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Author Topic: Multiple PSUs, had 1 burn out  (Read 1807 times)
the_joey_o
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June 18, 2011, 10:21:05 PM
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Howdy all,
I just added 2 ATI 5770s to my computer (I already had 1 5770 in there). One of the 5770s didn't fit inside my case, so I had to keep it on the table next to it. I used a PCI-E x1 -> PCI-E x16 adapter cable on the card outside the case. This was convenient, because my 550W PSU didn't have enough juice to run all 3 cards. I setup a second PSU, a 450W to run the card outside the case. On the 450W PSU, I shorted the 15 & 16 slots on the 24 pin cable, so it would think it's on. And I ran one of the 6 pin cables to the GPU outside the case. Well, the 550W PSU just died on me. I tested it to be sure, and it is toast. I noticed that even if I forgot to plug in the 450W PSU and started up my computer, the GPU's fan outside the case would still kick in. My question is: Is it possible that the third GPU was pulling power from the PCI-E slot (which would mean that it's pulling from the 550W PSU) and not the 6-Pin (which was connected to the 450W PSU)? Does anybody else use multiple PSUs to run their mining rig?
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the_joey_o
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June 18, 2011, 10:41:30 PM
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Don't run multiple PSUs without knowing what you are doing! The voltages are actually differences in potential, and if those aren't grounded on the same value, very bad things can happen. This is probably what happened to you.
But yes, the cards also draw power from the slot, but only a little compared to what they draw directly from PSUs.

Ok. Thanks for the warning. What does "grounded on the same value" mean? Might there be a guide out there for running multiple PSUs? Seriously, I'd love to learn how to do this the correct and safe way.
Swishercutter
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June 18, 2011, 10:46:36 PM
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Don't run multiple PSUs without knowing what you are doing! The voltages are actually differences in potential, and if those aren't grounded on the same value, very bad things can happen. This is probably what happened to you.
But yes, the cards also draw power from the slot, but only a little compared to what they draw directly from PSUs.

Ok. Thanks for the warning. What does "grounded on the same value" mean? Might there be a guide out there for running multiple PSUs? Seriously, I'd love to learn how to do this the correct and safe way.

Some PSU's require a minimum load on all rails...usually written on the side...if you have no load on them they burn out...very well documented...use google.


Edit:  I'll just explain...you need a load on the 3.3V, 5V and typically any 12V rail...if they are not there the psu develops too much heat internally and burns out...I have to modify PSU's for my RepRap's by adding 10ohm resistors to create enough constant current for the PSU to function in the way it was designed...some PSU's have these resistors internally added for safety...read the sticker..if it says minimum current under the rail specs it needs them added to prevent failure.

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June 18, 2011, 10:51:30 PM
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Sorry for your loss OP but thanks a lot because i planned to do this too

Don't run multiple PSUs without knowing what you are doing! The voltages are actually differences in potential, and if those aren't grounded on the same value, very bad things can happen. This is probably what happened to you.
But yes, the cards also draw power from the slot, but only a little compared to what they draw directly from PSUs.

Ok. Thanks for the warning. What does "grounded on the same value" mean? Might there be a guide out there for running multiple PSUs? Seriously, I'd love to learn how to do this the correct and safe way.
As Monoquark told you, voltages are actually differences in potential
For example, you ask to your PSU1 2V between wire1 and wire2 and to your PSU 2V between wire3 and wire4
But you can't know what difference you have between wires from differents PSU, you could have 0.5V or 6V

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June 19, 2011, 12:34:29 AM
 #5

the card will pull up to 75w out of the pcie slot, as for using a 2end psu to power the other gpu that's ok its not going cause the other psu to blow up what it soudns like to me is your uesign cheep psus go get a good 600W psu or a cheep 750w and you should be fine
the_joey_o
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June 19, 2011, 12:44:53 AM
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Sorry for your loss OP but thanks a lot because i planned to do this too

Don't run multiple PSUs without knowing what you are doing! The voltages are actually differences in potential, and if those aren't grounded on the same value, very bad things can happen. This is probably what happened to you.
But yes, the cards also draw power from the slot, but only a little compared to what they draw directly from PSUs.

Ok. Thanks for the warning. What does "grounded on the same value" mean? Might there be a guide out there for running multiple PSUs? Seriously, I'd love to learn how to do this the correct and safe way.
As Monoquark told you, voltages are actually differences in potential
For example, you ask to your PSU1 2V between wire1 and wire2 and to your PSU 2V between wire3 and wire4
But you can't know what difference you have between wires from differents PSU, you could have 0.5V or 6V

Ok. If I get 2 of the exact same power supply, will that solve these problems?

tunatime: While I am looking to save money here, the 550W wasn't a cheap power supply. And it's less than 6 months old.
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June 19, 2011, 01:21:21 AM
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Also, I may be searching for the wrong terms here, but for the life of me, I can't find any documentation on how to determine comparability between PSUs.
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June 19, 2011, 06:24:20 AM
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Don't run multiple PSUs without knowing what you are doing! The voltages are actually differences in potential, and if those aren't grounded on the same value, very bad things can happen. This is probably what happened to you.
But yes, the cards also draw power from the slot, but only a little compared to what they draw directly from PSUs.

