Dual PSU system, equal power sharing.

PSUs: The source of DC power for all components in the PC & often a big noise source.

Moderators: NeilBlanchard, Ralf Hutter, sthayashi, Lawrence Lee, Devonavar

Post Reply
Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Dual PSU system, equal power sharing.

Post by Ginja_Ninja » Tue Aug 02, 2005 2:14 pm

Hi there,

I am going to be building a system that will have 2 PSU's. What i am trying to achieve is power to be shared from both psu's. By this i don't mean, running the motherboard and its associated components on one, and the drives on another, i would like to have them both being used equally.

For simplicity lets forget the HDD and optical drives for a moment, how would i get both power supplies to work together so they share the work load 50/50 to the motherboard?

Suggestions welcome

Thanks for your time
P.S. Keep up this excellent work here at SPCR !


Take Care, G_N

teknerd
Posts: 378
Joined: Sat Nov 13, 2004 5:33 pm

Post by teknerd » Tue Aug 02, 2005 2:35 pm

The only way i can think would be to splice the lines together. Course that begs the question, why in god's name would you want to do such a thing?
[img]http://tinyurl.com/rqlff[/img]
[size=75]Main Rig: X2-4200+ | XP-120 | A8N-SLI Premium | 2GB RAM | XFX 6600GT w/VF700 | 74GB Raptor & 320GB 3200JD | P180 | SmartPower II 500W | 2x Dell 1704FPV (Digital)
Media Center: Athlon XP-M 2500+ @ 2.2GHz | ALX800 w/92mm Panaflo | 1GB RAM | 40GB WD | SLK3000B | Modulated, Fan-Swapped 380S PSU
[/size]

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Tue Aug 02, 2005 2:52 pm

Thanks for your reply,

hmm, will that still provide the correct voltages or will it double them ??


Take care, G_N

teknerd
Posts: 378
Joined: Sat Nov 13, 2004 5:33 pm

Post by teknerd » Tue Aug 02, 2005 2:58 pm

Ginja_Ninja wrote: hmm, will that still provide the correct voltages or will it double them ??
Take care, G_N
You would need to find that out from someone who remembers more E&M than i do. However i would not even consider risking it in my personal system.

I am curious though, why do you need to run the PSUs in such a manner?
[img]http://tinyurl.com/rqlff[/img]
[size=75]Main Rig: X2-4200+ | XP-120 | A8N-SLI Premium | 2GB RAM | XFX 6600GT w/VF700 | 74GB Raptor & 320GB 3200JD | P180 | SmartPower II 500W | 2x Dell 1704FPV (Digital)
Media Center: Athlon XP-M 2500+ @ 2.2GHz | ALX800 w/92mm Panaflo | 1GB RAM | 40GB WD | SLK3000B | Modulated, Fan-Swapped 380S PSU
[/size]

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Tue Aug 02, 2005 3:09 pm

I am curious though, why do you need to run the PSUs in such a manner?
A few reasons really, but mainly I want the PSU's to be fanless. They do get hot when there stressed, so 2 of them sharing would be easier for them, and they would'nt get "too" hot.


Thanks
G_N
Last edited by Ginja_Ninja on Tue Aug 02, 2005 3:14 pm, edited 1 time in total.

teknerd
Posts: 378
Joined: Sat Nov 13, 2004 5:33 pm

Post by teknerd » Tue Aug 02, 2005 3:14 pm

While each PSU would not grow as hot, the combined heat would still likely be higher than a single one.
While its an intersting idea, its not very practical. for one, the only cases i know of that can hold 2 psu's arent very quiet.
2) you can get fanned PSU's that are very quiet (seasonic s12) and can put out very high loads

what is your system setup? Maybe there is another way to work this without having to resort to such lengths.
[img]http://tinyurl.com/rqlff[/img]
[size=75]Main Rig: X2-4200+ | XP-120 | A8N-SLI Premium | 2GB RAM | XFX 6600GT w/VF700 | 74GB Raptor & 320GB 3200JD | P180 | SmartPower II 500W | 2x Dell 1704FPV (Digital)
Media Center: Athlon XP-M 2500+ @ 2.2GHz | ALX800 w/92mm Panaflo | 1GB RAM | 40GB WD | SLK3000B | Modulated, Fan-Swapped 380S PSU
[/size]

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Tue Aug 02, 2005 3:23 pm

teknerd wrote:While each PSU would not grow as hot, the combined heat would still likely be higher than a single one.
While its an intersting idea, its not very practical. for one, the only cases i know of that can hold 2 psu's arent very quiet.
2) you can get fanned PSU's that are very quiet (seasonic s12) and can put out very high loads

what is your system setup? Maybe there is another way to work this without having to resort to such lengths.
Thanks for your input.

My system setup does'nt exist right now, i am currently designing the final stages of a project i am working on. One of my requirements is fanless. Your right about the combined heat tho, but i am building my own case that will deal with that issue.

