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Is there a rule of thumb for power supply requirements in SLI/Crossfire Builds?


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#1 Me45805

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Posted 21 March 2015 - 09:49 AM

I am always looking at potential upgrades and lining up builds for others.  I have never had to do SLI/Crossfire yet, but just wanted to see if there was any "good practice" or "rule of thumb" tips.

 

For the sake of example:

The R9 290X needs a 750W minimum PSU by itself (I am aware this should be overshot by 50-100W to have overhead for the rest of the build).  So for one card I would get a 850W PSU rated 80 Plus Bronze or better.  What would 2 cards require?  How about 3 or 4?

Interesting side note, both the 280X and 290X require a 750W PSU.  Would their Crossfire requirements be the same in this case?

 

The GTX 970 needs a 500W PSU by itself, so I would get a 600W 80 Plus Bronze rated or better PSU.  What about running 2, 3, or 4 of these cards together?

 

Is there general rule of thumb, like increases by X percent for each card added, or add another 100W for each additional card?

 

 

Thanks in advance!



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#2 Serpius

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Posted 21 March 2015 - 05:44 PM

Me45,

 

Running two Radeon R9 290x will require 220 watts EACH. That will total to 440 watts.

 

Then you'll need around 250 watts for the rest of your computer components bring the total wattage to around 690 watts.

 

Total wattage for the power supply unit should be 750 watts or greater.

 

Here is my recommended power supply unit:

 

 
Total: $101.08
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-21 18:44 EDT-0400


#3 TheN00bBuilder

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Posted 25 March 2015 - 09:34 AM

Eh, I wouldn't want to cut that close, especially with a Bronze PSU. This EVGA Supernova is only $29 more, and you get modularity.

 

PCPartPicker part list / Price breakdown by merchant

Power Supply: EVGA 850W 80+ Gold Certified Fully-Modular ATX Power Supply  ($128.99 @ SuperBiiz)
Total: $128.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-25 10:33 EDT-0400


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#4 Serpius

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Posted 25 March 2015 - 01:53 PM

Eh, I wouldn't want to cut that close, especially with a Bronze PSU. This EVGA Supernova is only $29 more, and you get modularity.

 

PCPartPicker part list / Price breakdown by merchant

Power Supply: EVGA 850W 80+ Gold Certified Fully-Modular ATX Power Supply  ($128.99 @ SuperBiiz)
Total: $128.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-25 10:33 EDT-0400

The N00b,

 

That's a good power supply unit.

 

It's entirely up to the end user which option they want to go with.

 

I was a bit generous with my statement of '250 watts for the rest of the computer'.

 

There's the other side of the equation... Bronze versus Gold versus Platinum versus Titanium flavors of PSUs.

 

If you read up on this article shown in this link:

 

http://www.hardwaresecrets.com/article/Understanding-the-80-Plus-Certification/742

 

If you note on page 3 of that article, you'll see comparisons between the certifications.

 

For the average Jane and Joe... the 80+ Bronze would be sufficient for their daily use. Will that same person save money on their electric bill if they had a 80+ Platinum PSU? Yea, a little... but the differences in the prices between the Bronze and Platinum certifications in most cases are far apart enough that it would be hard to justify to Jane and Joe to pay more money for a 80+ Platinum PSU where the 80+ Bronze would be suitable for their needs.

 

When I do builds for my clients... I look at the "big picture" in terms what the client is going to use it for.

 

If that client is a heavy gamer and uses the computer literally 24 hours a day... then, yes, a 80+ Gold or Platinum would make sense for them.

 

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#5 jonuk76

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Posted 26 March 2015 - 10:55 PM

Those cards potentially consume more power than 220w each.  More like 330w in standard trim, and more for overclocked editions. http://www.techpowerup.com/reviews/MSI/R9_290X_Lightning/22.html
 
The 750w "requirement" AMD quote is not the card power consumption, but is a guess at a minimum power supply rating based on the typical system they are likely to be used in.  It probably allows for headroom and consumers buying cheaper PSU's etc.
 
