Thinking of using two psu's

[unsmart]

I've seen cases with two psu bays but what I can't find is how to hook them up to the MB and vid card. I know how to swich it on and how to power drives and fans, thats all over the net. What I'm looking for is what connectors on the MB/vid can be used with what psu. like can i run the ext 12v on my pcie card with one and my mobo on the other? can I put some of the mb power connector on one and some on the other?

 

[waylander]

typically speaking I don't like the idea of putting anything that connects to the motherboard onto two different psu's. There will be a voltage difference between the two psu's and that may cause issues. I personnaly would use one psu for the hdd's, optical drives, fans and lights (plus anything like card readers) and put all the core components on the other.

 

[weskurtz81]

Out of curiosity, why do you need two PSU's?

wes

 

[mrmez]

Out of curiosity, why do you need two PSU's?

wes

DX10 card in SLI
As ppl have said... with this config + a few HDDS etc... u can EASILY require 1Kw.

Its prob gonna be cheaper to go 500W x2 than 1000 x1.

I thought abt this awhile back, and im not sure how u can get them both to switch on... maybe a 2-1 cable. Then 1PSU runs... mobo/cpu and maybe 1HDD, 2nd PSU runs gfx cards, hdds/cdroms/fans etc...

:twisted:

 

[I]

Out of curiosity, why do you need two PSU's?

wes

PS2 (the typical ATX) form-factor was never meant for this much wattage, it's excessive and disproportional to build cost, how much a high wattage PSU costs. For example, two merely median grade 350W PSU at $30 can easily outperform one $100 500W, with lower heat density AND double the (active, fan powered) exhaust rate, which with thermally throttled fans can mean either much lower PSU temp, much lower fan noise, or a little of both.

 

[I]

First you need to estimate the power consumption per part, and with parts "potentially" electrically connected besides the data bus and a common ground, treat these as a combined "one" part for your calculations, else a bit of research about whether certain parts have common rails.

For example, you might take a multimeter and check continuity between your video card's 12V external power pin, and the CPU 12V, 4-pin connector. If there is no continuity between them, you can power them from different PSU. EDIT: Just be sure you have the right pins, and that your PSU is NOT plugged into anything yet, since it will obviously read continuous on a meter if you had the same PSU's 12V rail connected to both parts, even on most so-called split-12V-rail PSU.

Same for video card 5V, and motherboard ATX 20/24 pin connector 5V, pins... if there's no continuity between these, (which I would not assume as likely as separate 12V) again you can split which is supplied by which PSU- and it wouldn't be necessary for the same supply, supplying 12V to the card, to also supply 5V, but of course it might be a lot easier not having to start grafting individual power connectors between multiple PSU.

You might also consider powering some HDDs on a different PSU if there are several (more than 3), as the initial HDD spin-up draw is fairly high. No matter how you end up arranging it, you must have the grounds tied together, don't depend on both PSU having a good ground through the chassis-case or through the AC input ground.

 

[grant_77]

I was thinking of doing the same thing.

I would power the motherboard(and CPU) with one power supply and you could use the other power supply to power the graphics aux connectors and hard drives although you may want to run 1 hd off the motherboard hd.

I know you can run 2 different power supplies, 1 for motherboard, 1 for videocard thanks to thermaltakes special video card power supply... Its practically the same idea, however two full time power supplies would be much better because you could use them to power 4-8 hd...

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

Worse comes to worse you still ahve a power supply, buy the purepower for your new video card. Fits into a 5 Inch bay which most cases have 3-4 extra

 

[doolittle]

can i run the ext 12v on my pcie card with one and my mobo on the other?

Yes this is the preferred setup, I have done this this myself recently where I had a 250w unit dedicated to the mobo and the second unit powering the external GPU / hdd's / cd & dvd drives. I would connect at least one hdd or cd / dvd unit to the dedicated GPU motherboard to place some +5v load since some units act strange in a low +5v crossload situation. Definitly check the +12v output with a meter and if it is over 5% tolerance I would probably not use it, or try to add addtional load on the +5v with the load of more hdd's and recheck.

can I put some of the mb power connector on one and some on the other?

Do not do this! This will create a voltage difference in the rails, while it does not matter to the load the lower volatge PSU will have to take the back-current and I am not sure how SMPS will handle it. Best bet is not to break the mulitrail rule, the only way to safely do this on your motherboard is to have one unit power the 4-pin CPU connector and the other the ATX 20+4.

 

[Doughbuy]

I was going to recommend the PurePower also... seems like a much easier way to guarantee results, and it is also a decent price without requiring a special case either...

Look into that.. I'm fairly certain it'll work.

 

[weskurtz81]

Well, you probably won't need more than a decent 600W-650W psu to run two of them in SLI. You have seen the total system power consumption benchmarks with one of them right? Sure they are high.... but a quality PSU will push those cards. Like they said, under load it's only 4% higher than a X1950XTX..... you won't need anywhere near a Kw.

wes

 

[Guest]

Thats for the full system ~140 for the card.

Guess what 700W is plenty if it's a good brand!
PC Power&cooling has huge 12V rails, Seasonic 700W have 2X 36Amps 12V rails and 28 peak value, that'll run anything you throw at it!

