Todays Hot Mod: Reverse PSU Cooling

[mad-dog]

Some ATX power supplies are designed to pull fresh air from outside the case,draw it across the hot components of the PSU and exhaust it inside the case, this can and most often does increase case temperatures and make CPU cooling more difficult.
FYI: This mod requires voiding the warranty on the PSU....but if your a mod squad member like me then you could really care less.
Disassemble the case to the point that you have access to the fan/s, simply remove, flip over and reattach the fan/s then reassemble the PSU case and reattach the power leads.
Now the PSU will be working in harmony with the rest of the system and drawing cool air from the lower front across the motherboard then up and out the back of the case.
Before performing this mod please ensure that your PSU fan is indeed blowing air into the case and not drawing air out.
Good Luck n Happy Trails..

Side note: Most modern PSU's are designed to exhaust hot air out of the case which is correct.

Folding@Home

 

[erloas]

Umm... every PSU I've seen exhausts the hot air out the back of the case and not into the case. As far as I'm aware it has always been the case where the PSU intakes from the case and exhausts out the back.
I suppose its always possible to get a PSU that was put together wrong and has the fan installed the wrong way, but that should be a very very rare occurance for even the cheapest PSU manufacturers.

 

[Crashman]

Most ATX power supplies are designed to pull fresh air from outside the case,draw it across the hot components of the PSU and exhaust it inside the case, this can and most often does increase case temperatures and make CPU cooling more difficult.

You got it backwards...wow, you haven't been reading much THG then have you? Most full-sized power supplies pull warm air out of the case, across the PSU components, and expell it out the exhaust. That's why most cases have the power supply mounted above the CPU, to pull hot air away from the CPU. That's also why ATX cases normally have the PSU mounted "upside down" with the lid on the bottom, so that a lid-mounted fan can pull hot air away from the CPU.

 

[Crashman]

Umm... every PSU I've seen exhausts the hot air out the back of the case and not into the case.

You're right, most do. And that's one more reason why cases with the power supply on the bottom are a bad idea: Power supplies pull out more heat than they put in, and some systems have successfully used the power supply fan as the only exhaust fan.

 

[sirrobin4ever]

Definitely backwards. (Mad dog has more posts than me???)

 

[mad-dog]

Definitely backwards. (Mad dog has more posts than me???)

Yah, maybe i should edit slightly to reflect newer PSU technology

Folding@Home

 

[Crashman]

Most of my AT power supplies also pulled hot air out of the case, and AT predates ATX.

 

[korbin44]

You're right, most do. And that's one more reason why cases with the power supply on the bottom are a bad idea: Power supplies pull out more heat than they put in, and some systems have successfully used the power supply fan as the only exhaust fan.

Sorry Crashman, but if you take a look at most of the high end full tower cases, the PSU is mounted on the bottom of the case. Remember, heat rises. So, it would only make sense that the power supply mounted on the bottom would pull in cooler air than at the top. Thus, cooling the PSU's inner components more efficiently. Take my case for example, the Silverstone TJ09. The PSU is mounted at the bottom. At the top of the case you have two 120mm exhaust fans, and one intake fan directly behind the hard drive cages, and one fan in between the hard drive cages to cool the hard drives. Tell me again why you would want the PSU to pull out already hot air over already hot components?

 

[korbin44]

You're right, most do. And that's one more reason why cases with the power supply on the bottom are a bad idea: Power supplies pull out more heat than they put in, and some systems have successfully used the power supply fan as the only exhaust fan.

The only way that makes sense is if the PSU is the only exhaust in the system, and I would only do that in SFF cases, or HTPC's that put out barely any heat anyway.

 

[Crashman]

Remember, heat rises. So, it would only make sense that the power supply mounted on the bottom would pull in cooler air than at the top. Thus, cooling the PSU's inner components more efficiently.

Right, and the PSU is supposed to be more rugged than the other components in a system. The main reason companies now make cases with the power supply on the bottom is because their customers are stupid.

I watched the whole thing unfold, from the early customers believing claims that a system would run cooler with the power supply at the bottom, to Cooler Master adding this to its latest design. This is market driven, not engineering driven.

 

[Crashman]

The only way that makes sense is if the PSU is the only exhaust in the system, and I would only do that in SFF cases, or HTPC's that put out barely any heat anyway.

It worked fine in a bunch of systems before P4 came out. Works fine with A64 singles, plus many X2's and stock-speed Core 2 Duos so long as the graphics card doesn't run too hot and the PSU fan is 120mm.

