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Just To Make Sure....Another Amperage Question....

Last response: in Graphics & Displays
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March 2, 2010 3:03:53 AM

So I understand....dead horse here in many ways...but just for my own clarity (and sanity).

The Radeon HD5850 requires 75w per PCI-E connection.
It is assumed you understand it belongs in the 12v Rail.

75w / 12v = 6.25a

So with:

2 PCI-E Connections to 1 HD5850 that means

6.25a x 2 (For both connections to the one HD5850) = 12.5amps (150w).

01.) So one HD-5850 only really consumes (Or at least is required by ATI) to need 12.5 amps?
02.) If the aforementioned is true, then why are there people saying it needs 26 amps (Some saying as high as 40a), is this just a peak thing?

My whole reason for this question is I have the 18a/12v per rail kinda setup going and putting two of these rails that both supply 18a per into HD5850 would give me 36a....more than enough right?

If I'm understanding this correctly, thank God, I will stop beating this horse, otherwise shoot me.

More about : make amperage question

a b U Graphics card
March 2, 2010 3:18:10 AM

You forgot that the PCIE slot provides 75w's aswell, so the card has a potential max 3x75w = 225w
So 6.25 amps (per 75w like done above) x 3 = 18.75 amps max the card will draw.
http://www.tomshardware.com/reviews/radeon-hd-5850,2433...
Scroll down and look at the chart. 5850 max 151w under load. Note the 5870 with 188w load with the same two 6pins.
edit: it looks like most other reviews say the 5850 should be drawing closer to 170w.
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a b U Graphics card
March 2, 2010 3:24:50 AM

You may not have 36 amps all told, but you will have 18 amps per rail, when needed. You wont need 36 amps, anyways, unless you have alot of HDDs,memory,cd, and a heavy oc.
The 18amps is what youl have available per rail, no more than that.
The 5850 is set to use up to 150 watts, tho it will never use that much.
They dont have 50 watt connects going to the mobo or gfx cards, so its 75+75 only, even if it only needs 85 watts.
The mobo brings 75, a 6 pin brings 75 watts.
All told, including you cpu, all things being 12V on your system, is what those higher numbers are for, the entire system, not just the card, as no card needs 36amps to run, thats for the whole system
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March 2, 2010 3:56:36 AM

So onto question two....were these random comments (not from this site), saying that "I heard so and so from so and so say the HD5850 needs 36amps" pretty much a.) bs and b.) probably an overview of an entire system and not so much the graphics card alone.

I just want to understand it piece by piece....I know that the graphics card and cpu and everything else will be sharing wattage if they are on the same rail especially, I just was looking to know individually for the graphics card itself, but you did answer my question and I completely overlooked the card pulling the 75w from the mobo. Expanding on that:

The mobo delivers wattage in a 12v system as well?
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Best solution

a b U Graphics card
March 2, 2010 4:28:53 AM

Well, 36 amps is 432 watts, the 5850 only has 150 watts going to it, of which it never use all of it, so my guess its for the entire system.
Mobo is 12 watts from the PCI slot at 75watts available.
Then you have the 6pin, which is also 75 watts.
Again, the card will never use 150 watts, they always cover power needed by a bit, say 20 watts or so minimum, so if it got to say 140 watts, theyd make sure there was more power going to the card, and give it another 6 pin connect. Capeche?
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a b U Graphics card
March 2, 2010 5:12:25 AM

I would say the 36 amps is for the whole system.

http://www.tomshardware.com/reviews/radeon-hd-5850,2433...
http://www.techspot.com/review/206-his-radeon-hd-5850/p...

both of these reviews use similar test setups:
overclocked i7 975 @ 4.0ghz / i7 965 @ 3.7 ghz
SSD / 500 gb hd
6gb ram / 6gb ram

Both setups say their setups run at 305w and 319w respectively with furmark. This means that the 5850 is running at 100% and the cpu around 10%? (not sure exactly) but you can easily add 100w's to each value simulating that the cpu is running at 100%. That would give us 405w and 419w. Throw in a good 10% buffer so that the psu dose not run at more than 90% and we get 455.5w and 460.9w, which is just above your 36 amps (432w).
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March 2, 2010 2:24:54 PM

Best answer selected by milkeater.
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a c 195 U Graphics card
March 2, 2010 7:21:15 PM

What brand/model PSU do you have? Unless it is a quality unit, the label on it could be an outright lie, or reflect peak power output, which it can only provide briefly before choking, smoking and croaking.
Antec, Corsair, Seasonic, PC Power & Cooling, and Enermax are among the better brands.
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