Take care, G_N

teknerd
Posts: 378
Joined: Sat Nov 13, 2004 5:33 pm

Post by teknerd » Tue Aug 02, 2005 3:34 pm

wow, sounds like quite a quest for quiet computing.
completely fanless is extremely hard to achieve, but if you can, more power to you.
have you considered watercooling a PSU. It would let you use a single big one and just have a large external radiator, even easier if you are already using a W/C rig on this setup.
Another option would be to fasten the PSU to the side of the case (assuming its metal) and turn the side into a giant heatsink (similar to the Zalman TNN-500)
[img]http://tinyurl.com/rqlff[/img]
[size=75]Main Rig: X2-4200+ | XP-120 | A8N-SLI Premium | 2GB RAM | XFX 6600GT w/VF700 | 74GB Raptor & 320GB 3200JD | P180 | SmartPower II 500W | 2x Dell 1704FPV (Digital)
Media Center: Athlon XP-M 2500+ @ 2.2GHz | ALX800 w/92mm Panaflo | 1GB RAM | 40GB WD | SLK3000B | Modulated, Fan-Swapped 380S PSU
[/size]

BillyBuerger
Patron of SPCR
Posts: 852
Joined: Fri Dec 27, 2002 1:49 pm
Location: Somerset, WI - USA
Contact:

Post by BillyBuerger » Tue Aug 02, 2005 3:44 pm

The voltages would not be doubled. In theory, connecting the two 12V lines from each PSU would still give you 12V. This is assuming that they both have the same ground. Which as far as I know, computer PSUs are. If the grounds were not equal than power would be wasted as it went from one PSU to the other. Plus this would probably fry them. So the question becomes where the load will get pulled from? Will it be equal between the two sources? I guess the only way to find out is to try =) I would suggest two old PSUs for that. Speaking of which, I have two old Dell PSUs. Maybe I'll give it a try???

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Tue Aug 02, 2005 3:45 pm

teknerd wrote:wow, sounds like quite a quest for quiet computing.
ill say. I am tired of the wurring, if i can hear anything , its not quiet enough :) lol
teknerd wrote: Another option would be to fasten the PSU to the side of the case (assuming its metal) and turn the side into a giant heatsink (similar to the Zalman TNN-500)
Hmm now thats something to think about.

I will create a post when i have the finished porduct, with pictures etc, but for now i will continue to design, rub-out, redesign and drink more coffee :)

Take care

G_N

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Tue Aug 02, 2005 3:50 pm

BillyBuerger wrote:The voltages would not be doubled. In theory, connecting the two 12V lines from each PSU would still give you 12V. This is assuming that they both have the same ground. Which as far as I know, computer PSUs are. If the grounds were not equal than power would be wasted as it went from one PSU to the other. Plus this would probably fry them. So the question becomes where the load will get pulled from? Will it be equal between the two sources? I guess the only way to find out is to try =) I would suggest two old PSUs for that. Speaking of which, I have two old Dell PSUs. Maybe I'll give it a try???
Well thats good news. Your right, experimentation is the only way to be sure, need a way of testing the power draw from each at the same time. Right well, i need to olds psu's and some old components. I will have to dig around. Good thing there a second hand pc component shop near were i live, might have to visit him alot.

Take care all

sthayashi
*Lifetime Patron*
Posts: 3214
Joined: Wed Nov 12, 2003 10:06 am
Location: Pittsburgh, PA

Post by sthayashi » Tue Aug 02, 2005 4:51 pm

Quite literally, the easiest way of doing this is not an even split, but to have one PSU run the drives, fans, video cards etc, and the other PSU run the CPU & motherboard. If this is unsatisfactory, then you'll have some interesting problems attempting to level things out.

What happens when you have one PSU outputting 11.85V and another PSU outputting 12.15V? How much power will come from which PSU? Both are within 5% tolerance, but clearly you won't be drawing equal amounts of power here.
[size=75][url=http://www.twolf1300.net/sthayashi/SPCR/systems.html]My Power Rig, Storage Rig, HTPC and Main Rig[/url][/size]

BrianE
Posts: 667
Joined: Tue Mar 29, 2005 7:39 pm
Location: Vancouver, BC, Canada

Post by BrianE » Tue Aug 02, 2005 11:06 pm

Yeah talk about venturing into uncharted territory. I think sthayashi brings up some good points.

Another thing I was wondering about was about efficiency. Most power supplies achieve peak efficiency somewhere in the middle of their load range. If you have two lightly loaded PSUs running at 75% efficiency do they put out less or more heat than one PSU running at 80% efficiency?

My intution tells me that two devices designed to (wastefully) convert AC to DC voltage can't be as thermally efficient as a single device. At the very least you have twice as much wiring and built-in resistance.... I don't know very much about this field though, so those are strictly my non-expert thoughts on this. :P

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Wed Aug 03, 2005 1:57 am

sthayashi wrote:What happens when you have one PSU outputting 11.85V and another PSU outputting 12.15V? How much power will come from which PSU? Both are within 5% tolerance, but clearly you won't be drawing equal amounts of power here.
Yes, i do believe you have a very valid point. I have a feeling i will end up having some kind of regulator sat in the middle of the two. I will have todo more digging.
BrianE wrote:Yeah talk about venturing into uncharted territory. I think sthayashi brings up some good points.

