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PostPosted: Mon Aug 12, 2002 2:32 pm 
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Hello everyone, <br> <br>i've read a few things about running a PSU fanless, I've been fiddling with my Enermax 330W PSU recently, and i've just read Mike's article "Running a PSU without a fan?" with great interest. I've also made a silent PC for myself, and a site about this subject. And i studied physics and work in the field of heating, which also helps me understand this subject. <br> <br>All this put toghether, here's my opinion : <br> <br>First : convection means "Hot air rises up". So if one wants to cool fanless, it's essential to provide a path for the hot air, from the bottom to the top : something ressembling a wide enough and vertical tube (like a chimney indeed!). <br>So i think that when Mike puts the PSU upside, with the cover ON, he's getting closer... The "tube" is vertical, but it's rather obstucted at one end : you'd need to cut the back of the PSU open (the side that is opposite to the 80 mm fan). <br>Mounting such a PSU in this way (vertically) on a normal casing means making an opening on the TOP of the casing, contrary to the usual opening at the back. Of course it also means making wide enough openings at the bottom of the case, for proper air intake. <br> <br>Secondly : to cool by convection, one needs big heatsinks, and a limited amount of heat. <br> <br>- limited amount of heat : that means a PSU with a small power, a high efficiency, and not much load. Enermax are just too powerfull to be good candidates. Their aluminum heatsinks are not big enough either. <br>- big heatsink(s) : we need to look into the PSU, and maybe tweak or change the original heatsink... <br> <br>Among the currently available PSU with reasonnable price, I would try the Q-tech 300W : you rank it an 8, and say it has big heatsink. <br>A small PSU (90W, 140 or 150W maximum) like those found in (small) barebones is also very interesting. These barebones, with a low heat output-CPU is a very promising system to run totally fanless (but it would need to modify the case and PSU quite a lot). <br> <br>By the way, and bout small loads, I think the C3 is rather a false good solution, as downclocked Celerons or PIII are more powerfull CPUs than the C3, and the heat output must be in the same range. After studying your recommandations and the famous "electrical specifications of processors", i think that the 1,13 PIII-S downclocked to 100 Mhz FSB and downvolted is a very good candidate for a fanless yet rather computing-powerfull PC. <br> <br><!-- BBCode Start --><B>null</B><!-- BBCode End --><!-- BBCode Start --><B>To summarise all this : making a PC work fanless involves major tweating of the case and PSU. One can not just take the fan out of a normal PSU and hope this will work, as you proved it with your article. </B><!-- BBCode End --> <br> <br>Personaly i don't have the time and money to build a fanless PC, although i find it very challenging and interesting. <br> <br>At the time being, after making my silent PC as described in my site, i'll put both original fans of the Enermax PSU on 5V, with a 100 ohms rheostat (bought today) in series : at about 4V, they'll be silent and still cool the PSU. This is a similar approach as Mike's Panaflo on 5V, but it's even cheaper : about 2 dollars for the rheostat and it's button... These original fans are not bad, they're just spinning too fast! <br> <br>I don't have much time to take part in the forum at the time being, as i am already involded in a few french forums and it is time consuming... <br> <br>If you want to take a look at my own website on silent PCs (in french) : <!-- BBCode auto-link start --><a href="hhtp://hmeandsilentpc.free.fr" target="_blank">hhtp://hmeandsilentpc.free.fr</a><!-- BBCode auto-link end --> <br>It's not as good and complete as this one, but it's helpfull to those french people who dont read english... <br>SRPC will be added in my links in the next update. <br> <br>_________________ <br>my own site about silent pc (in french) : <br><!-- BBCode auto-link start --><a href="http://hmeandsilentpc.free.fr" target="_blank">http://hmeandsilentpc.free.fr</a><!-- BBCode auto-link end -->


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PostPosted: Mon Aug 12, 2002 2:32 pm 
