PSU Advice Please ?

[BrutalAce]

Hello everyone,

I recently purchase 2x Gigabyte GTX 980 G1 Gaming graphic cards and it is my first ever dual card setup.

I am using an old OCZ GameXStream 850w PSU which I purchased around 2007 and so far it served me very well but now with these two GTX 980s the first problem I have faced is the fact that both of these cards need 8+8 pin connectors so I should have two pairs to power them both but my PSU only has one pair of 8+8 (6+2 each) connectors while the other pair is just 6+6 so I cannot power second card with it therefore I have to use 4x Molex connectors to power the second one.

The second problem I am facing is that once the top card reaches 80c - 81c the entire system shut down and then turn back on after a second, I guess at 80c the card ask for more power and PSU getting over loaded just shut off. If I just use single card (either of them) then I don't face this issue but with SLI is just happens every time I reach 80c on top card.

For the moment I just down clocked the cards from 1366 to 1200 Mhz with power limit set on 85% including an aggressive fan profile which keeps the top card to 70c and the system runs fine but it is imminent that I need a new PSU to properly power these cards.

I was planning to buy Cooler Master V1000 which is easily available in my country and I read excellent reviews about it, one friend told me that a PSU should have at least 60A on +12 rail to power a high end SLI/CF system and this PSU delivers 83A on +12 rail.

Now if I compare V1000 with my OCZ PSU then V1000 only has one +12 rail with 83A while OCZ has 4 rails with 18a or 20a on each rail so that makes combined amperage of 80 (if we consider it 20a). From this perspective V1000 only has 3 extra amperes so is that really enough to power my entire system ? Please read OCZ GameSXtream 850w specifications here

http://www.overclock3d.net/reviews/power_supply/ocz_gamexstream_850w_atx_psu/2

and V1000 specs here

http://www.techpowerup.com/reviews/CoolerMaster/V1000/2.html

I really don't understand this multi rail vs one rail thing but people say one rail is better. According to this review they powered Tri SLI GTX 780 on this PSU and said it worked just fine so this means it can easily power up my system as well without getting pushed too far ?

http://www.fudzilla.com/32091-cooler-master-v1000-reviewed?start=4

My system is

1) MSI Z97 G45 Gaming Motherboard
2) Core i5 4960k @ stock (I plan to OC it after getting new PSU).
3) 8GB Kingston HyperX DDR3.
4) 4 Hard drives total (2x SSDs & 2x HDDs).
5) 5 case fans (including CPU fan).
6) 2x Gigabyte GTX 980 G1 Gaming in SLI. (I plan to keep them at default factory OC for now).

Please help me deciding and thank you for your time to read my long post.

 

[NeverBackDown]

With mutli rails, each rail has a certain amount of amps it can give. So if you put everything on one rail it will overload and cause the psu to shutdown. You need to spread it out. Single rail by design is pretty close to a multi rail but its functions slightly differently to multi rails. Single rails have everything loaded onto one rail so no need to spread them out. Though since i mentioned amps.. gtx 980's require 30amps according to Nvidia

GTX 980s in SLI i would go with a 650watt psu. Your system probably doesn't even use 500watts so you would be fine. 750w psu i would opt for if you plan on running high OCs on either CPU or GPU just for headrooms sake. If its a simple/mild CPU/GPU OC then 650watts would be fine. Not many 650w psu's provide 60amps though. Probably need to jump up to a 700+ unit but i don't think it would make much a difference tbh If anything stay away from a 1000watts psu. You don't need it.

Corsair/Seasonic/Superflower/EVGA(some units are made by superflower) are probably the top brands. Got nothing lower than 80+ gold though if possible. Saves on heat and prolongs the life of the system by delivering cleaner power.