My personal "rule of thumb" would be work out what you need and add very roughly 50%.  This is conservative but allows a certain amount of headroom/margin of safety and should have the peak power requirement in the middle of the efficiency curve.. The other ones are don't buy a cheap PSU in this kind of setup, and make sure the PSU can provide as close to 100% of it's rated output at 12v as possible. 

 

Say this for example has 2 x R9-290X's and according to PCPartpicker (reasonably accurate I think) needs 873w. In this case I'd go for a 1200w+ PSU.  They are expensive but in a costly system like that,  it's not worth skimping on.


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#6 Me45805

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Posted 27 March 2015 - 12:36 PM

Thank you all for the replies.  The cards I listed was literally just for theory or example.  I know the rule of thumb to get a PSU that is 50-100W greater than the single card requirement.  Is there a similar rule of thumb for Crossfire/SLI?

 

I know of power supply calculators such as http://www.extreme.outervision.com/psucalculatorlite.jsp but I was looking more for just a guideline or something like that.

 

Once again, is there a percentage or "X" watt increase for Crossfire/SLI of 2 or more cards?  I know every card is going to be unique so research is key, but I'm just looking for that starting point.

 

Let's say a card requires a 500W PSU, so get a 550-600W PSU for one card.  Without any additional information could there be a starting point assumption on what Crossfire/SLI of 2 or more cards would require?  What if it was a 750W requirement?  I would assume that a larger card would require more power per card in a Crossfire/SLI setup, or a higher percentage or "X" watt increase.

 

Like I said, just looking for a rule of thumb to follow if it exists.  If there is not one, that's cool too.

 

Thanks again for the quick replies :)



#7 Serpius

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Posted 27 March 2015 - 02:14 PM



Thank you all for the replies.  The cards I listed was literally just for theory or example.  I know the rule of thumb to get a PSU that is 50-100W greater than the single card requirement.  Is there a similar rule of thumb for Crossfire/SLI?

 

I know of power supply calculators such as http://www.extreme.outervision.com/psucalculatorlite.jsp but I was looking more for just a guideline or something like that.

 

Once again, is there a percentage or "X" watt increase for Crossfire/SLI of 2 or more cards?  I know every card is going to be unique so research is key, but I'm just looking for that starting point.

 

Let's say a card requires a 500W PSU, so get a 550-600W PSU for one card.  Without any additional information could there be a starting point assumption on what Crossfire/SLI of 2 or more cards would require?  What if it was a 750W requirement?  I would assume that a larger card would require more power per card in a Crossfire/SLI setup, or a higher percentage or "X" watt increase.

 

Like I said, just looking for a rule of thumb to follow if it exists.  If there is not one, that's cool too.

 

Thanks again for the quick replies :)

Me458,

 

I stand by my original statement that at 750 watt or greater power supply unit is sufficient.

 

Others have stated much higher wattage... that is still in line with my statement of 750 watts or greater. 

 

I feel that my recommendation of a 850 watt PSU is sufficient for your use... regardless of the brand or type of graphic card you get.

 

If you want to "play it safe", then go with a 1,000 watt PSU. Here are 3 listed that I would feel comfortable with.

 

 
Total: $159.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-27 15:11 EDT-0400
 

 
Total: $174.99
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-27 15:13 EDT-0400
 

 
Total: $224.98
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-27 15:13 EDT-0400


#8 Me45805

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Posted 27 March 2015 - 04:21 PM

Thanks for the reply.

 

I was looking for a rule of thumb like what exists for overshooting 50-100W for a single GPU, but apparently it does not exist.  I understand that is what you recommend for those GPU combinations, but that is not what I was looking for.  I used those for the sake of example only.  If I find a guideline/rule of thumb for Crossfire/SLI PSU requirements, I will be sure to post it.

 

I am considering this solved.  Thanks for all the responses.






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