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>>So i think that when Mike puts the PSU upside, with the cover ON, he's getting closer... The "tube" is vertical, but it's rather obstucted at one end : you'd need to cut the back of the PSU open (the side that is opposite to the 80 mm fan). <br> <br>Actually, with that particular Enermax, the side opposite the 80mm fan is very well vented. <br> <br>>> <br>>>Secondly : to cool by convection, one needs big heatsinks, and a limited amount of heat. <br>>> <br>>>- limited amount of heat : that means a PSU with a small power, a high efficiency, and not much load. Enermax are just too powerfull to be good candidates... <br>>>- big heatsink(s) : we need to look into the PSU, and maybe tweak or change the original heatsink... <br>>>A small PSU (90W, 140 or 150W maximum) like those found in (small) barebones is also very interesting. <br> <br>-- Not really. The way switching PSUs work, as long as you have some kind of load on them (say 20W), their efficiency immediately goes up fairly close the the max. There is very little in the way of a "threshold" or default power draw. This is very different from something like a Class A audio amp, which requires pretty close to full output from its PSU all the time. With computer PSU, the total heat/power dissipated is dependent on only 2 things: the current demand of the components, and the efficiency of the PSU. So if your 70% efficient 400W PSU is hooked up to components that draw 100W, the total wattage delivered by the PSU is 142W -- 100W as DC to the components, and 42W lost as heat due to the efficiency. If a 70% efficient 150W PSU is connected to the same components, the power draw is exactly the same. <br> <br>In fact, there IS an advantage in using the *bigger* PSU, if only because it will have bigger heatsinks and likely have components rated for higher current (read: heat) that will let you slow the fan down more safely. <br> <br>>>By the way, and bout small loads, I think the C3 is rather a false good solution, as downclocked Celerons or PIII are more powerfull CPUs than the C3, and the heat output must be in the same range. <br> <br>I'm not sure I'd call it false -- it's a simple ready-made solution: you buy it, you can use it, it is quiet. For most business apps, it works perfectly fine. I think it's just a matter of using ii for the right apps. <br> <br>>>After studying your recommandations and the famous "electrical specifications of processors", i think that the 1,13 PIII-S downclocked to 100 Mhz FSB and downvolted is a very good candidate for a fanless yet rather computing-powerfull PC. <br> <br>Yeah, that's probably a good choice, but not cheap, still. <br> <br>>><!-- BBCode Start --><B>To summarise all this : making a PC work fanless involves major tweating of the case and PSU. One can not just take the fan out of a normal PSU and hope this will work, as you proved it with your article. </B><!-- BBCode End --> <br> <br>I've mentioned this before but repeat it yet again (like a parrot): the difference between fanless and virtually inaudible is essentially zero, in practical terms, but it is so much more challenging to go fanless. <br> <br>>>It's not as good and complete as this one, but it's helpfull to those french people who dont read english... <br>>>SRPC will be added in my links in the next update. <br> <br>Thanks for the link, good to see so much interest in the topic in Europe! <br>>> <br>>>_________________ <br>>>my own site about silent pc (in french) : <br>>>http://hmeandsilentpc.free.fr
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PostPosted: Mon Aug 12, 2002 2:32 pm 
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I ran a fanless 486 for quite a while. The fan on the PSU had quit working after a few years, so I took it out, didn't seem to bother anything too much. The 486 chip never had a fan. The thing worked OK for quite a while, almost never had a case on the CPU box. <br> <br>Then, later on, I graduated to a pentium90, but same old junky power supply. This time the pentium chip-fan quit working so I just unhooked it. It didnt seem to get too hot, so I figured, whatever. No problem. This worked for a year or two as well. <br> <br>Eventually I got a pentium 233 with a broken fan. Oh well, it seemed to work with just a heatsink. Then one day I was measuring current draw of the computer, and realized that this 300W power supply I had was only putting out like 50 Watts. I figured, what the heck, why does it need a fan? But I didnt know enough thermodynamics and heat-transfer to feel like removing it...


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