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Dual PSUs

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May 19, 2010 8:58:53 PM

I'm new, so go easy on me with the electrical terms... I've got a good grasp on computer jargon, but the power supply is one component I still haven't mastered.
I'm building a ridiculously overloaded system...
Core i7 980x Extreme CPU @ 3.33GHz
EVGA X58 SLI Classified MoBo
24 GB Dominator RAM @ 1600 MHz
3 EVGA GeForce GTX 470 (Fermi) Superclocked video cards in SLI that require minimum 550w each power
3 2T hard drives, 1 750 GB hard drive and 3 500 GB hard drives
2 DVD+-RW
1BR RW
a wireless card, a card reader, liquid cooling components and several case fans (5)... I think that's about everything you can throw at it...

Obviously, one PSU isn't gonna do it. I've got a full tower Lian Li P77 case, and I still have plenty of space inside, but I'm not sure how to deal with the 2nd PSU... Where does it go physically? Do I hook it to the MoBo? Any guidance is greatly appreciated... I know how to use a system like this, but this is my first crack at building one myself.
I'm a little confused because when I use a calculator to figure power requirements, I don't get a figure anywhere near what I get when I add up what the manufacturer specifies as minimum power requirements. Even if I figure it under full load. Can somebody explain all of this?

Thanks in advance for any help anyone can offer!

Beth

More about : dual psus

May 19, 2010 9:05:11 PM

One PSU would be fine... You wouldn't need more then 1KW of power for that system.

But why? You realise in 2 years that system will be mediocre at best and you'll have wasted most of it.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

*EDIT* You realize the superclocked editions are just factory overclocked? Save yourself some money and get the standard ones. Nothing on earth will use more then 12GB of ram for atleast 5 years.

Oh and to answer your thing about the power requirements, it's saying that your video card would require a total of 550W from the entire system, not the video card. The video card would only use 100-200W at max load.
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May 19, 2010 9:08:04 PM

You can't build PC's with multiple PSU's, not without either heavy modding or proprietary hardware.

You should just get this PSU, Silverstone 1500w
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

3 480's tops 1K on load.

http://www.guru3d.com/article/geforce-gtx-480-3way-sli-...

Edit: Technically the good 1200 watt PSU's will do, but haven't found one with enough 8 pins cables yet, so that PSU above for now, unless someone else can find one with enough cables.
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Related resources
May 19, 2010 9:09:47 PM

The 470s don't require a minimum of 550W each. A single one requires a 550W PSU for the entire system. You don't just add up the minimum requirement for a single card, as the manufacturer quotes that for the entire system. Generally, each additional GPU will add about 200W to the requirement, so for three of them, you'll need a 950-1000W unit, but you may want to go a little higher due to everything else.

Most calculators spit out what's "recommeneded" for the size of a PSU. The recommended size is generally twice the required wattage, as PSUs operate most efficiently at 50% load. It's almost better to use a generic formula starting with the GPU's minimum power and adding amounts for the additional devices.

I also should point out that you get almost nothing out of adding the third GPU. You'd do just as well with two, and would only need an 850-950W unit for that.
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May 19, 2010 9:21:32 PM

According to SLI Zone, there are 10 or 11 PSUs that are rated for 3x 470. Most of them are 1200W.
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a b ) Power supply
May 19, 2010 9:40:13 PM

Quote:
You can't build PC's with multiple PSU's, not without either heavy modding or proprietary hardware.

Umm it's not that difficult really. All you need is a Dual PSU adapter cable such as this: http://www.frozencpu.com/products/5637/cpa-167/Lian_Li_...

Or hell if you want 4 PSUs: http://www.frozencpu.com/products/7137/bus-128/Bitspowe...

It's amazing what unusual things FrozenCPU carries.

IIRC, I learned this from a guy over at Bit tech who used some thing like this to power a QuadFire set up.
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a b ) Power supply
May 19, 2010 10:27:57 PM

^ I personally wouldn't get one of those 5.25" Auxiliary PSUs for the simple fact that they are not that well tested by the likes of Jonnyguru,etc.
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May 20, 2010 2:12:48 AM

Our 6GB database fits fine above the 4GB limit of XP x32
using RamDisk Plus, with room to spare for browser caches too.

Indexing with COPERNIC is really fast on 110,000+ files.


MRFS
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May 20, 2010 2:22:28 AM

Lian-Li's PC-A70:






MRFS
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May 20, 2010 3:03:05 AM

MRFS said:
> You can't build PC's with multiple PSU's, not without either heavy modding or proprietary hardware.

We did a specific search recently, and found quite a few
cases with room for 2 x PSUs e.g. CM HAF-932:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

http://www.newegg.com/Product/Product.aspx?Item=N82E168...


We have one of these HAF-932 cases: very nicely laid out,
and very roomy too: fits fine under a standard folding table.


MRFS



OK I stand corrected there. Totally didn't realize you could actually fit 2 PSU's in a HAF 932 (I guess it's not a surprise since that thing is bigger than my Manhattan apartment :D  )

I was thinking about it requiring heavy modding to fit 2 PSU's in a case or would require proprietary hardware, a la 5.25" bay based PSU's or a slightly modded redundant PSU.

