# Why!!!

## Recommended Posts

That's cool, thanks radodrill, I am understanding it much better now.

##### Share on other sites

Yep, you're actually going to pull more power than the machine uses since about 20% of the power is lost at full load due to heat and other inefficiencies. Thats why most say they are 80% efficient meaning they can turn 80% of the power they pull into usable juice for your PC.

##### Share on other sites

Someone should test how much more power is being pulled out of your wall outlet by one of these 1KW+ psus compared to a 500-700 watt psu.

##### Share on other sites

A good quality 1000W power supply with 80% efficiency when fully loaded will draw approximately 1250W from the mains. The other 250W is lost in the conversion from AC mains (110 or 230VAC) to DC outputs (3V3, 5.0, 12VDC, etc.) and most of it given off as heat.

Regards

Paul

##### Share on other sites

Wow, I never even considered all this before, thanks for open this thread. No wonder my electric bill has gone up.

What if you are only using a total of say a quarter of the power the psu can give and only using one 12v rail, how does that add up in way of power draw from mains?

##### Share on other sites

Looking at your signature I can make an educated guess at somewhere between 400 & 500W on average. I'm not sure what sort of power your two 8800GTS are pulling but I think you will be looking at between 500W and 620W from the mains.

Regards

Paul

##### Share on other sites

The PSU only provides as much power as the system actually draws; the power drawn from the mains is the power used by the system divided by the PSU efficiency.

Numeric example:

say the PSU has an efficiency of 80%, and the current draw on the rails is:

12V1: 30A

12V2: 25A

3.3V: 10A

5V: 10A

the total power used by the system is:

P_system = 12V * 30A + 12V * 25A + 3.3V * 10A + 5V * 10A = 743W

then:

P_mains = 743W / 80% = 928.75W

##### Share on other sites

That's an eye opener. Thanks guys.

##### Share on other sites

I think we all have Tim the tool man Taylor syndrome, more power uuugh!

I think people just want to buy that PSU that will do them for a long time no matter what they add to their rig. A 1000w good brand PSU is a great start in future proofing your rig for what may come in the next 2 years or even longer. With people adding more and more HDD's to their rigs and running 3 sometimes 4 RAID 0 setups, SLI and all sorts of bells and whistles, it makes sense to be a boy scout about your power and always be prepared..lol

##### Share on other sites
The PSU only provides as much power as the system actually draws; the power drawn from the mains is the power used by the system divided by the PSU efficiency.

Numeric example:

say the PSU has an efficiency of 80%, and the current draw on the rails is:

12V1: 30A

12V2: 25A

3.3V: 10A

5V: 10A

the total power used by the system is:

P_system = 12V * 30A + 12V * 25A + 3.3V * 10A + 5V * 10A = 743W

then:

P_mains = 743W / 80% = 928.75W

So with my GameXStream 700:

12V[1-4]: 18A ea

3.3V: 36A

5V: 30A

P_system = (12V * 18A) * 4 + 3.3V * 36A + 5V * 30A = 1132W

P_mains = 1132W / 80% = 1416W

Whats wrong with this picture?

##### Share on other sites
So with my GameXStream 700:

12V[1-4]: 18A ea

3.3V: 36A

5V: 30A

P_system = (12V * 18A) * 4 + 3.3V * 36A + 5V * 30A = 1132W

P_mains = 1132W / 80% = 1416W

Whats wrong with this picture?

There is a max on the different circuits. See

http://www.ocztechnology.com/drivers/GameX..._700W_chart.jpg

The 4 - 18 A can only output 680 W total, but only when the total output of the power supply doesn't go above 700 W. Actually is only rated at 700 W, can probably put out more than that but will be stressed, but not 1132 W.

##### Share on other sites

huh... Well, it powers my system, and only uses < 260w at full load (CPU and gfx card). Good enough for me!

## Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

×   Pasted as rich text.   Paste as plain text instead

Only 75 emoji are allowed.