Can DUal CPU's use Different Powersupplies

Have a Dual CPU rig. Can I have one Powersupply Power the Motherboard and 1st CPU, and the other power CPU 2 and GPU?

You can if you have a motherboard that supports this. If you have two 6- or 8-pin 12V connectors, you can connect different power supplies to each. There's no way to separate the 20-/24-pin ATX connector, but most of the power should come from the extra 12V connector. The GPU can also be connected to the second PSU.

In order to have them both turn on and off at the same time, you'll want to connect the green wire from the 24-pin connector that's connected to the motherboard to the green wire in the 24-pin connector for the second (slave) PSU. You'll also want to connect two of the black wires together (so they share the same ground). There are adapters you can use that do this cleanly, or you can just solder the wire.

I'm aware how to get them to start at the same time, but have an SR-2 with dual xeons that draw quite the power, esp with my setup. Just curious if one 8 pin form psu one can go to cpu 1, and one 8 pin from psu 2 can go to cpu 2.

Arkade said:

I'm aware how to get them to start at the same time, but have an SR-2 with dual xeons that draw quite the power, esp with my setup. Just curious if one 8 pin form psu one can go to cpu 1, and one 8 pin from psu 2 can go to cpu 2.

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Yeah you should have no problem as long as you make sure both PSUs are turning on at the same time.

Ok cool

I am aware that many people have been doing this for years generally without problems, and it's unlikely that something will actually break, but unless the motherboard is designed for multiple supplies, doing this may not be safe.

For example, even if the power on signal (green wire) reaches both PSUs at the same time, all the rails will still come on at slightly different times (because all PSUs are different).

If a circuit requires power rails to come up in a specific order, a common thing to do is power sequencing - basically have a FET on each rail and only turn them on when the previous rail reaches a certain threshold. This mechanism can potentially break if different parts of the circuit are powered by different supplies, and the circuits are not designed for that.

Also, the system may join the same rails on different supplies together, which can be problematic because then noise will affect each other, and in extreme cases can make PSUs' switching regulators unstable/oscillate.

Why not just use 1 bigger supply? Or does the system draw so much power that it needs to draw from 2 separate circuits?

This rig is my Skulltrail, D5400XS. Has 2 X5450's OCed enough to pull 180 watts each, and then I have Dual GTX 295 Red's from EVGA in it OC'ed and SLI'ed with 4 HDD's and a Couple High amperage(60 watts each) Delta Fans. I didn't have alot of money, so i got Dual 750watt corsairs, but don't have 2 8PIN cords, also, the PSUs have to stabilize before the PG wire carries a signal which closes the reset circuit and starts the system, which should give both PSU's the needed Risetime.

I have run dual-power-supplies before. It is a really bad idea to just plug two power supplies o Your motherboard without knowing more.

In a typical screwed-up installation, both the power supply boxes are connected to the case, but the grounds are at different levels. This can push 10 amps through what is supposed to be a ground on Your motherboard.

I trashed a nice system this way, a few years ago.

If I were You, I would buy a power supply designed for that kind of load. They are out there, especially when we're talking about dual-Xeon processor systems. Those server / workstation power supplies can be very cheap on eBay.

I've been told otherwise, Especially since the ground of the PSU's are joined through The ground. Along with this, I'm only powering a CPU. I've been told by numerous other sources as long as I don't join Rails, I'll be 100% fine.

Arkade said:

I've been told otherwise, Especially since the ground of the PSU's are joined through The ground. Along with this, I'm only powering a CPU. I've been told by numerous other sources as long as I don't join Rails, I'll be 100% fine.

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Plugging them both into the same motherboard joins the rails.

Incorrect, the 2 8 Pin connectors are electrically isolated by the CPU's them selves, the power IS NOT shared. Electrically, the ground do join, however this is not an issue.

Arkade said:

Incorrect, the 2 8 Pin connectors are electrically isolated by the CPU's them selves, the power IS NOT shared. Electrically, the ground do join, however this is not an issue.

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You could still have a ground loop, though, which is why you should also tie the grounds on the PSUs directly.

PSU grounds are tied to Earth Ground.

Besides that, I have the grounds tied already

I'm confused you asked a question and its been answered, seems you dont like the answer so you state multiple others have told you it will work. So if this is the case why ask again unless your not really sure if the other info is correct.

IMHO your best bet and always the best bet is to not skimp on the psu. I'd buy the bigger psu and be done with instead of risking losing several hundred dollars in mobo cpu and possibly everything else connected to the psu(s)

Arkade said:

PSU grounds are tied to Earth Ground.

