that demonstrated that cases with gazillion fans don't really have an advantage over a simple setup with one 120mm intake fan at the bottom front, and 1-2 120mm exhaust fans at the top back.

cyclone3d wrote:

You only have component heat issues if you have poor circulation through the case. Pretty much all cases with bottom mounted PSUs have good/great airflow through the case because of extra intake/exhaust fans.

With top mounted PSUs, you still get a nice pocket of hot air near the top of the case. With exhaust fans either in the top of the case or at the back edge right near the top, you don't get that pocket of hot air.. especially when you have exhaust fan(s) on the top of the case.

This is comparing apples and oranges. With decent airflow, that top-mounted PSU doesn't even get 10-25C hotter than ambient, let alone 10-25C hotter than the rest of the case. Of course a system with bottom-mounted PSU and exhaust fans will be cooler than a system with top-mounted PSU and no exhaust fans - but the big difference here is the fans, not the PSU. With a top-mounted PSU and an exhaust fan under it (or in front of it in the top of the case) you avoid that pocket of hot air just as you would with a bottom-mounted PSU and a fan up there.

I have no issues whatsoever with bottom-mounted PSUs (in fact my main i7 system has one, as does my daughter's), but if the mounting of the PSU significantly affects its temperatures, the real issue is airflow in general.

OK, some more clarification.

1. I don't have my old test data. I did those tests years ago. I also don't have any current cases with airflow issues but I can take some readings once I set up a system or two with top-mounted PSUs that don't have a top mounted fan/poor airflow. Not my top priority though. I originally did the tests on top mounted CPU cases without/with an exhaust fan or fans mounted in the top of the case. I did not switch to a bottom mounted PSU case for quite a while after that. It really did become a pretty moot point to me at least as good cases came out that actually had good airflow as opposed to the usual PSU fan and maybe an 80mm intake fan in the front of the case and if you were really lucky an 80mm or 120mm exhaust fan at the back of the case.

I'll do some testing as I am building systems and either post a separate thread here or on a web page with results. I am not planning on cutting up any cases to add more fans or exhaust holes, or relocated power supplies, so it will not be 1-1 results, but I can possibly leave the side off of the case or maybe even remove the top of the case depending on how it was made.

When there is air coming out of the PSU and the exhaust fan that is significantly warmer than the ambient air, you have less than ideal airflow through the case. I strive for, under full load, the air coming from the case exhaust to be barely noticeable in temperature by feel. I would have to do some actual tests for the exhaust air, but I would say maybe 3-5C difference from ambient is acceptable.

2. With a top mounted PSU and no exhaust fan in the top of the case or way for the hot air to escape, with the fan on the bottom of the PSU (almost ALL good PSUs are made this way now), unless you mount the PSU upside down, you are still going to have at least 3-4 inches in the top of the case where there is a pocket of hot air. And guess where the optical drives are normally mounted? Yep, in one of the upper 5.25 slots. Excess heat also kills those rather quickly.

3. Depending on the article about temps and caps, the range is from 7-10C for doubling capacitor life expectancy. It is also going to depend on the quality of the caps and the real temp rating on the cap. Crappy caps are all over the place, are often overrated for what they can actually handle, and have nowhere near the life expectancy that is given by the scam companies that make them.

dr_st wrote:

The talk about "prolonging the life of the PSU" is probably just nonsense. There is most likely not a single study that showed a […]
Show full quote

The talk about "prolonging the life of the PSU" is probably just nonsense. There is most likely not a single study that showed any effect of top vs bottom mounting PSU on longevity. Whatever small effect it might have would probably by negligible compared to other factors (luck of the draw most likely having the biggest effect).

The way I see it:

* You can have specific boards and/or cases that favor one configuration or the other, and you should research that.
* Bottom-mounted PSU helps the stability of the case by shifting the center of weight down.
* Top-mounted PSU favors small, cheap cases with no exhaust fan of their own, as the PSU will serve as the exhaust.

And I think these are all the relevant considerations.

Depend if the PSU is on the old style on top, and the damn CPU runs like stove damn hot, then it will lower the life of the PSU much, otherwise is all the same..
Old original builds can`t use new/modern cases that have bottom PSU mount. Also who will pay much money for new case to put inside the so called scrap from many uneducated people ?