Using an external 12V 7.5A PSU for 8-pin mobo connector...

[major_foad]

I built a computer into a small gun case (monitor, keyboard, and all) but I'm having some power problems despite some significant underclocking and other controls of power. This is not entirely unexpected as I'm using a Seasonic SS 250U (250W) to power...

ASRock P67 Extreme6
i7 2600k *undervolted @ 1.05V, 3.3Ghz
8GB (2x4) 1.5V DDR 3
9800GT low power (no 6-pin connector)
hard drive, optical, etc

The system runs fine but after a few hours the PSU heats up a bit, drops in efficiency, and the system BSOD (i suspect due to insufficient power) If I let it cool off for awhile it will run for another 3 hours, if not it goes ~20min. Other components are not heating to an alarming level at all.

Anyway....

I know I can build a PCI-E 6pin power supply out of a 12V 5A external adapter (like for a monitor) and solder on the appropriate connector...
What I don't know is if I can do the same for the motherboard's 8-pin EPS12V connector. My understanding is that electrically the 8-pin connector is allowed to be supplied from 2 separate 12V rails, one for each set of 4 pins. What I don't know is if the first set of 4 pins is expected to be provided from the same 12V rail as the main mobo connector.


I'm pretty sure I can provide at least 3.5A to half of the EPS12V connector this way, but does anyone know if I can provide the power for the EPS12V connector entirely from an external 12V 6.6A (EPS12V is spec'd @ 7A total) PSU? Will the motherboard not like this?


I already plan on getting a switching 12V 6.6A with <.1V ripple here http://www.short-circuit.com/product/80w-acdc.html or I can find one with a bit more power elsewhere, I just want to make sure I get one with low ripple vs typical 12V adapters.

Any advice is more than welcome. I can post pics if anyone is interested in seeing the mod, but it looks a bit crude as it's gone through several transformations over the past 5 years.

 

[Blue Fox]

While 18A at 12V is a bit low, it should still be just enough for that system. Efficiency isn't dropping as it's 80+ bronze certified, so even at 100% load, it's still at least 82% efficient. If the power supply is going out, wouldn't it just be easier to replace it with a slightly higher wattage variant? Plenty of 1U power supplies out there.

 

[major_foad]

Unfortunately the ss250 is 150mm long and I've only got about 165mm of space. I've yet to find a higher wattage psu in that size. I have some room elsewhere I can fit a smaller psu like a 12v power brick.