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 Post subject: Re: Read Through This and wanted to do similar
PostPosted: Sat Feb 14, 2009 6:46 am 
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jimc52 wrote:
I just read through these posts. Ha, its funny, I was wanting to know the same thing...having two PSU's in a computer.

I don't give one rat's rump about redundancy. So that kills that purpose.

I will be very clear here about what I am thinking I want to do with two
PSU's. I act as contributor to a number of PC forums assisting people building new computers or doing upgrading. Of course, the question comes in, how many watts do I need to purchase for a PSU? Rather than pay nearly $400 for a 1.2 Kw PSU, you could theoretically use two 650 watt PSU's which cost $70 each and maybe achieve the same thing but spend less than half the money. The people who usually want to know this question are people who are running SLI or Crossfire, usually dual cards, but sometimes triple and in rare cases quadruple cards.

I am just going to bone here for a minute gentlemen, and I am going to take like a 9800 GTX+ Overclocked card, i.e., and I am going to say at maximum game play like in Crysis, you are going to have to supply up to 250 Watts per card. So really, I need 500 working watts to run those two cards alone. Even gamers want to save money on their new builds, putting the money into another graphics card rather than into a big stinking whopping PSU. Hey, every penny counts!

So let me be blatantly frank here:

PSU1 supplies the motherboard with power and perhaps some of the IDE or SATA devices.

PSU2 supplies just the video cards and maybe IDE or SATA devices.

Now that should be clear enough. I see the jumper solution here so that one of the PSU's turns on or stays on all the time while the other one is ganged to the ON/OFF button. Of course, if they are both switching PSU's, you could manually turn them both off so that one of them is not running all the time. After all, what is the big sweat about flipping a switch? You have to bend over for 2 seconds and use your finger????

Now, let's take the scenario that BOTH PSU's are supplying power to the SATA and/OR IDE devices - will there be a conflict? Is this a dangerous thing to do considering there is probably some difference, even a 0.1V difference between to psu's?

What do you guys think? Hope I have been perfectly clear here and I don't want to mince words. Will two psu's work safely in tandem, together without blowing up the computer? Thanks,

First and before all else welcome to the MPC Forums!

Now I am not 100% sure about this but my read and my take on the overall power dissipation for the graphics cards you mention, the nVidia 9800 GTX seires OC is that combined in a SLI configuration would be about 228 Watts. That is the combined power for both cards. I base that on the information found here:

http://archive.atomicmpc.com.au/forums. ... c=7&t=9354

Though I have not personally tested every configuration for every card they cover on the few I did test I found their numbers to be pretty accurate. Either way, matters not for where we are going with this.

When it comes to using a pair of power supplies my thought when they will be configured to serve a multi role as in each used for different applications is a configuration where one PSU is slaved to the other. Meaning we allow the primary system PSU to turn on and off the secondary PSU when it is turned on and off. This is very easily done with the addition of a simple SPST (Single Pole Single Throw) relay that can be had from any Radio Shack or basic electronics parts house. This would allow the units to power up and power down together and from a cost point literally amounts to a few bucks.

Overall if we look at a system running intense GPU applications with today's graphics cards we don't have to look far to see the GPU is likely the main power consumer in the system. The motherboard & CPU draw little. Matter of fact a small PSU could be dedicated to the motherboard, drives and etc. while a larger PSU dedicated to the GPU(s).

The main problem we face with using a pair of PSUs in a system case originally designed for a single PSU is more a matter of logistics. Like how to fit 10 pounds of stuff in a 5 pound bag. :)

<EDIT> & damnit Quake you are quick! :lol: </EDIT>


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