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SFF PSU Article

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Demont

Member
Joined
Nov 6, 2001
I was wondering about this little column I read in the pcstats newsletter... ( i dont remember when or why i signed up, probably to try to win a video card or whatever...) But anyway this is it:

The High Tech Low Down

By: Chris Angelini



A small form-factor revolution is sweeping the industry. It seems that the compact, highly integrated boxes are designed to prove that in some instances, less is more. But is a minimalist approach necessarily the best?

I recently had the chance to review a pre-built small form-factor system based on the nForce2 platform. A marvelous machine by all accounts, the primary weakness I found was its 200-watt power supply. Along the same lines, FIC recently released its Ice-Cube system with a 150-watt unit. And MSI has a Slim PC with 180-watts backing it. Admittedly, I didn't encounter any problems with the Athlon XP 3000+ and RADEON 9700 Pro combination, but I can only wonder how long a configuration like that will operate reliably. I'm not saying that the latest hardware isn't going to work in one of these small form-factor systems, but there has to be a reason ATI recommends a 300-watt power supply in its retail packaging. I'm not trying to warn you away from a SFF chassis, either. They make great platforms for convergence devices and even LAN gaming systems. However, if you do decide to build a cutting edge system using a small form-factor box, be cognizant of thermal issues, as cooling is one of the most important points to take into consideration.

I wonder about the percived threat of the low wattage PSU's because I've been told computers use less than 200w at any given time and the current supplied is almost more important. Yes, amd and ati and such recommend 300watt psu's, but apparently MSI, shuttle, FIC etc don't find that neccesary. Whats the real deal here? I don't know much about electronics so this is why I'm posting this here. For the smart people to respond.

I shot of an email to the author that was rather rude and colorful because I was bored and didn't expect it to be read, but he or she did reply and referenced this link. http://firingsquad.gamers.com/guides/power_supply/page2.asp
and here, amongst other things, it says this:
You see, the Pentium III and all CPUs before it ran on the +5V rail. Since the CPU remains the largest consumer of electricity in an x86 machine, power supplies were engineered to provide significant amounts of current on the +5V rail. Modern CPUs such as the Athlon and Pentium 4 run on the +12V rail. The problem is that many power supplies are still based on older Pentium III-era designs and so even for many mid-range gaming systems, chances are that the +12V component of the power supply is not going to be adequate.

I was under the impression that all cpu's derived power from the 5v line and 12v line was for Hdd's and other drives etc.

So there it is, reply away, I'm sure I have several things wrong.
 
Nope Athlons are definately running off the 12v line. 5v is for drives and possibly some motherboard components as far as I know.
 
12V typically Fans and drives. Since Intel took the time to monkey around with the ATX standard and add a 12v connector at a guess P4's draw some power from the 12v as well.
AFAIK Athlons don't pull much from the 12v otherwise 6months to 1 year ago the Enermax/Epox 5v rail wouldn't have been a problem.

5v/3.3v cpu/pci/agp cards. Some devices pull from multiple outputs, so keep that in mind. I seem to remember the point of the 3.3v was for newer (at the time, post AT) chips to draw power from 3.3v. Course my memory may be faulty here.

As far as power consumption goes: Many modern systems are fine with quality 300W psu's (I've seen a pp303X have no problems with an Athlon xp1800, 4hds, 2 cd drives, 4 fans etc). Now overclockers tend to go higher because often they need to, to avoid their rails from dipping while overclocking, as well as being early adopters for the newest products.

As far as Manufactured recommendations they're often going to err on the safe side so saying 300W for use is probably more of a concern of the quality of 250Watt or less PSU's that are often in OEM systems. Besides it's an easy out as far as tech support goes (ie TS: Do you have a 300 Watt PSU? No, that's your problem, go get one and everything should be fine. etc), not that any company does that.

My personal view of SFF/MicroATX systems is that you are going to have make some trade-offs for the slim/small set ups. Just like in going for max cooling vs quiet, you'll have max goodies/vs system size.

Keep in mind I'm no expert, and I'm sure some others here can better answer the issues at hand.

AntecRep
 
A little history is helpful for understanding where we are, and how we got there.

In the early (AT) days I only noted power supply capacity out of curiosity. There where no practical ramifications, only that you needed one. Power supply failures were rare and 150W was fine, 200W normal, 250W large, and 300W for those few crazy customers that demanded not knowing that it was overkill. And it remained that way for a long time, even into the ATX era.

As time progressed transistor count doubled more times than I can recall offhand, and clock rates continued to spiral in lock step. These are the two factors that drive up power consumption. The fact that devices tend to operate on lower voltages as time goes on is no great help in this regard, as this implies a higher current load on the power supply, and even though lower voltage helps offset the power growth it grows nonetheless.

The first micro ATX boxes came in during the mid P2/early celeron days. I used them in numbers as the cost advantages were significant. But even with the low power consumption boxes of the day, they were trouble. Power supply failures on the micro ATX boxes I built (a thousand or more) were markedly higher, to the point that eventually drove the store I built for to replace micro cases and supplies with full size ones to prevent additional failures.

