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I think I know the answer to my own question, but looking for some advice on a PSU. I'm putting together my first rig, going to be going the skylake route and plan to add a GTX 970 of some description down the line. I have got a 650W PSU, will this be enough or would a 750W be a better fit?

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When choosing a power supply, wattage is important but don't base your purchase decision solely on that. You want something from a reputable brand that will provide high levels of current on each rail; there's a lot of nasty cheap PSU's out there (many of them with high quoted wattages and gold cases, that tend to die within 12 months) but you'd be better with something having a slightly lower wattage but a good name. Personally, I use Corsair in my the majority of my builds.

 

If you can afford it, modular PSUs provide much better cable management (and thus cooling air flow).

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When choosing a power supply, wattage is important but don't base your purchase decision solely on that. You want something from a reputable brand that will provide high levels of current on each rail; there's a lot of nasty cheap PSU's out there (many of them with high quoted wattages and gold cases, that tend to die within 12 months) but you'd be better with something having a slightly lower wattage but a good name. Personally, I use Corsair in my the majority of my builds.

 

If you can afford it, modular PSUs provide much better cable management (and thus cooling air flow).

 

+1. Cheap PSU is nothing but trouble.

And agree on corsairs. Got a RM850X now and love it. Middle class but good reviews on it.

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As mentioned above, it's not just watts, it's about quality.  You can buy a cheap 650 watt PSU that will quickly fail and maybe fry the motherboard and anything mounted to the motherboard or you can spend some money and get a quality PSU that will be reliable for many, many years.  As for wattage, I think for the majority of us the days of needed a 1000 watt PSU are gone.  Newer CPU's and graphics cards perform better while consuming far less energy.  These days, 650 watts is overkill for a huge number of systems.

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For the GTX 970 I recall Nvidia recommend 500 watts and 28 amps on the 12V rail.

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How much safety margin is built into that PSU calculator, or what amount of 'over-engineering' would be appropriate for a build?

 

I'D hate to cut it too fine and cause strain and maybe premature failure when a bit of margin could buy me a more reliable system. Or are today's supplies engineered to comfortably operate at their full rated capacity 24/7 for years without strain?

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How much safety margin is built into that PSU calculator, or what amount of 'over-engineering' would be appropriate for a build?

 

I'D hate to cut it too fine and cause strain and maybe premature failure when a bit of margin could buy me a more reliable system. Or are today's supplies engineered to comfortably operate at their full rated capacity 24/7 for years without strain?

As a rule of thumb [and it is only a rule of thumb] if you double the requirements of your graphics card you have a fair margin. That should put you at 50-60% load or somewhat higher depending on the kit you have installed, in essence in the most efficient range of the PSU. PSU's tend to be at their most efficient at 50% of max load. Having said that, many modern PSU's are pretty efficient at even higher loads.

 

So if your graphics card requires 300 Watts, a 600 - 650 watt PSU won't be far out... As I said though, that's just a rough rule of thumb to give you an idea of the efficiency range you fall into. In reality you also need to consider the other kit you have installed in your system and requirements for future expansion.

 

But yes, the PSU calculators are pretty accurate, in fact some would say a tad over, depending on the calculator. This applies to a quality brand though, dodgy brands don't perform anything like the claims and are built with low quality components.

 

The calculators include a factor for capacitor wear, so if you intend to run your system 24/7 and for many years it's worth adjusting that factor accordingly.

 

It's also worth rembering that 100 watts extra is pretty minimal in terms of cost, so given that none of us can predict future requirements accurately, I usually end up over specifying to a degree.

 

This is a nice calculator...

 

http://outervision.com/power-supply-calculator

 

It's worth considering multi-rail and single rail too. No difference in performance, but multi-rail PSU's are less likely to cock up other components in your system in scenarios like resistive loads.

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Thanks Martin. Your advise is pretty consistent with my gut. In my situation, it's not the cost of an extra 100W, but rather will my existing system/PSU tolerate a move from a gtx 680 to a gtx 980 ti. The calculator suggested 629W PSU if I ran with a 980ti 24/7. I have a Corsair 750W single rail PSU. Seems adequate but I am more comfortable when I know my PSU isn't going to break into a sweat.

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Thanks Martin. Your advise is pretty consistent with my gut. In my situation, it's not the cost of an extra 100W, but rather will my existing system/PSU tolerate a move from a gtx 680 to a gtx 980 ti. The calculator suggested 629W PSU if I ran with a 980ti 24/7. I have a Corsair 750W single rail PSU. Seems adequate but I am more comfortable when I know my PSU isn't going to break into a sweat.

 

I ran 970GTX with a Devil's Canyon clocked at 4.7GHz on a 750 and was ok but it did get warmer on load so I switched it to a 850 and now temps are in check. 980 is even bigger so take that in mind.

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Thanks Martin. Your advise is pretty consistent with my gut. In my situation, it's not the cost of an extra 100W, but rather will my existing system/PSU tolerate a move from a gtx 680 to a gtx 980 ti. The calculator suggested 629W PSU if I ran with a 980ti 24/7. I have a Corsair 750W single rail PSU. Seems adequate but I am more comfortable when I know my PSU isn't going to break into a sweat.

I always enter into the calculators what I anticipate I will upgrade to in the future, rather than what I run now.

 

Interestingly, the "I" versions of the Corsair PSU's, can be switched to multi-rail or single rail in the software. I'd definitely opt for multi-rail, especially for a high wattage PSU.

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650 is the minimum that I would personally go for, 750 or 850 being preferred. I originally went for a rm750 when I built my new system last month. A day later, newegg ran a sale on the EVGA 850W Platinum for 115 and I snatched it up. I have a very efficient PSU that has more than enough power now and later if I decide to go to an SLI set up and it also carries a 10 year warranty.

 

The Rm750 was a good psu for the few days that I had it and was dead silent, as is my EVGA. Both get my vote.

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I ran 970GTX with a Devil's Canyon clocked at 4.7GHz on a 750 and was ok but it did get warmer on load so I switched it to a 850 and now temps are in check. 980 is even bigger so take that in mind.

That surprises me to be honest Paul. 750 watts should be ample. Was it a dodgy make?

 

 

650 is the minimum that I would personally go for, 750 or 850 being preferred. I originally went for a rm750 when I built my new system last month. A day later, newegg ran a sale on the EVGA 850W Platinum for 115 and I snatched it up. I have a very efficient PSU that has more than enough power now and later if I decide to go to an SLI set up and it also carries a 10 year warranty.

 

The Rm750 was a good psu for the few days that I had it and was dead silent, as is my EVGA. Both get my vote.

Fantastic warranty on EVGA PSU's! That tells me they are confident in regard to the quality of their products. I went for Enermax Platimax, 5 year warranty.

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That surprises me to be honest Paul. 750 watts should be ample. Was it a dodgy make?

 

 

Corsair platinum just don't remember the exact model.

What I found out is that you need some overhead for safe operation plus it puts less strain on components.

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Corsair platinum just don't remember the exact model.

What I found out is that you need some overhead for safe operation plus it puts less strain on components.

Well yes, but 750 Watts should have been loads of overhead. The PSU shouldn't have been taxed at all.

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I'd be curious as to what was getting warmer, and by how much.

 

Cheers!

 

Luke

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