Dual non-redundant PSU's possible?

C

cleverhandle

n00b
Joined
Dec 20, 2003
Messages
5
Yes, it sounds a little odd. But here's the situation - I'm looking to build a dual-Opteron workstation in the somewhat near future and want to keep things near-silent. Now, you can do a lot with water-cooled procs and GPU heatpipes, but the PSU looks like a real obstacle for a dualie. Any dual system with the typical amount of high-end gear needs some substantial wattage, and power supplies over 400W or so are a notch louder than "near-silent".

So, assume (yes, I know the saying...) that I do the math and can come with a pair of near-silent 300W PSU's that meet the amperage requirements for all the components. Could I wire them together (is "relay" the word here?) and have everything work properly?

I have a non-standard case, plenty of patience, money, and an ex-EE buddy. But are there insurmountable obstacles I should know about before I start exploring?
 
The only obstacle is that you need to get the power on signal from the motherboard to both power supplies.

You could do this by using some sort of relay or you could open up the atx connectors and attach both PSU's to the motherboard power on signal bit. I can't imagine any problems with the second way although it may look a bit messy.
 
Don't do this. A single 300 W power supply doesn't have enough amperage on any of its rails (except the -5 V rail and the +5 V standby rail) to really support a dual Opteron system reliably, even the motherboard and related components alone. Sure, you can use that second power supply, but do you really want to splice in wires into the motherboard power connector to provide adequate amperage? Instead, do this. Buy a single robust power supply, one from PC Power & Cooling, Fortron, or Zippy/Emacs. Crack open the case carefully, and replace the fan! Wow! Amazing! Install foam based fan decouplers while you install that quiet fan to reduce vibrational noise. On a serious note, have an electrically adept person do this modification if you don't know what is going on inside a power supply.
 
I second xonik's advice. Wiring two ATX PSUs together using whatever method you can come up with introduces only a lot more variables which can result in spectacular failure or just a number of small problems which will give you a very bad headache.

It's fine to use two PSUs linked together using a relay, with the second PSU being used only to power fans and other non-critical components, though.
 
@Elledan - I can't tell if, by "a lot of variables," you're referring to something specific about power usage or just general complexity of a rig. Could you clarify?

Yeah, I've done a fan mod before, and have a passing knowledge of PSU parts. For anything more complicated than that, I'd talk to my friend who used to stress test and analyze electronic components for a living. The fan mod works to a point, but doesn't solve the root problem of trying to dissipate a large amount of heat through a single heat sink. I was hoping to split that heat between two heat sinks (two PSU's), and make the fans' job a little easier and quieter.

But, there would still be another problem - dual Opteron boards need SSI/EPSV PSU's. That rules out any of the typical near-silent PSU's out there. And I'd guess that SSI/EPSV units have a fan speed controller that's wired very conservatively, i.e. the fan blows hard, all the time.

Anyway, your advice is noted and appreciated. But I'm not convinced this is a terrible idea yet. A little crazy and possibly very expensive, yes. But I think the root principle of splitting the load between PSU's is sound.
 
Originally posted by cleverhandle
@Elledan - I can't tell if, by "a lot of variables," you're referring to something specific about power usage or just general complexity of a rig. Could you clarify?
Click to expand...
For example, if you've got PSU #1 plugged in the mainboard, and PSU #2 is used to power your beast of a Radeon 9800 XT, both PSUs have to turn on at pretty much the same time, or the system may not even boot properly.

Then there's the issue of grounding. Normally the ground level ('0') is determined by the PSU. If you've got two PSUs, even if they are connected to the same powerstrip, the ground level in one PSU might be a bit higher or lower than in the other PSU. If you know what a ground loop is, try to imagine one in your PC.


Anyway, your advice is noted and appreciated. But I'm not convinced this is a terrible idea yet. A little crazy and possibly very expensive, yes. But I think the root principle of splitting the load between PSU's is sound.
Click to expand...
You're more than welcome to try it, but as far as I'm concerned, it _might_ work, but there's no guarantee that it'll be a reliable long-term solution.
 
actually if you simply tie the two grounds (from each psu) it shouldent be an issue, i have done this many times and its worked fine

check out the Cool Cases FAQ for more info on wiring up dual PSU's
 
If you are concerned about noise, why don't you do what I've done in every recording studio I've built - remote the supplies....??

B.B.S.
 
Do not do not do not tie power supplies' rails together. Tying grounds together and running some stuff on one power supply and other stuff on another, but just don't mix them. Even if they are the same exact model of psu, with component and temperature variances they almost will never output the same exact voltages. If one puts out 11.94V and the other puts out 12.03V, then they are basically going to fight each other to draw the other one to the other voltage. Neither likes it, components get hot, they burn out or start a fire. Systems with redundant power supplies have special feedback loops and such in the psus to deal with this, and that's why those are so much more expensive. Just get a bigger power supply and change out the fan.
 
Thanks for the info, everybody. Still not certain whether I'll try it or not, but this is a good start.
 
i recon you should get one psu thats just enough to power the mboard and cpus (you might need to research the requirements for this) then get a second one to power all your other components like fans hd's optical drives etc, then the only mod between the two psu's would be the wires that switch them on. i've done this before in my rig just to provide more power to the cpu to see if it'd overclock more, it didnt but it did work.
 
You must log in or register to reply here.
Back
Top