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Some questions related to PSU

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Old 04-11-03, 11:16 PM Thread Starter   #1
Ian
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Some questions related to PSU


I am getting a new PSU soon to replace the current 330W Enermax (EG351P-VE, how misleading is the model name!), it just isn't good enough for overclocking my nForce2 system.

I was looking at the SPI/Sparkle/Fortron (whatever you call it) PSU and saw that they have several categories, namely ATX12V, ATX 2.03 and Active PFC.

I know that ATX12V is equivalent to ATX 2.03 rev1.2 and is the latest standard, according to this site: http://www.formfactors.org/

1) What is PFC? And what's the difference between the Active and Passive types?

2) Which rail (+3.3V, +5V or +12V) is the CPU on? I'm running a TBred B 1700+. What about the P4 systems?

3) How important is the +3.3V and +5V combined power?

4) Anyone using Aopen PSU here? I see that they have the same model names as the SPI units, wonder if they are the SPI clones.

5) Anyone know if current PSU (ATX12V/ATX2.03) will work with Athlon 64? Don't want to invest in an expensive PSU and later find out it need to be replaced when I upgrade in one or two year's time.

Thanks in advance.
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Old 04-12-03, 04:39 AM   #2
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I've read that PFC is a requirement in Europe allows the power grid to deliver more power with the same amount of equipment, but power companies don't bill residential customers for bad power factor, so PFC is of no benefit, except that it could allow a
smaller UPS to be used. IOW, probably useless, which is why so many people think they must have it.

If the mobo has a square four-pin connector or disk drive power connector on it, then it uses +12V for the CPU. Otherwise it uses the +5V for the CPU, and the combined power rating could matter. But I don't know how accurate the advertised ratings are. Virtually all the newer mobos use +12V.

C'T magazine found that an Athlon 2400+ XP with GeForce 3 Ti500 consumed no more than 180W, worst case. The motherboards that powered the CPU from the +5V consumed 2A @ +12V, 18A @ +5V, and 15A @ +3.3V (164W combined power), while motherboards that used +12V for the CPU consumed 9A @ +12V, 3.2A @ +5V, and 10A @ +3.3V (49W combined power).
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Old 04-12-03, 11:58 AM   #3
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Here's a link with an explanation: http://whatis.techtarget.com/definit...866381,00.html

Passive PFC in my 420w Channel Well consists of a capacitor and resistor wired across the 120v line input. Not sure about how Sparkle's active units differ.

Aopen does use Sparkle for their units - not a clone but the real thing. Not sure about Athlon 64 power needs, but it wouldn't be too smart of AMD to require a PSU upgrade to work with them. I'm sticking with my existing PSU until I find out otherwise.

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Old 04-13-03, 01:45 AM   #4
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That capacitor across the AC lines is for the EMI filter (the resistor discharges it when the plug is pulled) and probably actually worsens the PFC because PC PSUs are naturally capacitive. That probably explains why passive PFCed PSUs have that big coil wired in series with one of the AC lines. The one in the 300W Fortron ATX300-GT measures two ohms, which would waste about 25W at full load.
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Old 04-13-03, 12:15 PM   #5
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Yep, you're right - been working on too little sleep this week

Here's another link:

http://www.endpcnoise.com/cgi-bin/e/pfc.html

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Last edited by Oklahoma Wolf; 04-13-03 at 01:09 PM.
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Old 04-14-03, 07:43 AM Thread Starter   #6
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Just found this thread in AOA forums, turns out that CPU draws power from the +5V rail on my board (Epox EP-8RDA) and possibly all other motherboards with 3-phase power (?):

http://www.aoaforums.com/forum/showt...threadid=13078

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Old 04-14-03, 08:14 AM   #7
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Theres a nice sticky in this forum that may help you decide witch PSU to go with, well it will help you to answer question 3 anyway

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Old 04-14-03, 10:36 PM   #8
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I think you mean two phase power Ian. I think 3 phase power boards have the 12v Aux connector.
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Old 04-15-03, 06:54 AM   #9
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The ECS K7S5A and P4S5A use only +5V for the CPU (only one power connector) but have six large transistors and diodes. Does that indicate three-phase power?
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