When do you need a 500W PSU (over a <=430W)???

RDaneel · Post by **RDaneel** » Mon Jul 10, 2006 5:12 pm

Quick question - thanks in advance for any thoughts.

I'm starting to conjure up a new system, probably based on a Conroe processor and 7900GT. With Conroe dropping voltage, and the 7900GT being fairly well behaved in terms of power, is there a reason to go with a 500W S12 instead of the 430?

I'm guessing that in a single proc, single vid card, single HD system, I'm not going to be pushing over 300W anyway, so is it a waste to get the higher end model? OR, does it make a little future-proofing sense, as well as mean that I'll be running at lower power (and fan speed) most of the time if I get the beefier model? Let's pretend they cost the same, and will be in a generally well designed quiet system (Antec Solo, Scythe, Nexus, etc.). What do you think?

RDaneel · Post by **RDaneel** » Mon Jul 10, 2006 5:25 pm

Sorry to reply to my own post, but looking at the SPCR summary tables is further confusing me. It looks like:

250W:
430 - (82%, 29dba)
500 - (82%, 24dba)

300W:
430 - (80%, 32dba)
500 - (81%, 34dba)

The 500W model really jumps up in noise going from 250 to 300W output, whereas the 430 is louder to begin with (by 5dba!), but doesn't rise in noise as much. I'm inclined to do the 500 based on this, but the 430 is even quieter at 90-150W (18-19dba instead of 21-22dba)...

I think the bottom line is that both are very quiet PSUs and either would be fine - other components will probably generate more noise or at least negate any difference in these two models. In light of the minor differences, is there a better way to go?

Thanks again!

Devonavar · Post by **Devonavar** » Mon Jul 10, 2006 6:45 pm

Three things:

You're looking at the wrong efficiency numbers for the 500W model. You need to look in the postscript for the corrected results. You're also looking at the wrong noise measurements for the 430W model, which are for the older A1 revision.

Your system is unlikely to even break 150W output with both the CPU and the GPU going full tilt. At that level, the two models are more or less identical from a noise perspective.

Our noise results come from a very tough test that requires the PSU to exhaust nearly all of the heat generated by the rest of the system. If you plan your system well, the power supply should not have to deal with anywhere near that much heat, and will not increase in noise until much later.

In actual use, neither the 430W nor the 500W model is likely to increase above the minimum noise level unless you have a hungry CPU and either SLI or Crossfire.

I suggest reading through these articles before you make a decision:

SPCR's PSU Fundamentals
SPCR's PSU Testing Methodology
SPCR's PSU Test Platform V.3
Power Distribution within Six PCs

jaganath · Post by **jaganath** » Tue Jul 11, 2006 2:32 am

Conroe TDP will be 65W, non-OC'd 7900GT is also ~65W. Add 1 HDD (<15W at spinup), some RAM (<4W), some fans (<4W) and an optical drive (20W when burning, 0W when not in use) and mobo power consumption (~15W?), you're still below 200W. An S12-330 would power this fine, but you may want the S12-380 for the bigger heatsinks.

inti · Post by **inti** » Tue Jul 11, 2006 3:04 am

As you can see from my sig, I have five hard drives powered by a 430W PSU without breaking a sweat - actually I have tested up to 9 drives, alongside a SATA card and TV card. This suggests that 430W would be more than ample for your system even with the 7900GT.

RDaneel · Post by **RDaneel** » Tue Jul 11, 2006 3:53 am

Thanks for all the input. Devon, I thought I had the numbers right, must have been looking at the wrong page, I'll correct my post for posterity.

I didn't realize that the collateral equipment (fans, mobo, etc.) drew so little power - looks like there's no reason at all to go with the 500W model, and even the 430 would have nice headroom. I do like to have a reserve for worst-case scenarios, like upgrading to SLI down the road or the next gen vid card, so I'll probably get at least a 400W model.

Cheers,
RDaneel

Post by **MikeC** » Tue Jul 11, 2006 5:25 am

RDaneel wrote: I do like to have a reserve for worst-case scenarios, like upgrading to SLI down the road or the next gen vid card, so I'll probably get at least a 400W model.

[emphasis mine]
IMO, SLI is the biggest scam going in the PC world these days. You will almost always get better value for money (that means better performance for less money) by simply selling your vidcard and replacing it with a single higher performance one. Two previous gen or lesser performance vidcards demand more power, create more heat & rarely perform as well as a single next gen or higher performance card.

Owen1978 · Post by **Owen1978** » Tue Jul 11, 2006 5:42 am

MikeC wrote:
RDaneel wrote: I do like to have a reserve for worst-case scenarios, like upgrading to SLI down the road or the next gen vid card, so I'll probably get at least a 400W model.
[emphasis mine]
IMO, SLI is the biggest scam going in the PC world these days. You will almost always get better value for money (that means better performance for less money) by simply selling your vidcard and replacing it with a single higher performance one. Two previous gen or lesser performance vidcards demand more power, create more heat & rarely perform as well as a single next gen or higher performance card.

