PSU Overkill with some PC builders....

liquidsnake718

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I dont understand why many buy 1000Watt PSU's, Im assuming even a 650-750w 80plus PSU can handle SLI and Crossfire will full specs and peripherals is it just marketing or just future proofing? Because it seems that PCs, SSD's, HDD's, and GPUs are becoming power efficient thus negating the fact that we need to INCREASE in PSU wattage..... its going inversely now isnt it? Tech is becoming more efficient and the smaller nm chips use less power in CPU's and GPU's but why do we see newer 1000w PSU's and more?

I can understand for quad and tri SLI/Xfire but other than that most just use 2 GPU's and still get 1000watts of power supply, is it just overkill or just coz they think its needed??
 

phil_12

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It's Future Proof and easy on the wallet in the future since you won't have to upgrade your power supply if you're going to upgrade to a maybe 5870x2 in CFX when it comes out
 
well, when you start getting into tri crossfire/sli with highend cards (aka 3xGTX285/3x5870) you actually start getting closer when you do some massive overclocks (aka all gpu's and heavily OC'ed cpu)
 

jcknouse

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I always overkill the PSU in my machines (1 rig has an 1100, 1 rig has a 1300) because:

a) futureproofing - never know what you will wanna add, or if the next gen of video card will spike in power use

b) expansion - if I have a RAID 0 2-drive array and decide to go with a 5-drive RAID 5, add an internal tape backup, etc., I don't wanna be 40 watts short

c) stress - if the PSU is rated at 1200W and you're only pulling 780W across it, it's not going to work as hard, produce as much heat, and most important...stress the components as if you were constantly pulling 780W across a 1000W 80% PSU

I haven't had a PSU pop in years, since I used 450W jobs that came in the case, and used 3dfx video cards.

Plus like someone said...why buy a PSU right at the threshold of what you need and save $40-125, then have to go back later and spend another $190-275 for a much bigger PSU?
 

jcknouse

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JohnnyLucky - 780 was an arbitrary number. But, my old gaming rig might have drawn near that when I was multitasking.

My old gaming rig had 2x 8800GTX+s, 4-500GB HDs, 2 DVD-RWs, 4 HD cooler fans (3 mounted, 1 5.25" bay type), and 6 case fans (1 top, 1 front, 3 side 1 back) and a big CPU HSF (I think it was a NV120 or AC freezer 64...can't rememeber), plus an OCed AMD Athlon x2 9850 @ 2.8+GHz

I bet I was pulling quite a bit with all the hard drives active and video gaming...and since I had all the fans on 100%.

The rig never got overly hot tho. Imagine that :lol:
 
I doubt it. I estimate less than 500 watts:

2 GTX's - 240 watts total
4 HD - 20 watts each = 80 watts
2 opticals - 30 watts each = 60 watts
fans - maybe 40 watts
let's say 4 GB RAM - 20 watts
motherboard logic - 25 watts

I'd use a Corsair 750TX or 850TX, probably an 850. I like to run my PSU's at 50% - 70% of capacity.
 

jcknouse

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Tack on 125W for the CPU at stock 2.5GHz, and mine is OCed to 2.8+

I put my spec into an online calculator and it estimated 650-680W

It's pullin some juice tho. I haven't calculated my 720BE x4 w/8GB and a velociraptor and dual 9800GTX+s etc etc.

I just like beef in my supply, esp. for my next build, cause i'll start with 2 x 5850s and maybe upgrade to 2 more of them or swap out for 2x 5870x2s.

I wanna make sure to have juice. :)
 
Crap. :(

I haven't make that kind of mistake since ... since the last time I did. :)

The first time I ran the calcs in my head, I included the CPU and came up with about 600 watts. Then I did the add'm up and was puzzled because I seemed to have lost a hundred watts.

Actually, OC'ing a CPU does not increase the power budget that much. I OC'd a Q6600 from stock to 3.6 GHz. CPU power current increased from 8 amps to 9.5 amps as measured with a lab calibrated clamp-on ammeter.

