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Is my math correct?

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November 26, 2012 2:57:03 PM

Hi all. I've read most of the power supply guides on Tom's, but I still don't quite understand how to make everything work. Just wanted to make sure everything I was doing was right.

Right now, I'm sitting on a (hopefully) gaming PC that looks something like this:

Antec Case: http://www.newegg.com/Product/Product.aspx?Item=N82E168... - 1x 120mm Fan, 2x 120mm LED Fan, 1x 200mm Fan

RAM: http://www.newegg.com/Product/Product.aspx?Item=N82E168... 2x 4GB Corsair DDR3 1600 sticks

GPU: http://www.newegg.com/Product/Product.aspx?Item=N82E168... Nvidia GTX 650

CPU: http://www.newegg.com/Product/Product.aspx?Item=N82E168... Intel i5 2.9GHz

Added to that, I have two external HD's, one portable, one not, a PCi IDE card for wireless, and a single internal HDD (7200 RPM).

The PSU calculator says, if I did it correctly, that I require a minimum of 246W with a recommended of 300W, so I was thinking of going for the recommended Antec ea-380D http://www.newegg.com/Product/Product.aspx?Item=N82E168...


However, I also then realized that not only minimum wattage, I have to consider the Amperage of the PSU so...

My GPU says it requires a minimum of a 400 Watt power supply. Not sure if this is the number I should be using, but I don't have any other number so I'll take 400 -> 400/12 = some 33A. I'll add some 15A for my other stuff, and 5A for a safety margin, so I should be looking at some 55A for a PSU, correct? Or did I do something wrong...
The Antec PSU says it can give a total of 336W -> so that means its total amperage for its 12V rails are 28A, which seems to be nowhere near what I require so...

Going backwards, 55A seems to be 55A * 12 = 660W output on the 12V rails, so if I get http://www.newegg.com/Product/Product.aspx?Item=N82E168..., which has a combined output of 636W on the 12V rails, I should be fine... Right?

Is my math correct? Or am I overthinking things/did something wrong somewhere. Please help!

More about : math correct

a b ) Power supply
November 26, 2012 3:06:09 PM

you will need a 500-550w psu
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a b ) Power supply
November 26, 2012 3:07:48 PM

Well u are a bit wrong :p 

Gtx 650 consumes 64W

Cpu 95 W
16W Ram
15W Hdd
25W Dvd

=215W

So a Antec Vp 450 Is more than enough for this build.

64W/12V=5.3 A to run the card.
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a b ) Power supply
November 26, 2012 3:11:30 PM

go for a good 500W, and it'll do you proud should you want to upgrade your gpu.
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a b ) Power supply
November 26, 2012 3:14:20 PM

You could go for a 450W PSU, if it's a good one. But to leave room for a graphics card upgrade down the line, I'd recommend a 500-550W PSU too.
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a c 137 ) Power supply
November 26, 2012 3:19:13 PM

You are overthinking.

Once you get past the basic requirements for most of the components of a typical pc like yours,( perhaps 100W) it is the graphics configuration that determines the power you need.
Virtually all of that power comes from the +12v part, and it is the total +12v amperage that counts.
Cheap psu's will claim high wattage, but not deliver the watts on the +12v rails where it is needed.

Here is a handy chart that gives you the psu requirements for various graphics cards:
http://www.realhardtechx.com/index_archivos/Page362.htm

And... here is a list of psu quality tiers:
http://www.eggxpert.com/forums/thread/323050.aspx

A simple way to size a psu is to buy one that has sufficient 6 or 8 pin pci-e connectors for your graphics card.

The Antec earthwatts 380w unit will be fine for your GTX650.

If you want, it would not be wrong to overprovision the psu a bit.
I might look at a 600-650W unit.
A psu will consume only the power demanded of it, regardless of it's maximum capability.
A psu will operate more efficiently and quietly in the middle third of it's range.
A stronger psu will allow you to upgrade to a very strong graphics card such as the GTX680.

If you want the best, look at this great sale on a Seasonic X650 gold rated modular psu @$89:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

A very good unit would be the Corsair 650TX unit @$50 after rebate:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

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November 26, 2012 5:42:24 PM

Ah many thanks to everyone for their replies. I see where I went wrong in the Amperage calculation, though that does make me wonder...

How do I figure out the wattage that my GPU consumes? Is it on a chart somewhere or is there some other way of figuring things out?
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a b ) Power supply
November 26, 2012 5:45:37 PM

chikitani said:
Ah many thanks to everyone for their replies. I see where I went wrong in the Amperage calculation, though that does make me wonder...

How do I figure out the wattage that my GPU consumes? Is it on a chart somewhere or is there some other way of figuring things out?

You can check reviews, or look at detailed spec sheets (the power target or TDP, NOT the PSU wattage they "require").
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a b ) Power supply
November 26, 2012 6:12:14 PM

chikitani said:
Ah many thanks to everyone for their replies. I see where I went wrong in the Amperage calculation, though that does make me wonder...

How do I figure out the wattage that my GPU consumes? Is it on a chart somewhere or is there some other way of figuring things out?


I just made a little calc for your system wattage and there i included GPU wattage.

Bur here is the best link

http://mark.zoomcities.com/images/gfx/GFXpowerchartbybr...

The most accurate Gpu wattage.
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a c 137 ) Power supply
November 26, 2012 6:15:42 PM

chikitani said:
Ah many thanks to everyone for their replies. I see where I went wrong in the Amperage calculation, though that does make me wonder...

How do I figure out the wattage that my GPU consumes? Is it on a chart somewhere or is there some other way of figuring things out?


A pci-e motherboard slot will power many graphics cards by itself.
It can consume up to 75w(or 75w/12v) or 6.25W @12v.
Each 6 pin pci-e power connector that your card needs can consume up to another 75w.
Each 8 pin pci-e power connector can deliver up to 150W
If you allow for all of these "up to's" you will have an idea of the maximum power draw of your card.
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