 

[korbin44]

Right, and the PSU is supposed to be more rugged than the other components in a system. The main reason companies now make cases with the power supply on the bottom is because their customers are stupid.

I watched the whole thing unfold, from the early customers believing claims that a system would run cooler with the power supply at the bottom, to Cooler Master adding this to its latest design. This is market driven, not engineering driven.

Okay, so by your account, all those engineers who are paid to make better products are stupid and don't know what they're doing. Don't be ridiculous, crashman. It's a matter of heat. Once again, heat rises. Heat also degrades your components over time. I want my system to maintain its current performance for a long time. By using the PSU to draw out all the heat in your case, your are destroying the PSU components much more quickly. It only makes sense to have the PSU pull in cooler air to COOL the components, no matter how rugged the PSU is supposed to be. Obviously you are not an enthusiast, or else you wouldn't be talking nonsense.

 

[Crashman]

Okay, so by your account, all those engineers who are paid to make better products are stupid and don't know what they're doing. Don't be ridiculous, crashman.

I'm not being rediculous and the "engineers" are very smart: They build what people buy. Nothing else matters but selling a product. And BTW, I seriously doubt that many of these cases are "engineered" anyway, they're more likelky designed by mechanical designers like me, who are paid to make whatever the customer demands.

Power supplies are supposed to be made to take the heat. We were using the original ATX design with hot P4's and the good power units lived for many years.

 

[mad-dog]

It's all my fault, I'll take full irresponsibility..

Folding@Home

 

[korbin44]

Honestly Crashman, it only makes sense from a design perspective to put the PSU at the bottom of the case. I have built many computers with many different cases. My Silverstone TJ09 has the best cooling solution of any case I've ever used. One of the reasons is that the PSU is on the bottom. Besides that, I have a PC Power and Cooling Silencer 750 that powers an oc'd QX6700, 4 hard drives, 2 video cards and a 226 watt peltier. Now, why would I want more heat to be pulled in to the PSU with all that hardware already heating up the internals of the power supply? I wouldn't. That's why I chose the case I have. Look, if I had a choice, which I do, to have my PSU cooled by hot air or cool air, I would choose the cool air. Who wouldn't? Obviously you wouldn't, or we would not be having this conversation. But hey, you can continue to 'heat' your power supply while I 'cool' mine. To each his own, right?

 

[Onus]

IMHO, a top-mounted PSU is better able to assist with general case cooling, which is why it is usually there. OTOH, in better cases that provide more than enough cooling without that assist, it would be slightly better for the PSU to mount it at the bottom.
It seems to me that in a case with good airflow, the slightly warmer air going through a top-mounted PSU is still going to be sufficient to cool it, and the effect on its lifespan will be insignificant. All bets are off if the case airflow is poor and/or the PSU is a $15 special.

 

[korbin44]

Sure, the difference can be very small. But, when dealing with high end systems and extreme overclocking, heat is a killer. Any reduction in the amount of heat moved out of the system, without 'heating up' any additional hardware in the process is worthwhile. Besides all of that, most fans inside a PSU are only 80mm. A case with a bottom mounted PSU and one or two 120mm exhaust ports on the top and/or back of the case will move out more air, and be much quieter than a noisier 80mm PSU fan. It just doesn't make sense to make the PSU do more work than it should.

On the lifespan issue, when dealing with overclocking you run the risk of shortening the life of your hardware considerably. I don't want to take that chance. So any little tweak or improvement I can do to eliminate heat, I will do just that.

 

[mad-dog]

Sure, the difference can be very small. But, when dealing with high end systems and extreme overclocking, heat is a killer. Any reduction in the amount of heat moved out of the system, without 'heating up' any additional hardware in the process is worthwhile. Besides all of that, most fans inside a PSU are only 80mm. A case with a bottom mounted PSU and one or two 120mm exhaust ports on the top and/or back of the case will move out more air, and be much quieter than a noisier 80mm PSU fan. It just doesn't make sense to make the PSU do more work than it should.

On the lifespan issue, when dealing with overclocking you run the risk of shortening the life of your hardware considerably. I don't want to take that chance. So any little tweak or improvement I can do to eliminate heat, I will do just that.

Amen

 

[Onus]

Well, someone selling a $200 case is probably betting that the buyer is more likely to be a heat-stressed overclocker than a someone building a business machine.

 

[DJ_Jumbles]

I'm not being rediculous and the "engineers" are very smart: They build what people buy. Nothing else matters but selling a product. And BTW, I seriously doubt that many of these cases are "engineered" anyway, they're more likelky designed by mechanical designers like me, who are paid to make whatever the customer demands.

