Power supply sizing bull

[returno]

I've seen people on this forum recommending 500W+ power supplies. The latest ATI/Nvidia offerings have 300/350W recommended minimums. Then I see AnandTech's review of the Soltek QBIC EQ3801 loaded up with an ATI 9800 PRO and the system sports a whopping 250W power supply. All the SFF systems have such power supplies more or less, it seems. And these things are 'hot' OCer boxes and used for LAN parties with high-end graphics cards.

One word: HUH?

I've seen people say "well it is easy to size your power supply, just add up all the power requirements of every component of your system and bingo there you go." Apparently this reasonable-sounding advice is total bullshit. And how about all that talk about how each rail of the power supply can only do so much and so and so. Such discussions always end with "buy the biggest damn power supply you can afford". That too must be total bullshit.

The ATI and Nvidia web sites give NO information on how much power their chips actually draw - so there goes the "add em up" strategy. So, since I don't want to buy a 500W power supply if I don't need one, and I'd actually like to use a state-of-the-art graphics card in an SFF, what should I do? The best idea I've had is to wait until someone tests the exact configuration I want to buy. Arghhh!

 

[dinde]

stop being cheap. buy a good power supply.

 

[3chordcharlie]

The minimums tend to get inflated because it is very cheap to make a power supply that could in theory provide 400-500W of power to a computer with a mix of components that simply doens't exist.

A high-quality (hahaha as opposed to "hi-kwality") 250-300W PSU is more than adequate for a modern CPU, VGA, HDD, and single optical drive system (except maybe the high-end 6800 video cards). Remember that SFFs rarely have multiple HDD or optical drives, which is one reason they can get away with a little less PSU compared to a full desktop system.

You don't 'need' a 500W psu, but if you don't want to buy a high quality 350Wish power supply, then you need a cheap 500W one to get the job done. Since most people odn't know too much about quality WRT power supplies, manufacturers tend to overstate requirements to minimize customer complaints.

 

[So]

Buy a brand name 350-450 watt power supply and be done with it.

 

[Fern]

"The best idea I've had is to wait until someone tests the exact configuration I want to buy. Arghhh! "

You don't have to wait. Just go HERE and plug in your config. The site will calculate your requirements.

Otherwise, Welcome! to the forums.

 

[Lonyo]

I have a 300w PSU, 15A on the 12v rail, and my 12v rail needs more amps, I am pulling too many. (Voltage drop type too many)
My dad bought a 400w PSU to make a lower spec machine just work, and it has 12A on the 12v rail.

It may say 400w, but it would be worse than my 300w PSU for my system, because of the low 12v rail.
This is why they don't say "250w is fine), because there are many poor quality no name brands out there. They say high numbers, but those numbers mean nothing a lot of the time.

 

[VirtualLarry]

AMD used to actually have a quick worksheet-type thing that you could use to calculate a rough estimate of the PSU you would need for a system, based on the count of components from each category, and their average power draw.

You really don't need much more than a 300W PSU for most mid-range systems these days (exception if you have a recent high-powered video card), but the problem is that most of the generic "300W" PSUs, are closer to 200-230W in truth. That's why you can see people running powerful rigs on a, say, Fortron Source 300W PSU, and yet others can't run a system even as loaded as that on a "450W" generic PSU.

I would assume that most of the SFF boxes on the market, being as they are a bit more of a niche product, and pricier because of that, also come with higher-quality PSUs. So that's one reason why they don't seem to have too many issues.

 

[imported_SpitFire]

Originally posted by: Fern
"The best idea I've had is to wait until someone tests the exact configuration I want to buy. Arghhh! "

You don't have to wait. Just go HERE and plug in your config. The site will calculate your requirements.

Otherwise, Welcome! to the forums.

I plugged in some equipment in that and got 300 minimum (athlon 64, 2 sticks of ddr, 6800 gt, hard drive, dvd burner). Now that configuration is known to run VERY WELL on a shuttle with a 240-250 Watt power supply... seems a little strange.

 

[Steve]

The only reason anyone would need excess wattage is if all those devices were running at full load all at once.

Fern, that site is BS. Look up the products on the makers' websites to find out actual power consumption.

I've a friend who runs a Barton 2800+, Radeon 9800 Pro AIW, optical combo drive, two hard drives, on a 200 watt unit. Stable and problem-free.

 

[mechBgon]

Fact: Shuttle is beginning to build SFF's with 350W PSUs.

Fact: Dell is beginning to equip Dementias... err, Dimensions... with 350W PSUs, and their XPS gaming rig has been running a 460W for a while now.

~ hmmm

A good-quality power supply can last a while. What seems like overkill today, may not be overkill later in the PSU's life. When OEMs are moving up to 350's for their limited-capacity boxen, it kinda tells you something.

Personally, I have no qualms about going "overboard" on the PSU's wattage rating. I certainly wouldn't buy a new car that has "just enough" power to cruise up a 3% grade at 60mph, and I'm not going to buy a PSU that has to run near its redline at ANY time in order to power my system. I've thrown away $20-$30 on much worse things than an extra 100W on my PSU's capacity rating... and I bet most of you have, too. Think about it.

 

[Holobits]

Other than a little heat running a higher power supply than your computer needs it isn't going to hurt you. It will also allow some room for expandability in the future. My next rig is going to have the PC Power and Cooling Turbo Cool 510 Deluxe in it. It wont require all that but i am looking forward to a OCed rig with an OCed BFG 6800U 2 optical drives 2 SATA hard drives and atleast 1 gig of premium ram.

 

[Chaotic42]

Originally posted by: Fern
"The best idea I've had is to wait until someone tests the exact configuration I want to buy. Arghhh! "

You don't have to wait. Just go HERE and plug in your config. The site will calculate your requirements.

Otherwise, Welcome! to the forums.

They have the MP processors on there, but they only give the power rating for one?

That says I should have 410W. That seems about right.

 

[JesseKnows]

Just to confuse further: I am running a Coppermine PIII + 640MB DDR 266 + 7 (seven) hard drives + CD-ROM in a server, with a 300W no-name PSU. Never had a problem. I used to run the same drives with a dual PIII / 768 SDRAM with the same PSU, no problem.

I guess I am lucky

 

[Steve]

Originally posted by: mechBgon
When OEMs are moving up to 350's for their limited-capacity boxen, it kinda tells you something.

It tells me they're trying to sell units. The consumer ain't always right.

Chaotic42 - as you've found out, that site is at best a rough guide. Very rough.

 

[3chordcharlie]

Originally posted by: JesseKnows
Just to confuse further: I am running a Coppermine PIII + 640MB DDR 266 + 7 (seven) hard drives + CD-ROM in a server, with a 300W no-name PSU. Never had a problem. I used to run the same drives with a dual PIII / 768 SDRAM with the same PSU, no problem.

I guess I am lucky

Nope, not lucky, Ridiculous power requirements pretty much started with K7 / P4.

 

[Fern]

Originally posted by: SpitFire

Originally posted by: Fern
"The best idea I've had is to wait until someone tests the exact configuration I want to buy. Arghhh! "

You don't have to wait. Just go HERE and plug in your config. The site will calculate your requirements.

Otherwise, Welcome! to the forums.

I plugged in some equipment in that and got 300 minimum (athlon 64, 2 sticks of ddr, 6800 gt, hard drive, dvd burner). Now that configuration is known to run VERY WELL on a shuttle with a 240-250 Watt power supply... seems a little strange.

That's pretty much online with what others have said - That it's conservative an overestimates by about 50 watts.