can 40 amps do it

[clide005]

I am a total noob. Please be kind. I bought a EVGA gtx 770 and an EVGA PSU 500w. I calculated the total watts needed at a full load to be 433 for the whole system and figured I was good. However, I got the GTX 770 and it says it needs 42 amps on the 12 v rail. The PSU is only rated for 40. Am I up a creek or am I close enough?

 

[Brantyn Gerik]

40 amps will do it, but no overclocking headroom safely.

 

[TropicoSuarez]

It's never a good idea to feed your graphics card less power than it says it requires. It will cause errors and stuff. You'll be better off buying a new PSU. XFX, Seasonic and PC Power and Cooling make the best PSU's. Just make sure that the PSU has atleast 42 amps on the 12v rail, preferably more.

Good Luck!

 

[hunter315]

For a single GTX 770 and a high powered CPU a 500W PSU with a 40A rail is sufficient, i wouldn't see how far you could overclock it on that psu but you could do some light OCing without issue.

 

[Brantyn Gerik]

42 amps is the max artificial stress test load when on the average max overclock of the cards on the stock bios.

so yes, you can run the 770 on a 40 amp 12v rail, but should you? probably not the safest thing in the world...kinda like having a near empty tank in winter...you can and in all reality it will likely start and run, but it's just not good practice

 

[Shneiky]

Well I will very very STRONGLY advise you not to test it. It will be better to return the PSU and get a 600W (550W worst case scenario) model with at least 50 amps on the +12. Do not forget that a PSU looses its initial capacity over the years. I strongly advise you not to skimp on the PSU as you will regret it later. Take a Seasonic, Seasonic made (XFX and others) or quality HEC or FPS made PSU like bequiet!. Do not take Corsair CX PSU, that one is bad, but Corsair AX are good.

 

[Brantyn Gerik]

Corsair CX is by no means "bad" but it is indeed a lower quality power supply. while i completely +1 the above post about not skimping on a power supply, it is the one item that if you do screw up, you tend to break more than just it.

So do you need 50 amps on the 12v rail? absolutely not. do you need 42, yes, almost no one will actually recommend that you get lower
do you need more than 500 watts for a single gpu and single cpu solution? No
should you get more than 500 watts for a high end gaming card like the 770. It is highly recommended to get at least 600 watts with the correct amperage on the 12v rail.
Rosewill are not the highest quality power supplies out there right now, but they ARE extremely affordable and tend to have very strong 12v rails for single gpu setups

 

[clide005]

Okay new power supply it is. since I am planning on going to SLI at some point anyway I might as well get the beast of a PSU I need right now since I will have to go through the hassle of returning the current PSU anyway why not go for the gold. So my questing is do I need a PSU that now has 84 amps on the 12 v rail to be sufficent for for SLI on gtx 770 ?

Thanks for all your help guys

 

[Brantyn Gerik]

minimum of 850 recommended with hopefully 2 12v rails @ 42 amps each

 

[Shneiky]

http://www.realhardtechx.com/index_archivos/Page2917.htm

Seasonic, Superflower, some of FPS and some of HEC designs are the best out there. These are the tops OEMs, which the other major brands re-brand under their name.

All of Rosewill's Superflower designed PSUs are top of the top. A lot of people tend not to realize that the OEM of the PSU is more important then the brand under which is it sold.

As far as Corsair CX - that is total piece of tin trash. Long ago the CX line was manufactured by Seasonic. Now it is by CWT. And how CWT makes the new CX - it is below average. It costs too much for what it is.

As a rule of tumb and I might be a bit overreacting, but I tend to keep safe with Seasonic, Superflower or re-brands of them, like XFX or Corsair AX and some Rosewill, EVGA Supernova line (has some FPS models) or quality FPS/HEC like bequiet!. In the end there are so many PSU sellers and they change OEMs that frequently that a quality PSU you bough 6 months ago, now can be a complete disaster. (current Corsair CX line)

 

[Brantyn Gerik]

http://www.newegg.com/Product/Product.aspx?Item=N82E16817553008
little bit pricey, but has 6 25 amp 12v rails, which will allow for 3 770's. I know cougar as a brand to be quite exceptional for the price you pay, but at the same time, i realise this may be slightly more than you want to spend on your power supply. just a good futureproof suggestion

 

[hunter315]

Hang on, WTF happened with you guys and being able to do math?

A GTX 770 has a peak power draw of about 230W, if he has a 125W CPU that still only puts you at 355, 80W for the motherboard and you are only at 435W, that is still only about 85% of the capacity which is fine. The EVGA was reviewed by jonnyguru and did fine, it was docked points for average ripple suppression and average voltage regulation. It took a small hit for using Teapo caps which are still second tier which is fine.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story6&reid=351

You already have a PSU that will work, it won't be the best thing in the world but it will do the job just fine, there is no point spending even more money on a PSU when you already have something that will work.

