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Dual power supplies

L

Legolas

n00b
Joined
Nov 10, 2009
Messages
30
I need some PSU guidelines. I installed a XFX 5870 video card on 11/03/09 and my system run perfectly the next 20 days. I updated my BIOS to #1804 from 1605 on my ASUS P6T Deluxe m/board. I started having crashes and lock ups of mainly black screens. I tried my old 4870 video card with the same results, I had to replace my BIOS chip to get back to version 1605, I also replaced my memory all to no avail. Finally my Corsair HX1000w PSU appeared to fail and I had 2 Antec 500w on hand which I attached to my system running one to the m/board and the second to the drives and video card. My system has never run so good. With my Noctua NH-U12P CPU heat sink and 2 fans I have a screen door side on my CoolerMaster Praetorian case. As I found improved performance with my 2 500w PSUs I decided to modify my “screen door side” to allow PSU #2’s cabled to enter my case and keep this setup. Unfortunately from my cut in the screen a small wire protruded and shorted one of my 500w PSUs as I stuffed this rig back into my OakExpress roll top computer desk. I put my (failed???) Corsair 1000w back in running the video and drives and seems to be running faster than ever! How much power can this system want? Some of the articles I have found recommend using 2 identical PSUs. I started out this way but have found a performance boost from my mis-matched 1000w + 500w dual PSU “rig.”

Intel COREi7 965 EE
6gb kit DominatorGT 1866mhz memory
Three 150gb VelociRaptor hard drives in RAID0
80gb Barracuda hard drive
XFX 5870 video card
US Robotics PCI fax/modem
One 120mm case fan
Two 80mm CPU heat sink fans
Two 40mm case fans
Corsair memory cooler 2 fans
1 Antec EarthWatts 500w running m/board, memory, fans and PCI slots.
1 Corsair HX1000w running XFX 5870 video card (two 6 pin plugs), 4 hard drives, 2 optical drives and 3.5” floppy.
 
The second power supply is unnecessary. The 1kw Corsair is more than enough alone.
 
The HX1000 must be faulty, since there is no way in hell that you are using anywhere near 1000W of power with that system.
 
The video card draws the most power from the PSU and since you only have one video card you don't even use a partial of 1k watts.
 
i recall reading that there's a potential safety issue with doing something like this...
 
Zero82z said:
Either using an adapter designed for this, or doing it yourself while making sure everything is wired properly and there are no exposed leads.
Click to expand...

Well................ and sure, don't spill water on it. :)

This guy describes what I'm vaguely recollecting. There are some useful links earlier in the thread.
http://club.myce.com/f7/wire-dual-power-supplies-together-one-motherboard-111640/#post908491

It seems like you need a list of dos and don'ts so as to not implode the universe.
 
Well yes, of course you would not splice the wires together. All you would do is bridge the power on circuitry of both PSUs so that the second one turns on with the first. Then, you just connect some devices to one PSU and other devices to the other.
 
Ok so the rule is don't ever connect one psu directly to the other.

Thinking about this, that probably means that the motherboard (atx, 12v, etc), graphics cards (6/8-pin pcie connectors), must all be connected to the primary psu. Only hard drives, case fans, cd drives, etc can be connected to the 2nd psu.

But.... in order for them both to turn on, they have to be connected at the ATX connector, right? Those lines for the power-on logic must not be "regulated" I suppose...

Except that the motherboard won't know what to do if one PSU fails to give a "power good" signal.
 
In the past you could theoretically burn out the powersupply that is not connected to the motherboard by doing this, The reason is the 3.3V, 5V and 12V rails had a minimum load. In some cases this was 1A but now I believe most have reduced or even eliminated this minimum load on some of the rails. Back 6 years ago when I made a fileserver for work that had 20 x 250 GB sata1 hard drives I added resistive load (i believe 2 10 ohm wire-wound resistors in parallel) to the 3.3V rail because it needed a 0.5A load.

By ohms law
3.3V / 5 = 0.66A

About a year ago one of these supplies died so I replaced the two with a 1KW zalman.
 
Last edited:
venm11 said:
Thinking about this, that probably means that the motherboard (atx, 12v, etc), graphics cards (6/8-pin pcie connectors), must all be connected to the primary psu. Only hard drives, case fans, cd drives, etc can be connected to the 2nd psu.
Click to expand...
Anything can be connected to either PSU. You just can't connect the PSUs to each other.
venm11 said:
But.... in order for them both to turn on, they have to be connected at the ATX connector, right? Those lines for the power-on logic must not be "regulated" I suppose...
Click to expand...
They are regulated. Here is an adapter that can be used to connect two PSUs together. Hopefully you can understand how it works by looking at the image: http://www.performance-pcs.com/cata...e=product_info&cPath=34_186&products_id=21193
venm11 said:
Except that the motherboard won't know what to do if one PSU fails to give a "power good" signal.
Click to expand...
If one of the PSUs gives the power good signal, the PC will boot.
 
Ok that adapter has the lines that the mobo uses to turn ""on" the PSU with some simple logic. That's probably fine.

Now say you connect the motherboard to PSU1 and a PCIE gx card to PSU2. That means that the gx card is getting power from both PSU1 through the motherboard and from the PCIe 6-pin plug from PSU2. I'd think this would indirectly connect them and strain any regulation on the gx card or mobo as the PSUs compete. Or, if the pcie power is fed directly from PSU1, that's worse.
 
venm11 said:
Ok that adapter has the lines that the mobo uses to turn ""on" the PSU with some simple logic. That's probably fine.

Now say you connect the motherboard to PSU1 and a PCIE gx card to PSU2. That means that the gx card is getting power from both PSU1 through the motherboard and from the PCIe 6-pin plug from PSU2. I'd think this would indirectly connect them and strain any regulation on the gx card or mobo as the PSUs compete. Or, if the pcie power is fed directly from PSU1, that's worse.
Click to expand...

Nope, no strain whatsoever.
 
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