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You're Gonna be OK

Firecrackers
  • 66 months ago

https://www.youtube.com/watch?v=55fKOG8C9qc

Here we have a guy using a 620W power supply with 970s running in SLI (Factory OC'ed) running at around 96% usage each card. His TDP is around 530-540. I believe these watts are being pulled from the wall.

This reminded me that a lot of people believe that a good 1000W Power supply will only give about 800-900W (80-90% efficiency) which is simply not the case. A 1000W (good one) will deliver 1000W to your computer, but the draw from the wall depends on the efficiency. That means a 100% Efficiency would draw 1000W, while a 50% would take 2000W from the wall (excuse my math atm, but the point is the PSU will deliver its rating).

All this post is saying is that if you are worried about spending money on a new power supply in certain cases, you don't have to. You really only have to upgrade if you are throwing in a 4-way SLI system with a huge rad/pump config.

Edit: another guy using SLI 970s and switched to 980s: https://www.youtube.com/watch?v=mdBIZb6VJ_w with a 600w PSU. His PSU was a very good one, but it still shows that an upgrade won't be a problem. (Though I would not recommend buying a 600w PSU when buying a setup for Dual 980s, perhaps a bit bigger).

Comments

  • 66 months ago
  • 2 points

If people would actually read the OP, they'd see that basically he's saying what you are saying; there's no disagreement here. The headroom you need for safe operation is something like 20% on a good PSU. Some people think it's higher than that, but they're objectively wrong.

Where things get tricky is at the higher end (1000W PSUs, for example). 20% of that is 200W - do you really need to undershoot 1000W by a whole 200W? Does it really scale linearly? That's a hard pill to swallow. I've never needed to build a system with that much power, but personally, my guess is that by the time you get up into that range, your theoretical max draw will actually be the real-world draw so few times that it might as well be negligible; you could probably get a system that draws right up to 1000W theoretical max and never break a 1000W PSU in the course of normal operation.

  • 66 months ago
  • 1 point

So dual 970's will be fine with an evga 750w gold psu? If so... :>

  • 66 months ago
  • 1 point

It would work... And its the lowest I'd go for that setup

  • 66 months ago
  • 1 point

No single solution to this one other than going with best practices. I'd never allow any workstations to run at 80% loads on PSU, let alone 90% (3-4 yrs of hardware life).

My method: calculate entire PC Wattage and look for Gold/Platinum PSU. Load? 50-60% considering better power delivery and noise. E.g.,:

Heavy Z97 workstation build with 550W full system load: 1000W platinum/gold PSU max.

  • 66 months ago
  • 1 point

not a good practice. A pair of 970s use about 300w (roughly the same as one 290X), and use up to about 500-550w of power at max, so 650w is the absolute lowest I would go.

  • 66 months ago
  • 1 point

And that's assuming the cpu and gpus are all stock and not over clocked

  • 66 months ago
  • 1 point

True. Generally 750w is the go-to amount for the 900 series cards, like 850w was for 700 series.

  • 66 months ago
  • 1 point

Ya, 750w can be considered safe for the majority of builds like this one with a bit of oc

  • 66 months ago
  • 1 point

Well I know a friend using a 680 on a 420 Watt power supply.

  • 66 months ago
  • 1 point

Yeah this is a big misconception. A good PSU rated at 1000W will deliver 1000W, the efficiency just dictates how much power it will pull from the wall. An RM1000 will pull 1350W or so from the wall to deliver 1000W to components.

However, there is still reason to go for a higher wattage PSU. In the instance of Corsair PSUs again, the fan doesn't spin under 40% or less load on their RM, HXi, and AXi series. <sidenote>This isn't just a Corsair thing. I realize other brands have it.</sidenote> If you have a 400W expected wattage, the fan will spin up a lot on the RM450, but only spin up when you're pushing it hard on an RM650. Also it's best to add some buffer for overclocking. In an interview with JohnnyGuru on Corsair's YouTube channel, he recommended adding the TDP of your CPU and GPU, adding 150W for fans, drives, etc., and adding 100+W for overclocking, then adding 10-20% for a bunch of different reasons, including the fan thing.

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