Using 2 power supplies in overclocked rig

[Poobah]

Forgive me is this isn't the best forum.
If your anaswer is "Go buy a 600w Seasonic", please save the bandwidth.

OK, here's the deal: I've got an Athlon64 X2, 7900GS, Epox 9NPA+ ultra, 2 x 1gig of DDR, a couple hard drives, burners and a couple fans all hanging off a Thermaltake 420w power supply (yes, I know, it was one of them ZOMG! $9 after rebate newegg type things that I couldnt resist, but I digress).

I used to have a 6800GS and an Opty 144 and all was fairly good, other than the occasional "IRQ less than or equal.. blah blah" BSOD. Since I upgraded the cpu and vid card, I get hard locks, no blue screen, just everything comes to a halt. swapping back either component gets the system stable, which rules out either component being bad, and possible single to dual core windows issues.

My assumption here is that the power supply can't handle the load, its older and crappy. So, until I get the afore mentioned Seasonic, I thought I might use a 2nd power supply to take the load off the main one. I've seen a few articles on how it is done, but I have some questions about it.

I've got more than a few spare 300w or so ATX supplies lying around here, so its a nice free solution until I get a real power supply.

Typically, I've seen the articles do the wiring, then power fans and whatnot with the 2nd PS. What I'd lilke to do is power the motherboard and vid card from ps #1, and everything else from PS #2 (drives, fans etc.). Any problems with that approach?

My 2nd thought was to run the drives and the aux power for the video card (the PCI-E aux connector) off the 2nd supply to split the load better. Would there be any issues with the video card getting fed by 2 different sources (with some potential minor variations on the 12v)

Thoughts, comments and ideas greatly apprecaited.

Thanks!
-Ken

 

[the Chase]

My vote goes to the 2nd option and splitting the load up more. Very curious on how this works for you as I'm contemplating doing the same thing.(Espec. when G80 arrives).

 

[Atheus]

OK, this is not safe, and will not cure your stability problems as they existed before you even upgraded. It should allow you to run the new components temporarily though.

Personally I would use the Thermaltake (yuk) unit to handle the motherboard, processor, and any current drawn through the PCI-E slot by the graphics card. I would use the old 300W on the PCI-E auxiliary power, the HD and optical drives, and the fans. You will have to jumper the green wire on the mobo connector to get the secondary supply to fire up. Also the wiring will look like a huge mess and you'll have to leave the case open all the time to get the wires in.

As for voltage variations between the units, I expect the graphics card has some pretty good regulator components in there, so it shouldn't cause too many problems. If you're still worried (and you probably should be) you can open up one of the units and see if it's got some pots to control the voltage. Again, this is not safe in any way, the caps can zap you very bad even if the unit is unplugged.

 

[Poobah]

I should add that my system is mounted in an old Asus server case - it's nearly 30" tall, and has mounting provisions for a 2nd supply. I will be able to close things up, and have room to be neat with the wiring.

Atheus- When you say 'not safe' could you clarify? I think option 1 (drives and fans) would be pretty safe, the two supplies aren't really mixed - there should be some isolation between the logic and power on the drives. In the 2nd case (PS 2 feeding the AUX PCI-E connector), I'm a little more concerned, though the power section on the card seems pretty beefy, and I'd imagine there is some isolation here as well.

Thanks!

 

[the Chase]

Yeah if you could clarify on the caps zapping you or other safety hazards I would appreciate it as I just did this very thing(2nd supply feeding aux. PCI-e on vid card and 2 HD's). I can now overclock my vid card farther with better stability than before and gained some added CPU stability. But if I'm going to die a firey death from this I think I might change it back....

 

[jiffylube1024]

Originally posted by: Poobah
Forgive me is this isn't the best forum.
If your anaswer is "Go buy a 600w Seasonic", please save the bandwidth.

OK, here's the deal: I've got an Athlon64 X2, 7900GS, Epox 9NPA+ ultra, 2 x 1gig of DDR, a couple hard drives, burners and a couple fans all hanging off a Thermaltake 420w power supply (yes, I know, it was one of them ZOMG! $9 after rebate newegg type things that I couldnt resist, but I digress).

Thermaltake has traditionally overrated their PSU's - a 420W Thermaltake is like a ~360W Antec/Enermax. I'm not sure about the new ones ("Toughpower") but the old ones were inflated.

