What wattage is needed for video card?

csq · Jul 11, 2014

I intend to purchase a video card and a PSU. The video card description says:
"Minimum Recommended System Power (W) - 600W".

Considering 600W is the minimum, what would be a safe wattage for the future PSU to have? The aim is that even at max load, the PSU and card should not fry or be otherwise damaged. In other words, I don't need top-of-the-line wattage, just a safe, reliable wattage.

What would that number be?
(Optionally: Is there any formula to calculate it?)

Thanks.

markwp · Jul 11, 2014

What card are you looking at? What psu are you considering?

Wattage requirements are not the best way to evaluate power needs. There are multiple web sites that list the amperage requirements for gpus, which is a much more effective way to determine your needs. This also applies to psu's. You can find a bargain psu that says it will provide 600w, but closer inspection of the specs will show that a large part of that value is made up by the 5v rail. What you really need to consider is how much amperage is available on the 12v rail(s).

There is much more to this than just "needing 600w".

Onus · Jul 11, 2014

What video card is it?
Graphics card manufacturers always overstate PSU wattage requirements, in the often futile attempt to compensate for all the liar-labeled PSU-objects that are still somehow being sold; units like Apevia, Logisys, Diablotek, Raidmax, Sunbeam, etc. that may not be good for even half of what is on their labels.
Consider PCIe specs. The PCIe slot can provide up to 75W. Each 6-pin PCIe power cable can also provide up to 75W. An 8-pin PCIe cable is rated for up to 150W. If you add up the types of power connectors a card has, that will tell you the maximum it could possibly draw (in actual use, it will always be less). For example, a card with a single 6-pin PCIe power cable will need no more than 150W (75W for its slot + 75W for the single power cable).
As you can see from this, a 380W Antec Earthwatts is sufficient for any card with only that single 6-pin adapter.

csq · Jul 11, 2014

markwp :

I was looking at a Geforce GTX 770 or GTX 760 (if more details are needed I will provide them).
Now:
- what good PSUs exist for these two cards?
or
- tell me how I can find them myself (what values/parameters should I look for).

Either way, I don't need state-of-the-art; just physically reliable and not prone to frying the video card.

LucoTF · Jul 11, 2014

12v amperage is waaaay more important than total wattage, as others have said

Onus · Jul 11, 2014

For model recommendations, you can use http://www.johnnylucky.org/power-supplies/psu-recommendations.html . He's got a Lemon List there too, of units to avoid.

Most GTX760s have one 6-pin and one 8-pin PCIe power cable. This means it can need no more than 75W (slot) + 75W (6p) + 150W (8p) = 300W.
A GTX770 may have a pair of 8-pin adapters, so you get 75W + 150W + 150W = 375W. Note these are MAXIMUM loads these cards could pull without exceeding PCIe specifications. In actual use, the load will be considerably less. Depending on your CPU and the number of drives and fans you have, you may need another 100W-200W for the rest of your system.

csq · Jul 11, 2014

LucoTF :

And where do I find the amperage of a video card? I've searched a few video cards producers' sites and I haven't found that info.

Pondering · Jul 11, 2014

Antec HCG 620M $65 after $20 rebate

http://pcpartpicker.com/part/antec-power-supply-hcg620m

I have that one personally and it is solid and basic but it is seasonic made and comes with a 5 year warranty

I can't find the video card amperage requirements either, but everyone says that they find it on the manufacturer's websites however I still have issues finding it. I will have to ask the other people on the forums where they find the amperage information. Power supply amperage is a double check to make sure that the power supply can provide a certain wattage continuously since for some reason label wattage can be inflated but the amps information is accurate for the power supplies.

Onus · Jul 11, 2014

That's an excellent choice.

