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Frying PSUs


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#1 Stag

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Posted 07 August 2012 - 05:07 AM

Just ordered a FOURTH PSU for "The Wife's" machine, after it went tits up again. A mate reckoned it was the memory that was causing the bother, well, I replaced that and it still went down. Getting annoyed I started looking for the culprit and found that the recommended numbers for my her graphics card are +12v output with a current rating of 38A. Well, the units I've been using were rated at 20A. I suspect this is why they're dying, but can anyone confirm?

#2 mikew

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Posted 07 August 2012 - 09:40 AM

Yes, quite likely.
It may be that the Graphics card draws a bit over 20A in normal use which overstresses the PSU.
If the graphics card tried to use the full 38A, I would have expected the PSU to shut itself down...or not start up at all, in which case the PSU may be merely resting.

#3 Stag

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Posted 07 August 2012 - 10:21 AM

Cheers for the reply. No, it's definitely tits up. Well, Now I know what to look for, but I've come across ads for PSUs that don't even specify the current rating, so it never occurred to me that it was so important.

It certainly isn't clearly specified on the PSUs documentation, either, so I guess this is a new situation.

#4 mikew

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Posted 07 August 2012 - 10:53 AM

PSUs are normally rated in Watts, so with that graphics card you'd need 38x12=456 Watts just for the 12V rail.
Therefore, you'd need PSU with a capacity something greater than that, say about 650W.

It can be a problem if you upgrade the graphics card in an OEM PC like HP/DELL/ACER etc, where you may find that a generic PSU does not work.

#5 Stag

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Posted 07 August 2012 - 12:52 PM

If I build something, I tend to overbuild for possible future expansion. The PSUs I've been fitting have all been rated at 750w, even though my worst case estimates put the power draw at a little over 400.

#6 mikew

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Posted 07 August 2012 - 02:36 PM

Ah, that sounds strange.

750W should be adequate for any single graphics card.
What else have you got attached? USB arc welder?

What's usually going on when the PSUs die?

#7 The_Nephilim

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Posted 08 August 2012 - 06:15 AM

Well Amps are more important then watts but Not saying Watts are not Important.. But there are PSU calculators that will get you the Watts any system will use, but the Amps on the 12v Rail are more important.

IF your vid card requires 38a and is only able to draw 20a that is a recipe for disaster likely burining out the PSU like you have seen..your lucky you have Only fried a PSU or two..

http://extreme.outer...culatorlite.jsp


Try that Calculator and that will get you in the Ballpark and set the Both CPU load and System load on 100% and 15% Capacitor aging.. Then determine the Amperage needed on the 12v 1st, 5v 2nd, then 3.3v 3rd.. Also get a Single 12v Rail..

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