Dual Rail PSU's

[McGreggor]

Ok, I've been running my new system for a week or two now, specs in my sig. The problem I'm having is random hangs, bsod's etc, it just wont get past CPU test 2 in 3DMark05 if I run all tests in order, however it will run that test if I don't run any others. I've put these down to one of two things:

1) overheating RAM, as its hot to touch, and/or overheating PWM chips on my graphics card. Both are normally passive cooled, and becuase I've replaced the nearby fans for waterblocks, neither are getting much airflow over them.

2) PSU Power. Its rated at 480W, with 18A on the 12v rail.

Though I've not had any warnings about low power from the gfx card, I think the latter is the problem. I've seen the 12v dip to 11.39v underload, baaad!
So what I did was to rig up 2PSU's to take some load off to test. Connected via relay, the second PSU powers on with the first, and they are plugged in as follows:

PSU1 - Watercooled 480W (12v+ 18A) [Unbranded but Decent enough quality]

Main 20pin ATX plugged in (via 20->22pin adapter)
Four pin Floppy connector -> Floppy Drive
Four pin Floppy connector -> MoBo
Four pin power connector -> x2 Maxtor 7200rpm 120GB SATA drives
Four pin power connector -> Dual PSU relay (Doesn't draw much if any current)

PSU2 - Aircooled Unbranded 550W (12v+ 15A) [yuk!]

Main 20pin ATX plugged in to relay (No current drawn)
Four pin ATX extra power connector plugged in to MoBo
Four pin power connector -> 6pin GFX card power connector
Four pin power connector -> Motherboard extra power connector

So I would have thought that would be enough to take the load of my 480W PSU, but no! Its still having the odd crash, and the 12v+ rail still drops below 11.4v (not as much as before)

So I'm now concerned that more amps are required than just 18? If this is the case, no matter how I rig up a 2nd PSU it wont be enough, unless one of them has more than 18A... Which is a BIG PROBLEM when my replacement PSU on order has dual 18A 12v+ rails, which I thought would be more than enough.

[Steve]

Run your motherboard and graphics card off the half decent PSU, run the drives off the not so decent PSU - don't mix the power source going into the motherboard/graphics card.

See what happens then.

[arthurleung]

You seriously need a new PSU. Even a 330W Antec Truepower has 22A on 12V. And Antec's 12V rail is famous of being "short" already. You don't even need 2 PSU, just get a 550W from quality brand will sort out your problem. I doubt you can call your PSU decent. Quality PSUs will always have +-3% voltage on all rails regardless of load, once exceed max load it will just cut off by itself.

You better stop using the 2 PSUs right away or they may blow very soon (bringing your nice stuff together to hell). Why using those crappy PSU when you have 6800 Ultra, 4000+ and 2G ram?

For the ram and PWM chip you need a fan, a 12cm fan at 5v should do the job.

EDIT:
Since ram+cpu will only take about 120W, load won't be >10A for motherboard. 6800U takes 90 odd watts max so same there should not be over 8A for GPU.

That means your two PSUs don't even meet their specified ratings, let alone giving more than that.

[McGreggor]

Run your motherboard and graphics card off the half decent PSU, run the drives off the not so decent PSU - don't mix the power source going into the motherboard/graphics card.

See what happens then.

Will try that setup after this post, cheers.

You seriously need a new PSU. Even a 330W Antec Truepower has 22A on 12V. And Antec's 12V rail is famous of being "short" already. You don't even need 2 PSU, just get a 550W from quality brand will sort out your problem. I doubt you can call your PSU decent. Quality PSUs will always have +-3% voltage on all rails regardless of load, once exceed max load it will just cut off by itself.

Yes, hence why i have an enermax 550W on order, also watercooled. I know the second PSU isn't "needed" and that its poor quality, it was just for testing! My 480W, although only 18A, is of good study build and it's not light like most crappy PSUs.

You better stop using the 2 PSUs right away or they may blow very soon (bringing your nice stuff together to hell).

Doubt that somehow, I've been running my file server with 2psus for two years now, (yes it needs them both) no smoke yet....

Why using those crappy PSU when you have 6800 Ultra, 4000+ and 2G ram?

For testing again, the 480W one should have been enough from what im told, Gainward recomend at least 480W for running their watercooled 6800, and that uses a waterpump run off the PSU where mine is off seperate 240v power. As for the mobo/cpu, from what I've read, a PSU with 18A on 12v rail is the minimum that should be ok to use, but I guess not from my setup.

For the ram and PWM chip you need a fan, a 12cm fan at 5v should do the job.

ram yes, and I'm looking at watercooling atm. pwm no, my temps are 45-49 idle and rarely past 60 underload. You dont have to worry untill it reaches 100, and then they're rated up to 120! Still, I'm looking at watercooling options for PWM too, for when I oc

Since ram+cpu will only take about 120W, load won't be >10A for motherboard. 6800U takes 90 odd watts max so same there should not be over 8A for GPU.
That means your two PSUs don't even meet their specified ratings, let alone giving more than that.

From what I think your saying, >10A + >8A = >18A, so my single 480W 18A PSU should do it as the minimum spec as I said earlier? With two PSUs, it should be enough power as I see it, even if one is only good as a big gold paper weight. I think its just a matter of getting the right setup power-wise.

I'm sure my enermax PSU will cure all problems next week when it arrives, but I'd still like to get it running right in the mean time.

[arthurleung]

I didn't mean not to run dual psus but not that two specific one That two can run some low power server fine, but setup as decent as your current rig is quite dangerous IMOH.

Yes Enermax PSUs are quality. Pretty amazing your system can still run at 11.4V on 12V. My HDDs wouldn't boot up at 11.4, let alone WinXP.

May be getting a high power PSU is a waste of money, but better safe than sorry, even I don't need 550W (I think not even 430W). PSU is kind of one-off investment anyway.

[McGreggor]

At idle, I had around 11.77 on the single PSU, under load it would occasionally drop that low, but with the 2nd PSU, idle is around 11.88v, and it drops to low 11.4's underload. I'm still gonna try Kez's suggestion to see if that helps.

[McGreggor]

Well, with the different setup, its no different. Smartguardian reports idle voltage at 11.45 now, MBM has it at 11.75, and i think its MBM thats out as it has no config for this board yet. the previous volages were mainly taken from mbm, so are probably out too. While running 3DMark05, i saw smartguardian report voltages as low as 11.26v during the vertex shader test! but run those tests all ok untill the 2nd CPU test again, strangly the 12v voltages during that test are slightly higher at 11.39v.

[Steve]

Throw your software voltage readings out of the window and use a multimeter - it's the only way you can get reliable readings.

[McGreggor]

Throw your software voltage readings out of the window and use a multimeter - it's the only way you can get reliable readings.

Can you recommend one? Does it need to put bridged over any particular part of the mobo, or can you just stick it in a spare molex connector?

[arthurleung]

Motherboard reading should be fine.

just stick in a spare molex connector should be fine, make sure you have it set to the right mode though. No idea if your PSUs have short circuit protection or not...