[coreboot] Will a KCMA-D8 boot without the 8pin EPSV12 cable if you are using a 35W CPU?

Angel Pons th3fanbus at gmail.com
Fri Oct 19 11:49:07 CEST 2018


> Probably not for a 35W CPU, but generally: Using adapters for the
> EPS12V connector is dangerous. They have more than two pins for a
> simple reason: The electrical current through each pin/connection must
> not get too high. There are adapters that route the whole current
> through a single pin on the other end (e.g. a single old-school PATA
> drive connector). Never use these unless you know they can take the
> current you expect! (e.g. not much more than 3A for a 35W TDP, that
> might be ok for a single pin, but you should read each connectors
> specs)

Agreed. I have seen a cheap power supply whose ATX12V wires got warm
because of this. I oblviously rebuilt the power supply, including replacing
said wire.

> Same applies to the tiny connectors for (hard)-drives on the PicoPSU,
> if the current goes through less pins on the PicoPSU side, don't do it
> (unless you know what you are doing).

I have some SATA DVD units that can use up to 2.5 A on the 12V line, and
another PATA unit (with a Molex connector) which uses the same. Using two
+12V wires from two different connectors should be enough to power the CPU.

> There are PicoPSUs that have a 4-pin EPS12V connector btw. So I'm not
> sure what the original question was; would it work w/o full 8 pins? or
> would it work w/o any? The former likely yes, the latter likely no.

I think so. In fact, I have a 95W CPU on a 8-pin motherboard powered by a 4-pin
power cable, and the computer runs fine. And none of my boards run without
the 12V CPU power cable (I forget about it too often).

I found the w.r.t. power supplies and connectors:
 - https://www.hardwaresecrets.com/everything-you-need-to-know-about-power-supplies/
   (page 3 is probably the most relevant)

 - http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=207
   PicoPSU roundup (from 2010, somewhat old, but still interesting)

Best regards,

Angel Pons Pons

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