Ok. Thanks for the warning. What does "grounded on the same value" mean? Might there be a guide out there for running multiple PSUs? Seriously, I'd love to learn how to do this the correct and safe way.

Grounded on the same value means that either the lower or the higher potential in the mentioned difference needs to come from the same source. While it would be nice to assume that this it what happens when you get power from your wall socket, in fact it can be totally different due to the transformations occuring inside the PSU. Even using two of the same kind won't save you from any material differences. There might be a way to do this by connecting the "ground"-cables between the PSUs, but since I never built a PSU I'm not quite sure that would really work and cause no damage.

True...but what is the difference between using 2 PSU's and having multiple 12v rails...technically are they not different voltage regulators, otherwise you could not separate the rails.

I still think the cause of the PSU burning out was improper load balance/not loading all the rails to their spec. causing the PSU to have to dissipate the full load voltage inside the PSU causing issues...in some PSU's they won't even turn on the fans if the +5v rail is not properly loaded.


http://www.instructables.com/id/ATX--%3E-Lab-Bench-Power-Supply-Conversion/

That should give you some idea of what I am talking about.

Edit: http://web2.murraystate.edu/andy.batts/ps/PowerSupply.htm

Even better.
newunit16
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June 19, 2011, 07:35:53 AM
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before big power supplies got "cheap", you could find "GPU PSU's" which wer basically PSU's with 6pin/6+2pin connectors for your video cards. i think newegg still sells one. it would fit inside a 5.25" bay and plug into the wall.

of course, using one of these you will still be drawing the ~70watts from your mobo's PCIe slots. you can split a riser cable and splice in a molex connector, though. one guy on the BTC forums here sells them pre-made. kind of pricey though, for something that takes 4.72 minutes to make.

sounds to me like you way overloaded the originating PSU.

also, as far as minimal load goes, GPU's pull 180+ watts each. run two of those on one power supply alone, and its loaded.


i consider myself a rather intelligent computer nerd, i mean its kind of my job. well, networking is my job, but im decent at hardware. but it would be nice if we could find someone with experience in this area to chime in. i myself would like to do this. got 4x 5830's, 530watt PS and a spare 320watter. it would be nice to just run risers and have the full pull from the 2xtra cards come from the powersupply i have stagnating around.

to me, what you were doing appears to be precisely what a "GPU PSU" does. it just seems you were drawing that extra ~140watts from the mobo's PCIe slots into the external cards.
Swishercutter
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June 19, 2011, 07:37:48 AM
 #10



also, as far as minimal load goes, GPU's pull 180+ watts each. run two of those on one power supply alone, and its loaded.




That does not account for the +5v and +3.3v lines that typically also need load but you are correct as far as the 12v lines are concerned.
newunit16
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June 19, 2011, 08:14:36 AM
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That does not account for the +5v and +3.3v lines that typically also need load but you are correct as far as the 12v lines are concerned.

yup. though in the OP's case the main 550watt PS blew, the one that had a load on all the rails. either way it would be trivial to put a load on the 3.3 and 5v, if you were so inclined.

ive been surfing around for the last hour looking up info on this jizzy jazz. antec p190 case came with 2 PSU's. seemed they imagined you would use one for mobo/video and the other for everything else.
Swishercutter
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June 19, 2011, 08:48:01 AM
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That does not account for the +5v and +3.3v lines that typically also need load but you are correct as far as the 12v lines are concerned.

yup. though in the OP's case the main 550watt PS blew, the one that had a load on all the rails. either way it would be trivial to put a load on the 3.3 and 5v, if you were so inclined.

ive been surfing around for the last hour looking up info on this jizzy jazz. antec p190 case came with 2 PSU's. seemed they imagined you would use one for mobo/video and the other for everything else.

I must have missed that...I stand corrected in this case.  Still true statements though...I mod these for benchtop/reprap use all the time...adding resistors to one for one of my printers as I get off this post actually.
newunit16
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June 19, 2011, 09:44:27 AM
 #13

our hackerspace (lvl1 Smiley has a makerbot that had power supply issues. i wouldnt be surprised if it didnt ship pre-modded. i wouldnt know though, i dont mess with it.

what do you use to load up the rails? those big ass resistors?

im thinking... load up the 5/3.5v rails and wire the control pin on the 20/4 connector to a relay fed from the main powersupply so that it switches on when the main PSU is active.

PCIe extenders with 12v molex spliced in.
Swishercutter
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June 19, 2011, 02:19:05 PM
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our hackerspace (lvl1 Smiley has a makerbot that had power supply issues. i wouldnt be surprised if it didnt ship pre-modded. i wouldnt know though, i dont mess with it.

what do you use to load up the rails? those big ass resistors?

im thinking... load up the 5/3.5v rails and wire the control pin on the 20/4 connector to a relay fed from the main powersupply so that it switches on when the main PSU is active.

PCIe extenders with 12v molex spliced in.

I use these to load the rail...gives 1.2A@12V, .5A@5V

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=825F10RE-ND
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June 21, 2011, 01:34:30 PM
 #15

What about the grouding? do the grounds have to go together? I'm in a situation where I need to do this now.

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