I wouldn't feel safe running 2 PSU's from different brands, etc. Especially a 300W one (double especially if it's generic!). What if one of the PSU's fries because of current draw? It could be messy and frankly if one PSU fries it could take some parts with it and screw up your whole plan (save a few bucks). Then what do you do? An ounce of provention is worth a pound of cure.

Do yourself a favour and get one of these excellent PSU's for $99 and forget your troubles:

Enermax FMA 2 535W 22A on both +12V rails. I own this one. It can do SLI/Crossfire with ease. $99 on sale now.

OCZ PowerStream 520W . One of the most solid PSU's ever. $99 with MIR.

OCZ GameXStream 600W. $104.99 with MIR.

 

[Poobah]

Originally posted by: jiffylube1024

I wouldn't feel safe running 2 PSU's from different brands, etc. Especially a 300W one (double especially if it's generic!). What if one of the PSU's fries because of current draw?

Well, I'm no power supply guru, but i think that there will be less current draw with the load split then with my current setup. I'm not sure how a video card will respond without the aux connector powered, but if the 2nd PS goes tits up, all the drives shut down, and so does the aux connector. I also am not sure of the relevance of the brand.

I dug through the pile, I have an extra 365w enermax that looks like it will be the victim. (probably better than the thermaltake!)


Thanks again

 

[jiffylube1024]

Originally posted by: Poobah

Originally posted by: jiffylube1024

I wouldn't feel safe running 2 PSU's from different brands, etc. Especially a 300W one (double especially if it's generic!). What if one of the PSU's fries because of current draw?

Well, I'm no power supply guru, but i think that there will be less current draw with the load split then with my current setup. I'm not sure how a video card will respond without the aux connector powered, but if the 2nd PS goes tits up, all the drives shut down, and so does the aux connector. I also am not sure of the relevance of the brand.

There would be less current draw, that's not the issue.

If the 2nd one screws up, all the drives shut down, but the motherboard, which still has power, is sending them signals via the SATA or IDE ports. They are grounded cables at least, but I wouldn't try it.

Someone more experienced with this might chime in and say it's perfectly OK. Personally, I wouldn't test this kind of thing on my main rig. A spare one with old parts? Sure, go ahead .

 

[Poobah]

So, I hooked up the O-scope to 12v and gave the system a workout.

Points of note:
1) 12v line is a bit high, 12.4 volts
2) looks fairly noisy: about 80mV pk-pk just idling in Windows
3) hard drive activity causes big down spikes, up to 0.5 volts
4) intense operation (3DMark06) gives way more noise, 0.3 to 0.4 pk-pk

 

[myocardia]

According to your last post, it doesn't look like your power supply is causing your instability. Having your 12v rail @11.9v isn't a big deal. Of course, the reason it's so noisy is because it's such a cheap psu. But, I wouldn't suspect that using a second psu would change your instability.

 

[The Borg]

If you have not mentioned it, one other very important thing to do os connect the ground wires toghether - the black wire. At lestt hen the PUS's have a common point. Otherwise the difference (or closeness) in the votages mean nothing.

I would also only connect independant items to the second PSU. ie, don't have two supplied connected to one item - your vid card.

 

[imported_Lothar]

Originally posted by: Poobah
If your anaswer is "Go buy a 600w Seasonic", please save the bandwidth.

Go buy a 520w OCZ

 

[Poobah]

Originally posted by: jiffylube1024

I wouldn't feel safe running 2 PSU's from different brands, etc. Especially a 300W one (double especially if it's generic!). What if one of the PSU's fries because of current draw?

So, I'm poking around Newegg for a deal on a Seasonic 600W :evil: and I come across this little monster FSP X3 SLI PSU

Immediately I ask myself... exactly what is the difference between this and a 2nd 'normal' PSU? (aside from form factor). Looks like exactly what I've been babbling about in the entire thread.

Any takers?

 

[myocardia]

It's always been safe to run more than one psu. It's just always been thought of as ghetto, by the elitists. By the way, if you decide to use the second psu, you don't need to leave the side of your case off, as was mentioned earlier. You just have to drill a small hole in your case, so you can turn off the second psu, after the primary psu shuts down. And it's easy to make them both start at the same time, if you own a soldering iron, and buy some heatshrink.

edit: Nevermind, you can't make them both start when you press the power button. You just have to throw the switch at roughly the same time as you press the power button. You still have to have a soldering iron and heatshrink, though.