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Holy Smoke

Question about running two PSUs in one system

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Holy Smoke    0

Howdy all,

I'm looking to buy a CM Stacker case, and noticed that it is possible to run two PSUs side by side using a supplied dongle. I was wondering if anyone could clear up some of the basics for me, such as:

Can any two PSUs be used together?

Do they need to be the same wattage?

Does their combined power go into the motherboard, or is the second PSU limited to powering devices like fans, hard drives and optical drives?

Is it safe?

The reason I'm asking is because I have a 400w PSU that I've been using for a couple of years, which has a rather weak +12v rail. I do, however, have easy access to a number of old 200-300w PSUs and if I could use one of those to power some/all of my drives, it would save me from buying a new PSU. I also think the biggest question I'd like answered is whether both PSUs will be supplying power to the motherboard, as it seems a bit unsafe.

Thanks in advance

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xstax    0

I'm not a Stacker expert but as I was looking into buying one and I'm pretty certain that there's no special requirements for using 2 PSUs other than having 2 PSUs.

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Guest Mindless Moron   
Guest Mindless Moron

nope no requirements but be careful you put enough load on both psu's otherwise you will damage your other components, the stacker currently ships with a dongle to fit 2 20pin psu's to you currently cannot get 2 24pin psu's working

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Holy Smoke    0

Thanks for the replies. But that leaves the last question: Does the motherboard get the combined current from both PSUs or just from one? If it gets a combined one, is it safe? That is what I'm most concerned about, since, say, if one of the PSUs accidentally becomes unplugged would easily be able to kill the motherboard.

Edit: Also, my present PSU is a 24-pin one, but split into 20-pin line and a 4-pin one. Am I right in thinking that I can still use this, since they're split up (assuming the current isn't combined)? The problem most people have with 24-pin connectors is that they can't connect the other 4 pins to the motherboard, right?

Thanks again.

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Thanks for the replies. But that leaves the last question: Does the motherboard get the combined current from both PSUs or just from one? If it gets a combined one, is it safe? That is what I'm most concerned about, since, say, if one of the PSUs accidentally becomes unplugged would easily be able to kill the motherboard.

only one PSU will power the MB and CPU so you have nothing to worry about.

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Holy Smoke    0
Thanks for the replies. But that leaves the last question: Does the motherboard get the combined current from both PSUs or just from one? If it gets a combined one, is it safe? That is what I'm most concerned about, since, say, if one of the PSUs accidentally becomes unplugged would easily be able to kill the motherboard.

only one PSU will power the MB and CPU so you have nothing to worry about.
Excellent. So (just to be perfectly clear), if my primary PSU (the 24-pin one) connects the 4-pin line directly into the mobo (since the lines are separate), and the 20-pin line through the supplied lead and then into the mobo, then I should be able to do this as long as the secondary PSU is a 20-pin one?

Edit: And since the secondary PSU will only be powering the drives and case fans, the whole point of using the supplied lead is only to kick-start the second PSU to begin with, right? There is no other current passing through it's 20-pin line?

Sorry if I sound stupid, but I'm new to this and I want to get it right the first time.

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Holy Smoke    0

Update: Just got my Stacker... It only took a look at the supplied lead to figure out how it works, and now I just feel a bit silly.

Anyway, thanks for the help all.

BTW, this case is doing wonders for my comp. My HD temps went down by 15c, my CPU temps by 10c, and case temps by 7c. It makes me want to make sweet, dirty love to it's engineers.

Ta.

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Thanks for the replies. But that leaves the last question: Does the motherboard get the combined current from both PSUs or just from one? If it gets a combined one, is it safe? That is what I'm most concerned about, since, say, if one of the PSUs accidentally becomes unplugged would easily be able to kill the motherboard.

only one PSU will power the MB and CPU so you have nothing to worry about.
Excellent. So (just to be perfectly clear), if my primary PSU (the 24-pin one) connects the 4-pin line directly into the mobo (since the lines are separate), and the 20-pin line through the supplied lead and then into the mobo, then I should be able to do this as long as the secondary PSU is a 20-pin one?

Edit: And since the secondary PSU will only be powering the drives and case fans, the whole point of using the supplied lead is only to kick-start the second PSU to begin with, right? There is no other current passing through it's 20-pin line?

Sorry if I sound stupid, but I'm new to this and I want to get it right the first time.

No you do not sound stupid and yes you are correct. The adaptor pretty much serve to kick both PSU on when the power button is pressed.

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mike503    0

yeah i also have 2 24-pin ATX power supplies, and a motherboard that wants a 24-pin connection.

i was told by the guy at silenx (who makes my PSU) that the difference between 20 and 24-pin is negligible for the most part.

however, i ruined the dongle that came with the stacker case trying to retrofit the 24-pin off one power supply into a 24-pin adapter (just the black and green wires) for the slave PSU to be able click on/off...

does anyone know where i could possibly buy a dongle (all 24-pins) and save myself the hassle of having to hack my own together?

also - he said since the second power supply will only be using the 12v rails, i should put a load on the 3.3v and 5v rails, by putting some sort of resistor on. has anyone had any experience with that?

quote from anandtech:

(Q) the new "xyx" motherboard has a 24pin plug - so do i need a new 24pin PSU ?

Not necessarely. All the upcoming new boards (eg. Nforce 4) SHOULD be capable of running with an "old" ATX 1.3 20pin-plug equipped PSU as well as with a new ATX 2.0 24pin PSU.

The question here is rather whether the PSU itself is a good brand name PSU with sufficient wattage. Dont expect a recent high-end system with pci-express card(s) and A64 CPU to run flawlessly off an old 350W noname PSU.

(Q) I got a 20pin PSU and i will get the "xyx" motherboard which uses a 24pin connector. So...i can get one of these PSU "20pin -> 24pin adapters" to make my old 20pin PSU 24pin compatible ?

See above. I dont THINK you really need one. But..there are certain *concerns* regarding this "20pin to 24pin" adapter. Do NOT confuse with the "24pin -> 20pin" adapter which often comes with new ATX 2.0 motherboards.

The 20pin->24pin PSU adapter will split your ONE rail/wire (eg. the 12V rail) coming from your PSU in two and create the "artificial" extra 4 pins.

The result is that your PSU will draw much more power from the one rail than it was originally intended to. While a real "dual rail" PSU will provide two seperate rails the solution with the adapter will draw twice the power now from one 'wire'.

What was rated at 72W max. before (remember ? 6A * 12V = 72 W) will now all of a sudden draw up to a max. of 144 watts.

Also..the thermal load (eg. heat !) will increase 4 (four !) times.

The most strain wil be on the adapter/plugs itself. You will get some nice, hot wires and plugs...

I cannot see this as an elegant solution - HOWEVER it might work.

But remember: You probably wont even NEED the adapter.

Just plug your 20pin old PSU plug in the new 24pin connector on the mobo (its downwards compatible !) the right way...leave the four extra pins out. This SHOULD work and you wont really need an 20p -> 24p adapter !

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