 

[unsmart]

From what I've heard the 5v rail acts as a regulator for the other rails. So I was thinking if I didn't cross the 5s then it shouldn't be a prob. The power usage calculator thing said I'm about where I need to be[ 320w ] it's just the psu is dual rail with 12 on one and 11 on the other. So I was thinking of running the board and hard drive off the 320w psu and every thing else[OCed x1800 xl,fans and dvd] off one of my old 300w psu's. Which brings up crossing 12v rails on the 320w which I think is fine, I think. The thing is I have room in my case and the psu's I have. My spec's are
cpu opty 146@3gh
x1800 xl @ xt speeds on core
1gb ocz ddr @ 466mh
5 80mm fan's on fan controller
80gb sata hard drive
dvd rom
I plan on getting a dfi sli or ultra board [ I just fried one after a week ] or a ati3200 if the price is right. the specs are what I was running in my MSI neo4/sli except the cpu what 2,972mh not 3gh, that 28mh just killed me. thats why this whole thing came up. I was running a crappy 600w psu and the voltages where low so I got a 320w enermax for $20. Right now I would like to put my money in to my htpc where my MSI board is and not a $100+ psu for my gaming system. So whats the verdict on putting both rails off the 320w it to the mobo, it seems most think running vid off the other psu is ok.

 

[waylander]

As mentioned, most cases that can handle two psu's come with the cable to turn both on at once. There are other ways to do it including manual switches or jumping the green and black on the second psu with a cable from a 4 pin molex (with a simple switch installed between the two).

The easiest is the buy a case that comes with the cable.

 

[XMSYellowbeard]

You can always add a simple relay.

 

[weskurtz81]

Well, from what I have seen with those cases, wouldn't you end up spending alot more buying that case, and then getting the two PSU's, then just a normal case with the one? Not to mention that is just one more componet that can fail. A good 600W PSU would be more than enough to run them in SLI, but if you guys want to waste your money (IMHO), then it's your money to waste and I am sure where ever you purchase the stuff from will appreciate the donation.

wes

 

[unsmart]

I'm not spending anything. I have stacks of old psus from 75-350w and I can fit one with no modding to the front 80mm fan hole in my case. If I just power drives and fans the I can stick one[ sff ] in a drive bay by gutting and old cd drive. I do agree it makes less since for a new build but if you have the stuff to do it with just sitting in a box.
I'm going to remove all but the cables I need to keep the case clean. I've do this before and it's really easy. As for the switching I'm going to replace the reset with a non momentary switch and connect the on and reset with a acrylic strip[less then .5" long]. Yeh it's half as* but it should work.

 

[waylander]

the use of two psu's can depend on a few factors. I recently had to upgrade my psu from a 600w to a 750w in order to power my water cooling on top of my sli and OC'd rig. I know this isn't the standard but I'm also looking at a peltier and that will require another 200w or so. I looked at buying a cheap 300w psu just to power my water cooling, fans, hdd's and optical drives but decided against it but I do have that 600w just sitting around so if I sli/crossfire the new dx10 cards then I might have a use for it (put in a peltier at the same time).

 

[I]

Well, from what I have seen with those cases, wouldn't you end up spending alot more buying that case, and then getting the two PSU's, then just a normal case with the one? Not to mention that is just one more componet that can fail. A good 600W PSU would be more than enough to run them in SLI, but if you guys want to waste your money (IMHO), then it's your money to waste and I am sure where ever you purchase the stuff from will appreciate the donation.

wes

The typical full tower case has enough room above the PSU mount, to mount a second. You merely need a piece of cardboard to trace the hole and make a template to cut out a 2nd fan/plug sized hole above it.

You have a higher risk of failure running one PSU that two on a system that's demanding enough to make use of two. It is due to higher current density, heat, and half the airflow (two PSU = more exhaust area and fan effectiveness).

The above assumes decent PSU, if you chose two generic 300W junk units then all bets are off.

The idea of wasting money and donation, nonsense, pretty well indicates that you haven't tried it and therefore, would hope to assume it is worse. The truth is it's LESS expensive, you can get over 60A 5V, 48A 12V, etc, capacity from two PSU costing less than 60% of what one that can REALLY do that would cost.

If you wanna get really fancy, there are a few different topologies for DIY power sharing boards which would be that much better, but beyond the skill of most and a lot more time to implement, more of a hobby proposition than time effective although this doesn't consider that if done well, a power sharing board could be reused until ATX connector pinout changes some year in the future.

 

[bazza]

if you short the 2 green cables (PWR ON) they will power on at the same time, and power off the same time

one thing to note, after you soft-off, best to turn off both the PSUs at the same time

 

[weskurtz81]

I understand what you are saying, but I still disagree.

If you have two 300W PSU's, or one 600W PSU, you have twice as much opportunity for failure having double the number of PSU's. If you have addequate airflow, the psu exhaust should not be an issue as you can always just mount a 120mm exhaust fan where you would have mounted the second PSU.

As far as price, that would seem to me to be the only advantage of having the two PSU's. It can end up being quite a bit less expensive to purchase 2 300W dual rail PSU's, than 1 quad 600W psu. I was checking prices and the most expensive 300W FSP psu's on newegg were $44x2=$88. While the 600 quad was $140. A little over $50 less for the 300W psu's.

wes