Besides that, I have the grounds tied already

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If your PSU is properly grounded and your electrical wiring is done properly, then yes they're tied together through earth ground.

But even so, that's a very long path to ground, which is why you need to worth about ground loops and why you should connect the PSU grounds together near the mobo

kayson said:

If your PSU is properly grounded and your electrical wiring is done properly, then yes they're tied together through earth ground.

But even so, that's a very long path to ground, which is why you need to worth about ground loops and why you should connect the PSU grounds together near the mobo

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I tied 8 Ground Wires at my custom 24 Pin connector.

Anyways, I posted this question on about 4 different forums and others responded a bit quicker is all, however, I'm still iffy on this answer. The machine pulls almost 1400 Watts at full power. I don't have near such cash to buy a powersupply of such size, my only option is to buy 2 smaller PSU's. I've debated buying a 8 Pin to Double 8. While I normally welcome all advice, I was hoping to get answers from people who definite. No problem guys, just in a rush to get the machine running. And I'm a bit broke right now, so my only option was using a CX750M I already had, Buying another CX750M with a newegg Gift card, then buying 24 Pin connectors and Making a cable for Double starting and Ground Joining. My other question comes from, Electrically speaking, this is actually no different that using a second PSU with GPU's connected to the mobo, especially because the grounds have to travel through that small PCI-E x16 connector. I could be very wrong according to you guys, but this shouldn't hurt the system. You guys are the only ones giving me doubts.

Arkade said:

I tied 8 Ground Wires at my custom 24 Pin connector.

Anyways, I posted this question on about 4 different forums and others responded a bit quicker is all, however, I'm still iffy on this answer. The machine pulls almost 1400 Watts at full power. I don't have near such cash to buy a powersupply of such size, my only option is to buy 2 smaller PSU's. I've debated buying a 8 Pin to Double 8. While I normally welcome all advice, I was hoping to get answers from people who definite. No problem guys, just in a rush to get the machine running. And I'm a bit broke right now, so my only option was using a CX750M I already had, Buying another CX750M with a newegg Gift card, then buying 24 Pin connectors and Making a cable for Double starting and Ground Joining. My other question comes from, Electrically speaking, this is actually no different that using a second PSU with GPU's connected to the mobo, especially because the grounds have to travel through that small PCI-E x16 connector. I could be very wrong according to you guys, but this shouldn't hurt the system. You guys are the only ones giving me doubts.

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You should definitely be careful about doing this. It's not something I would do without doing research, and especially checking out how the supplies are routed on your mobo. Tying the grounds at the 24 pin is probably the best way to go. If you're doing that I wouldn't be worried about ground loops. That's big concern #1. Big concern #2 is shorting rails between power supplies. While its not guaranteed to cause any problems, the potential is there. The safest way to check what rails are connected together is with a multimeter.

The things I would check are: CPU#1 & CPU#2- the 12V ATX connectors, and also the 24-pin connector. I'm guessing the two 12V ATX supplies are isolated, but I'm not sure about the ATX. That's probably also separated. You have to be careful about the GPUs too. PCIE has a 12V supply on it, so it could be connected anywhere on the mobo or even on the GPU. For that you'll wanna plug the GPUs into the slots and check if there's a connection to either CPU or the 24-pin connector. The fans don't really matter as long as you're not drawing too much power. You could split the fans over both supplies if need be. If you can set up the supplies in such a way that the two PSUs are not shorted together, you're good to go.

Where else did you post? I'm curious to see what other people have said.

Last couple places were private forums. I had a post on EVGA, but i lost it myself X_X. Anyways, From what I understand, I've been told everything is fine as long as I don't combine Powersupplies on a GPU. Idk, As far as I'm aware the 12V connectors shouldn't be joined. Would it be better just to buy a double 8 pin adapter?

Arkade said:

Last couple places were private forums. I had a post on EVGA, but i lost it myself X_X. Anyways, From what I understand, I've been told everything is fine as long as I don't combine Powersupplies on a GPU. Idk, As far as I'm aware the 12V connectors shouldn't be joined. Would it be better just to buy a double 8 pin adapter?

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You definitely don't want to use 2 PSUs on a single GPU, if that's what you're saying. Double 8-pin adapter for the CPUs is the safest bet if you have enough current on the 12V rail. You still have to be careful with the GPU PSU shorting to other PSU though