Power Supplies 101: A comprehensive guide

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Re: One more inaccuracy

Postby Twisty » Sat Jul 29, 2006 2:12 am

jonnyGURU wrote:
jumpa wrote:You state that motherboards do not use the -12V rail. This is incorrect.....


Could you please point to where I said that. I looked and couldn't find it.

Your statement is correct. But if I said something wrong, I need to know where I said it so I know where to correct it. ;)


I guess he is referring to the paragraph

And never pay any mind to the -5V or -12V reading in software. Those are typically EXTREMELY off simply because most power supplies have no -5V lead and most motherboards don't use the -12V lead. The software simply does not know how to report back the nonexistent readings and some pretty wacky numbers are often the result.


I guess that either
a) with no load on -12V in the PC system the power supply is unable to maintain the voltage to specification as discontinious current occours.

b)The motherboard voltage monitoring chip is not connected to -12V.
I have now left the Building :tongue8:
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Postby jonnyGURU » Sun Jul 30, 2006 6:43 pm

Webster :P wrote:
jonnyGURU wrote:
jumpa wrote:You state that motherboards do not use the -12V rail. This is incorrect.....


Could you please point to where I said that. I looked and couldn't find it.

Your statement is correct. But if I said something wrong, I need to know where I said it so I know where to correct it. ;)


I guess he is referring to the paragraph

And never pay any mind to the -5V or -12V reading in software. Those are typically EXTREMELY off simply because most power supplies have no -5V lead and most motherboards don't use the -12V lead. The software simply does not know how to report back the nonexistent readings and some pretty wacky numbers are often the result.


I guess that either

a) with no load on -12V in the PC system the power supply is unable to maintain the voltage to specification as discontinious current occours.

b)The motherboard voltage monitoring chip is not connected to -12V.


I'm going to go with "b"

But I have seen "a" happen in practice. Without a load on -12V, I've seen the -12V out of spec. PC-Club actually put the ex-nay on carrying the Ultra V-Series PSU because it wasn't within 5% without a load on it. :p

I don't think that's the paragraph in question, though. I said it's not used in most motherboards.

Although perhaps I should have said it's not used in most BUILDS as the lead is used by the motherboard, delivered to the appropriate pins of the appropriate slots.. but nobody said that anyone was actually USING it. ;)


Doc Overclock wrote:That would of course help yes.... :D


Doc. When are we going to get you hooked up? Do I have to fly to Cali or something? ;)
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Postby noviceh » Mon Apr 13, 2009 2:03 pm

Question re other power supply cables

When the voltages in the main 20-pin or 24-pin motherboard connector are being measured using the "paper clip" method what should be done with the other power supply cables?

Should they be disconected from to the motherboard, drives and add-in cards or can they be left connected?

- Novice
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Postby evasive » Mon Apr 13, 2009 9:34 pm

Unsure of the effects so as a good measure of safety for the rest of your stuff (if you think the PSU scr*wed up) disconnect them.
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