SOLVED How much psu is enough?

[yaiie]

When building a PC how do you guys gauge how much of a psu you'll need? When your graphics card says you need a "minimum 500 watt power supply" do they mean to run the whole system or just for the gpu?

With my current rig what'd be the minimum psu you'd have put in it? How did you come to that conclusion?

Thank you!

 

[ATMINSIDE]

I'd run a GOOD QUALITY 500W unit any day for that rig.

 

[Pierre3400]

I will agree with above, but if you can room for dual GPU's in the future, i'd pick a good quality 700watt. Above 80+ rating.

 

[yaiie]

I'd run a GOOD QUALITY 500W unit any day for that rig.

Question... As the PSU gets older does it lose some performance? If you had a 500 Watt PSU (Which is what the gpu says is the minimum required) as it got older would you start running into power issues?

I personally haven't overclocked but I was curious... How much of a difference overclocking would have on power consumption?

 

[ATMINSIDE]

You'd still be fine on that 500W with overclocking.
For Crossfire, I'd grab a good quality 750W and call it a day.

The only performance loss would be aging capacitors. Shouldn't see that for 5+ years when you buy quality parts though.

 

[manu2b]

^Yes, and running full load 24/7!

 

[Mandrake4565]

Question... As the PSU gets older does it lose some performance? If you had a 500 Watt PSU (Which is what the gpu says is the minimum required) as it got older would you start running into power issues?

Don't know.

I personally haven't overclocked but I was curious... How much of a difference overclocking would have on power consumption?

Even if you Overclocked the pee out of the Cpu and Gpu you would be fine with a "Quality" 500w Psu. Though if that was in the cards I'd play it safe with a 600-650w.

 

[ATMINSIDE]

Here's some quick math for you:

3750k = 77W
7970 = 250W
Mobo/HDD/RAM = 40W
Total: 367W

Let's overclock it:
25% on CPU = 77 x 1.25 = 96.25W
20% on GPU = 250 x 1.2 = 300W
Mobo/etc = 60W
Total with OC = 456.25W

Chances you'll actually pull 456W? Almost zero.

Add a second GPU with OC = 756.25W
Again, chances of pulling that much are almost zero.

Take that value (456W or 756W) and divide by 12V
456W/12V = 38A on the 12V rail.
756W/12V = 63A on the 12V rail.

This PSU is 550W and excellent quality. It supplies 45A on its 12V rail.
This PSU is 760W and also great quality. It supplies 63A on its 12V rail.

Edit: Stick to a PSU off this list and you'll know you're getting quality

 

[yaiie]

Here's some quick math for you:

3750k = 77W
7970 = 250W
Mobo/HDD/RAM = 40W
Total: 367W

Let's overclock it:
25% on CPU = 77 x 1.25 = 96.25W
20% on GPU = 250 x 1.2 = 300W
Mobo/etc = 60W
Total with OC = 456.25W

Chances you'll actually pull 456W? Almost zero.

Add a second GPU with OC = 756.25W
Again, chances of pulling that much are almost zero.

Take that value (456W or 756W) and divide by 12V
456W/12V = 38A on the 12V rail.
756W/12V = 63A on the 12V rail.

This PSU is 550W and excellent quality. It supplies 45A on its 12V rail.
This PSU is 760W and also great quality. It supplies 63A on its 12V rail.

Edit: Stick to a PSU off this list and you'll know you're getting quality

Thank you all for your responses... And a big thank you Atmin for this awesome write up!

 

[ATMINSIDE]

Thank you all for your responses... And a big thank you Atmin for this awesome write up!

No problem!