Power supplies are supposed to be made to take the heat. We were using the original ATX design with hot P4's and the good power units lived for many years.

RE: Engineers...
I work for a major food manufacturer as a maintenance supervisor. In my opinion, here's how it works: The engineers design something and say: "This will work". Now technically, it SHOULD work, but because of all the practical factors involved with installation or from outside factors, 90% of the time it DOES NOT WORK AS IT'S DESIGNED. Everything that we have "engineered" by engineers gets re-engineered on the floor over and over again by mechanics or our process electonic technicians until it finally is working the way it was supposed to have worked when the engineers designed it. Engineers design it, we (the little people without advanced scientific degrees) make it work.

I think that you all are arguing over something that is not really understood by most of you. The PSU is not made up of fine transitorized circuitry like your CPU. It's made up of more rugged electronic components that do just fine under moderate to high heat conditions. Heat is the enemy of smaller, more micronized IC circuitry as it applies inside a computer case. The CPU, GPU, and Northbridge chips all have 90, 65, or 45nm transistors, making them more prone to failure in high heat conditions. PSU's are rugged devices made to withstand much higher heat thresholds than the more delicate and expensive components of your system. The only downside to passing warmer air over the PSU is that you might lose some efficiency because of the increased thermal load, but relatively, you're not risking burning up your PSU any faster.

 

[I]

If it ain't broke, don't fix it. The (first?) ATX spec did call for PSU that intake through the back and exhaust into the system but most manufacturers didn't adhere to that because they knew it was a bad idea, so they stuck with what had proven to work in prior AT designs.

If you happened to come across such an ancient ATX PSU today, it's time to retire it due to old age, no point in flipping the fan. The difference in parts locations to offset some idea of heat rising and causing a chimney effect is minimal, because this is not a passively cooled system. The difference is trival so long as the case has the proper placement of air intakes such that this faster moving stream flows past the hotter parts.

PSU in top or bottom doesn't matter much, if in the bottom it will throttle down the fan some due to being cooler, which allows it to increase in heat slightly. At the same time, moving the PSu exhaust from the hotter zone towards middle and top means the upper rear fans have to move more air themselves, offsetting the potential noise reduction of the slower spinning PSU fan. Either config can work fine, and neither config has enough benefit to place much weight upon instead of the other merits of any particular case.

 

[techgeek]

I'm not sure where people get the idea that the ATX spec called for the PSU fan to be an intake fan. Here is the ATX PSU Design Guide:

http://www.formfactors.org/developer%5Cspecs%5CATX12V%20PSDG2.01.pdf

If you look at section 4.3 which deals with fan direction/placement it says that in general a rear mounted exhaust fan is used.

The reason this is, is original ATX design specs called for air intake at the bottom front, exhaust at the top back. This spec was originally created before the advent of any other additional cooling (case fans) were used. So the PSU fan was responsible for ejecting all the warm air from the case. Later it became popular (as CPU and graphics cards became hotter) to have a fan in the lower front to assist in drawing cool air in. Of course as extra cooling was needed we seen the advent of side door fans and rear panel fans. This leads to why case makers felt that it was possible to move the PSU to the bottom of the case. Since nearly every new ATX case has at least one rear panel fan (usually 120mm), the PSU was no longer the only form of exhaust for the warm air arriving at the rear of the case. I am sure some case designer seen that it was no longer absolutely necessary to draw the warm air at the rear top of the case into and through the PSU (and thus make the PSU warmer). By placing it at the bottom the PSU gets cool air directly from the front of the case, and the CPU and GPU heat will also get a portion of the same cool air to draw the heat out through the rear panel fans. This should increase the lifespan of the PSU since it should maintain a cooler internal temperature on average when compared to a top mounted PSU. The hotter the PSU is, the shorter the lifespan of the electrolytic capacitors will have. This design change should also have minimal impact on the temperature of the rest of the case, because of the addition of rear panel fans that eject the heat from around the CPU, GPU area.

 

[korbin44]

RE: Engineers...
I work for a major food manufacturer as a maintenance supervisor. In my opinion, here's how it works: The engineers design something and say: "This will work". Now technically, it SHOULD work, but because of all the practical factors involved with installation or from outside factors, 90% of the time it DOES NOT WORK AS IT'S DESIGNED. Everything that we have "engineered" by engineers gets re-engineered on the floor over and over again by mechanics or our process electonic technicians until it finally is working the way it was supposed to have worked when the engineers designed it. Engineers design it, we (the little people without advanced scientific degrees) make it work.

