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How many watt PSU I need?

by ionast / January 24, 2008 9:43 AM PST

Hello to all,

I about to upgrade my PC and I am not sure how many watt PSU I need.
The parts:

Mobo: Asus P5E3 Deluxe
CPU: Intel Q9450
RAM: DDR3 2GB (2x1GB) 1600MHz
VGA: 2x Sapphire HD3870 (512MB)
HDD: 1x WD Raptor-X (150GB) 2x WD 500GB SATAII 1x WD 300GB SATA
Audio: Creative SB Audigy 2 ZS
Drives: 2x IDE DVD-RW

In the beginning i was thinking to buy an Enermax Infinity 720W but then I tried the Asus Watt Calculator and it said that I need a 1100W PSU and now I am comfused!

I'm waiting for your answers!
Thank you in advance all:)


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That's quite a humdinger.
by R. Proffitt Forum moderator / January 24, 2008 11:04 AM PST

The high number is likely due to a calculator that is factoring in aging and "derating". That's quite a lot of machine so I'd error in the 1000 Watt range.

That CPU looks to be some 95 Watt peak so just find the peak for each major device and you get to your just about 1K Watt pretty fast.

That dual video card is interesting. Are you trying to see if you can run CRYSIS in full glory?


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650w minimum
by ramarc / January 24, 2008 11:36 PM PST

i know someone's going to totally dis me, but even that PC won't need that much power. if a video card requires a 450w power supply, it doesn't mean that having two of the cards requires a 900w power supply. the 450w requirement is a rule of thumb based on a fairly 'full' pc and the real determining factor is the amperage the power supply can deliver on the 12v rails. and since you plan on dual cards, make sure the power supply has multiple PEG plugs and plugs that support the 8-pin config.

enermax is a good brand but they've been somewhat stagnant lately and other brands are offering better performance. Take a look at these reviews/rounds and take a look at coolermaster and corsair power supplies.

p.s.: if you don't already have the hd3870s, consider a hd3870x2 (dual gpus on one card) instead.

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Solution found! but GPU is now a dillema :)
by ionast / January 26, 2008 6:35 AM PST
In reply to: 650w minimum

Thank you all for your valuable replies. probably a corsair psu around 850W will be OK to avoid any overload or overheating in the rails. What about the HD3870X2 ramarc? You think it will work better than 2 HD3870 in crossfire mode? The price is the same for both choices!

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by ramarc / January 26, 2008 8:30 AM PST

will make life simpler and should perform about the same.

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Anandtech Bench
by ionast / January 30, 2008 6:57 PM PST
In reply to: benchies for hd 3870x2

Quite dissapointing bench but as it says the catalyst drivers are more responsible for the low performance. Anyway, thank you mate for your interest Happy

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Check out or try...
by Willy / January 25, 2008 12:02 AM PST

With all those goodies, its always best to have extra wattage as possible. The rails will be dragging under such a load. The system is packed and airflow will be full of hot air and this causes any psu to become less stable. If you like check with for their result on wattage demands. I'm pretty sure the psu you mentioned will do OK, I believe after a yr. it will be taxing itself, IMHO. Remember, a stable and capable psu is the foundation that any good system needs. The psu is so taken for granted :(.

tada -----Willy Happy

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If you haven't built it already...
by wheelzup / February 1, 2008 2:37 AM PST

I have a very similar system up and running now. I'm using an ABS Tagan ITZ series 800 W PSU (it is no longer available) and everything ran right from the start and some 2 months later after the build it's still going strong for the most part. I didn't go with the P5E3 Deluxe but the P5E works quite well with a QX6850, 4GB of DDR2 800 RAM, 2 HIS HD 3870's running in Crossfire (at least they both worked at first..more on this later)150GB Raptor HD, 2 x 500GB SATA 3.0 WD Hard drives, PCI Express X-Fi sound a pair of dual Layer DVD burners with Lightscribe all in a Cooler Master Cosmos 1000 case with Vista Ultimate 64 bit version.

Back to the video cards, Crossfire worked right out of the box with the pair of HIS HD 3870 cards but the one that was running as the slave died after about 3 weeks of light use. I RMA'd it and when the replacement card came I dropped it back into my system and nothing happened, it seemed to be DOA so I tried it in a working PC to make sure it was dead and not the pcI-e slot on my board, it didn't work so it's going back for a refund and I'll replace with one from another manufacturer. From what I was able to learn it doesn't matter if the cards were from different companies just as long as they use the same GPU. ATI/AMD just came out with version 8.1 catalyst drivers but for some strange reason they don't want to install properly so I'm waiting on a reply from tech support for a solution.

I did manage to play COD 4 but had to back the video setting down to what the game defaulted to for my system. I tried running it maxed out but after about 10 minutes of play the game would crash out to the desktop even with the most recent patches for it. The catalyst 8.1 drivers were supposed to help that issue but for now I can't say they will since I can't get them to install. Even at the default settings the game looked amazing and ran well. The only problem I ran into was if I played it for 3 plus hours my system became unstable and the 7.12 drivers went haywire on me but they did recover on their own. Everything is running at stock speeds so I figure it's a driver issue and ATI knows about it now.

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