 

[Brantyn Gerik]

It's not just about math on the wattage. the current is equally important especially since he has stated that he does plan on doing sli in the future

 

[clide005]

Yeah I agree, the wattage is fine. But the EVGA gtx770 calls for 42 amps on the 12 v rail and the psu I have only supplies 40amps.
I was planing on going to SLI at some point and just figured I would buy a beefier PSU when I did that, but here we are and the PSU I have may not cut it with just on video card. I also wasn't sure if a new power supply I buy will need to be 84 amps or if that once I am past 42 amps I just need to worry about the increase in wattage of the second card. I don't fully understand electrical theory all that well.

 

[clide005]

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
little bit pricey, but has 6 25 amp 12v rails, which will allow for 3 770's. I know cougar as a brand to be quite exceptional for the price you pay, but at the same time, i realise this may be slightly more than you want to spend on your power supply. just a good futureproof suggestion

That looks like the rails only support 25amps a per 12 volt rail. I am probably not understanding something.

 

[hunter315]

Manufacturers grossly over estimate their PSU requirements to account for the shoddy brands that label a unit as 600W when it is only a 450W continuous unit, they also overrate them to account for the cheap units that are rated at 20C instead of 40C which is a realistic temperature for it to be running at. A GTX 770 needs about 230W(19.16A) from the 12V rail, i don't know why EVGA is speccing 42A but that is grossly higher than needed.

When you add a second GTX 770 you will only increase your power draw by about 230W so you will only need about that much more capacity. A good 750W unit will run two GTX 770s without issue as it will have about 60A available on its 12V rails. You will not need 84A because first off you don't need 42 to start with, secondly that is the recommended capacity to support the entire system and you haven't doubled the power draw of the CPU, motherboard, or drives simply by adding a second GPU so you don't need to double the system power requirement.

Its been a while since i have seen the system requirements they are specing the power requirements with but last i saw it was a 150W CPU, high end motherboard and 6 drives which grossly over inflates the required power for most people. Notice how they never spec a small power supply? A GT 630 has a power draw of 65W(~5.5A), but still comes with a recommendation of a 350W power supply because they are accounting for a rather power hungry base system behind it.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130821

Also never trust PSU calculators on newegg or PSU manufacturer's websites, they tend to be largely inflated to help sell bigger units which turn a better profit margin. Figure out how to calculate power draw yourself and you will get accurate estimates and not enough up with PSUs that are the wrong size for your needs. Case and point, newegg says i have a recommended PSU wattage of 556W, if i throw prime95 and furmark on and load everything up my kill-a-watt tells me i don't even draw more than 400W from the wall.

 

[clide005]

Manufacturers grossly over estimate their PSU requirements to account for the shoddy brands that label a unit as 600W when it is only a 450W continuous unit, they also overrate them to account for the cheap units that are rated at 20C instead of 40C which is a realistic temperature for it to be running at. A GTX 770 needs about 230W(19.16A) from the 12V rail, i don't know why EVGA is speccing 42A but that is grossly higher than needed.

When you add a second GTX 770 you will only increase your power draw by about 230W so you will only need about that much more capacity. A good 750W unit will run two GTX 770s without issue as it will have about 60A available on its 12V rails. You will not need 84A because first off you don't need 42 to start with, secondly that is the recommended capacity to support the entire system and you haven't doubled the power draw of the CPU, motherboard, or drives simply by adding a second GPU so you don't need to double the system power requirement.

Its been a while since i have seen the system requirements they are specing the power requirements with but last i saw it was a 150W CPU, high end motherboard and 6 drives which grossly over inflates the required power for most people. Notice how they never spec a small power supply? A GT 630 has a power draw of 65W(~5.5A), but still comes with a recommendation of a 350W power supply because they are accounting for a rather power hungry base system behind it.
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130821

Also never trust PSU calculators on newegg or PSU manufacturer's websites, they tend to be largely inflated to help sell bigger units which turn a better profit margin. Figure out how to calculate power draw yourself and you will get accurate estimates and not enough up with PSUs that are the wrong size for your needs. Case and point, newegg says i have a recommended PSU wattage of 556W, if i throw prime95 and furmark on and load everything up my kill-a-watt tells me i don't even draw more than 400W from the wall.

That makes a lot of sense. I didn't think about the fact that they're throwing in everything else in the system as well to come up with the recommended supply. After hearing that I will probably just sit on my evga 500 watt PSU with the 40 amp rail and wait to upgrade the PSU when I buy the second 770. Thanks for everyone's input.