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how do I know what size power supply I need

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  • Power Supplies
  • Computers
  • Systems
Last response: in Systems
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April 22, 2013 7:02:37 AM

This is a general question. I was wondering, how do I know what size power supply I need when building a system.

Is there a rule of thumb I can go by?

For instance, on my computer, I have 3 sata drives, 1 ssd drive, 2 cdrom, and an amd radeon hd 6950.

If I am building another machine, is there a way to guestimate what I'll need when ordering?

Thanks!

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a b ) Power supply
April 22, 2013 7:09:48 AM

Any one of a number of power supply calculators

ThermalTake
NewEgg
PCPartpicker
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April 22, 2013 7:11:08 AM

There isnt a "must" rule for power supplies but here in this link you can pick the parts in your system and see a reference list to check how much power your system can consume... according to the assumption you shall pick a slightly higher powered psu...

http://pcpartpicker.com/parts/partlist/

(today's systems usually need at least 450W power (with single gpu), this isnt peak power but stable continuous power)
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April 22, 2013 7:18:21 AM

great thanks!

I'm marking the one that has the most info on it as my answer but thanks for everyone's input.
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a c 142 ) Power supply
April 22, 2013 7:19:38 AM

You've got some good links to check out there (and there are even more calculators than those) but one thing you should be aware of when looking at the calculators... some will show you a suggest power requirement (PSU Wattage) while others will show your actual power draw. They will be two very disproportionate numbers with the suggested PSU wattages averaging almost double of the actual system power needs. This is done purposely for a few reasons but the most important (I think) is that modern PSU's tend to run most effeciently in the 50% draw range.
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April 22, 2013 7:20:52 AM

C12Friedman said:
You've got some good links to check out there (and there are even more calculators than those) but one thing you should be aware of when looking at the calculators... some will show you a suggest power requirement (PSU Wattage) while others will show your actual power draw. They will be two very disproportionate numbers with the suggested PSU wattages averaging almost double of the actual system power needs. This is done purposely for a few reasons but the most important (I think) is that modern PSU's tend to run most effeciently in the 50% draw range.


50%? that I did not know! ty!
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a c 142 ) Power supply
April 22, 2013 7:39:20 AM

It's actually a range 50% being the mean there. One other thing I should point out is some calculators are more accurate than others so use a few different ones - I've seen the addition of a 5W HDD result in a 100W increase in PSU recommendation.
You can alway list the hardware of your build here (including CPU) and I'm sure you would get (at least) a few good recommendations.
To calculate your own power needs without the calculator, for most hardware the power needs are available so you can take your specific parts and add those things which draw power; CPU, HDD's, SSD's, Ram, PCIe cards, fans, lights, etc. (calculators are easier but not as accurate)
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April 22, 2013 7:40:47 AM

It is mostly efficient in 50% power draw, yes this is the case if you are really aiming for the 80% power efficiency, etc.
This however does not say that you can not use the PSU with 80% or 100% power draw.
Note: constant 100% all the time is bad!
Adding more room while adjusting with your budget and future plan (e.g. SLI/XFire, OC, etc.) is also important.
I used the website I posted for years and I have never get problems. The thing is, if the website recommends let say 450W (not minimum), I buy 500W. So, a bit more but not much.

The next important thing for choosing PSU beside power rating is the brand. DO NOT BUY JUST ANY PSUs! Get something decent only from well-known brands such as Seasonic, Antec, Corsair, PPC, etc. (Tt, OCZ, etc. is not included)
My favorites are Corsair and Seasonic

Note:
I have a good analogy in choosing a PSU...regarding the power rating...
you having a lot more money than you need and you having not enough money to live :) 
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