Another thing I was wondering about was about efficiency. Most power supplies achieve peak efficiency somewhere in the middle of their load range. If you have two lightly loaded PSUs running at 75% efficiency do they put out less or more heat than one PSU running at 80% efficiency?

My intution tells me that two devices designed to (wastefully) convert AC to DC voltage can't be as thermally efficient as a single device.
I think your probably right. hmmmmm

/me runs away to look at some figures

Thanks all

G_N

kesv
Posts: 300
Joined: Fri Nov 07, 2003 8:44 am

Re: Dual PSU system, equal power sharing.

Post by kesv » Wed Aug 03, 2005 3:38 am

Ginja_Ninja wrote:I am going to be building a system that will have 2 PSU's. What i am trying to achieve is power to be shared from both psu's.
What is the powerdraw from your system going to be like ?

Let's take the Antec Phantom 350 as an example. It's actually most efficient near the maximum specified power output (88% at 300W) according to the test here at SPCR. Now let's suppose your system draws 200W of power. At 200W the Phantom has an efficiency of 86%. Interpolating from the other measurements let's say the efficiency at 100W is 77% (76% at 90W and 81% at 150W). Now with a one PSU setup you would have 28W power converted to heat in the PSU. With two PSUs you have 46W of excess heat. That's over one and a half times as much heat.

With a system that draws 300W, which is a lot for a quiet system, the figures would be 36W for a single PSU and 57W for two. Still more than one and a half times the heat.

The only way I can see this effort to use two powersources to make any sense from a silence perpective, would be if you had a system that draws a lot of power. I'd say this doesn't start to look attractive with anything less than 350W of powerdraw, but then such a system likely wouldn't be silent anyway.

Highend server systems often use two PSUs to provide failover, but in those setups both PSUs are (obviously) big enough to power the system by themselves. If you still want to do this, getting your hands on the failover circuitry from such a server could be the easy way to do this. Those circuits should divide the powerdraw between the two PSUs evenly as long as both PSUs are working. It's possible that you'd have to devise your own connectors to run a normal ATX PSUs on such a system though.

Ginja_Ninja
Posts: 10
Joined: Tue Aug 02, 2005 2:09 pm

Post by Ginja_Ninja » Wed Aug 03, 2005 11:07 am

hmm, there are ATX redundant hot-swapable systems available, need to get my hands on a second hand one.

teknerd
Posts: 378
Joined: Sat Nov 13, 2004 5:33 pm

Post by teknerd » Wed Aug 03, 2005 11:18 am

just a heads up those things are anything but quiet. They usually use 40mm fans and since they are designed for enterprise environments they follow the thinking of "noise be damned, we need high airflow"
[img]http://tinyurl.com/rqlff[/img]
[size=75]Main Rig: X2-4200+ | XP-120 | A8N-SLI Premium | 2GB RAM | XFX 6600GT w/VF700 | 74GB Raptor & 320GB 3200JD | P180 | SmartPower II 500W | 2x Dell 1704FPV (Digital)
Media Center: Athlon XP-M 2500+ @ 2.2GHz | ALX800 w/92mm Panaflo | 1GB RAM | 40GB WD | SLK3000B | Modulated, Fan-Swapped 380S PSU
[/size]

peterson
Posts: 256
Joined: Sat Jan 15, 2005 2:09 am
Location: Gothenburg, Sweden

Post by peterson » Tue Aug 23, 2005 1:28 am

In the Stacker case i got there's room for 2 PSU's and it came with an adapter to connect two PSU's together. It's a green and a black cable that gets connected between the PSU's 20 pin connectors. Edit: Pin 16+17. PS_ON# and COM

What if i got 2 identical PSU's.
How would the power get distributed?
Equal from the same PSU or is there a primary and secondary one? That makes the secondary kick in...when?
What about the 12V rails? Could i have one 12V rail from 1 psu take care of the motherboard and cpu and the other psu take care of the gpu etc?
If so, there's not the same requirement for split 12V rails? I mean, there'd be a 'true' 12V split. :)

Any PSU recommendation? What it would run? anything/everything. :)

justblair
Posts: 545
Joined: Fri Jul 15, 2005 12:33 pm
Location: GLASGOW, SCOTLAND, UK
Contact:

Post by justblair » Tue Aug 23, 2005 2:42 am

Just to throw my tuppence in.

Why not take a single PSU and convert it to passive operation with an external heatsink. It would be more practical. There are instructions on this site to do it. (I'm too lazy and busy to hunt, but I found it easily on a search for passive psu before) And clearly you take pleasure in making life difficult for yourself, so the complexity of the project should entertain you.

And if you get it wrong, you are only one PSU down (assuming mobos are indestructable :? )

I've been pricing this up, and I reckon component wise I can do it for well under £10
[url=http://www.justblair.co.uk]www.Justblair.co.uk[/url]

Post Reply