During this same era emachines popularized the notion of a $500 PC, an concept dependant on a micro ATX form factor. Gateway and Micron adopted the mcro form factor for a significant number of machines, conditioning the market to accept them.

Also during this period the introduction of the Ahtlon, and later the coppermine P3 and the Geforce video card changed the face of power consumption. P3 coppermine CPU's rolled out of the gate at 800MHz, and were soon running at a full gig. Athlons were always thirsty beasts, using brute force voltage to allow the clock speed that AMD's deficit in fabrication technology made very difficult (a trend that continues today, albeit in much less severe porportions). And the Geforce256 changed the face of 3D acceleration at the same time it drew copius amounts of 3.3V power. All conspired to raise the bar for power supplies.

300W was no longer overkill, rather a practical minumum. I saw tremendous failure rates amongst anything micro ATX, and even among 235 and 250W ATX supplies. Quality Sparkle 250W supplies (300W in any other brand) became the de-facto standard for consciencious PC builders out of necessity, the necessity to have a product you could afford to warranty. Bigger PC manufactures like Dell could pressure their supply sub-contractor (Delta) to provide increasingly beefy lower wattage rated supplies, but the do-it-yourself guys had to step up to higher wattage models to gain the fault tolerance needed.

Just as the Geforce killed the 3.3V and the Athlon the 5V, the P4 killed the 12V. Intel ammended the ATX specification to include a 4-pin 12V lead just to feed the switching power supply that runs the processor itself, as the total power demand had made satisfying it on the 5V rail inneficient. The effect of all three of these developments (thirsty, transistor laden graphics cards, thirsty cpu's, and shift of the cpu load to the 12V) has been to make 300, and now 350W supplies a smart idea to allow the supply to operate in a load condition that is conducive to long life.

Asus has made micro ATX P4 and AXP barebones for some time (the Terminator series) These have 180W supplies. Some micro supplies are now rated at 200, even 230W. But the truth is the micro form factor dictactes a power supply chassis so small it cannot dissapate the heat of a true 230W load. While it is technically feasible to run a 9700, a AthlonXP or P4 cpu, and a few drives off a micro supply doing so tests them to their limits, a load condition that invites failure, imposes thermal constraints, and jepordizes stability and overclocking potential. It can be (and is) done, but I cannot condone the practice nor recommend less than the Sparkle 300W full ATX (200W 3.3+5V) supply if you really care about the quality of the results.

The economic and space savings attractiveness of the micro, and the descendants of, form factor will continue to appeal. Just as surely the power consumption will remain high, and probably growing, for the foreseeable future. The stage is set for a clash between the electrical and thermal realities of powering modern PCs with the expectations for progress in space effectiveness and cost. Either people are going to have to forgo the latest processing and graphics advancements, be realistic about the size of the machine, (neither likely) or power supplies will have to drastically improve to bear the load and stay cool enough to promote high stability and long life. As I see it we don't quite have the capability today, although some may risk pushing the boundries in the quest for increased market share in a ferociously competitive market.
 
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I believe current stuff like the NF2 runs the cpu off the 12V, I'm not sure exactly where the line lies between Athlons that run off the 5V and ones that utilize the 12V.
 
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Here a list of consumption and of what rail:

  • Component Requirement Line(s) Used
  • ATI Video (ext power) 40-70W +3.3V and 12V (Radeon 9500, 9700 ...)
  • AGP Video Card 30–50W +3.3V
  • Average PCI Card 5–10W +5V
  • 10/100 NIC ~4W +3.3V
  • SCSI ControllerCard ~20W +3.3V and +5V
  • Floppy Drive ~5W +5V
  • CD-ROM 10–25W +5V and +12V
  • DVD-ROM 10–25W +5V and +12V
  • CD-RW 10–25W +5V and +12V
  • DVD-(+)RW 12-30W +5V and +12V
  • 7200rpm IDE HD 5–20W +5V and +12V
  • 10,000rpm SCSI Drive 10–40W +5V and +12V
  • Case Fans 1-3W(ea.) +12V
  • CPU Fan 3-15W +12V
  • Mobo (w/o CPU/RAM) 25–40W +3.3V and +5V
  • RAM 8W per 128M+3.3V
  • Pentium III Processor ~38W +5V
  • Pentium 4 Processor ~70W +12V
  • AMD Athlon Processor ~70W +12V

Hope this helps

A.


PS : If someone can tell me how to format text for tables here in the forum I'd make it look better next time :D
 
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Thanks for the info.

You can use the list formatting. [ list=1] for numbered, [ list=a] for letters, [ list=] for bullets and just [ list] as well. then put [ *] in front of every item on the list

[ list=]
[ *]One
[ *]Two
[ *]Three
[ *]...
[ /list=]

(just remove the spaces and....)

  • One
  • Two
  • Three
  • ...
    [/list=]
 
Thx Demont, but it doesn't seem to do anything for the spacing or tabs in between "Component Requirement Line(s) Used"

A.
 
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