LucoTF · Jul 11, 2014

csq :

Amperage requirements:

http://forum-en.msi.com/faq/article/power-requirements-for-graphics-cards

Although I think some of these are a little generous and some others are a bit light. The GTX 670/760 sound about right btw (30a)

+1 to the Antec 620w

csq · Jul 11, 2014

First, thanks for the link to the video card amperage FAQ.

I reviewed the Antec PSU linked in a previous post and tried to see if it would be enough for a GTX 770 from your FAQ. The 770 requires 42A, but the PSU lists:
"+5V@24A, +3.3V@24A, +12V@48A, -12V@0.8A, +5VSB@2.5A".
What does that mean? and is it enough to reach the required 42A?

LucoTF · Jul 11, 2014

csq :

That PSU is +12V@48A - enough for a 770, 780, 780ti, titan... although it's a bit closer with the 780 onwards

This is an example of why that site can be misleading. If 30 amps for a 760 is correct then logically the requirement for a 770 would be 35amps because there's 5 amps difference between the thermal design power of the two cards (170w vs 230w). But instead that site jumps 12 amps, that's 144w difference!

LucoTF · Jul 11, 2014

Let me show you how to work it out.

Watts = volts x amps
amps = watts / volts

volts is always 12 for GPU, watts are given by your CPU and GPU manufacturer. So, take an i5 and a gtx 770 for example

i5 haswell is 84 watts
770 is 230 watts
The rest of the system (12v rail load only) is about 50-60 watts

So that's 374 watts, 364 / 12 = 31.17 amps on the 12v rail!

Multiply this by 10/7 (for 70% load) and you have 44.5 amps, so any good quality PSU that is rated for 45 amps on the +12v rail will power this setup with room to spare.

I've been conservative in a couple of places - firstly, the wattage used for the cpu and gpu is for MAX load and they tend to run less than this in the real world, and secondly the 70% load margin is a very decent cushion.

At least, that's how I've always worked it out...

csq · Jul 11, 2014

LucoTF :

Thanks but I got something more complicated. A potentially good Thermaltake PSU lists:
+3.3V | +5V | +12V1 | +12V2 | -12V | +5VSB
24A | 15A | 30A | 22A | 0.3A | 2.5A

What is the final amperage that it provides?

Onus · Jul 11, 2014

Hmmm, Thermaltake... What model? If it is one of the older, non-80+ ones, it is not good for its label.

+12V amperages are not strictly additive. There should be an additional entry on the label that lists the max combined. It could be as little as 40A in this case.

csq · Jul 11, 2014

Onus :

Here is the link. Bottom half of page under Output Table header. All I need to know is if it can run a GTX770 that needs 42A.

LucoTF · Jul 11, 2014

Google says max combined is 48a for that psu

csq · Jul 12, 2014

LucoTF :

If I understand correctly, 48A takes care of the 42A GPU requirement; but being that my computer has other components as well (HDDs, MB, DVD unit etc.), don't these add to the amperage requirement of the PSU? and how much?

LucoTF · Jul 12, 2014

csq :

It's all been taken into consideration in the 42a requirement. But if you want to know how much each component uses (both idle and at load) then here's a rough guide:

http://www.buildcomputers.net/power-consumption-of-pc-components.html

Not all of this goes just through the 12v rail though - much of the motherboard components (like the chipset) use the 3v and 5v. Rule of thumb - if it needs a motor then it uses 12v.

CPU, GPU, disk drives, fans, DVD drives all use 12v

I'll keep it really simple though - that Antec HCG is awesome and it's everything you could need for a single card setup, even with lots of drives and fans.

All of the PSUs below are also more than enough for your needs:
http://pcpartpicker.com/part/xfx-power-supply-p1550sxxb9
http://pcpartpicker.com/part/xfx-power-supply-xfxts550w
http://pcpartpicker.com/part/xfx-power-supply-p1650snlb9
http://pcpartpicker.com/part/rosewill-power-supply-capstone750

Buy any of these and you'll be good to go

(Also, that is an excellent deal on the 750w Rosewill for $60)

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