Problems with 12V and 5V lines on a PC ATX supply

Commander Kinsey · 2020-02-19T16:46:49+00:00

Why do (cheap? expensive ones may be better) PC ATX power supplies need current drawn from the 5V line to make the 12V line work correctly?I have a PC with 3 graphics cards running scientific applications. I acquired three old graphics cards that take about 300W each, and have loads of cheap (CIT) PSUs that are rated at 650W on the 12V line, which is what those cards use. So I run each card off its own supply. But the 12V line at no load, or even at 300W, is only giving out 10 to 10.5V. If I attach a small dummy load of an amp or so to the 5V line, the 12V line suddenly becomes 12V.Why are the two lines related in any way?Sorry for the crosspost, I'm not sure which of these groups are active.

Feb 19, 2020 Last reply: 6 years ago 62 Replies

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Commander Kinsey 6 years ago

I can't see any evidence in my newsreader that I asked in there, did I say I was going to? I only see it in s.e.basics.

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Rod Speed 6 years ago

Like hell you do.

Yeah,, yeah, some drunken drug crazed letterbox stuffer knows a lot more about everything than any designer does.

Yeah, right.

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Commander Kinsey 6 years ago

I just found a 1kW one from China for under £40. The people over in the electronics groups seem to think they're fine. And since my policy is to always run a PSU at 50% load for extra reliability, longevity, and voltage stability, it should work. If not I'll be getting my money back and a free supply that will work for something else.

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Commander Kinsey 6 years ago

You only add the n if the next word begins with a vowel.

And I am not Scottish in any sense of the word.

Nope, they love foreigners, which is why they're letting in all the immigrunts.

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