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Daisy Chaining 2 PSU's (600w/750w) for quad sli?

post #1 of 11
Thread Starter 
I have 2 ultra PSU's, one 600w and the other 750w. My purpose in daisy chaining is to allow myself to be able to run 2 9800gx2's without flopping more money to get 1 single sufficient powersupply. The 600w has around 36-38 amps on the 12v rail but only has 6 pin connectors, therefore I need to buy the 6 to 8 pin connector for the first. The 750 has over 60a on the 12v rail and has one 8 pin connector and two 6 pin connectors so im good there. I planned on buying the $10 adaptor to power both power supplies and I was wondering if anyone recommended or shunned this idea at all?. Im thinking that it will be more than sufficient but Id like to get some opinions on this method just to make sure before I buy the adaptors. Any help would be appreciated. Thank You.
post #2 of 11
Just make sure you provide adequate load on both PSU's 3.3+5v rails... or else.
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post #3 of 11
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
Just make sure you provide adequate load on both PSU's 3.3+5v rails... or else.
How would I go about doing that?. Im new to this method so bare with me lol.



EDIT: Crap I just saw the sticky on running two power supplies in this forum. I guess my main concern is if the 6-8 pin adapter could cause a fire hazard being it that the 6 pin gives 75w and the 8 pin needs 125-150w.
Edited by hairston630 - 6/25/08 at 9:19am
post #4 of 11
Quote:
Originally Posted by hairston630 View Post
How would I go about doing that?. Im new to this method so bare with me lol.
Do the PSU specs tell you the minimum loads on the 3.3+5v rail?
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post #5 of 11
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
Do the PSU specs tell you the minimum loads on the 3.3+5v rail?
Just the maximum I think.

Max

Ultra x-finity 600w: +5v: 30a +3.3v: 25a

Ultra LSP 750w: +5v: 32a +3.3v: 28a
post #6 of 11
Quote:
Originally Posted by hairston630 View Post
How would I go about doing that?. Im new to this method so bare with me lol.



EDIT: Crap I just saw the sticky on running two power supplies in this forum. I guess my main concern is if the 6-8 pin adapter could cause a fire hazard being it that the 6 pin gives 75w and the 8 pin needs 125-150w.
Doesn't really matter as long as it has 18AWG cables. There is no fire hazard as 18AWG can handle much more current safely at these lengths. It is more a vDrop/resistence issue.

Quote:
Originally Posted by hairston630 View Post
Just the maximum I think.

Max

Ultra x-finity 600w: +5v: 30a +3.3v: 25a

Ultra LSP 750w: +5v: 32a +3.3v: 28a
These are older design PSUs.... you want a 1-2A load on the combined 3.3+5v rails of each. Two hard drives on each should be enough.
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post #7 of 11
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
Doesn't really matter as long as it has 18AWG cables. There is no fire hazard as 18AWG can handle much more current safely at these lengths. It is more a vDrop/resistence issue.


These are older design PSUs.... you want a 1-2A load on the combined 3.3+5v rails of each. Two hard drives on each should be enough.
So your saying that these psu's will not work with 2 9800gx2's If I daisy chain them? Or are you saying that I need something to utilize that power? (I went ahead and repped you for your help so far)
post #8 of 11
Quote:
Originally Posted by hairston630 View Post
So your saying that these psu's will not work with 2 9800gx2's If I daisy chain them? (I went ahead and repped you for your help so far)
I never said that...

Many PSUs do not perform correctly unless there is a load on the 3.3+5v rail. If you daisy chain them and use only the +12v rail from one PSU, that PSU voltage regulation's may be out of specification.


Here's my testing of two cheaper/older PSUs: http://www.overclock.net/power-suppl...balancing.html

Voltage regulation went from like 2.5% to .5% with some HDs on the +5v rail.
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post #9 of 11
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
I never said that...

Many PSUs do not perform correctly unless there is a load on the 3.3+5v rail. If you daisy chain them and use only the +12v rail from one PSU, that PSU voltage regulation's may be out of specification.


Here's my testing of two cheaper/older PSUs: http://www.overclock.net/power-suppl...balancing.html

Voltage regulation went from like 2.5% to .5% with some HDs on the +5v rail.
Ahh ok so your saying I could do the dual psu but I should connect some hardware to the second psu so that it will draw some power instead of just drawing power out of the 12v rail?...Am I understanding that right?
post #10 of 11
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