Replace CX400W to run GTX 970?

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SixPotBelly

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I know someone has already asked they should buy a 400W to run the new GTX 970, and the wise advice given was it would be better to go for a 500W instead. The difference here is that I already have a fairly decent 400W. It has served me faultlessly since I got it, three builds ago, and there's no fan noise at all that I can hear. I wouldn't have thought it possible to grow attached to a PSU, but I guess I have.

My current build is:

Mobo: Asus H87M-Pro
CPU: Xeon E3-1230v3
GPU: Sapphire HD7750 passive
RAM: 2 x DDR3
Drives: 3 x SSD
Case fans: 4 x low rpm
PSU: Corsair CX400W

I'm not a heavy gamer but I do dabble now and then. The HD7750 was chosen because the pc doubles as an home theatre pc, and I value silence over outright performance.

Now that the GTX 970 has launched, I realised I had a new option. Both Asus and MSI are offering these in a semi-passive design, so now I can have a silent pc most of the time but a much better FPS when gaming (I don't care about the noise then). I've ordered the Asus Strix.

Question is, am I asking for trouble if I keep my PSU? For those that are unfamiliar with the CX400W, they were built by Seasonic for Corsair and is of a different design to the later all-Corsair CX models. It can supply 30A on the 12v rail, and reviews at the time showed it to be about 82% efficient.

Reading a recent test published on this site, it looks like a GTX 970 pulls around 170W at full load. Which is 14A. Other sites tell me my CPU maxes out at 96W, or about 8A. So that would total 22A in a worst case scenario, leaving 8A which should be more than ample for anything else that's powered off the 12v rail plus quite a bit of headroom. Correct?

Or is this complete madness and I should buy a S12ii/M12ii-520 before even thinking about installing the GTX 970?
 
Solution
Shneiky
Go with the Seasonic S/M series before you even think of plugging the 970. Since you have a CX series from Seasonic, it means it is close to 3 years old. With age, PSUs degrade and they can no longer output their rated wattage. My bet is that your CX won't be able to go beyond 300W now from 3.3V, 5V and 12V rails combined.
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Shneiky

Shneiky

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Go with the Seasonic S/M series before you even think of plugging the 970. Since you have a CX series from Seasonic, it means it is close to 3 years old. With age, PSUs degrade and they can no longer output their rated wattage. My bet is that your CX won't be able to go beyond 300W now from 3.3V, 5V and 12V rails combined.
 
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SixPotBelly

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Ah, the current CXs (eg CX430 etc) may be from Channelwell but the old CX400W was definitely from Seasonic! It's a good quality PSU, but is it powerful enough for the 970?
 
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SixPotBelly

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Thanks. You make a good point about degradation. I hadn't thought of that.

 
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SixPotBelly

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Have been researching PSU ageing this morning. There was an interesting thread over on Jonnyguru. Consensus there is a PSU with quality caps wouldn't age particularly, at least not in the handful of years we're talking about. I'm not saying they're necessarily correct, but let's say the effects are debatable.

So let's rule ageing out by rephrasing my question: Would a quality PSU with 30A (360W) available on the 12V rail be insufficient for my system?
 
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Shneiky

Shneiky

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There is constant power consumption and peak power consumption. Peak power consumption is fractions of a second spike in the power draw. All-in-all, I would strongly advise to go with at least 36A on the V12.

All PSUs age. Some can go as far as 50% of their initial wattage in 3 years. Quality PSUs also age, but in the range of 10-20% in 3 to 5 or more years, depending on the PSU.

On a side note - even though it was build by Seasonic - the CX is still a budged offering. The caps over there are nowhere near the quality of a descent PSU. And the new CX is even worse.
 
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SixPotBelly

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Sep 23, 2014
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Decision made. I've cancelled my order for the 970. I'm going to wait and see what performance and pricing is like for next month's GTX 960. The reference design for that has only a single 6-peg connector, indicating an (even) lower power requirement. Coming from an HD7750, I'm sure it would still bow me away, and I have every confidence it would be fine with my existing PSU.

But if it's poorly reviewed when released (unlikely, I would have thought), or over-priced (who knows), I can still get a 970 + 520W PSU combo then.
 
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