Good pointout with that adapter cable shadow.


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a b ) Power supply
May 20, 2010 3:52:44 AM

The only real criteria is - DO not connect PSU 1 Voltage to PSU 2. for example if you have a video card with 2 6 Pin connecors. You would NOT connect PSU1 +12 V to one connector and connect PSU2 to the other connector without verifing (ohms check) that the +12v connector one is NOT shorted to +12 V connector 2 (Probably are.)

You can parallel to Batteries, (same voltage) but not Power supplies.
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May 20, 2010 6:21:50 AM

Wow! I'm truly overwhelmed at the length every1 went to in providing me information... someone actually found my case with the mod for the second PSU. That's impressive. The electrical terminology needs to come down to about a kindergarten level for me to comprehend it. The service guy at TigerD explained how to use a stripped jumper wire to connect two PSU's together... which I assume means I only need one switch... Is it better to have dual switches, wire the PSU's together, or use a bridge like Shadow suggested?
I get the miscalculation of loads. I assumed TD would have the right answer, but it didn't make a lot of sense 2 me given the number of SLI users I know who have only 1 PSU, so thanks 2 all for explaining that in a way that makes sense.

The whole "...do not connect PSU1 Voltage to PSU2..." from Retired Chief is exactly what worries me. I see where there could be a huge problem, but I'm not exactly sure how to be certain to avoid it, and I'm not sure how to connect anything in order to safely connect the components at this point.

See me through to the other side guys!
Thanks!
Bethy
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a b ) Power supply
May 20, 2010 3:31:07 PM

Easy way is just make sure that only one PSU is connected to graphics card.

IE PSU 1 - connect to MB (24 Pin & 4/8 Pin. and GPU #1.
- PSU 2 - connect to GPU #2, #3.
HDD/DVD drives may be connect to #1.

That said, I think a single large suppy is the best choice.
Based On:
http://www.anandtech.com/show/2977/nvidia-s-geforce-gtx...
It would appear that your max Power requirements are
w/cyris - 668 W (SLI) + 250 Watts (3rd) = approx 918 watts
w/furmark (worst case) 851 Watts + 371 Watts = approx 1225 Watts
NOTE Added - other reviews indicate lower power The Anatech is the highest I've seen most indicate aprrox 600 - 650 for one + 200 per additional card wich indicates a 1 KW would be absolut min with the 1.2KW being a good choice.
Personnaly I think you would be OK with a quality 1200 Watt PSU
Here is a 1.5 KW PSU.
http://apcmag.com/thermaltake_toughpower_1500_watt_psu....

Added:
Bear in mind the the pobaility a a PSU failure is higher with two PSUs (it in not doubled)
Ex - quality PSU. If the possibility of NOT having a failure in 3 years is 90 %, then the probability for Daul PSUs would be 80 % for NOT having a failure
Note Math is from analysis of a missle hitting a given target.

Make darn sure your case air flow is adequte for the 3 GPUs
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May 20, 2010 3:37:34 PM

I would think the two psu's would have to be the same amps, no?
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a b ) Power supply
May 20, 2010 4:14:44 PM

^ No. In the above case a 600 - 650 Watt would work for PSU 1 and a 500 - 550 watt for PSU 2.

Added: explation -
As in batteries you can parallel say 3 "D" cells with 3 "C" cells (same family). You can use multi Powersupplies say +12 V, of differnt current capabilities to power different circuits on the same circuit board AS LONG as the circuits DO NOT short (Tie) the +12 V supply lines together.
EX: we use 3 28V Power supply to provide power to a system - The three supply lines do not "short" to one another, even thoght the E out is within 0.01 Volts

Reason you can not tie two PSUs (again +12v as an example) is that they will not have identical outputs. One might be +11.8 and the 2nd migth be 12.4 V in this case one PSU would "TRY" to raise the other too the same voltage level resulting in very high current. In the case of batteries this also happens, but only for a short time untill the lower voltaged battery is equal to the higher battery. With electronic PSUs they would not equalize.
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May 20, 2010 4:23:02 PM

Just to point out, but the odds of failure do double. In you example, it's 10% chance of failure on both PSUs, and 20% that either fails. Just to make you feel a little better, the odds of not having a failure is actually 81%. I'd say a 19% chance that a single PSU fails is quite a bit more significant than a 10% chance. Though the 1% chance of leaving you with a non-fuctional build opposed to a 10% chance is pretty nice...
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May 20, 2010 4:29:00 PM

I'm going to reiterate RetiredChief's earlier suggestion that you should just go with a single large power supply. Is there any reason to not do that? Do you already have one power supply and you're considering getting a 2nd?

And I'll mention again -- the link I posted above to slizone.com has about 10 PSUs that nVidia has certified for 3x SLI.
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a b ) Power supply
May 20, 2010 4:37:53 PM

MadAdmiral
Going back too may years, But I don't think calculating a failure rate was that straight forward. You could be right - will try to check out.
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May 20, 2010 4:49:10 PM

It's not actually adding them together. You add the two probabilities of failure (.1+.1) then subtract the probability that they both happen (.1x.1) for a total of .19. The results are just close if the events are highly unlikely.
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