Dual PSU concerns

Hi.. I've got to get more power to run my max CPU oc. Max is 2.75ghz but I can't run it cause my X1800XT eats all the power. I found max with cheapo card.

So I am considering a dual PSU setup. My main Antec 550W to power mobo, CPU and drives and the slave PSU for X1800XT. I've already done 12v sense wire mod on Antec so np cutting wires up. I will do the simple, Pin 14 to Pin 14 and gnd to gnd.

But!! Am I right that this would mean that when the main PSU is switched on the second one will also be switched on? I imagine that is the case and that is how it's supposed to work.

My concern is when the main PSU is on but mobo is switched off. The mobo is obviously still grounded and the main PSU is still feeding power to it. I guess when using only one PSU the X1800XT is still getting power, and I would guess also that the X1800XT fan is controlled by mobo status, i.e only when mobo on.

As you can see i'm bit confused. I killed my previous X850XT by reading 3.3v rail from 20 pin when molex was still plugged into gfx card. This I was told was because mobo wasn't grounded .. my mistake stupid I know.

So with two PSUs mobo is always grounded right, as long as the main 20 pin is plugged into mobo? Is it grounded even if I completely remove power from main PSU? Basically is there any possible way I can damage X1800XT using two PSUs.

I think this will work np, but I wanted to be sure before going ahead with it.

I posted this at TechPowerUp too but got no response yet.

Many thanks.

Bump..

No replies, that's either don't know or not sure!!

Is anyone powering GFX card with a slave PSU?

Atm I've got to unplug a drive and disable some things in bios to make it work in D3D. It does work for hours though, np. I can't afford a decent new PSU so this is only option atm.

So far only thing I heard can be damaged is the slave PSU from having no load, some rails can take 0 amps some can't so i'll have to look out for that in specs.

I honestly can't see why there would be a problem? The PSUs run in series totally separate, as long as the slave PSU isn't too cheapo nasty and rails are ok ..

Well it seems there are actually proper PSUs for GFX cards which work exactly like this.

http://www.thermaltakeusa.com/product/Power/PurePower/w0099/w0099.asp

One thing I just thought of was if the main PSU over voltage protection ever kicks in. Is the power completely off when this happens?

If so then perhaps the mobo would no longer be grounded and the slave PSU is still maybe giving power to GFX card and so fries it like my x850xt!!

Or if the main PSU OV protection kicked in perhaps it would automatically switch off the slave?

What would happen if for some reason the slave switched off? That would be like taking the molex out of GFX card with a single PSU system when it's up and running OS .. could that cause damage?

Do I have need to be concerned ??

Any ideas what the AC PCI slot is for?

AC power cord: connect through the PCI-Slot

I've read just about everything on this subject and it seems the only problem is differences in voltage fluctuations.

Here http://forum.abit-usa.com/showthread.php?t=67647

..advise against powering the extra power connector on a video card with the secondary psu, the theory that minute unbalanced voltage fluctuations might cause damage.

Click to expand...

I guess this means that the mobo is using voltage from main PSU, in my case I set my Antec to 12.28v and then the slave PSU will be feeding a different voltage say 12.05v but that doesn't seem to be the problem.. the problem is that they will both fluctuate differently.

If that's the case then how can Thermaltake produce a PSU for SLi!!? Would someone in the know care to elaborate.. is there any truth behind what Navig said?

The idea behind dual PSU's from my understanding of it was that the primary (a high 12V amped model) was used with a secondary (older higher 3V and 5V) to have and possibly power the fans and drives (anything with a motor) from the 12V on the secondary.

Ive heard of problems using two to power the mobo and GFX(s), I havnt seen much other then the thread in the volt moding section about it really. (other then chatting with people)

Yes it is safer to only power drives and fans on slave but I don't understand how Thermaltake would make a PSU solely for GFX if it could cause damage to the cards!!

On that Thermaltake link I made above the way it's setup is exact same as pin 14 to pin 14 and gnd to gnd except it doesn't involve chopping wires up. The GFX PSU is not connected to main PSU at all - it's exactly like these dual PSU setups.

So what problems did you hear about, was it about actually getting it to run or about it causing permanent damage? My Antec is very good PSU, rails are all good and hardly any fluctuation even at 2.75ghz, my slave PSU will be good quality too, possibly Enermax 270W .. you can be sure that the fluctuations will be minor although not in sync.

Doesn't the GFX card 12v from PSU get regulated and doesn't the 12v to mobo get regulated too??

power regulation in the board possibly flaking out and overvolting, damaging the mobo.. They were not entirely sure of what happened though.

I didnt notice the SLI powersupply link.. strange

Well I honestly don't believe that differences in voltage fluctuations between the 12v on main and slave can cause damage. The two PSU 12v do meet at the GFX card and so it's easy to think there might be some conflict somewhere.

But on second thoughts I think it will work fine as long as both PSU are good quality and the mobo is strong and stable.

At a guess I don't think a PCI-E card gets a raw 12v, it's regulated to different levels and i'd bet the parts that do this job these days on these modern cards and mobos are very good quality and reliable.

I think the only thing that can go wrong is if actual parts on card or mobo break. Maybe even on a dual 12v PSU the fluctuations are slightly different!!

So imo it's nonsense and perfectly safe to power card from Slave.

On a side note I don't think I need one now lol, realized my X1800XT is running at 2D VGPU for 3D clocks!!

Please go through this, and see if any of your questions are answered.
http://www.ocforums.com/showthread.php?t=88976

Oh course I read it, only 9 pages ..

In short there is little mention of using second PSU only for GFX. There is some stuff on problems with unloaded rails but that's probably only affecting AT or older ATX PSUs, the regulators in more modern good quality PSUs would allow no load on 5v and 3.3v I imagine - not 100% sure on that one.