ATX Power Supply Quality

Discussion about old PC hardware.

Re: ATX Power Supply Quality

Postby obobskivich » 2015-2-21 @ 14:01

Evert wrote:I wanted to start a new topic on this, but then I realized that this is something that has been discussed before on the forum and it's best to probably contribute to what is already there. I'm in the fortunate position that I own a brand new Rosewill RV350 (ATX v1.3 spec) power supply. It has a very quiet fan and a -5V line, so it's perfect for old systems. I've recently obtained a mint condition Abit KT7A-Raid motherboard and an Athlon Thunderbird 1.4GHz CPU. This is from the era when most of the power came from the 5V and 3.3V lines, is it practically even possible to power a system like this with an ATX v2.3 power supply? You have to literally buy a 750W power supply just to get a meager 150W on both the 3.3V and 5V lines with 25A of current each. My Rosewill provides 28A for the 3.3V line and 35A for the 5V line and it can supply 200W of power to both lines. So a very powerfull modern PSU can barely meet these specifications. A Thunderbird CPU uses about 70-75W of power, an AGP slot can provide up to 50W of power to a card. RAM can use up to 5W of power, PCI cards can draw up to 20W of power. So if we add it all up that means, worst case scenario you're looking at (75 + 50 + 5 + 20)W = 150W of draw on from the 3.3/5V lines. I'm not sure what the margins are, but doesn't this mean that the PSU will more often than not shut itself down because of an overdraw of power?


I think you're over-estimating the draw/requirements of computers from 15 years ago relative to modern PSUs. A lot of these machines "back in the day" (even with Pentium 4 CPUs) lived quite happily on 150-250W PSUs for many years (my EE still does!). Very high power AGP cards will always have a 4-pin auxiliary connector (most cards over 30W TDP have aux power), and will draw a good portion of their power via the 12V rail. Those kind of cards also aren't contemporaneous for a circa 2000-2001 Athlon - for that kind of machine you're talking about something like GeForce 2/3, not GeForce FX 5950. On the Thunderbird, the 1.4GHz is "only" 72W max TDP, but most of the series (and pre-Thunderbird Athlon chips) tend to use significantly less than that (generally 40-60W). These are maximum figures as well, not 24x7 all the time numbers. Finally, "heavy 5V loading" does not mean "exclusive 5V loading" - older machines are still drawing power via the 12V rail, just not the bulk of their power. :blush:

Now, you aren't wrong that in 2015, a ~700W PSU may be required to have a decent 5V rail. But there are exceptions to that rule - like the Thermaltake I linked some posts up, and some of the Seasonic and Corsair models that are also popular these days. :happy:
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Re: ATX Power Supply Quality

Postby Evert » 2015-2-21 @ 15:51

I've been searching around the internet and I stumbled across this from Anandtech (published back in 2000). They tested a bunch of power supplies on the following system:

  • AMD Athlon 750 (Slot A)
  • Gigabyte GA-7IX Motherboard
  • 128Mb PC-100 Samsung RAM
  • IBM Deskstar DPTA-372050 20.5GB 7200 RPM Ultra ATA 66
  • Philips 48X CD-ROM
  • nVIDIA GeForce 256 DDR
  • SB Live! Sound Card
  • Linksys LNE100TX NIC
  • Windows 98SE

As it turns out, they recommended an Antec PP-303TX Power Supply. I searched and found an image of the spec sheet:

Image

As you can see, it can supply 14A on the +3.3V line and 30A on the +5V line and it can provide a total of 160W for both lines. I am someone who will admit that he is wrong when he was in fact wrong. I've been unable to source a lot of power supplies locally that can get close to those figures. Most 650W-750W power supplies available locally (South Africa) will provide about 25A on +3.3V and 25A on 5V for a combined output of 150W.
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Re: ATX Power Supply Quality

Postby Dreamer_of_the_past » 2017-9-04 @ 02:59

Does anyone remember any legendary Enermax units?

Is this is one of them? Enermax EG475P-VE
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