I think that you all are arguing over something that is not really understood by most of you. The PSU is not made up of fine transitorized circuitry like your CPU. It's made up of more rugged electronic components that do just fine under moderate to high heat conditions. Heat is the enemy of smaller, more micronized IC circuitry as it applies inside a computer case. The CPU, GPU, and Northbridge chips all have 90, 65, or 45nm transistors, making them more prone to failure in high heat conditions. PSU's are rugged devices made to withstand much higher heat thresholds than the more delicate and expensive components of your system. The only downside to passing warmer air over the PSU is that you might lose some efficiency because of the increased thermal load, but relatively, you're not risking burning up your PSU any faster.

Actually, you can burn up your PSU faster by increasing the heat. Especially if you use a POS PSU made of inferior components. I know that PSU's use more rugged components, but that is not to say they can't be abused. In my case, I'm using a lot of the total watts of my PSU because of the components used in my setup. The PSU I use is a high end power supply, so I'm not that worried about it failing. But, I have done my homework and read tons and tons of reviews on power supplies and computer hardware in general. In a setup like mine, efficiency is key. If my PSU starts to falter and the efficiency goes up and down, I'm subjected to other hardware, like my processor, failing. Some hardware could even short circuit due to the fluctuations in my power supply. So, putting my PSU in the bottom of my case benefits me in more than just one way. I'm also protecting the efficiency of my power supply which in turn makes sure all the other hardware is getting the correct voltages.

Too many people who build their own systems ignore the power supply. Not in terms of forgetting to put it in their systems, but rather the quality of the build they are getting in the PSU they buy. The cheaper you go, the more likely you are to have it fail and/or damage your system. Besides, these days it's all about performance per watt, and total power used. To have an inefficient power supply affects your bottom line(electric bill), especially if your system is always on. So, to increase the heat of the PSU is, i.e., to increase the money you burn.

 

[korbin44]

I'm not sure where people get the idea that the ATX spec called for the PSU fan to be an intake fan. Here is the ATX PSU Design Guide:

http://www.formfactors.org/developer%5Cspecs%5CATX12V%20PSDG2.01.pdf

If you look at section 4.3 which deals with fan direction/placement it says that in general a rear mounted exhaust fan is used.

The reason this is, is original ATX design specs called for air intake at the bottom front, exhaust at the top back. This spec was originally created before the advent of any other additional cooling (case fans) were used. So the PSU fan was responsible for ejecting all the warm air from the case. Later it became popular (as CPU and graphics cards became hotter) to have a fan in the lower front to assist in drawing cool air in. Of course as extra cooling was needed we seen the advent of side door fans and rear panel fans. This leads to why case makers felt that it was possible to move the PSU to the bottom of the case. Since nearly every new ATX case has at least one rear panel fan (usually 120mm), the PSU was no longer the only form of exhaust for the warm air arriving at the rear of the case. I am sure some case designer seen that it was no longer absolutely necessary to draw the warm air at the rear top of the case into and through the PSU (and thus make the PSU warmer). By placing it at the bottom the PSU gets cool air directly from the front of the case, and the CPU and GPU heat will also get a portion of the same cool air to draw the heat out through the rear panel fans. This should increase the lifespan of the PSU since it should maintain a cooler internal temperature on average when compared to a top mounted PSU. The hotter the PSU is, the shorter the lifespan of the electrolytic capacitors will have. This design change should also have minimal impact on the temperature of the rest of the case, because of the addition of rear panel fans that eject the heat from around the CPU, GPU area.

Nice find. I'm glad someone else can see it from my perspective and put some hard evidence behind it!

 

[Crashman]

Yes, so the power supply should be at the top to assist the exhaust fans because the internal air temperature in a well built system is only around 35C, well below the threshold at which top-end power supply companies test their units.

After all, few people are stupid enough to put a generic PSU in a $200 case.

But removing the PSU from the top removes some case exhaust flow. Because of that, many cases with the power supply mounted at the bottom have a 120mm fan at the top rear.

Because you're now using more fans, your system becomes noisier. Because the fan faces out the top of the case rather than into the underside of the power supply, its noise has a more direct pathway to your ears. So the CPU gets the same cooling effect by adding components and making the system noisier.

Then comes the cable routing nightmare, which can only be solved by designing the case with the motherboard upside-down. And upside-down heatpipes don't work right, so you're more likely to suffer chipset overheating. Etc etc etc.

I'm glad we all agree!