Dual PSU's

I have an old HP desktop with integrated video. I have just upgraded to 1Gb RAM but want to squeeze a little more performance out of it. I have a spare PCI video card (512 Mb VRAM) but the PSU is only 275W and I am afraid that the system may be underpowered. I also have another spare 275W PSU from a similar HP that I have upgraded. The system I am upgrading is old and I want to put as minimal $$ into it using spare parts. Is it possible to use dual PSU's as my case has the room for it with proper ventilation to the outside? If it is possible, any suggestions on how to split up power requirements? Components include: (2) 275W PSU's, (1) IDE HHD, (1) CD/DVD RW, 3 1/2" floppy, (1) GsForce 8400 GS video card, 1 Gb RAM, Intel Celeron 2.0 Ghz processor, Windows XP SP3. Any input would be appreciated

 

Greetings, Maudibe...

Interesting questions - don't know if I've ever considered dual supplies...

I'm sure there are ways to split the loads, as far as optical and disk drives, as they are pretty much standard with their power requirements...I think the troubles would start when trying to connect to the motherboard - I wouldn't even try to get into specifics such as APCI characteristics, splitting rails, etc...

So - IMO, your're faced with:

1. Trying one 275W, see if it's capable of running your machine (you may be pleasantly surprised)...

2. Modifying your case and mounting two supplies to split the loads, maybe one PSU handling drives, the other the mobo...

3. Forking out the $50 to buy a new unit that'll handle anything you throw at it...

Again: IMO, option 3 is the way to go, but if you do decide to split supplies, please give us some feedback on the hows and whys...

Good luck!

 

Sure, it can be done. In fact, there are now cases that support dual supplies.

The most important thing to ensure is that both power supplies are at the same "ground" potential and this is best achieved if both are screwed into the case, and plugged into the same power source.

I agree with Caliban that only one PSU should be attached to the motherboard, and the other used for drives and fans. Since the one attached to the motherboard will power the motherboard and graphics card, that is still a fairly large load.

I ultimately agree with Caliban's option 3. Since the only thing you can shed off to the second PSU is drives and fans, you are still looking at the majority of the load on one supply. And no matter how you look at it, 275w is not very big.

However, looking here, it says those cards have a maximum draw of 71 watts. That is not very much (compared to modern cards). When you install the card, you can disable the on-board (if it does not do so automatically). That will result in the motherboard itself drawing a little less power. So, one 275w supply may just work. When I toss in your specs to the eXtreme Calculator Lite, and set capacitor aging to 30%, I get a recommended PSU of 277w, with 227 as a minimum. Still, I think the better solution is a new supply - one with a little more headroom.

Adding the card will also mean all your system RAM will be dedicated to the system instead of a large chunk for graphics. So you will see a significant performance boost by having a better GPU with its own dedicated graphics RAM, and a little system RAM increase at the same time.

 

Makes sense to keep the mobo and graphics together (PSU#1) while all other peripherals/fans on the second (PSU#2). The big question lies in powering the system on. PSU#1 will start with the power button (controlled by the system). Is it ok to turn on PSU#2 using the on/off switch on the PSU itself prior to to powering up the system without damaging the components it is connected to?
I also agree that it would be wiser just to fork out some bucks for a new PSU but I want to spend as little as possible, put some spare parts to work, and mostly, satisfy my curiosity to see if it can be done. Thanks for the input

 

Agreed - this could be a fun and informative exercise, especially if these aren't your main machines...

I'd guess the first step would be to isolate the power switch path, and slave the two PSUs to the control, maybe with a toggle switch...

Or, this: Dual PSU 24-Pin Adapter Cable...

 

The master power switch found on the back of PSUs does not power up the PSU, it just puts it in standby mode (as does plugging in PSUs without rear master power switches). You would have to use another means to power on the 2nd PSU.

I still don't think this is a good idea.

I don't know about that adapter. My worries are that it is just a connector connecting the two power supplies together. It provides no balancing or isolation and I feel that is necessary because there is no way both supplies output exactly the same voltages. Note the tolerances for +12VDC, for example, as required by the ATX Form Factor standard:

http://i195.photobucket.com/albums/z181/Digerati_Bill/One-Time%20Upload/PSUTolerances.jpg​

If PSU 1 is down 5% and PSU 2 is up 5%, one PSU may freak when it sees the other's 12VDC is 10% away - nothing too that HP was not noted for using the best quality PSUs they could find.

 

Yeah, I'd have to research the adapter, although the guys at Performance-PC are usually on the money...

Not talking about the "master power switch found on the back of PSUs" - I was referring to the motherboard/power switch circuit...tie the on/off control voltage through a simple toggle (probably DPDT, depending on the layout), and I'm sure there'd be no problems...apologize for any confusion...

I agree that this whole thing could turn out to be an experiment...but, in this case (pun intended), curiosity may turn out to be the Mother of Invention!

 

I was responding to Maudibe's question,

The only switch on an ATX PSU, if one is present, is the master power switch on back.

A DPDT switch would work to power them up, but so would simply tying a parallel set of wires to the Power On connection of the main connector for the 2nd PSU.

Or kill the cat. As I said, this is not a new idea.

Antec sells a Dual PSU setup - http://www.speedy3d.com/articles/case_mod_p3/index.shtml

And there are a few tutorials around for modders - probably the best one (that does it right) is http://www.procooling.com/index.php?func=articles&disp=56&pg=1.