How many watts PSU do I need?

pwnerx · Post by **pwnerx** » Mon Sep 24, 2007 12:43 pm

My new system will have:

- E6600 CPU @ stock
- 680i mobo
- 2x 1gb 800mhz RAM
- 7950GT or X1950 PRO video card
- 2 optical drives
- 1 floppy drive
- 3 SATA hard drives
- Antec solo case
- 1 120mm exhaust fan
- 2 92mm intake fans
? PSU ?

I've heard that the more wattage the better, but wasted wattage isn't good for my wallet >.> I've also read on this forum that some people are doing fine with a 380 watt PSU.

How many watts do I really need for this setup? How many amps total should there be on the 12v rails? I also want this PSU to have a little headroom if I decide to overclock. I'll be using this PSU for 12-16 hours everyday and want it to last for at least 3 years.

quest_for_silence · Post by **quest_for_silence** » Mon Sep 24, 2007 12:55 pm

pwnerx wrote:How many watts do I really need for this setup?

Just as a first look, maybe you wanna try also this: eXtreme Power Supply Calculator Lite v2.5 .
As far as I know, there's even a pro version which is able to estimate how many amps you'd eventually need.

Luca

angelkiller · Post by **angelkiller** » Mon Sep 24, 2007 1:31 pm

Ok, lets take the components individually. Please note that I will be overestimating, and your actual results should be lower.

E6600= 65W, Mobo= 30W, RAM= 10W, Video Card =80W, Hard Drives= 35W, Optical Drives(s)= 20W, Fans= 5W.

Total: 245! And this is overestimated! So pretty much any modern PSU will accommodate your setup. As for quiet ones, Seasonic 330W, 380W, 430W, or you could get a Corsair VX-450. All would be sufficient.

Hope this helps.

merlin · Post by **merlin** » Mon Sep 24, 2007 1:35 pm

quest_for_silence wrote:
pwnerx wrote:How many watts do I really need for this setup?
Just as a first look, maybe you wanna try also this: eXtreme Power Supply Calculator Lite v2.5 .
As far as I know, there's even a pro version which is able to estimate how many amps you'd eventually need.

Luca

Please do not use that calculator, it is imho absolutely terrible. It will overestimate your needs by 150-300W over the actual.

You really need probably 250W, but to be safe, get something of high quality 300W or better. Any Seasonic, Earthwatts or the Corsair VX450 would be perfect.

Atmosper · Post by **Atmosper** » Mon Sep 24, 2007 1:37 pm

Do NOT use PSU calculators! They almost always give very exaggerated recommendations. They include to many "what if's" and wrong flu assumptions. From experience I would estimate your system to draw no more than 150 W.

My system draws about 150 W from the wall at idle. Which means about 120 W from the PSU (~80 % efficiency). That is with a E6600 and a Geforce 8800. It runs fine on a Seasonic S-12 380 W. At load ~180 W from the wall. Even two graphics cards won't break 380 W DC from the PSU.

With a less powerful gpu (Geforce 7600GS) my system draws about 100 W from the wall.

Airshark · Post by **Airshark** » Mon Sep 24, 2007 1:59 pm

You know, you really can't tell just by the PSU's rating what kind of current it supplies. If you'd got a power draw of 250W, but your PSU's only 70% efficient, a 350W supply will be inadequate. And remember, power draw bounces considerably, which is why you generally need a PSU that's bigger than you actually draw.

The trick is to get a high-quality PSU, one that's efficient and steady. Far more important than its actual rating. Lately I've been going with purely Corsair PSUs. I have three 620s and a 520, they're the best PSUs I've ever owned. I had to throw away an Antec Neopower, an Antec Phantom 500, and an Enermax PSU recently, all failures. Only the Neopower was dead, the others were just hiccuping (causing reboots). Replacement with Corsairs, and voila, everything is great. These PSUs are made by Seasonic, so I suspect Seasonic's PSUs would be fine too.

smilingcrow · Post by **smilingcrow** » Mon Sep 24, 2007 2:21 pm

Airshark wrote:You know, you really can't tell just by the PSU's rating what kind of current it supplies. If you'd got a power draw of 250W, but your PSU's only 70% efficient, a 350W supply will be inadequate. And remember, power draw bounces considerably, which is why you generally need a PSU that's bigger than you actually draw.

Power supplies are rated for DC output whereas the reviews that you read that include power data typically show AC input.
With an 85% efficient power supply a system that uses 250W AC is actually using 212.5W DC. A 350W supply should easily manage that.
You do need to check how much the unit can provide to the 12V rail(s) as thatâ€™s where the power draw is these days.

merlin · Post by **merlin** » Mon Sep 24, 2007 2:39 pm

Airshark wrote:You know, you really can't tell just by the PSU's rating what kind of current it supplies. If you'd got a power draw of 250W, but your PSU's only 70% efficient, a 350W supply will be inadequate. And remember, power draw bounces considerably, which is why you generally need a PSU that's bigger than you actually draw..

As also noted by smilingcrow, this is an incorrect assumption. PSU's are always rated by how much ACTUAL DC power they supply. This means a 70% efficient 350 psu actually uses 455W AC power. This is correct, a 350W psu can draw far more from your power outlet. That's a minor warning in terms of power usage too

Also I honestly have never seen my power draw bounce much at all unless I physically do something to change it. Such as running at high load. The biggest bounce is startup, after that you're in clear sailing as long as load power usage is stable.

pwnerx · Post by **pwnerx** » Mon Sep 24, 2007 9:51 pm

Thanks for the replies. I have an Antec Earthwatts 380 that I'm currently using. I may use this for my next system.

I have another question. Should I replace this 380 Earthwatts with a Corsair/Seasonic for the 120mm exhaust fan?

The Earthwatts PSU pushes very very little air... I can't feel anything when sticking my hand directly over the exhaust fan. If I decide to reuse this PSU in the Antec Solo, I don't think I'll be able to run my rear 120mm exhaust fan on low and maintain reasonable temperatures at the same time.

If I get a PSU with a 120mm fan, I think I'll be able to maintain good airflow with both my case and PSU fans on low.

Btw I live in Hawaii and room temps approach 32c somedays.

What do you guys think? Is it worth the $100 or so to get a new PSU?

EsaT · Post by **EsaT** » Tue Sep 25, 2007 10:06 am

pwnerx wrote:If I get a PSU with a 120mm fan, I think I'll be able to maintain good airflow with both my case and PSU fans on low.

Btw I live in Hawaii and room temps approach 32c somedays.

IMO would be better to have case where PSU is on bottom and doesn't need to take part in exhausting heat produced by components.

How many watts PSU do I need?

How many watts PSU do I need?

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