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Who here has used two PSU's on the same machine?

N

NoStateofMind

Diamond Member
I'm going to be running 3x5830's come Friday. Problem is my Corsair 650w will not support them all. I plan to use the Corsair for two and the rest of the system while using a wire (green wire to black on 24pin connector) to "short" a different PSU (350w?) into thinking its connected to a motherboard. Then just connecting the PCIe connectors directly to the third card. Do you see any issues with this? Any recommendations? (besides a single higher wattage PSU of course)
 
it "should" work as you described jumping the PSU. However in the past i have run into PSU's that will not power up without a draw on the 5v rail, which the PCIe connectors will not give you.
 
works fine.. i recommended it to someone else a few days ago when they had giant discussion thread about how big of a psu he needed.
 
PC Surgeon said:
I'm going to be running 3x5830's come Friday. Problem is my Corsair 650w will not support them all. I plan to use the Corsair for two and the rest of the system while using a wire (green wire to black on 24pin connector) to "short" a different PSU (350w?) into thinking its connected to a motherboard. Then just connecting the PCIe connectors directly to the third card. Do you see any issues with this? Any recommendations? (besides a single higher wattage PSU of course)
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I've done it with no issues. And, if you don't want to ghetto mod the 2nd PSU startup, they make a 24 pin adapter that will turn on the 2nd PSU when you power up.

As noted, check the 2nd PSU you are using. A single 5830 may not push it hard enough to cause an issue but if you have a PSU that requires a 5v load, there is potential for trouble. I killed a PSU a while back doing this because I was pulling a HEAVY load on the 12v rail and had no load on the 5v rail.
 
It is okay to do as many supplies as you want provided you do not connect the supplies in a way that they share any of the same rails. You can connect one supply to the video card and another supply to the rest of the system fine. What you do not want to do is connect two different supplies to the same video card. In that situation one supply will be providing the voltage reference for the other supply and try to regulate each other causing anything from poor output to blown supplies.
 
i have a ml110 with dual power supplies. they are new - cheap tower servers with redundant power. slick. it's a pita to deal with SLI and all with redundant power the way the rails are setup. they default to 95% on P1 and 5% on P2 (active/passive) so that you get energy star rating. it's not additive so 350 * 2 = 350 (and then some) until one unit fails.
 
Modelworks said:
It is okay to do as many supplies as you want provided you do not connect the supplies in a way that they share any of the same rails. You can connect one supply to the video card and another supply to the rest of the system fine. What you do not want to do is connect two different supplies to the same video card. In that situation one supply will be providing the voltage reference for the other supply and try to regulate each other causing anything from poor output to blown supplies.
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This will be difficult, since video cards draw from the PCIe bus. So it's not possible to avoid this situation at all -- one PSU will always be connected to all the video cards in the system.
 
theAnimal said:
Depending on the rest of the system, you may be OK with the 650W.
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It's not the wattage, it's the connectors. I have the same problem. A 650 watt Antec PSU with 2x PCIe plugs. And all the molexes are on the same daisy chains, so a 2x molex to 1xPCIe plug is not safe.

Unless I'm full of crap and it's not the gauge of the wires that's the problem, it's the power draw of molex connectors that is the gating factor. In which case, yeah, 5830s draw about 140 watts per at full blast, so a 52 amp on the 12v rail PSU should be just about sufficient assuming low power CPU and no disks.
 
v8envy said:
This will be difficult, since video cards draw from the PCIe bus. So it's not possible to avoid this situation at all -- one PSU will always be connected to all the video cards in the system.
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The supplies into the card do not share connections between the power connector and the bus. The reason for not sharing is to prevent the bus being used as a power source for the cards high current gpu. The power connectors on the card feed directly into an smps that converts to power for the gpu without ever connecting to the bus.
 
Modelworks said:
The supplies into the card do not share connections between the power connector and the bus. The reason for not sharing is to prevent the bus being used as a power source for the cards high current gpu. The power connectors on the card feed directly into an smps that converts to power for the gpu without ever connecting to the bus.
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So would it be possible to simply turn off the PSU feeding the second/third graphics card if you don't need these cards running?

Here's an example, you have three 580(s) (or if I'm a bit-miner, four 5830(s)), but lately you're just browsing the net. So you boot the computer with the second PSU "off," which allows you to boot the computer with the unnecessary GPU(s) "off."

My guess is the computer wouldn't boot, but what if it did boot? Has anyone tried it?
 
rolodomo said:
So would it be possible to simply turn off the PSU feeding the second/third graphics card if you don't need these cards running?

Here's an example, you have three 580(s) (or if I'm a bit-miner, four 5830(s)), but lately you're just browsing the net. So you boot the computer with the second PSU "off," which allows you to boot the computer with the unnecessary GPU(s) "off."

My guess is the computer wouldn't boot, but what if it did boot? Has anyone tried it?
Click to expand...

Bad idea IMO. The card would sense that it has no auxilliary power and most likely not allow the system to boot. It would probably also make an very annoying whining noise.
 
rolodomo said:
So would it be possible to simply turn off the PSU feeding the second/third graphics card if you don't need these cards running?

Here's an example, you have three 580(s) (or if I'm a bit-miner, four 5830(s)), but lately you're just browsing the net. So you boot the computer with the second PSU "off," which allows you to boot the computer with the unnecessary GPU(s) "off."

My guess is the computer wouldn't boot, but what if it did boot? Has anyone tried it?
Click to expand...


Technically as long as the bios sees at least one working video card to pass the post check I don't see why it wouldn't work. Cards not powered from the PSU will not try to draw from the bus because engineers designing them know that the current isn't available. /Without power for the GPU the card wouldn't initialize and would appear dead in the slot.

It really depends on how the cards engineers powered the initialization phase of the card. I have seen some cards that have no connection at all to any of the power lines on the bus using only the data lines.
 
If I had to guess, my guess is that the non powered card is going to start that annoying whining siren sound to let you know that it has no auxilliary power. This is an interesting test. I'm curious now.
 
I just gave away an old Athlon 64 build to my parents, it would have been a great machine to test this out.

Interesting point about the siren (no aux. power). Didn't know about it. Although I've never made the mistake, I can see how easy it is to hastily overlook the power connection. Come to think of it, a simple configuration warning like this makes sense (especially to the manufacturer).
 
As much as I switch hardware around, I have forgotten a few times to plug in the auxilliary power to the GPU(s) a few times. The last time it happened, the machine stopped in POST and the screen turned red and the siren started. There was a message on the screen advising me to connect the auxilliary power. I can't imagine this stopping just because there are 2+ GPUs in a system. Each GPU is going to want its power and will complain if it does not get it. At least, that is my theory.
 
know its an old thread but I was planning on getting a gtx 295. I was planning on using a quality 2nd psu to power the gpu since neither this psu or my main psu have enough watts to power the hwhole system. Just making sure this is safe to do and wont break my gpu? I understand when turning the computer on i should turn the gpu psu on first and should also power my dvd/cd drive with my gpu psu to get the load on the 5v rail. Is this true? Thanks
 
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