You can approximate the increase by:
OC'd voltage squared divided by stock voltage squared times stock power consumption.
 

jcknouse

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It's okay. I think last time I put a spec for a computer up, I forgot to do certain stuff. We're all human. Well, rumor has it I am at least half-human. :lol:

I was looking at the 1000W corsair, but I think it went off the special it had with a case. If I could get it and a good case in combo, I'd get it. I've never heard a consistently bad comment about that PSU.
 

liquidsnake718

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SO at least a 750 80plus PSU is garnerd and deemed a safe bet... Even for SLI? Its not like im replacing my old 550realpower 80plus as I will still use my old build for basic madia and work files but for a gaming rig I am already planning on building it early next year.... just waiting on word from Nvidias next gen GPUs and DX11 for those....

We already lost USB3.0 for at least a year so thats bad news.....
 

jcknouse

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Yep, and it seems you can't get a 58xx series from NewEgg, so I can't order parts for the new machine.

I even have it queued up to order, if they'd just get them in stock!!! grrrr :pfff:

As for SLi, what are you doing it with? if you're SLi-ing 2 295s...um...I wouldn't think a 750 would be enough.

I know you have to look at what your components are gonna draw from the 12v rails, then figure out what the PSU has on those rails (each rail's Amps and total Amps across all rails), then figure out what video card setups the available amps can support.

Thing is, I can never seem to find on AMD/ATI's video card site the amp-draw spec for the GPUs, and most video card makers don't put it in a spec that I can find.

Anyone else have details on a good site/link that has the specs for amperes used by each/any video card.

BTW, liquidsnake: From what I gather from others on here, you should be able to Crossfire 2 5850s with the Corsair 850. That's what I took from things I have been told, but I haven't verified it yet.

YMMV
 
jcknouse - I don't know of any chart depicting current (amps) for a variety of video cards. Technical reviews usually only show total power draw at the wall outlet for the entire system.

A high quality 600 watt power supply with 40 amps on the 12 volt rail(s) can easily power a system with two ATI radeon HD video cards. That information is right on the ATI web site. Technical reviews confirm it.
 

Xbitlabs generally provides a chart that compares power consumption of several card's in thier reviews ( not always though )
 

Caught on to that last week, haven't gotten used to it yet, but they do provide larger comparison charts.
 

jcknouse

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That would be for a standard build though, right? Rated for single HDD, single burner, no OC type thing?

I usually end up figuring out the draw is watts / 12v for video cards when I find it. I didn't know it was on the ATI website. I had been going to their gaming card reference to see the PSUs that they tested, and it seems lacking for the 5800 series in Crossfire.

BTW, I found on another website a thing that said supposedly ATI didn't order enough wafers from TSMC for the 5800 series, so that's why they're in such short supply. Supposedly the 5800x2 series is out next month. Might have to wait and see how their release impacts the 5700 and 5800 series.

Like I've said before, maybe I'm just paranoid. But, I like putting in a PSU that doesn't have to strain to do the work. Plus, I always SLi (haven't used ATI since the Rage Fury Maxx, but looking to build an ATI Crossfire build next time), have multiple HDDs/DVD-ROMs, etc. So, I've never really sat down and figured if the 1100W supply was too much or not.

I guess I'm king of PSU overkill with an ABS Tagan 1300W PSU huh? :lol:

Thanks for the info tho, Johnny. I'll look more at the ATI site.
 
jcknouse - It would work with an overclocked Intel Core i7 920 system with two 5870's in Crossfire mode . Hardcore gaming sessions use much less power than stress testing with OCCT or Furmark. Have you bothered to look at the technical reviews?

Kari - Very nice chart. I'll have to add it to my references.

"Maximum: Furmark Stability Test at 1280x1024, 0xAA. This results in a very high non-game power consumption that can typically be reached only with stress testing applications."
 

jcknouse

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Yeah I have. I have read Toms for years and have for about a year looked at sites like AnandTech and OverClockersClub and what not.

I just tend to build a box different. I add fans, run 2-5 HDDS, dual DVD-RWs, etc. I have a bit more power consumption than a Tom's box with a single HDD, single DVD, single video card, etc. I almost build PCs for gaming like a fileserver to maximize the disk access speed for improved gaming performance.

As for hard core gaming sessions...well...I have run 10 sessions of Shadowbane along with Ventrilo and AGC on 4 cores and peaked all 4 cores and brought my machine to a crawl. So even tho I don't run something like Crysis, I task a machine really hard.

I guess I just have a different build methodology with my systems than you and others. Nothing personal.