Dear Alex, My many years of experiance :0) suggest that whenever possible you should use AC line powered to cool your systems where possible. Example:'piggy-back' a 80mm AC fan to your power supply blowing OUT. The vast majority of dead PCs I have encountered died because their Power Supply DC fans had crapped out for some reason. The typical PS fan is VERY cheap ( less than $0.15 each in China). The DC fans that run at 12v have very little torque for the current they draw (easily stopped by the slightest friction or bearing 'goo'). Line voltage AC fans have much more torque and therefore much harder to be stopped by 'gunk' . Where ever possible you should design your cooling system to flow outside air into the system and hot air out. That may seem simplistic but you would be surprised to know how many systems I have seen where there were a bunch of fans just blowing hot 'inside the case' air around the case. With a properly installed AC fan you can draw the heat out of your system best by putting air inlet holes near the hottest components ( HD and such); the general flow of air will come in near the heat sources, pick up the heat and flow up to the PS and out. I have one PC now that has a few HOT scsi drives and I added a line powered fan outside the case to enhance the flow over the HDs and assist the PiggyBack AC fan on the PS. Of course the CPUs need DC fans and good heatsinks w/ good thermal conduction 'goo' but unless there is a good volume of air flowing OUT of the case the CPU fans will be stuck with attempting to cool the CPUs with HOT air. The ATX standard had improved heat flow and elimination as a goal. Mostly it achieved that goal by putting the CPUS below the bottom air grill in the PS and using a slightly more powerfull fan to exaust the heat of the PS AND the CPUs, but they did not take into account the heat of other in-case components. Yes you can put additional PS's into the case for the HDs, but be sure that the additional PS's also move the hot air OUT of the case as well. Try at all times to eliminate any fans working 'against' the other fans; this is just a waste of watts and the fan is also generating heat. The only down sides to using Hi-Flow AC fans are the added noise and the dust that will accumulate. The amount ot dust deposited is a function of the amount of air flowing into your case, so make it a regular task to open your case and blow out the dust. In the Mainframe world they use near one horsepower fans with filters; the most important thing there is to keep the filters clean and flowing. They have highly paid professionals to vacuum out those filters regularly. So, in summary: Heat is the enemy, get it OUT of the case, don't just move it around. The most powerfull and efficient way to get that hot air out is an AC fan. and by 'piggy-backing' it in series with the PS fan you minimize the chance of frying your sys because the $00.10 DC fan quit. additional cooling can be had by adding holes in the case near the heat producing components, and even more by adding a AC fan blowing IN near them. Adding another PS to a PC is ok as long as its heat is not allowed to enter the case. Now a word about reliablity. If your need for reliability is 24/7 then you should consider a "pro' system from one of the big vendors; and I don't mean Dell or HPAQ. Old addage in computing: You want it : Reliable Cheap and Fast ; Pick any 2. Good Luck ....................... Peterb p.s. www.allelectronics.com has a good selection of AC fans On Saturday 07 December 2002 02:08 pm, Alex Daniloff wrote:

Hello SuSE folkz, I've assembled a new dual AMD SuSE8.1 Linux DB and web server. It has to work reliably 24X7. Unfortunately, its 460W Extended ATX PS has not enough fan out current to power motherboard, 20 fans and 16 SCSI hard drives at once. Is it possible to add another regular ATX 400W PS to power just hard drives on this system? I can ground both PS housings together with an additional wire. Or I stack to buy a new dual redundant PS? Could somebody please give me a practical advise on this matter.

Many thanks in advance. Alex

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