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Turning a regular ATX power supply into a Pentium 4 supply

by bigdaddya / March 3, 2006 9:28 AM PST

I've a number of non-pentium 4 ATX power supplies laying around. So, when I started thinking of building another computer system I was originally going to purchase a new power supply suitable for a Pentium 4 when I came across an adapter on ebay that plugs into one of the molex connectors of a non pentium 4 power supply and, voila!, supposedly makes it into a pentium 4 power supply. Does this really work without cooking the processor or motherboard? The wattage of the power supplies is OK, they just lack the connector.

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I wouldn't trust it
by ikjadoon / March 3, 2006 10:43 AM PST

I think you need a special plug from a PSU that plugs in near the CPU... I wouldn't risk it, but if you feel lucky, throw in some old hardware, but I wouldn't try putting in the adapter and "voila!" on new hardware. P4 PSU's are different from regular PSU's because, I think, the actual processor took more power than the previous series... Just what I think.


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If the adapter creates the
by Ray Harinec / March 5, 2006 2:05 AM PST

4 pin connector and has sufficient wire guage from the supply it may work. HOWEVER the 12 volt rail must also have the capacity to handle the extra load.

Before this the mobos powered the onboard regulators for the CPU from either the 5 volt or the 3.3 volt rails. The high current demands of the P4 caused too much current to flow, mainly in the printed wiring on the mobo. This could cause poor regulation due to varying voltage drops, but in some cases melted the lands.

By trading voltage for current they got the power at a lower current. Then the onboard regulators had to reduce the higher source voltage down to the very low voltages that the CPU uses. The total load on the supply doesn't change however the 5 or 3.3 rails get unloaded but the 12 volt rail gets increased loading.

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(NT) (NT) Ah.. Thanks!
by ikjadoon / March 5, 2006 4:06 AM PST
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how to tell if the power supply has the oomph needed?
by bigdaddya / March 7, 2006 1:47 AM PST

Thanks for the reply. Is there any way to tell if the atx power supply I intend to use has the "oomph" needed on the 12 V rail, say with a multimeter or is it just " you pays your money and you takes your chance"? Or is it a matter of having a high enough wattage power supply? Also, is the main power supply to the motherboard a different form factor for the p4 board than the plain atx mobo?

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Many PS labels provide
by Ray Harinec / March 7, 2006 4:22 AM PST

such info for the max current per rail. If not, go to the PS mfr's website for such info.

Remember a little kicker:

The current for each of the voltages 3.3, 5, and 12 are given. HOWEVER further down in the spec it will give a limit to the total combined of the three, however that is in Watts. [Voltage times the current = watts].

Remember some of these P4's are at least 80 Watts, and some pushing 100.

So if the 12 volts can provide 80 watts [approx 7 to 9 amps] above all the other 12 volt loads you'll have some idea.

They are basically the same form factor. Exact smae four screw mounting pattern such that they can only be mounted one way. Solves any confusion for those with two or three fans, can't go wrong. LOL

Here's a link so that you can find the max current for Intel CPU's;

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Maybe I misinterpreted this statement
by Ray Harinec / March 7, 2006 7:40 AM PST

""Also, is the main power supply to the motherboard a different form factor for the p4 board than the plain atx mobo?""

Are you asking about the power connector that connects to the mobo [other than the new 4 pin one that started the thread]?

The newer mobo use a 24 pin connector while the older ones use a 20 pin connector. Adapters for either direction can be bought. The extra 4 pins are one each of 5, 3.3, 12, and GND [common/return, however you prefer to refer to it].

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Thanks - I was referring to the 20 and 24 pin connectors
by bigdaddya / March 8, 2006 4:07 AM PST

Thanks for all the help! I know just enough to be dangerous and all of the above posts helped a lot!

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