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Question About 4 Pin Molex -> PCIE 6 Pin & Multiple GPUs

post #1 of 11
Thread Starter 
My basic question is this. Power supplies only come with certain number of PCIE 6 pin power connectors. But we can use 4 pin molex -> 6 pin PCIE (either 1x 4 pin molex or 2x variants) to add more.

4 pin molex draws from the same rail as the 6 pin PCIE right? The 12v rail? I'm pretty sure the answer is yes but I wanted to be sure.

I'm about to add a 4th GPU to a rig of mine and am working some things out first. Almost all the power draw is from the GPUs. ATM it pulls a bit less than 550W at the wall. Given the PSU is 87% efficient at minimum, the system is pulling 478.5W from the PSU. My PSU has 4 12v rails at 34A each and provides 732W via the 12v rail. I'm currently using the 4 built in 6 pin PCIE connectors and 2x 4 pin molex -> 6 pin PCIE. My plan is to add 2 more molex -> PCIE.

Assuming my math and assumptions are correct, I shouldn't have a problem adding a 4th card. I just wanted a little input on this from this knowledgeable community.

+rep for any help
post #2 of 11
Quote:
Originally Posted by Dezixn View Post
My basic question is this. Power supplies only come with certain number of PCIE 6 pin power connectors. But we can use 4 pin molex -> 6 pin PCIE (either 1x 4 pin molex or 2x variants) to add more.

4 pin molex draws from the same rail as the 6 pin PCIE right? The 12v rail? I'm pretty sure the answer is yes but I wanted to be sure.

I'm about to add a 4th GPU to a rig of mine and am working some things out first. Almost all the power draw is from the GPUs. ATM it pulls a bit less than 550W at the wall. Given the PSU is 87% efficient at minimum, the system is pulling 478.5W from the PSU. My PSU has 4 12v rails at 34A each and provides 732W via the 12v rail. I'm currently using the 4 built in 6 pin PCIE connectors and 2x 4 pin molex -> 6 pin PCIE. My plan is to add 2 more molex -> PCIE.

Assuming my math and assumptions are correct, I shouldn't have a problem adding a 4th card. I just wanted a little input on this from this knowledgeable community.

+rep for any help
Why don't you just tell us the make and model of the power supply in there and what cards you have / plan on adding.
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post #3 of 11
The PSU experts are going to need details in order to help you...
post #4 of 11
Thread Starter 
Quote:
Originally Posted by railfan844 View Post
Why don't you just tell us the make and model of the power supply in there and what cards you have / plan on adding.
Quote:
Originally Posted by Majin SSJ Eric View Post
The PSU experts are going to need details in order to help you...
Well I forgot to mention the cards... But I did give all the relevant details about the PSU.

They are 5830's. PSU is http://www.newegg.com/Product/Produc...3&Tpk=rx-850ae
post #5 of 11
OP, I wouldn't add any more cards to your setup. 850w is already pushing the limits for 3, especially with a brand like Raidmax.
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post #6 of 11
Thread Starter 
Quote:
Originally Posted by railfan844 View Post
OP, I wouldn't add any more cards to your setup. 850w is already pushing the limits for 3, especially with a brand like Raidmax.
I guess I'm not understanding how I'm pushing the limits of the PSU if it is only drawing 550W at the wall and even less from the actual PSU.
Even with the additional card I would well under the total wattage limit and under the 12v wattage limit of 732W.
What am I missing here?
The cards are doing work similar to folding so the power consumption is constant and steady.
post #7 of 11
Quote:
Originally Posted by Dezixn View Post
I guess I'm not understanding how I'm pushing the limits of the PSU if it is only drawing 550W at the wall and even less from the actual PSU.
Even with the additional card I would well under the total wattage limit and under the 12v wattage limit of 732W.
What am I missing here?
The cards are doing work similar to folding so the power consumption is constant and steady.
What I mean is it's just too sketchy. Sure, the math works out, but keep in mind this is a Raidmax power supply. Who knows how much it will actually supply before it blows something.

There's no reason why you couldn't do it according to the math, but I strongly discourage you from doing so.
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post #8 of 11
Question is were these Wattage reading taken at MAX load of the CPU and GPU, Because i seriously doubt it... I mean yeah you could add another card to the system but im with railfan here, I strongly advise against it untill i have more info on the PSU OEM. The Rated wattage means less than the sticker its printed on with some PSUs so if it goes pop it may take your whole rig with it.
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post #9 of 11
Thread Starter 
Quote:
Originally Posted by railfan844 View Post
What I mean is it's just too sketchy. Sure, the math works out, but keep in mind this is a Raidmax power supply. Who knows how much it will actually supply before it blows something.

There's no reason why you couldn't do it according to the math, but I strongly discourage you from doing so.
I would totally agree with you if I was approaching or going over like 90% usage of the PSU. But even with the 4th card I would be at about 75% of the PSU's maximum capacity. Is 75% unreasonable?

I never expected to pull 850W from this PSU but ~637.5W sounds reasonable.

Quote:
Originally Posted by jammo2k5 View Post
Question is were these Wattage reading taken at MAX load of the CPU and GPU, Because i seriously doubt it... I mean yeah you could add another card to the system but im with railfan here, I strongly advise against it untill i have more info on the PSU OEM. The Rated wattage means less than the sticker its printed on with some PSUs so if it goes pop it may take your whole rig with it.
The 550W reading is taken at maximum load. Every GPU is maxed and the CPU. And that's only at the wall.
post #10 of 11
Molex has +5V and +12V as well as ground, but the adapter to PCIe obviously just uses the +12V and ground leads.

You should have no problem adding the 4th GPU. However, don't expect a less-than-enthusiast power supply to last years and years with a heavy sustained load. Unfortunately the warranty is only 2 years.

Actually, you're drawing a little more DC power than you may expect, because Raidmax is apparently a bunch of lying ****heads with regards to this unit:

http://www.overclock.net/14017307-post6.html
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