 

[Kamel]

i think of course you've been given excellent advice, but i thought i'd give some additional advice regarding how to choose how much of a PSU you should get (should you get more PSU than you need, just enough, or what).

first i'd like to point out that if you get a new power supply and your performance increases, that means your prior power supply was under powered. for example, if i already had an overpowered PSU (lets say 750 watts and i only needed 500) then i bought a new PSU that was 1000 watts, i wouldn't notice any difference in the way the PC performs at all (again, unless there was an issue with the last power supply).

what you will notice, however, is a power supply certainly be the limiter of your PC and quite frankly can cripple it pretty good. i've experienced this first hand. you might notice downright weird things happening like USB devices disabling on their own, random system crashes, etc. troubleshooting the issue down to the PSU in my experience can be tough too.

finally, PSU's tend to age well. in computer terms, a PSU is a good investment as it wont be outdated as quickly as some of your other components. getting a good quality PSU designed for higher wattage than you need right now might mean you'll be using that PSU for many years to come for only a few bucks more than that "barely get you by" PSU that you'll have to buy all over again when you get a new PC.

so having said all of that, i strongly recommend purchasing something around 20% greater than your current needs and of a good quality (quality is super important with PSU's, DON'T believe the notion that the only difference between PSU's is their wattage rating [which quite frankly is a totally bogus number on cheap PSU's]). in my opinion this will be a decision you wont regret.

good luck!

 

[yaiie]

i think of course you've been given excellent advice, but i thought i'd give some additional advice regarding how to choose how much of a PSU you should get (should you get more PSU than you need, just enough, or what).

first i'd like to point out that if you get a new power supply and your performance increases, that means your prior power supply was under powered. for example, if i already had an overpowered PSU (lets say 750 watts and i only needed 500) then i bought a new PSU that was 1000 watts, i wouldn't notice any difference in the way the PC performs at all (again, unless there was an issue with the last power supply).

what you will notice, however, is a power supply certainly be the limiter of your PC and quite frankly can cripple it pretty good. i've experienced this first hand. you might notice downright weird things happening like USB devices disabling on their own, random system crashes, etc. troubleshooting the issue down to the PSU in my experience can be tough too.

finally, PSU's tend to age well. in computer terms, a PSU is a good investment as it wont be outdated as quickly as some of your other components. getting a good quality PSU designed for higher wattage than you need right now might mean you'll be using that PSU for many years to come for only a few bucks more than that "barely get you by" PSU that you'll have to buy all over again when you get a new PC.

so having said all of that, i strongly recommend purchasing something around 20% greater than your current needs and of a good quality (quality is super important with PSU's, DON'T believe the notion that the only difference between PSU's is their wattage rating [which quite frankly is a totally bogus number on cheap PSU's]). in my opinion this will be a decision you wont regret.

good luck!

Thank you Kamel. I really appreciate you taking the time to write that out!

About eight months ago I built this rig. I ended up going with a Thermaltake Smart Series Modular 850W... She's been good to me! Actually great... No noise, no power issues... Plenty of juice!

Back then I was asking a ton of questions, reading manuals... Trying to make informed decisions... Now fast forward to today I was thinking about building a server and all the logic / reason for doing what I did... What does what... Have since faded and i'm trying to pick up the pieces!

You guys have helped a lot! When I built this PC I did it with the help of the forum and there suggestions! If I do end up building this server it'll be largely in part thanks to the forum again!

Thanks everyone!

 

[madcratebuilder]

I like to add about 25% headroom when looking at psu's, having to much power does not hurt anything, not having enough power does. Running a psu at it's limits well decrease it's lifespan and increase heat produced. There's always the $$$ to factor in.

My OC box has a AXi 1000, kind of overkill. My mail/web surfer runs on a budget Rosewill 530W Gold.

 

[EarthDog]

first i'd like to point out that if you get a new power supply and your performance increases, that means your prior power supply was under powered.

Nope. Not true at all. It either works, or it doesn't.

The rest was, ok...at least the underlying message.

 

[Kamel]

Nope. Not true at all. It either works, or it doesn't.

The rest was, ok...at least the underlying message.

I concede, I was over-generalizing and I think I may have misrepresented a little bit in my post. Admittedly a failed attempt at dumbing down a more complicated response

Allow me to explain in terms of personal experience.

I had some very strange problems with my PC. Specifically, devices not showing up, USB devices not being recognised. Sometimes, I would be able to fix it with unplugging and replugging the device, other times not. I also was experiencing random PC crashes.

All of these issues were caused by an underpowered PSU. After replacing it, everything worked properly.

I don't know if I would consider that "works or it doesn't work", but I can say that I would collectively consider that "underperforming", maybe not necessarily "less points in 3dmark" type of underperforming.