SirNickity wrote:

Keep in mind that the AT/ATX thermal design philosophy relies on the PSU fan not only to cool the supply, but to draw cool air from outside and exhaust warm air from inside the case.

So what if it is a "thermal design philosophy". Doesn't mean it was/is a good one.

Look at newer ATX cases. Many of them now are made so that the power supply only cools itself with outside air and is isolated from the heat from the rest of the computer.

That is a WAAAAAAAAY better design as it means the power supply not only runs more efficiently but also cooler which increases the life expectancy of the components, especially capacitors, in the power supply.

cyclone3d wrote:

So what if it is a "thermal design philosophy". Doesn't mean it was/is a good one. […]
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SirNickity wrote:

Keep in mind that the AT/ATX thermal design philosophy relies on the PSU fan not only to cool the supply, but to draw cool air from outside and exhaust warm air from inside the case.

So what if it is a "thermal design philosophy". Doesn't mean it was/is a good one.

Look at newer ATX cases. Many of them now are made so that the power supply only cools itself with outside air and is isolated from the heat from the rest of the computer.

That is a WAAAAAAAAY better design as it means the power supply not only runs more efficiently but also cooler which increases the life expectancy of the components, especially capacitors, in the power supply.

Neither of you are wrong but you're comparing apples to oranges.

Newer higher wattage PSUs cram more parts into the same space so cooling their internal components becomes more of a problem.

Regardless of the tech level more cooling in the PSU is a good thing even if not strictly necessary.
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AT power supplies and computer design methodologies cannot really be compared to current design methodologies.

A typical AT computer has very little in the way of actual power hungry components. A cpu that may use 20W on the high end, or a video card that might require a heatsink if you were lucky. There really isn't much in an AT computer that used much power, or required too much cooling.

So it doesn't really surprise me to see that originally AT PSUs were designed to move air through the entire computer, or that you could easily reduce the airflow through an AT supply if you were careful to make sure it doesn't get completely stifled.

This is an interesting discussion. ATX PSUs almost always have exhaust fans on them, they are designed to push hot air from within out of the case. Were AT PSUs fitted with reversed fans to act as intakes for the case, to create ventilation? I don't think this is a great idea as the air pushed into the case would be warmed by the PSU, but then I never saw a single AT computer with any fans other than the PSU fan so I suppose that was better than nothing in most cases? Granted, pushing the air out would create negative pressure into the case and theoretically draw air in from elsewhere, but the problem is most AT cases don't have anywhere else to draw air in from 😵

appiah4 wrote:

This is an interesting discussion. ATX PSUs almost always have exhaust fans on them, they are designed to push hot air from within out of the case. Were AT PSUs fitted with reversed fans to act as intakes for the case, to create ventilation? I don't think this is a great idea as the air pushed into the case would be warmed by the PSU, but then I never saw a single AT computer with any fans other than the PSU fan so I suppose that was better than nothing in most cases? Granted, pushing the air out would create negative pressure into the case and theoretically draw air in from elsewhere, but the problem is most AT cases don't have anywhere else to draw air in from 😵

Never seen a AT power supply that blew into the case.

From what I know, when ATX was originally designed, there was a thought that the ATX fan case would blow in over the top of the CPU, but that was quickly dropped and very few computers were designed this way.

canthearu wrote:

appiah4 wrote:

This is an interesting discussion. ATX PSUs almost always have exhaust fans on them, they are designed to push hot air from within out of the case. Were AT PSUs fitted with reversed fans to act as intakes for the case, to create ventilation? I don't think this is a great idea as the air pushed into the case would be warmed by the PSU, but then I never saw a single AT computer with any fans other than the PSU fan so I suppose that was better than nothing in most cases? Granted, pushing the air out would create negative pressure into the case and theoretically draw air in from elsewhere, but the problem is most AT cases don't have anywhere else to draw air in from 😵

Never seen a AT power supply that blew into the case.

From what I know, when ATX was originally designed, there was a thought that the ATX fan case would blow in over the top of the CPU, but that was quickly dropped and very few computers were designed this way.

You are right but how they usually do it is actually a poor design where lower cost was given priority over a better design.

The standard way is called a negative ventilation system.
That means the case internals are at a slightly lower pressure than outside the case.
That means that air leaks -in- at every opening - which pulls crap into optical and floppy drives, USB ports and any other crevice.

A positive ventilation system would put the case at a higher pressure than outside and keep all the crap out of everything.
To work it needs to have filtered fan(s) blowing in with enough grunt to overcome any exhaust fans.
Cases with zillions of vent holes or mesh panels are detrimental to a positive pressure system because the fan(s) can't build enough pressure.
If you have drive racks with fans they should be filtered or blowing out to keep the drives clean. If no filters the fans need reversed.

I used to go to all the trouble and it works well but since we moved to the desert and I usually just leave the side off the case and blow it out once in a while.
There is no practical fix for the fine dust we have so things need blown out no matter which ventilation plan you go with.
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Don't forget SFF Slot1 systems (Vectra series comes to mind) that were designed to utilize the PSU to draw air inwards (wouldn't get heated up much as these were mostly only 70-90 watts PSUs). Then - via an airduct - the air would be guided towards the passive cooler of the Slot 1 CPU.

I have since reverted this airflow in all my machines of this kind. But for the time being (example PIII-500, passively cooled), it was enough. Later PIIIs would get too hot this way, though.