Totally agree, the might as well make a super xfire/sli where it can hold 100 sli/xfire cards.

Whats the point of putting more and more cards, why cant they rely on clever engineering like the gx2 cards - i.e dual gpu's.

Same goes with psu's, saw a thread about a 700W psu - WTF?, why would u need that much power? when will that stop? next we will be seeing 1000w psu's or even better nuclear psu's!!!!

If intel & amd can put mutliple cores on a single cpu why cant the ati & nvidia do the same?

BillyBuerger · Post by **BillyBuerger** » Tue Jul 11, 2006 6:31 am

They already have 1000W PSUs.

I don't think people think about what it would be like if you really had a PC that drew 1000W of power. It would be like leaving your vacum cleaner on all day. Aside from sounding like a vacum, think of the electric bill for that!

Tephras · Post by **Tephras** » Tue Jul 11, 2006 11:31 am

And soon there will be 1200W consumer PSUs available.

El Doug · Post by **El Doug** » Tue Jul 11, 2006 11:33 am

MikeC wrote:
RDaneel wrote: I do like to have a reserve for worst-case scenarios, like upgrading to SLI down the road or the next gen vid card, so I'll probably get at least a 400W model.
[emphasis mine]
IMO, SLI is the biggest scam going in the PC world these days. You will almost always get better value for money (that means better performance for less money) by simply selling your vidcard and replacing it with a single higher performance one. Two previous gen or lesser performance vidcards demand more power, create more heat & rarely perform as well as a single next gen or higher performance card.

When I found a guy moving out of town and parting his rig, i could not resist passing up a second 7800gtx for $150. Considering it's top of the line, there is no card to replace these 2 with. Now granted, my situation is not usual.... However, cooling and noise have been no problem, with my original card on a reserator and the second with a 5v AC Silencer

@RDaneel - Im running a 4400+ with dual 110nm 7800gtx's with my phantom350. Im sure youll pull even less power with the Core 2.

Owen1978 wrote:If intel & amd can put mutliple cores on a single cpu why cant the ati & nvidia do the same?

I believe I read somewhere that due to the calculations that GPUs perform verses those of a CPU, it is inefficient to have a dual core processor

Howard · Post by **Howard** » Tue Jul 11, 2006 11:58 am

It's more accurate to add up the amount of +12V current used by each component and check if it's lower than the combined max of the PSU, since 80%+ of the power is drawn off the +12V rail(s) in modern PCs.

Conroe - 65/12 = 5.5, though Intel's TDP are quite optimistic
Mobo - 2-3A
HDs - check the manufacturer specs, usually around 0.5A per drive
Optical drives - check manuf specs, usually around 1A
Video card - Google for your specific card, usually between 4-10A
Fans - check the current rating on the label
etc.

Most 400-450W PSUs have a combined max current of 29A on the +12V rail(s). 350-380, 25A, 450-500, 32-34A, etc.

RDaneel · Post by **RDaneel** » Tue Jul 11, 2006 2:02 pm

I agree, MikeC, the newer cards will probably always be better price/performance buys, not to mention requiring only one cooling solution (and its attendant noise). The only way I see going SLI is for El Doug's reason - a cheap second card. My monitor is 1600x1200, and that isn't changing any time soon, so the 7900gt level is perfect for me.

As for the PSU wattage, I really wish SPCR had been able to test a S12 380 against the 430, I'd go for the 380 if it was even more quiet at my probable draw. The 430 is just SO silent at 150w draw that it is hard to turn that down for the lower end model (that might be working a little hotter to put out 150w). I *really* appreciate all the advice, and am glad that I asked the question and avoided buying way too much PSU (though I guess I'll still end up with some extra!).

roadie · Post by **roadie** » Wed Jul 12, 2006 3:21 am

MikeC wrote: IMO, SLI is the biggest scam going in the PC world these days. You will almost always get better value for money (that means better performance for less money) by simply selling your vidcard and replacing it with a single higher performance one. Two previous gen or lesser performance vidcards demand more power, create more heat & rarely perform as well as a single next gen or higher performance card.

I completely agree, apart from when you are running at insane resolutions on 24" and 30" LCD monitors. 2 graphics cards do make a difference then.

jurrasstoil · Post by **jurrasstoil** » Wed Jul 12, 2006 4:17 pm

Hi,

a guy in a german forum is using an Enermax Liberty 500W to run Quad SLI (2x 7900GX2), 4 HDDs, 2gig ram, 8 case fans and an overclocked AMD 64. A Hyper 750W PSU wasnt able to run this setup stable...
So, a good brand 430W PSU should be enough for the most SLI/Crossfire Systems...