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From: Michael W Ryder on 3 May 2010 21:35
me wrote:
> I have a P4P800 I want to install into a box with an older PS. (I do
> plan to check to see if there are enough watts in the PS for the new
> setup).
>
> Question: Can I put a molex -> "CPU 4 pin" adapter on a power
> connector safely? Do the built in 4-pin connectors have larger gauge
> wire for more amps than you normally pull through molex connectors? Or
> are they just another connector on the same gauge wire as normal?
>
I would be leery of using an adapter as the 4 pin connector provides two
12 volt and two common connections to power the CPU. As the older
motherboards mainly support processors with much higher power demands
than the newer ones it will place a much higher demand on the connection
and having an adapter just adds another point of failure. I am not even
sure that a 4 pin molex can supply the 100+ watts on the 12 volt line
needed for some of the older processors.
From: Paul on 4 May 2010 08:02
me wrote:
> I have a P4P800 I want to install into a box with an older PS. (I do
> plan to check to see if there are enough watts in the PS for the new
> setup).
>
> Question: Can I put a molex -> "CPU 4 pin" adapter on a power
> connector safely? Do the built in 4-pin connectors have larger gauge
> wire for more amps than you normally pull through molex connectors? Or
> are they just another connector on the same gauge wire as normal?
>

You would need to go from two Molex disk drive connectors, to one ATX12V.
Each Molex would be on its own cable. You would not put other loads on
the same Molex, such as disk drive connectors (the voltage drop on 12V
would be upsetting the disk drive, rather than the Vcore regulator which would
not care so much).

PSU --------X---X---Y
\
+-----Z Adapter. Y=Molex, Z=ATX12V
/
PSU --------X---X---Y (Using two Molex chains to get enough 12V amps.)

What that would give you, is 6 to 8 amps to play with, on each Molex.
Or 12V * (6A + 6A) for a total of 144W. 144W flowing to Vcore, with
a conversion efficiency of 90%, gives enough power for a 130W processor.
If your S478 processor uses less than 130W, then the two Molex feel less
stress.

The current sharing on the wires, is not guaranteed. It depends on
the path resistance of each path. Say one Molex was making a bad connection
on its yellow wire. That would cause the other Molex to carry more of the
total load. At a high enough current flow level, the Molex pin can burn.

Then, you have to check the label on the power supply. Say your power supply
is 12V @ 15A, which I consider a minimum for an S478 computer. If you used
a 130W S478 processor, now you have about 3 amps left. 0.6A for disk drive on
12V, 1.5A for CDROM on 12V, 0.5A for fan cooling from 12V, takes 2.6A. Now your
margin is 0.4A, which is cutting it too close to the capacity limit of the supply.

Generally speaking, the power supply itself probably doesn't have the
capacity needed, if the necessary wiring is missing. It kinda works that
way on PCI Express as well. If a power supply has no PCI Express video card
connectors, then by the time you analyze the available power on the supply,
there really aren't enough Molex cables, enough current capacity on 12V,
to make the usage of adapters that good a prospect.

So yes, you can use adapters, but do the math and consider how close to
any limit, you might be getting.

In this picture, is an adapter. But notice they're only using one Molex.
That means the max 8 amps from the molex, can supply up to 96W to the
regulator for Vcore. 96W * 90% = 86.4W for the processor itself.

http://www.playtool.com/pages/psuconnectors/12v4pinadapter.jpg

You can use the part number for the processor, and look it up here,
to find out what power it uses.

http://processorfinder.intel.com

You really want an adapter like that, to be using two Molex, to give
you more headroom. To some extent, the scheme also depends on the Molex.
I've noticed a decline in the quality of Molex connectors. The one that
burned on my video card, never fit quite right, and required a lot of
wiggling to get the pins centered. The Molex (mini-fit jr) used to be
a reliable connector, but I wonder if the patent expired, and any
hillbilly can make them now ?

This one isn't quite right either. This is two Molex to a 2x4, whereas
you'd want two Molex to a 2x2.

http://www.playtool.com/pages/psuconnectors/epsadapter.jpg

You can make your own adapter cable. For example, snip this extender cable
in two, cut up some Molex Y cables, should give you enough connectors and
wires to make an adapter. You wire up black and yellow wires, to make the
ATX12V. I use "shrink wrap tubing" or polyolefin tubing, to cover
any bare wires, on home brew connectors. The tubing shrinks under hot air -
and works fine as long as you don't overdo it, and melt the insulation
on the wires themselves.

http://www.startech.com/item/ATXP4EXT-8-ATX12V-4-Pin-P4-CPU-Power-Extension.aspx

I get shrink wrap tubing at a local electronics store (not RadioShack). I
keep about five different sizes. The tubing should be a bit larger than
the thing you're insulating - you don't want to have to force
it into the tubing. It is easy to buy too small a tube for a project,
and have to go back and buy the next biggest size (happens to me all the
time).

http://heatshrinktubing.net/content/view/18/32/

Paul
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